TIGHAR
Amelia Earhart Search Forum => Celestial choir => Topic started by: Mark Petersen on June 25, 2010, 04:48:42 PM
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The more I've thought about navigating using an advanced LOP, the more it seems completely logical to employ the offset method (http://tighar.org/Projects/Earhart/forum/FAQs/offset.htm). If a person doesn't use an offset method then they arrive at some point on the advanced LOP and then have to make a decision to go north or south on the line. Choosing incorrectly means flying for some time in the wrong direction before eventually giving up and then doubling back to get back to one's starting point, in short not a great option for a long flight with limited fuel reserves. Choosing incorrectly represents a 50-50 chance which seems pretty risky.
With that in mind, what was the norm for LOP navigation back in AEs day? Did FN typically employ the offset method or was it's use more sporadic? I realize that the goal was to eventually get within radio range, but you would think that if FN had a preference for the offset method he would have employed it during the lost flight.
Let's assume for a moment that FN had employed this method, wouldn't it make sense to come in north of Howland and then traverse down the LOP knowing that if Howland could not be found they might reach landfall at the other islands (like Gardner)? If they used the offset method how much offset would they need to use to correct for the large dead reckoning errors that would occur during such a long over water flight? Would they have enough fuel reserves to reach Gardner or the other islands if they used a large offset and come in from the North? If the answer is no then this might be one reason why the offset method would not have been used (insufficient fuel reserves).
The FAQ that I linked to says that there is no evidence that shows that offset was used, but some evidence to suggest an offset wasn't used. What evidence is this?
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what was the norm for LOP navigation back in AEs day? Did FN typically employ the offset method or was it's use more sporadic? I realize that the goal was to eventually get within radio range, but you would think that if FN had a preference for the offset method he would have employed it during the lost flight.
Back in AE's days nobody routinely tried to find islands by LOP navigation. Pan Am was the only airline flying the Pacific and they used Radio Direction Finding (RDF) to navigate to their island destinations. For example, when a clipper flight departed California for Hawaii if tracked outbound on a bearing from the Alameda station until it was out of radio range. The navigator then kept the flight more or less on course until it came within range of the Mokapu station which guided it in. Earhart and Noonan planned to find Howland by the same method.
For Noonan to have used the offset method to find Howland he would have had to know that RDF was not going to work when they were still far enough out to make the offset. Earhart was still trying to use RDF as late as 1930Z (0800 local) after they had already reached the advanced LOP.
The FAQ that I linked to says that there is no evidence that shows that offset was used, but some evidence to suggest an offset wasn't used. What evidence is this?
At 1912Z (0742 local time) Earhart said, "We must be on you but cannot see you...". If you are using the offset method there is no moment when you can say that you "must be" at your destination. Earhart probably meant that, according to the clock, they had now reached the advanced LOP and no island was in sight.
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Mike Piner
We have little or no indication of sunrise, from the radio logs, how did she know she was "about 200 miles out", and "must be on you".
Time alone wont guarantee you are at Howland. what is your best supposition? Mike piner LTM
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what was the norm for LOP navigation back in AEs day? Did FN typically employ the offset method or was it's use more sporadic? I realize that the goal was to eventually get within radio range, but you would think that if FN had a preference for the offset method he would have employed it during the lost flight.
Back in AE's days nobody routinely tried to find islands by LOP navigation. Pan Am was the only airline flying the Pacific and they used Radio Direction Finding (RDF) to navigate to their island destinations. For example, when a clipper flight departed California for Hawaii if tracked outbound on a bearing from the Alameda station until it was out of radio range. The navigator then kept the flight more or less on course until it came within range of the Mokapu station which guided it in. Earhart and Noonan planned to find Howland by the same method.
Thanks for the info. It sure seems like a leap of faith to fly out over the open ocean and put all of your trust into the reliability of the RDF gear. But from what you're saying that was the norm. It really brings home the phrase "on a wing and a prayer". Ultimately it was this misplaced trust that was the undoing of AE and FN.
In your book you mentioned that AE made one last RDF test flight at New Guinea which ended in a failure and yet they still attempted the flight. I find this pretty shocking if RDF was their primary navigation method. But then again AE assumed that the Coast Guard would be able to take a bearing on them if the RDF in the Elektra failed. If anything this goes to show that putting ones safety entirely in the untested hands of another person or entity (the coast guard in this case) is a very bad idea.
For Noonan to have used the offset method to find Howland he would have had to know that RDF was not going to work when they were still far enough out to make the offset. Earhart was still trying to use RDF as late as 1930Z (0800 local) after they had already reached the advanced LOP.
Makes sense. Also since the flight was so long and at night (when it would be difficult to get a bearing on the wind direction and speed), it would have meant using a large offset and perhaps cutting into the fuel reserves that much more.
At 1912Z (0742 local time) Earhart said, "We must be on you but cannot see you...". If you are using the offset method there is no moment when you can say that you "must be" at your destination. Earhart probably meant that, according to the clock, they had now reached the advanced LOP and no island was in sight.
Yup that makes sense as well. Thanks for the history lesson :)
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Mike Piner
We have little or no indication of sunrise, from the radio logs, how did she know she was "about 200 miles out", and "must be on you".
Time alone wont guarantee you are at Howland. what is your best supposition? Mike piner LTM
Yes that makes sense. I don't think a person would say that if they employed the offset method.
Now that I think about it the other drawback to the offset method comes when there is a large offset. With a large offset wind drift will come into play as one travels down the advanced LOP. Was it typical back then to estimate wind drift and fly on a wind corrected LOP? If not a person could be well off the LOP by the time they reach the desired intersecting point.
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how did she know she was "about 200 miles out", and "must be on you".
Supposition of course, but "about 200 miles out" was probably a sunrise position. Noonan then could have advanced the sunrise LOP through Howland and estimated how long it would take them to reach that line. He probably then gave AE a note saying something like "ETA Howland at 1900 hours" (they were using Greenwich time). Or maybe it was 1906 or 1910. In any case, at 1912 Earhart told Itasca "We must be on you but cannot see you..." . Of course, Noonan knew that they would only see Howland at the estimated time if they hit the line at the right spot. All Earhart knew was that the time had arrived and no island was in sight. Remember, communication between Earhart and Noonan was carried out by written notes even if they were sitting side by side. The noise level in the 10E was horrendous and by the 19th hour of flight they were both almost certainly nearly deaf.
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Was it typical back then to estimate wind drift and fly on a wind corrected LOP? If not a person could be well off the LOP by the time they reach the desired intersecting point.
A navigator always corrected for wind. The problem was figuring out what the wind was doing. During the night, the flight appears to have experience overcast conditions, thus preventing Noonan from correcting their course with star sightings. After sunup he could estimate the wind by observing the surface of the ocean using a drift sight.
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Ric,
If AE said we are 200 miles out and then later said we must be on you but cannot see you, does this fall in line with flying an offset course?
If you are flying an offset course when you reach the LOP you are not going to be “on” the final target. You will be, by design, somewhere either right or left of your target. Only after flying the distance of the offset will you then be “on” the target. If one could estimate the time between the “200 miles out” comment and the “we must be on you” comment couldn’t it be estimated how much of an offset was built into the flight plan?
Ted Campbell
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Earhart also is reported to have said that she was 100 miles out (although I can make an argument that she never said that). Earhart's announced plan was to use RDF to make a straight-in approach to Howland. She kept trying to use RDF until she was where she thought Howland ought to be. I know of no evidence that she used an offset, but we'll never know and, ultimately, it doesn't matter.
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Was it typical back then to estimate wind drift and fly on a wind corrected LOP? If not a person could be well off the LOP by the time they reach the desired intersecting point.
A navigator always corrected for wind. The problem was figuring out what the wind was doing. During the night, the flight appears to have experience overcast conditions, thus preventing Noonan from correcting their course with star sightings. After sunup he could estimate the wind by observing the surface of the ocean using a drift sight.
So they were probably flying a wind corrected 157/337 then correct? In other words their compass heading probably deviated a few degrees from their true heading correct?
I know of no evidence that she used an offset, but we'll never know and, ultimately, it doesn't matter.
You're right we'll probably never know. But if we did know it would probably matter as it most likely affected their fuel reserves.
It's also fun to play "what if" games :) My guess is if they had planned on using the offset method they would have to decide in advance if they wanted to intersect with the advanced LOP north or south of Howland. With that in mind the only logical sense is to come in north of Howland so that if they didn't find the island they could continue on the LOP and hope to find other islands in the group. To do otherwise (come in south of Howland) means flying out into a vast expanse of open ocean. With the straight in RDF method they could also come to the same conclusion to fly south on the LOP, but it means making this decision during a time of high stress after flying all night. Both are logical outcomes but one is possibly a little higher probability than the other...
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So they were probably flying a wind corrected 157/337 then correct? In other words their compass heading probably deviated a few degrees from their true heading correct?
Correct
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... I know of no evidence that she used an offset ...
To me, the fact that the last recorded transmission said, "We are flying the line north and south" (http://tighar.org/wiki/%22We_are_on_the_line_157_337%22) makes it pretty clear that they were not using the offset method. If they had used that method, they would have 'known' (i.e., had good reasons to believe that they knew) which way to turn toward Howland.
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... I know of no evidence that she used an offset ...
To me, the fact that the last recorded transmission said, "We are flying the line north and south" (http://tighar.org/wiki/%22We_are_on_the_line_157_337%22) makes it pretty clear that they were not using the offset method. If they had used that method, they would have 'known' (i.e., had good reasons to believe that they knew) which way to turn toward Howland.
That is a good argument, but it depends on how literally a person wants to give the exact wording of the logs from the Itasca radio operators. I think Ric's book mentioned the possibility that the actual transmission could easily have been "on the line from north to south". It's amazing what a difference recording "and" vs "to" makes. In this case it would have completely changed the entire direction of the post-loss search activities and the USS Lexington would have thoroughly searched Niku.
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It's amazing what a difference recording "and" vs "to" makes.
Your not kidding. The worst aviation accident in history was partly a result of one pilot hearing "at" the runway and the other pilot hearing "on" the runway. Moments later two 747's would be consumed in a huge fireball.
Sometimes details do matter.... to bad we never know until after the fact....
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That is a good argument, but it depends on how literally a person wants to give the exact wording of the logs from the Itasca radio operators. I think Ric's book mentioned the possibility that the actual transmission could easily have been "on the line from north to south". It's amazing what a difference recording "and" vs "to" makes. In this case it would have completely changed the entire direction of the post-loss search activities and the USS Lexington would have thoroughly searched Niku.
See "Last Words" research bulletin (http://tighar.org/Projects/Earhart/Research/Bulletins/49_LastWords/49_LastWords.html) for a detailed analysis of what can and cannot be surmised about the last recorded transmission.
Finding Amelia (http://tighar.org/wiki/FA), p. 100:
"The log is a mess, but it appears that Earhart made a transmission at her regularly scheduled time. Those who heard the message understood her to say, “KHAQQ to Itasca. We are on the line 157 337. We will repeat message. We will repeat this on 6210 kilocycles. Wait.” A minute or so later she added, “We are running on line north and south.”
Pp. 101-102:
"Her statement that she was 'on the line 157 337' was presumed to be a reference to a line of position—a navigational line heading south-southeast (157 degrees) in one direction and north-northwest (337 degrees) in the other—but the line was meaningless without a reference point. She probably meant she was on a line of position that passed through Howland. 'Running on line north and south' would make sense as a means of locating the island given the failure of radio direction finding."
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That is a good argument, but it depends on how literally a person wants to give the exact wording of the logs from the Itasca radio operators. I think Ric's book mentioned the possibility that the actual transmission could easily have been "on the line from north to south". It's amazing what a difference recording "and" vs "to" makes. In this case it would have completely changed the entire direction of the post-loss search activities and the USS Lexington would have thoroughly searched Niku.
See "Last Words" research bulletin (http://tighar.org/Projects/Earhart/Research/Bulletins/49_LastWords/49_LastWords.html) for a detailed analysis of what can and cannot be surmised about the last recorded transmission.
Thanks for the link I'll give it a read. Although it sounds like the logs were such a mess that I think we can only infer rather than know conclusively.
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Ric,
(or anyone)
Slightly changing subjects....
At the time, was there any reliable way of determining magnetic declination for the flight enroute and/or the immediate Howland Island area. Has your research material provided any evidence to suggest what deviation angles may have been used? Especially along the 157/337 line.
The isogonic lines in the area appear much more volatile and unpredictible than those more uniformly spaced on the mainland. I could easily imagine a window of +/-15 degrees error given the remoteness and limited detection techniques back then.
It goes without saying that inaccurate heading angles (not to mention wind correction) could have huge consequences over long linear distances.
Curious to what your research has uncovered...
(http://upload.wikimedia.org/wikipedia/commons/4/43/Earth_Magnetic_Field_Declination_from_1590_to_1990.gif)
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Quickly, back to the original topic:
Ric or anybody, is there a best educated guess as to where, that is how far from Howland, the craft might have arrived at the LOP? For example, might one say a reasonable estimate is that they met the LOP 55 miles southeast of Howland and turned right onto it heading toward Gardner? Possibly they met the LOP 35 miles southeast of Howland and turned right? 75 miles southeast and turned right?
Wouldn't we have to estimate them arriving at the LOP just far enough south to have also missed Baker? What might even a remote educated guess be as to about where?
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Ric or anybody, is there a best educated guess as to where, that is how far from Howland, the craft might have arrived at the LOP? For example, might one say a reasonable estimate is that they met the LOP 55 miles southeast of Howland and turned right onto it heading toward Gardner? Possibly they met the LOP 35 miles southeast of Howland and turned right? 75 miles southeast and turned right?
Wouldn't we have to estimate them arriving at the LOP just far enough south to have also missed Baker? What might even a remote educated guess be as to about where?
Randy Jacobson ran a Monte Carlo simulation of the flight (http://tighar.org/wiki/Monte_Carlo_Simulation_of_Flight): The highest probability, based on various assumptions, was that "when Earhart believed she was at Howland, the plane was actually somewhere about 100 to 135nm to the SW of Howland. Caution must be used, however, as it was assumed that Earhart did not have a single celestial fix to update her flight, and that her entire Expected Path was based solely on dead reckoning."
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Thanks much for the reply - yes, what a detailed study.
So, sounds like maybe a remote but natural guess is they came onto the LOP possibly just far enough south of Baker for Baker to be out of visual range? If so, who knows if there wasn't even a detectable speck of Baker behind them?...
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Thanks much for the reply - yes, what a detailed study.
Randy does nice work.
So, sounds like maybe a remote but natural guess is they came onto the LOP possibly just far enough south of Baker for Baker to be out of visual range? If so, who knows if there wasn't even a detectable speck of Baker behind them?...
Who knows? They said they were running north and south on the line (http://"We are on the line 157 337"). They were certainly doing their best to detect Howland (http://tighar.org/wiki/Howland). If Baker was detectable, they seem not to have detected it.
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Do we know if the 157/337 LOP was based TRUE heading or MAGNETIC heading?
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Do we know if the 157/337 LOP was based TRUE heading or MAGNETIC heading?
The original Line of Position (LOP) (http://tighar.org/wiki/%22We_are_on_the_line_157_337%22) seems to have been derived from a dawn sighting. I presume, but do not know as a matter of fact, that the tables used for celestial navigation would have given results in true rather than magnetic terms. Drawing the line that indicates one's location at dawn isn't at all dependent on compass readings but a trigonometric calculation based on visual information (seeing the sun break the horizon), altitude, and time. The line comes as the answer to the question, "Where in the world would you have to be to see the sun come over the horizon at that time of day?"
Strictly speaking, a line of position (http://tighar.org/wiki/Line_of_position) on a map is not a "heading," although it may help a navigator to decide what headings the plane should fly to reach its destination. To achieve a real celestial "fix," it takes three lines of position to determine location. None of those LOPs may have anything to do with the direction in which a plane is "heading."
So your question really becomes, "Do we know how often and how well AE and FN corrected for the difference between true north and magnetic north during the 20+ hours of the fatal flight?" The correct answer from reading the logs of the radio traffic during the final flight (http://tighar.org/wiki/Category:Final_Flight) is "no."
At this point, everyone is welcome to jump in with information, conjecture, and fantasies about what they coulda, woulda, shoulda done. In the absence of evidence, we have a shovel-ready site on which any story may be constructed.
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Marty, thanks for posting the link of the Monte Carlo Simulation, I'm still in the process of digesting it. But one question immediately jumps out. The simulation puts the highest probability of the 10E far to the west of Howland and well off the advanced LOP. As I understand it there will likely be a large degree of navigation error as to where they would intersect with the LOP which is mostly due to wind drift from the long flight, but my understanding was that they would hit somewhere along the advanced LOP with a fair degree of accuracy because of the ease of noting sunrise (true LOP) and the limited amount of wind drift that occurs from traveling from the true LOP to the advanced LOP that intersects with Howland. If the advanced LOP could be be determined with reasonable accuracy, I would expect that the 10E would be either north-west of Howland or south-east (one the advanced LOP). Apparently though the simulation thinks that there was a fair degree of error in calculating the advanced LOP. Any idea where that error comes from?
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... As I understand it there will likely be a large degree of navigation error as to where they would intersect with the LOP which is mostly due to wind drift from the long flight, but my understanding was that they would hit somewhere along the advanced LOP with a fair degree of accuracy because of the ease of noting sunrise (true LOP) and the limited amount of wind drift that occurs from traveling from the true LOP to the advanced LOP that intersects with Howland. If the advanced LOP could be be determined with reasonable accuracy, I would expect that the 10E would be either north-west of Howland or south-east (on the advanced LOP). Apparently though the simulation thinks that there was a fair degree of error in calculating the advanced LOP. Any idea where that error comes from?
Nope. I don't know whether Randy reads the forum. I suppose (guess, speculate) that the simulation is trying to find out where the most probable flight paths from night-time navigation cross the dawn LOP (northward or southward of the ideal route) and then, maybe, project the rest of the path from there.
Maybe the simulation didn't give enough weight to the dawn line as a pretty reliable guide to actual E-W location.
Your argument certainly seems quite reasonable to me--but I'm neither a navigator nor a statistician.
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Your argument certainly seems quite reasonable to me--but I'm neither a navigator nor a statistician.
I'm not a navigator either (but I am an engineer), my guess is that determining the dawn line may be more complicated than we know. Randy's paper also mentions that a person needs to assign a relative probability to each of the events and data sets and I assume that this would provide a great resource to perform "what if" scenarios. Do you know if the code for the simulation still exists?
It also sounds like more work has been done on the nature of the radio propogation of AEs 10E since the simulation was first run and it might be worthwhile to add this and freshen the model. Such is the dynamic nature of research :)
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The original Line of Position (LOP) (http://tighar.org/wiki/%22We_are_on_the_line_157_337%22) seems to have been derived from a dawn sighting. I presume, but do not know as a matter of fact, that the tables used for celestial navigation would have given results in true rather than magnetic terms. Drawing the line that indicates one's location at dawn isn't at all dependent on compass readings but a trigonometric calculation based on visual information (seeing the sun break the horizon), altitude, and time. The line comes as the answer to the question, "Where in the world would you have to be to see the sun come over the horizon at that time of day?"
I would hedge my bet that the tables at the time gave TRUE "headings". I concur that the line drawn would not be a "heading" per se, but rather a perpendicular tangent derived from three primary triangulation sources of x, y, and z. Sunrise calculated longitude (x), latitude (y), and height altitude (z). I suspect that it would be up to the individual navigator to figure any localized magnetic variations and convert them to headings for their specific purpose.
Strictly speaking, a line of position (http://tighar.org/wiki/Line_of_position) on a map is not a "heading," although it may help a navigator to decide what headings the plane should fly to reach its destination. To achieve a real celestial "fix," it takes three lines of position to determine location. None of those LOPs may have anything to do with the direction in which a plane is "heading."
Agreed. As a matter fact the "line" wouldn't even be line at all, but rather a curved arc over a spheroid depending on the sun's annual position and the map projection being used. For simplicity purposes to most of us, it might help to think of it as a line. Since the LOP line was being flown north and south, presumably AE was navigating via magnetic compass headings at that point. For purposes of invesitgation, plotting a magnetic LOP (157/337) on a typical map projection, one would first have to subtract the magnetic variation to derive the TRUE course. I'm assuming that TIGHAR factored this into the equation. If so, what types of sources were available (both now and then) to come up with accurate deviation angles in that part of the world?
So your question really becomes, "Do we know how often and how well AE and FN corrected for the difference between true north and magnetic north during the 20+ hours of the fatal flight?" The correct answer from reading the logs of the radio traffic during the final flight (http://tighar.org/wiki/Category:Final_Flight) is "no."
Here's where it gets interesting. It would be curious to find out more about how (as opposed to how often) AE/FN calcuated for magnetic variation, if at all. Did vintage charts at the time have published isogonic lines like today's sectionals? Where there even any accurate measuring techniques for the middle of the ocean like that back then? In a unusual kind of way, I suspect the celestial navigation would have given better angles than the magnetic compass. It's possible FN calculated course corrections to turn left/right 'x' number of degrees rather than a fixed magnetic heading. During the daytime and especially on the LOP, it would be a whole different story. Here I bet they used magnetic heading almost exclusively.
At this point, everyone is welcome to jump in with information, conjecture, and fantasies about what they coulda, woulda, shoulda done. In the absence of evidence, we have a shovel-ready site on which any story may be constructed.
True. It sure is fun discussing the subject matter! Stimulates learning and creates indirect relationships for other facets of the investigation. This helps with solving the much bigger, deductive reasoning, puzzle. Keep cooking!...........
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I'm not a navigator either (but I am an engineer), my guess is that determining the dawn line may be more complicated than we know.
I wouldn't be surprised. But a relatively accurate dawn line seems to me to be part of the argument that following the parallel, advanced LOP is what got AE and FN close enough to see Niku.
Randy's paper also mentions that a person needs to assign a relative probability to each of the events and data sets and I assume that this would provide a great resource to perform "what if" scenarios. Do you know if the code for the simulation still exists?
No, I don't know. I've never seen the code nor heard any details of what kind of machine and language were used.
It also sounds like more work has been done on the nature of the radio propagation of AEs 10E since the simulation was first run and it might be worthwhile to add this and freshen the model. Such is the dynamic nature of research :)
That's true. The 3105 donut (http://tighar.org/TTracks/2008Vol_24/1008.pdf) came well after the Monte Carlo simulation, I think.
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According to the cockpit photos of the of the Electra and Lockheed literature, the 10E had a heading indicator or directional gyro which allowed Earhart to fly a true course. She also had a Sperry gyro-horizon, Pioneer compass, altimeter, airspeed indicator, turn and bank, rate of climb and a Sperry autopilot which held the plane on the course selected. The magnetic compass was a standby compass and had a deviation card which indicated the compass heading to steer a true heading.
When Noonan clocked the sunrise he knew according to his nautical almanac where the dawn line that he was on was located and that the angle of that line was, 157/337, for that day. The line was a true heading plotted on his chart. He knew what the sunrise time at Howland was and therefore he knew how far away they were from the line that ran through Howland.
When, according to his chronometer, they arrived on the LOP looking for Howland, he had Earhart
turn on to a heading of 157 or 337 using the heading indicator which would have been a true heading. To correct for wind, Noonan would figure the wind correction angle and tell Earhart what heading to steer. According to what I have read the wind was most likely out of the NNE, therefore, going down the 157 line they would have had a left quartering tailwind.
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According to the cockpit photos of the of the Electra and Lockheed literature, the 10E had a heading indicator or directional gyro which allowed Earhart to fly a true course. She also had a Sperry gyro-horizon, Pioneer compass, altimeter, airspeed indicator, turn and bank, rate of climb and a Sperry autopilot which held the plane on the course selected. The magnetic compass was a standby compass and had a deviation card which indicated the compass heading to steer a true heading.
OK.
When Noonan clocked the sunrise he knew according to his nautical almanac where the dawn line that he was on was located and that the angle of that line was, 157/337, for that day. The line was a true heading plotted on his chart.
I would like, if possible to preserve the word "heading" for a single compass direction in which one pilots an aircraft. A line on a map doesn't have one heading; it has two (e.g., 337/157), and the two are not interchangeable (flying a heading of 157 degrees is about as different as you can get from flying a heading of 337 degrees).
Noon almost certainly kept a track of the plane's estimated position and heading on his charts as he took fixes or did dead reckoning. From those he would derive a heading for AE to fly. The original dawn LOP on the chart would have been intersected by the line representing their estimated course made good across the ocean and their current "heading."
He knew what the sunrise time at Howland was and therefore he knew how far away they were from the line that ran through Howland.
When, according to his chronometer, they arrived on the LOP looking for Howland, he had Earhart
turn on to a heading of 157 or 337 using the heading indicator which would have been a true heading. To correct for wind, Noonan would figure the wind correction angle and tell Earhart what heading to steer. According to what I have read the wind was most likely out of the NNE, therefore, going down the 157 line they would have had a left quartering tailwind.
OK.
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According to the cockpit photos of the of the Electra and Lockheed literature, the 10E had a heading indicator or directional gyro which allowed Earhart to fly a true course. She also had a Sperry gyro-horizon, Pioneer compass, altimeter, airspeed indicator, turn and bank, rate of climb and a Sperry autopilot which held the plane on the course selected. The magnetic compass was a standby compass and had a deviation card which indicated the compass heading to steer a true heading.
?? I don't understand what is meant by the directional gyro allowing her to fly a true course. Didn't the DG have to be set to match the magnetic compass? The deviation card for the magnetic compass would only give corrections for magnetic errors unique to the plane, not for magnetic variation.
Mona
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When Noonan clocked the sunrise he knew according to his nautical almanac where the dawn line that he was on was located and that the angle of that line was, 157/337, for that day. The line was a true heading plotted on his chart.
I would like, if possible to preserve the word "heading" for a single compass direction in which one pilots an aircraft. A line on a map doesn't have one heading; it has two (e.g., 337/157), and the two are not interchangeable (flying a heading of 157 degrees is about as different as you can get from flying a heading of 337 degrees).
Noon almost certainly kept a track of the plane's estimated position and heading on his charts as he took fixes or did dead reckoning. From those he would derive a heading for AE to fly. The original dawn LOP on the chart would have been intersected by the line representing their estimated course made good across the ocean and their current "heading."
Good point. Some definition clarifications:
Heading = The direction the plane's nose is pointing. This can obviously be very different from the plane's actual direction of travel, especially with wind correction angles. Pilots call this phenomenon 'crabbing'.
Bearing = The direction the plane is actually traveling across the ground (or in this case water). Sometimes referred to as track or course.
* when speaking of these two, it is extremely important to differentiate between TRUE and MAGNETIC *
Magnetic Variation = This is the angle between TRUE north and MAGNETIC north. Sometimes also called magnetic declination. This number has an infinite number of possiblilites depending upon the earth's magnetic field and your geographic location.
Magnetic Deviation = Similar to variation, this is the correction angle to account for localized magnetic disturbances of the metal in the airplane itself. This number is usually a fixed number and does not change as long as you are always in the same airplane.
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According to the cockpit photos of the of the Electra and Lockheed literature, the 10E had a heading indicator or directional gyro which allowed Earhart to fly a true course. She also had a Sperry gyro-horizon, Pioneer compass, altimeter, airspeed indicator, turn and bank, rate of climb and a Sperry autopilot which held the plane on the course selected. The magnetic compass was a standby compass and had a deviation card which indicated the compass heading to steer a true heading.
?? I don't understand what is meant by the directional gyro allowing her to fly a true course. Didn't the DG have to be set to match the magnetic compass? The deviation card for the magnetic compass would only give corrections for magnetic errors unique to the plane, not for magnetic variation.
Mona
Correct.
The DG (directional gyro) would have had to have been manually adjusted for both magnetic variation and magnetic deviation.
There was not a way back then (or even today) to 'automatically' adjust a DG for these types of variables. These would have to be constantly adjusted throughout flight.
Typically today, a deviation card on the compass and isogonic lines on charts are used to make these corrections. Back then, I would be curious to know what source of information was available for magnetic variation? And equally important is how accurate that info would have been?
The earth's magnetic field is very tricky. Remember, 1 degree of angle equals 1 mile of error over the course of 60 miles. This would have been especially critical when dealing with flying along the LOP itself, as it is most likely that magnetic compass would have been the primary means of navigation.
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I would like, if possible to preserve the word "heading" for a single compass direction in which one pilots an aircraft. A line on a map doesn't have one heading; it has two (e.g., 337/157), and the two are not interchangeable (flying a heading of 157 degrees is about as different as you can get from flying a heading of 337 degrees).
Noon almost certainly kept a track of the plane's estimated position and heading on his charts as he took fixes or did dead reckoning. From those he would derive a heading for AE to fly. The original dawn LOP on the chart would have been intersected by the line representing their estimated course made good across the ocean and their current "heading.
You are correct. When AE reached what Noonan thought was the LOP, if she turned NW to 337 she would be flying a heading of 337, if she turned SE to 157, she would be flying a heading of 157, both would be true courses. The LOP would be a true course line as opposed to a magnetic course line as someone previously wrote.
Noonan certainly would have kept track of his estimated position and heading as he progressed and would give AE a true heading to fly. What he probably did not know was what the wind was doing to their track across the water. Ric has estimated that they arrived at the LOP about 200 miles SE of Howland, that being the case, then there was a very strong crosswind component out of the NE.
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According to the cockpit photos of the of the Electra and Lockheed literature, the 10E had a heading indicator or directional gyro which allowed Earhart to fly a true course. She also had a Sperry gyro-horizon, Pioneer compass, altimeter, airspeed indicator, turn and bank, rate of climb and a Sperry autopilot which held the plane on the course selected. The magnetic compass was a standby compass and had a deviation card which indicated the compass heading to steer a true heading.
?? I don't understand what is meant by the directional gyro allowing her to fly a true course. Didn't the DG have to be set to match the magnetic compass? The deviation card for the magnetic compass would only give corrections for magnetic errors unique to the plane, not for magnetic variation.
Mona
Yes,the DG must be set to the mag compass. This is one of the final checks a pilot would make before takeoff. The gyro is either electrically or vacuum operated. The primary advantage of the heading indicator is that it is much easier to make standard rate turns and roll out on a specific true heading as opposed to using a mag compass. In my experience, the heading indicator does not need to be reset all that often. On an instrument check ride, one of the emergency procedures is to be able to fly on the mag compass if the DG fails. I don't recall reading anywhere that AE had a problem with her flight instruments. The only problem recorded, alludes to the Cambridge Exhaust Gas Analyzer.
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A couple of comments on statements earlier in this thread:
The original Line of Position (LOP) seems to have been derived from a dawn sighting. I presume, but do not know as a matter of fact, that the tables used for celestial navigation would have given results in true rather than magnetic terms. Drawing the line that indicates one's location at dawn isn't at all dependent on compass readings but a trigonometric calculation based on visual information (seeing the sun break the horizon), altitude, and time. The line comes as the answer to the question, "Where in the world would you have to be to see the sun come over the horizon at that time of day?"
Marty is correct. Celestial navigation is a matter of mathematics, not earth science, so all directions derived from it are True (meaning referenced to the North Pole). The art of celestial navigation is based on spherical trigonometry and the relative motion of the earth and other heavenly bodies, not on the wandering location of our Magnetic North Pole. Latitude and longitude are measured with reference to the True North and South Poles, the Equator and an arbitrary line through the Royal Observatory in Greenwich.
Good point. Some definition clarifications:
Heading = The direction the plane's nose is pointing. This can obviously be very different from the plane's actual direction of travel, especially with wind correction angles. Pilots call this phenomenon 'crabbing'.
Bearing = The direction the plane is actually traveling across the ground (or in this case water). Sometimes referred to as track or course.
* when speaking of these two, it is extremely important to differentiate between TRUE and MAGNETIC *
Magnetic Variation = This is the angle between TRUE north and MAGNETIC north. Sometimes also called magnetic declination. This number has an infinite number of possibilities depending upon the earth's magnetic field and your geographic location.
Magnetic Deviation = Similar to variation, this is the correction angle to account for localized magnetic disturbances of the metal in the airplane itself. This number is usually a fixed number and does not change as long as you are always in the same airplane.
Personally I like the term track to describe where someone or something has actually been. Bearing can mean a couple of things in navigation; usually the direction of a sighting of something besides whatever you're in or on. You can have bearings on different things at the same time, a lighthouse, a radio beacon and a point of land. Three-arm protractors have three arms for a reason. Plus they're fun to play with. More fun than "Bearing constant, range decreasing!", which is navspeak for a collision course.
For my money, 337-157 is pair of reciprocal directions. Nothing more, until you give me a point that it passes through. Now it is a LOP. If you're on it and travelling SSE, now it is a heading of 157 and the 337 is your six o'clock . Hopefully there is some land ahead.
Magnetic North is somewhere in Canada at the moment and travelling Northwest. Magnetic compasses point to it wherever it happens to be, so you have to account for the difference in polar locations in order to get from a celestial observation or other True direction, to a magnetic one. At any particular location, this difference is an angle and it is called Variation, and it changes depending on where you are in the world. Variation is marked on a marine or aeronautical chart by a compass rose, with True North marked on the outer ring and Magnetic on an inner. The variation is listed inside the rose (at least on a NOAA chart) along with the year it was determined and the rate and direction of annual change. So, to get from True to Magnetic, you need to know roughly where you are (Charleston, SC 32 47' N 079 55' W) and the year (2011). The harbor chart 11524 shows variation of 7 deg 15' W in 2008 with an annual increase of 3'. 3' per year for the three years since 2008 gives me a 2011 variation of 7 deg 15' W plus (3 x 3) equals 7 deg 24' W.
So if I take a magnetic compass and sight across the center and 007 degrees 24 minutes, I will be looking at True North.
Unless there's some iron nearby. Cuz that can mess up a compass. So now we need to account for local conditions. Metallic aircraft or boat structure or wires carrying electric current can deflect a compass by interfering with the earth's magnetic field. Once a compass is installed in a ship or aircraft, you can only account for the local (as-installed) weirdness by preparing a Deviation Card (http://www.google.com/imgres?imgurl=http://myreckonings.com/wordpress/Images/MagneticDeviation/DeviationCard.png&imgrefurl=http://myreckonings.com/wordpress/2009/04/18/magnetic-deviation-comprehension-compensation-and-computation-part-ii/&h=348&w=286&sz=65&tbnid=dITil3REEp_xyM:&tbnh=120&tbnw=99&prev=/images%3Fq%3Ddeviation%2Bcard&zoom=1&q=deviation+card&hl=en&usg=__mx7F0VAmtm1kTRIis0Drz94gsKk=&sa=X&ei=Rp5WTdLWBtSztwfxo_DiDA&ved=0CCsQ9QEwAg).
Deviation can and will change depending on your heading, so a card will show deviations at a number of directions all around the compass. Most recreational marine compasses have adjustments that allow you to limit deviation with small magnets; big units for ships have large iron balls that are used to compensate for local effects. Either way, unless deviation is zero all around, the only way to accurately account for it is to develop, maintain and use a deviation card.
This is done by "swinging the compass" - actually turning the boat, ship or plane in known directions and reading the compass indications. Take the readings in each direction, compute the errors and appropriate corrections and retain for future use on a deviation card.
Not that I think it had anything to do with the loss, but it's a common mistake to think that if the compass is off by plus 5 degrees heading east, it will also be off by plus five heading west. If you have a tool or wire to the right of the compass, it might make the compass magnet at its north pole deflect to the right (east) when you're heading north, resulting in a low compass reading , but pull it to the right (west) when you are heading south, leading to a high reading .
Check the DC illumination wires on a compass, they are probably twisted together to try and cancel out magnetic effects. The same for other series circuit wiring in a well done binnacle.
Now for the mnemonic:
True
Virgins
Make
Dull
Company
So,
Add
Whiskey
True plus Variation = Magnetic, Magnetic plus Deviation = Compass. Westerly corrections are added, so that's the last part. Works in reverse, too, for when you/re trying to get from the real world to a nautical almanac.
We tend to ignore stuff like this in the days of satellite and other electronic navigation because our guidance systems either are not subject to them or do the compensation for us, but in 1937, this was find it or don't type stuff. Maybe even life or death type stuff and FN took it seriously. They swung the compasses in the Miami hanger before they left on the last test flight and rechecked them once in the air over ranges familiar to FN. He may have been willing to bet his life that the RDF would work, but he wasn't missing any bets on being able to do his own DR. Remember, he'd made numerous RDF departures and approaches, so he would know just how lost they would be without it.
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Mark Petersen . If a navigator lets communicate his craft is on an Line of Position , after having messaged to be over a small island , two conditions are clear : 1. The LOP runs over the island´s coordinates , 2. The APL (Aircraft Progression Line) was along the LOP. Most probaly the One Line Approach (Noonan was experienced with it) was used from a point 150 st.mls. off Howland on the main 072 T course with a 102 mls offset lane to compass 055 T. The risk , namely , to miss a very small target by direct approach is so considerable that the "Find the Island" (name given by Francis Chichester) fashion is the first only with a good reliability , first demonstrated bij captain Sumner in 1837 by one observation on the sun , the LOP in the direction of a lightvessel which actually showed up after some time sailing the line along. At 1744 Z Earhart asked for a bearing "on the hour" , to verify the aircraft having Howland straight ahead when still on the main course (072) , at 1815 she asked for a bearing at 1845 to assure the offset being northward when nearing the TOP (turn Off point) for steering 157 T. Howland did not run in sight for reasons explained elsewhere , by which the target was 16 miles on the port bow in lieu of below the APL at 1912 GMT. It is true that a "Fixed Square Search" , set in if a target does not run up , is the most reliable under all circumstances. It is however , very waisteful on fuel so that it can only be used if reserves are for several hours. One of the indications that fuel was low (45 US gall. all in) at 1912 Z is that a FSS was not tried : such operation , namely , has a 100 percent succes rate.
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If a navigator lets communicate his craft is on an Line of Position , after having messaged to be over a small island ,
Neither Earhart nor Noonan ever messaged that they were over a small island.
The risk , namely , to miss a very small target by direct approach is so considerable..
You have a basic misunderstanding of Earhart's plan for finding Howland Island. It was never intended that Noonan would find the island by celestial/DR. His job was to get the flight close enough for the final run in to be accomplished by Radio Direction Finding. By the time Earhart realized that RDF was not going to work she was already on the advanced LOP ("We must be on you..." - too late to use any kind of offset.
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T.Campbell / Moleski. A sunset fix was established at 175453 GMT over coordinates 178deg47´-W/00deg09´N from 1,000 ft altitude with the mariner´s sextant. The 200 miles out message originated from Nikunau Atoll having been reached at 1540 GMT and concerned 300 st.mls made good at 1740 GMT. The precomputed distance Nikunau-sunrise on board was 348 mls whereas 50 miles , 20 min. later ("100 mls out" , 181453 GMT , radio 1815) the offset course 055 T was set in for a 102 mls distance to the turn-off-point on the 157-337 line at 30 mls northwest of Howland´s assumed position. Arriving in the Howland region could never be done by RDF at random so that astro was necessary , as well as a one-line approach , especially since the aircraft was not flown over the great circle but by loxodromic (rhumb line) curves. Up to 1815 speed over ground was 150 mph , afterwards 140 mph , to "arrive" over Howland 1912 GMT. For island not running in sight see elsewhere. It has been recorded (letter capt. Irving Johnson who 1940 visited the Gilberts for search) that an aircraft flew , high altitude , over the island Tabiteuea in the same 1deg23´ latitude as Nikunau , the aircraft (Earhart´s) coming from an initial point 123 mls southwest of Nauru ("Lights in sight ahead" , radio) for a distance of 766 mls.
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A sunset fix was established at 175453 GMT over coordinates 178deg47´-W/00deg09´N from 1,000 ft altitude with the mariner´s sextant.
Baseless speculation.
The 200 miles out message originated from Nikunau Atoll having been reached at 1540 GMT and concerned 300 st.mls made good at 1740 GMT.
Nikunau is not an atoll and it's 506 statute miles from Howland.
The precomputed distance Nikunau-sunrise on board was 348 mls whereas 50 miles , 20 min. later ("100 mls out" , 181453 GMT , radio 1815) the offset course 055 T was set in for a 102 mls distance to the turn-off-point on the 157-337 line at 30 mls northwest of Howland´s assumed position.
Baseless speculation.
Arriving in the Howland region could never be done by RDF at random so that astro was necessary,
Yes, that was Noonan's job, to use astro and DR to get the flight to the Howland region - i.e. within RDF range. That is exactly how the Pan Am flights were made and how Noonan and Manning navigated the Oakland/Honolulu flight in March 1937.
as well as a one-line approach , especially since the aircraft was not flown over the great circle but by loxodromic (rhumb line) curves.
It is irrelevant whether Noonan used a great circle or rhumb line curves. The fact is that he clearly got the airplane to with radio reception range of Howland.
Up to 1815 speed over ground was 150 mph , afterwards 140 mph , to "arrive" over Howland 1912 GMT.
You're backing into the numbers.
For island not running in sight see elsewhere. It has been recorded (letter capt. Irving Johnson who 1940 visited the Gilberts for search) that an aircraft flew , high altitude , over the island Tabiteuea in the same 1deg23´ latitude as Nikunau,
In his letter to Bessie Young of June 4, 1940, Irving Johnson says only that a missionary on Beru told him that he had from a native that "...it was believed that the Earhart plane had flown eastward high up over the island of Taputeouea." The missionary cautioned that "it was hard to tell whether some ignorant native had actually seen an airplane or wished he had.." Maybe a plane was heard or seen, maybe not, but to say that it was reported "in the same 1deg23´ latitude as Nikunau" is incorrect. Tabiteuea is a long skinny atoll stretching from 1° 06 ' in the north to 1° 32' in the south. Johnson's third-hand account says nothing about where on the atoll the plane was supposedly heard or seen.
the aircraft (Earhart´s) coming from an initial point 123 mls southwest of Nauru ("Lights in sight ahead" , radio) for a distance of 766 mls.
The reported message heard by Nauru was "Ship in sight ahead." Probably SS Myrtlebank but no way to be sure.
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R.G. "Mariner´s sextant for back up only" . Whereas a bubble sextant is needed to observe from higher altitudes (no visible horizon) , the mariner´s sextant is useful c.q. needed for two reasons : 1. at lower (p.e. 1,000 ft) altitudes with visible horizon. 2. If sunrise of the upper limb is to be observed. Almanac tables register "sunrise" in LMT for U.L. on the horizon. Only the U.L. is useful since due to refraction the lower limb suffers severe distortion. Thence , for a sunrise position check flying low and using the mariner´s sextant are unconditional necessities. An artificial horizon sextant is unable to register on the upper limb. A sunrise fix at p.e. 1744-45 GMT at 200 mls off Howland was impossible since the sun was for the longitude still below the horizon. As a third point mariner´s sextant observation features considerably more precision w.r.t. operating the bubble sextant. The ship´s sextant was p.e. also used by Francis Chichester for one line approaches ("Find the Island") to small islands (a.w. Lord Howe) when crossing the Tasman Sea by airplane.
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It has btw been said by researchers that Noonan´s bubble sextant observations may have been injured by Coriolis disfigurement of the bubble position w.r.t. the vertical crosshair. Coriolis displacement (to r.h.side for N-hemisphere) is a function of the Coriolis force , this being very small , and the speed of the aircraft which consequently must be very high to induce miscalculation. The maximum Lockheed Electra airspeed was by far too slow for occasioning any measurable bubble shift.
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"lights in sight ahead" . In an article , National Geographic , 1935 , Earhart confirms the non-visibility of ships by night from an aircraft 8,000 ft up : she thought it unlikely that she would ever see any vessel generally on the surface of the large sea when flying thousands of feet above it. When flying the great circle (chord no.9) it would have been possible to see the ship Myrtlebank the more or less ahead. But the great circle was not flown and it seems best to follow those who heard "Lights in sight ahead" : the lights of Nauru at 1030 GMT from 123 mls distance.
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"When flying the great circle (chord no.9) it would have been possible to see the ship Myrtlebank the more or less ahead. But the great circle was not flown and it seems best to follow those who heard "Lights in sight ahead" : the lights of Nauru at 1030 GMT from 123 mls distance.
I say again, the correct quote is "ship in sight ahead."
The original source is a State Department telegram from Sydney, Australia dated July 3m 1937, which reads: “Amalgamated Wireless state information received that report from ‘Nauru’ was sent to Bolinas Radio ‘at 6.31, 6.43 and 6.54 PM Sydney time today on 48.31 meters (6210 kHz), fairly strong signals, speech not intelligible, no hum of plane in background but voice similar that emitted from plane in flight last night between 4.30 and 9.30 P.M.’ Message from plane when at least 60 miles south of Nauru received 8.30 P.M. Sydney time, July 2 saying ‘A ship in sight ahead.’ Since identified as steamer Myrtle Bank sic which arrived Nauru daybreak today."
the lights of Nauru at 1030 GMT from 123 mls distance.
"New Nauru fixed light latitude 0.32 S / longitude 166.56 E five thousand candlepower 560 ft above sea level visible from shios to naked eye at 34 miles"
Earhart was heard to say "Ship in sight ahead" at 1030Z. Roughly three hours earlier she had said she was at 8,000 feet "over cumulus clouds." We don't know her altitude or the cloud conditions at 1030Z but you're suggesting that she saw "lights" (not a light) from 123 miles away.
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The problem I see with the concept of making this flight by the offset method is based in the uncertainty associated with flight parameters and the accumulated errors produced by them.
Offsets only make sense if they don't add more risk or error than they compensate for. For example, if you're flying from Havana to Key West (roughly 020T) and for some reason don't have enough fuel to continue on to mainland Florida if you miss to the west, it makes sense to shade your course to the right (say 030T) and turn west when you see the Keys. The Keys are fixed, visible to the naked eye, they lead to Key West and you have a very high probabliity of finding them, so you're not introducing new error or uncertainty. You are, however, guaranteeing a longer flight.
Doing the same thing based on a DR track buys you very little, and at quite a price in terms of risk and uncertainty. For simplicitys sake, consider a flight from a point on the equator to a small island 1000 nm east on the equator. If you think an offset is a good idea, go ahead and fly to a spot in the ocean (not an island, coastline, depth contour or lighted range, just a random-looking patch of ocean) exactly 100 nm south of the island, then hang a left. The island will be exactly 100 nm ahead of you. Piece of cake.
If: You were able to hit the correct longitude. At night. No identifiable landmarks. No decent winds aloft data. Maybe a single LOP a couple hours before ETA.
If AE and FN intended to try this, it would require that they not home in on the RDF bearings they intended to be picking up. As Itasca and/or Howland came into range, they would have to watch the bearing move from almost dead ahead to straight off the port wing and then and only then only then turn at that point. Then fly into their destination from a direction 90 degrees from their origin.
Without telling the people that would be looking for them that they would be coming in from the south.
Seems a bit of a stretch to me.
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A/c came in from the North in this case , the offset distance being shortest , radio communications give the impression that bearings were asked for to verify having Howland head on , later to starboard up to 90 deg. I see btw that the nav handbook here copied ends 1924 ; no problem in itself but developments 1935 were far ahead.
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The problem I see with the concept of making this flight by the offset method is based in the uncertainty associated with flight parameters and the accumulated errors produced by them.
Offsets only make sense if they don't add more risk or error than they compensate for.
Well said.
If AE and FN intended to try this, it would require that they not home in on the RDF bearings they intended to be picking up.
The only reason to do that would be if you trust your LOP calculations more than you trust the RDF bearings. In the middle of the Pacific there's not much chance that you're homing on the wrong station.
In this situation an offset makes no sense and there is zero evidence that an offset was used.
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Probabla Noonan´s D.R. and astro checked navigation was very accurate and it must be considered true that the crew had seen Howland appear by continuing on the 72 T heading after sunrise (1755 GMT , distance off 161). So in this specific case a one line approach created an additional risk for failure. However , by generic point of view , the one line approach is a very reliable fashion , given that reaching the (advanced) position line is a direct hit. In the Earhart case it was not , with the additional draw back that a small (say 10-15 st.mls) spot off error does not come to light because the same (sun´s) altitudes continuously appear on the error line with a small flight distance difference : the longer a navigator navigates the wrong line , the more he gets convinced to be over the correct one.
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... I know of no evidence that she used an offset ...
To me, the fact that the last recorded transmission said, "We are flying the line north and south" (http://tighar.org/wiki/%22We_are_on_the_line_157_337%22) makes it pretty clear that they were not using the offset method. If they had used that method, they would have 'known' (i.e., had good reasons to believe that they knew) which way to turn toward Howland.
This is only true if the intersection of the offset track and the advanced LOP was a direct hit on the correct line. If a line east-or westwards of the right one has been taken , your destination does not run in sight and it is this occurrence which took evidently place at July 2. The one line approach was not used sporadically , it was on the contrary a very reliableroutine operation , also to find islands during Noonan´s exploration flights with PanAm , for which RDF was hardly or not necessary : one bearing to or from destination verifying having it head on before steering on the offset could do. The method has been found in 1837 by Sumner and it has since been used universally in sea and air navigation.
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also to find islands during Noonan´s exploration flights with PanAm , for which RDF was hardly or not necessary : one bearing to or from destination verifying having it head on before steering on the offset could do.
Nonsense. Can you produce ANY documentation that Noonan EVER used an offset when navigating for Pan Am during the survey flights? In describing his navigation methods (1935 letter to P.V.H. Weems published in Popular Aviation in 1938) Noonan makes no mention of using an offset. The chart Noonan used on Earhart's Oakland/Honolulu flight are on file at Purdue. They show that no offset was used. The chart Noonan used to navigate Earhart's South Atlantic crossing shows that the flight made landfall on the African coast well south of the intended destination (Dakar) but there is no indication that it was an intentional offset.
Show us some documentation to back up your statements of fact or stop wasting our time.
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It is mentioned in several biographies that Noonan was familiar with the offset fashion. When however, a flight finishes by landfall in a region with a vast mainland behind , or at big with high ground islands , the operation is not needed. Honolulu and the coast of Africa are examples for such case. For very small islands surrounded by waters only , the offset approach was generally considered to be a necessity to avoid the risk of passing the destination beyond visual range.
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It is mentioned in several biographies that Noonan was familiar with the offset fashion.
I am not aware of any biography of Fred Noonan. What you're saying is that you have read biographies of Earhart in which the author claims that Noonan was familiar with the offset method. Maybe he was, but an author's claim doesn't make it so unless the author cites a primary source. If you want to claim that Noonan was familiar with the offset method you need to provide a primary source for that statement.
For very small islands surrounded by waters only , the offset approach was generally considered to be a necessity to avoid the risk of passing the destination beyond visual range.
That's why Pan Am built large, expensive RDF stations at all of their island destinations.
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R.G. The primary source is Earhart herself : when she says to fly a position line heading 157-337 compass , she admits that the one line approach has been executed , especially when communicating "we must be on you". Besides this , a direct approach to so small an island when coming from a 10 hrs. plus nightflight was for practice suicidal , uniformly notified in textbooks.
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R.G. The primary source is Earhart herself : when she says to fly a position line heading 157-337 compass
Earhart did NOT say "to fly a position line heading 157-337 compass." She said, "We are on the line 157 337.."
she admits that the one line approach has been executed , especially when communicating "we must be on you".
I disagree with your guess about what she meant.
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Besides this, a direct approach to so small an island when coming from a 10 hrs. plus nightflight was for practice suicidal, uniformly notified in textbooks.
Practice suicidal? Where did that come from? ???
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R.G. At 2014 GMT she additionally said : "..We are running north and south .. "
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Ashl. 5 to 10 % of the flight length is the possible deviation in latitude : for a 350 mls flight between 17.5 & 35 miles , asking for 26.5 (30) miles offset by way of example to be sure yo are northward or southward of a small island when on the Turn-off-Point , then having the destination straight ahead. The offset operation has 2 lanes , so to be laid out that upper and lower TOP both are north or south of your target. Under ideal weather Howland from 1,000 ft altitude is visible from 10-12 mls with the unarmed eye , the optical angle from westwards then being 2 arcmin whereas the eye´s resolution asks for a 1 arcmin angle minimum for a detectable projection on the retina. With smaller opening angles the image point falls in between two cells and there is no vision.
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The primary source is Earhart herself : when she says to fly a position line heading 157-337 compass , she admits that the one line approach has been executed , especially when communicating "we must be on you". Besides this , a direct approach to so small an island when coming from a 10 hrs. plus nightflight was for practice suicidal , uniformly notified in textbooks.
This is only one of many possible interpretations of this transmission. Unfortunately, this is also the least likely interpretation as well. As Ric has already said, there is nothing to indicate any intent of using an offset course. Indeed, past practices in and of themselves argue against it.
Clipper Route SOP was to navigate direct ( or as direct as was possible ) until in the vicinity, and then at that point ADF was used to 'home' on the destination. PanAm built large high powered transmitting stations at all of their ports-of-call for just this purpose.
You appear to forget that this was also the intent when it came to finding Howland. This flight was no different from the scores of Clipper Routes that Noonan had personally laid out and flown. There was never any plan for Noonan to be the sole source of navigation to Howland....only to (once again) get them into the neighbourhood and then let the ADF take them in.
A more or less workable plan, when everything functions properly. When it doesn't....well, we've seen what happens then.
No...for better or worse, there is no evidence that I have seen to indicate an offset route. Indeed, when one is planning to home an ADF/NDB signal the last several miles, an offset would be more a hinderance than help. Not to mention that doing so would also require more fuel....not a sterling plan when you're already offloading items to reduce weight and fuel consumption in the first place.
....TB
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Th.B. Agreed , but by a one line leg + LOP you have 2 succes ratings : the offset plan itself plus RDF in case of failure. If both fail , one really (RDF) and one (One Line) seemingly : stay on the line (what they did) , or going astray gets on stage. In our case , RDF went first (bearings asked for 1800 , 1845 GMT) to establish A/c´s position w.r.t. the island , OLA was second , and anyway the reached position line was erroneous , not by precomputation but by observation fault. The OLA took 32 additional mls for roughly 8.5 USG. Remark : for direct approach without sunrise fix etc. you do not inch down to 1,000 ft , on the contrary you stay as high aloft as possible to the effect of having a large image of the island´s surface.
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Mike Piner
We have little or no indication of sunrise, from the radio logs, how did she know she was "about 200 miles out", and "must be on you".
Time alone wont guarantee you are at Howland. what is your best supposition? Mike piner LTM
200 mls off Howland may have been derived from DR on the 498 mls track to Howland from Nikunau , reached 1540 GMT : 1740 - 1540 hrs x abt. 150 mph = 300 made good , 200 to go on direct. The 100 mls out position was recorded after sunrise @ precomp.150 mls out @ 1755 Z + 20 min further at the 100 mls out precomputed initial point for commencing OLA. AE said : "Must be on you but do not see you" after flying (140 mph) the LOP from the turn off point (1859Z) to ´Howland´, 30 mls , ETA 1912 Z. All these figures seemingly look too definitive for Anglo-Saxon usance , but they are open to discussion from a fixed model ; in the other case the theory would begin with doubt in lieu of statements , the latter to more European principles the point of departure for referees.
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All these figures seemingly look too definitive for Anglo-Saxon usance , but they are open to discussion from a fixed model ; in the other case the theory would begin with doubt in lieu of statements , the latter to more European principles the point of departure for referees.
Anglo-Saxon usance???? European principles???
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Or reversed , A-S scientific publications : long sentences , carefully proceed . E-publication : short sentences , definite statements. E : : Elephants eat grass. A-S : Elephants eat grass, for the period of our investigation.
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All,
Look at Kelly's aircraft performance report Page 3 item (g): "100-150 miles out (set up a ) power glid at 250-300 fpm and maintain cruse power setting".
Why would you follow this program if you were approaching an imaginary line (an "off-set on the LOP") on a map in the cockpit? You get there then what? Do you then cruse along at 1000 feet eating up fuel and time trying to find your landing point.
Or do you set up a direct approach to Howland basis your navigator's instructions and when you get there, no island, say "we must be on you but can't see you"?
I would suggest the latter - straight-in approach and at a higher speed then normal cruse for the last 100-150 miles; see the discussion on the site regarding the "200 miles out and the 100 miles out time question"
Ted Campbell
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Why is it then , this head on approach supposedly being first choice , that the island did not run in sight ?
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Why is it then , this head on approach supposedly being first choice , that the island did not run in sight ?
(sigh) No one knows (including you) but we do know that the RDF they were relying on for the final run in to Howland did not work. One reasonable possibility is that they hit the advanced LOP well south of Baker ("We must be on you ...") and started searching for Howland by flying along the advanced LOP - first "up" the line, then "down" the line ("We are on the line 157 337 ..running on line ... north and south.") Running southeastward on the line was their best chance of finding land.
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Or reversed , A-S scientific publications : long sentences , carefully proceed . E-publication : short sentences , definite statements. E : : Elephants eat grass. A-S : Elephants eat grass, for the period of our investigation.
Obligatory old-time philosophy of science joke, entirely relevant to the question of how to assess evidence: three philosophers are riding through Scotland in a train and look out the window to see some black sheep grazing in a pasture. The first says "Ah, I see the sheep in this district are black." The second says, "More correctly, some of the sheep in this district are black." The third clears his throat and says, "Some of the sheep in this district are black on at least one side.."
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Very good , that is what I mean.
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Very good , that is what I mean.
You're the guy drawing firm conclusions about what happened based upon your own assumptions, many of which we have shown to be groundless.
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Not all my own conclusions : W.L.Polhelmus , navigator @ 3rd decennium flight , 1967 , by A.Holtgren c.s. studied nav tables of the era and thinks Noonan having made an error when computing the Single Line Approach. Mechanic Koepke saw the island first from 10-12 miles away.
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T.Cmpbll . One line approaches are helpful at the end of long flights of which the accumulated error is non detectable ; because of the offset circuit plus LOP concept , no ETA can be given : TA is when the destination runs in sight below the APL. On the contrary , for a straight line flight into destination , ETA can be given on basis of known speed and distance. Good question : why did the Earhart crew not communicate "100mls out ETA 1855Z" i.l.o. "We must be on you...." at 1912Z ?
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An ETA was given at the departure of 18 hrs. I would question why there wasn't an update along the way but either way a straight in approach seems to be the best guess.
Ted Campbell
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TG.Cmpll. For a direct flight into destination a pos.lne. , advanced or not , is of no use since @ ETA both the elevation and the azimuth of (for this case) the sun have changed since sunrise when the LOP was established. A very good navigator could attain 5% DR uncertainty at the end of a long range over ocean flight ; for a last check point at 500 mls off destination this accounts for a 12 1/2 miles radius circle of uncertainty , representing the direct approach risk of overshoot being 100% if the target visual range is less. From 1,000 ft altitude westwards the optical field width of Howland is 1 arcmin for 12.5 mls distance in clear air, this being the lower limit of resolution for the eye to form an image. No dutyful navigator would venture a direct spot on hit for Howland , with the sun ahead and early morning haze present. The "18 hrs time" @ takeoff message , btw , was not an ETA , but an assessment of duration.
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For the umpteenth time:
The intention was never to find the island by celestial and DR alone. The plan was for a direct approach using RDF. There is nothing - repeat nothing - in the literature to suggest that an offset approach was contemplated. Endlessly repeating groundless speculation does not increase its credibility. Unless you have hard evidence to offer to support your theory either give it up or take it someplace else.
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R.G. Before commencing RDF exercitions it is necessary to bring your aircraft within simultaneous radio range coverage , by DR checked celestially. I never saw a document stating that single RDF head on approach was planned , is it somewhere available ?
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R.G. Before commencing RDF exercitions it is necessary to bring your aircraft within simultaneous radio range coverage , by DR checked celestially.
Exactly.
I never saw a document stating that single RDF head on approach was planned , is it somewhere available ?
Not to my knowledge. Neither is there a statement of the intention to use an offset. Noonan's methods when navigating for Pan Am are documented in his letter to P.V.H Weems, subsequently published in Popular Aviation magazine's May 1938 issue. There is no mention using an offset. Noonan's methods when navigating for Earhart are documented in the charts he used on the Oakland/Honlulu flight of March 17/18 1937 and the Souith Atlantic Crossing of June 7, 1937. In neither case did he use an intentional offset. In short, there is zero evidence that Noonan ever used an offset. It's reasonable to suppose that he was familiar with the method but nothing to suggest that he used it on the Lae/Howland flight. Your entire theory is based upon your opinion that he SHOULD have used an offset, but arguing that something happened because it should have happened is folly. Should Earhart have set off around the world without understanding how her RDF worked? Should Earhart and Noonan have tried to fly around the world in 1937 without knowing Morse code? Should Fred Noonan have bet his life on the aeronautical competence of a person who had already nearly killed him in a pilot-error accident? Harry Manning had the good sense to bail. Noonan was more desperate. In my view, to have any chance of solving the mystery of the Earhart disappearance it is essential to first grasp the staggering level of arrogance and negligence that permeated every aspect of the world flight. The only surprise is that they got as far as they did.
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R.G. Agreed . I somewhere have read that , when "gingerly inching down" , Earhart was by the navigator advised to keep the radio (bearing) station slightly to the right when being 80 mls off . Will try to find back.
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"gingerly inching down" - pay attention! What did Kelly recommend as an approach power setting? I've pointed this out to you before.
Ted Campbell
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TG.Cmpbll . The report "Inching down" etc. is from Earhart herself in one of her books written before July 1937.
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TdG.Cmpbll . If all your RDF exercitions went awry when on a direct to target course , so that you do not know where exactly you are. Question : how would it then be possible to announce "We must be on you ..." at a defined point of time ? The answer is that besides RDF you have another fashion of fixing your course tracks.
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Question : how would it then be possible to announce "We must be on you ..." at a defined point of time ? The answer is that besides RDF you have another fashion of fixing your course tracks.
You're hoisted with your own petard. We know that the RDF aspect of the flight did not work so if Noonan used an offset there was never a time when he (or AE) could say "We must be on you..."
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R.G. If you steer on your offset circuit @ 1815 GMT (sunrise o/b was @ 175453 , @ 1815 supposedly 100 mls out , alt.1,000) , the offset lane being 102 mls , you reach the Turn Off Point on the position line @ 1859 GMT , then 30 mls offset to go course 157T and you arrive @ the Howland (assumed) coordinates at 1912 GMT , A/c´s groundspeed 139-140 mph.
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TdG.Cmpbll . "gingerly inching down". The C.Johnson report mentioning "power glide @ 100-150 mls off" is of June 19 , 1936 , hence it concerns the "1st" attempt with at the end of the flight the vast (´main´) land of New Guinea , with no risk to miss it when being off course.
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MkPetsn. For a navigator like Noonan it was child´s play , when on any land point , to establish their latitude of position by the sun at noon and the sun a few hours later. It was even possible to measure the longitude (by the s.c. Douwes Formula) , or by a two-star fix. Why then , transmit useless bundles of words " received" by "Betty" in lieu of the coordinates they were close to , or the island they were at ?
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Boy are you way off in your understanding of Kelly's data and aircraft operational specifications! If you think Kelly drew up op specs based upon where AE was going to land you have no idea of what an aircraft goes through to be certificated.
Stick to your navigation mumbo jumbo and stay away for aircraft performance.
Ted Campbell
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TdG.Cmpbll . Sounds not very scientifically . I btw for the purpose studied Aircraft Performance Theory at Delft , The Netherlands , U.O.T. , Aeronautical Faculty , 1988-2004.
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T,Cmpbll . 1815 to 1912 GMT is 57 minutes. !815 " 100 mls out" radio . For straight in approach A/c should have made 105 mph (this being considerably below "Johnson") , or , A/c should have arrived at 1840 for "Johnson" , lower limit . The difference of 32 min to 1912 represents an any length detour D = X - 100 within reasonable speed limits of A/c.
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What?
Ted Campbell
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[... post deleted by author in an attempt to elevate the overall tone ...]
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for Alan...
That, my friend, is a Classic post ! Thank you for stating so eloquently what we've all been thinking.
Well done, sir !
pd
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"What's our vector Victor?" "We have clearance Clarence!" "Roger.....huh?" "Roger, over.....What?" "Roger...huh?"
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OK, folks, we've had one (1) complaint from a Forum member who thinks that the last few replies to h.a.c. have been unfair.
Let's try to elevate the tone, if possible. If you don't have an argument to make against h.a.c.'s posts, perhaps you could just pass over them in silence. I don't buy those parts of his posts that I can decode--his conclusion seems to be that AE and FN splashed down within a minute after the last transmission--but, so far, we have not set adherence to the Niku hypothesis (http://tighar.org/wiki/Niku_hypothesis) as a precondition for participation in the discussion. In fact, there has been, from time to time, some enthusiasm expressed for the tradition of skepticism as part and parcel of the methods used by scientists. That's a double-edged sword. While it licenses us to express doubt about other people's views, it also licenses them to return the favor.
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OK, folks, we've had one (1) complaint from a Forum member who thinks that the last few replies to h.a.c. have been unfair.
Let's try to elevate the tone, if possible. If you don't have an argument to make against h.a.c.'s posts, perhaps you could just pass over them in silence. I don't buy those parts of his posts that I can decode--his conclusion seems to be that AE and FN splashed down within a minute after the last transmission--but, so far, we have not set adherence to the Niku hypothesis (http://tighar.org/wiki/Niku_hypothesis) as a precondition for participation in the discussion. In fact, there has been, from time to time, some enthusiasm expressed for the tradition of skepticism as part and parcel of the methods used by scientists. That's a double-edged sword. While it licenses us to express doubt about other people's views, it also licenses them to return the favor.
In response to your reasonable request I have gone back and removed my snarky comment. But I would suggest that in this particular case, the objection to many of the posts in question does not appear to be based on whether or not the poster subscribes to any particular hypothesis, it is based on the poster's somewhat difficult-to-read style, which some interpret as deliberately obfuscatory. I suspect that the poster's native language is other than English, and that, accordingly, he should be granted a good measure of consideration before we jump on him for his writing style.
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OK, folks, we've had one (1) complaint from a Forum member who thinks that the last few replies to h.a.c. have been unfair.
Let's try to elevate the tone, if possible. If you don't have an argument to make against h.a.c.'s posts, perhaps you could just pass over them in silence. I don't buy those parts of his posts that I can decode--his conclusion seems to be that AE and FN splashed down within a minute after the last transmission--but, so far, we have not set adherence to the Niku hypothesis (http://tighar.org/wiki/Niku_hypothesis) as a precondition for participation in the discussion. In fact, there has been, from time to time, some enthusiasm expressed for the tradition of skepticism as part and parcel of the methods used by scientists. That's a double-edged sword. While it licenses us to express doubt about other people's views, it also licenses them to return the favor.
In response to your reasonable request I have gone back and removed my snarky comment. But I would suggest that in this particular case, the objection to many of the posts in question does not appear to be based on whether or not the poster subscribes to any particular hypothesis, it is based on the poster's somewhat difficult-to-read style, which some interpret as deliberately obfuscatory. I suspect that the poster's native language is other than English, and that, accordingly, he should be granted a good measure of consideration before we jump on him for his writing style.
My guess based on this post is the Netherlands
TdG.Cmpbll . Sounds not very scientifically . I btw for the purpose studied Aircraft Performance Theory at Delft , The Netherlands , U.O.T. , Aeronautical Faculty , 1988-2004.
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If only they'd used their GPS and Sat-phone, all this unpleasantness could have been avoided.
:o .......What?
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M.Molsk. The magnetic variation and TC/MC was given for 3 regions by C.S.Williams in the great circle chords listing & chart , see illustration p.29, EJN-2008 article.
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H. A. C. Van Asten,
Would you just post the point you are trying to make! Make it as simple as you can so most of us can follow your point.
Thanks,
Ted Campbell
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I'm thinking it's time for another viewing of Amelia ... and even if Fred didn't actually say it, grin at what is surely one of the great movie quotes of all time: "Got room for 180 pounds of -------. ?"
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Mr Gillespie ,
You replied several times to my remarks on the One Line Approach having been used or not in the roads of Howland. Your last statement is that the OLA was not common fashion in the era and in addition you say that Pan American Clippers of the 1935-1940 era , on the Alameda via Guam to Manila etc. way , were always flown inbound the range of land RDF stations that homed them straight in after their signal had been received on board . Well then , in document "Francis Chichester , 1922 Portuguese flight , Navigator , p. 238 , we read : "April 12 , 1922 . At 1815 navigator found plane to be on a LOP which , extended to the left , cut through the tiny rocky objective. Pilot changed course accordingly and objection was attained" . And on p. 239 : " Pan American World Airways later made island landfalls on transoceanic flights by using the same technique" . It is herewith clear that F.Noonan , navigation officer of the Clipper air services from the beginning, knew the method and that he had experience with the methodology. The term "preventer" for a marine sextant in addition to the bubble sextant/octant may henceforth be transcribed as "in reserve" , namely for the event that an aircraft , already flying low inbound , lost the RDF signal in which case the marine sextant and the unblended horizon would be a perfect godsend.
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Well then , in document "Francis Chichester , 1922 Portuguese flight , Navigator , p. 238 , we read : "April 12 , 1922 . At 1815 navigator found plane to be on a LOP which , extended to the left , cut through the tiny rocky objective. Pilot changed course accordingly and objection was attained" . And on p. 239 : " Pan American World Airways later made island landfalls on transoceanic flights by using the same technique" .
Is that a book or an article? Who wrote it? Please provide a proper citation.
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R.G. It is a book , as seen by the footnotes. Wil try to find back with Google & report.
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Warning! Stupid question
As it says above!!!!
If you had a LOP and were flying North and South,could you use a simple compass to keep yourself on the line?
(I have zero navigational/pilot knowledge or experience) Its just something I wanted to ask. :)
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Well then , in document "Francis Chichester , 1922 Portuguese flight , Navigator , p. 238 , we read : "April 12 , 1922 . At 1815 navigator found plane to be on a LOP which , extended to the left , cut through the tiny rocky objective. Pilot changed course accordingly and objection was attained" . And on p. 239 : " Pan American World Airways later made island landfalls on transoceanic flights by using the same technique" .
Is that a book or an article? Who wrote it? Please provide a proper citation.
Francis Millet Rogers, “Precision astrolabe: Portuguese navigators and transoceanic aviation,” Academia Internacional da Cultura Portuguesa; [distributed in the U.S.A. by W. S. Sullwold, Taunton, Mass.], 1971, 397 pages
Google digitized it in 2008 from a copy at the library of the University of California -- Davis, but only snippets can be seen online with Google Books.
From page 238,
Realizing that the late-afternoon LOP's were trending ever more toward a NS stance, navigator at 1715 recommended to pilot that he turn right and start to cut across the LOP's. At 1815 navigator found plane to be on an LOP which, extended to the left, cut through the tiny rocky objective. Pilot changed course accordingly and objective was attained.
The second quote given by Mr. van Asten is shown to be at the top of page 239, with what appears to be a footnote number of "8". To see from whom that statement about Pan American's use of the technique came will probably require a visit to a library. Copies of the book are said to be in the vicinity of Washington, DC, at the Library of Congress, the Smithsonian, NOAA (in Silver Spring, MD), and in the Nimitz Library at the U.S. Naval Academy.
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Warning! Stupid question
As it says above!!!!
If you had a LOP and were flying North and South,could you use a simple compass to keep yourself on the line?
(I have zero navigational/pilot knowledge or experience) Its just something I wanted to ask. :)
Not a stupid question.
A compass tells you which direction the nose of the plane is pointing. That's valuable information, but it doesn't tell you which direction the plane is moving over the ground. The compass doesn't know if the plane is flying in the same direction it is pointing, sitting on the ground, or moving sideways, etc.
If there were no wind, then the plane would move in the same direction it was pointing, and if you pointed the plane straight South you would end up at some point due South of where you started. But if there were a wind blowing from the East and if you were to point the plane straight South, then you will end up somewhere to the Southwest, depending upon how fast the wind is blowing relative to how fast you are flying.
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OK bear with me "stupid warning If I knew I was running on a LOP like FN may or may not have plotted, could i not just use the compass to keep a bearing of ?South, South East? to head towards the Phoenix group. If the wind was against me could I not just keep to a heading that I had in mind?
(this is based upon the idea that as a hill walker in fog/mist and lost if i just keep to a compass bearing that directs me towards something then i should get there?)
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Mr.R.G. Book on OLA by PanAm is : F.M.Rogers , Precision Astrolabe , W.S.Sullwold , Taunton Mass 1971.
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OK bear with me "stupid warning If I knew I was running on a LOP like FN may or may not have plotted, could i not just use the compass to keep a bearing of ?South, South East? to head towards the Phoenix group. If the wind was against me could I not just keep to a heading that I had in mind?
(this is based upon the idea that as a hill walker in fog/mist and lost if i just keep to a compass bearing that directs me towards something then i should get there?)
The problem is the difference between heading (the direction in which your plane or ship is pointed) and course - the track you are following over the ground. This is a new concept for people who are used to using a compass while walking, or in a car, because on foot and in a car, the ground stays still (i.e. point south and walk in a straight line and you go south). But in a ship or a plane, the water or air does not stay still. Point a plane south and fly in a straight line and you go south x the wind velocity. Unless you have a very good estimate of what the wind is doing (in a plane) or current (in a boat), you can't steer to a course, only to a heading.
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OK one final stupid question and thanks for your patience.
On foot i walk and if i stray to my left as is common i can use my compass to see this? Why not see the arrow in my compass on a plane move?
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The second quote given by Mr. van Asten is shown to be at the top of page 239, with what appears to be a footnote number of "8". To see from whom that statement about Pan American's use of the technique came will probably require a visit to a library. Copies of the book are said to be in the vicinity of Washington, DC, at the Library of Congress, the Smithsonian, NOAA (in Silver Spring, MD), and in the Nimitz Library at the U.S. Naval Academy.
As you correctly imply, we can't judge the credibility of the allegation unless we know the source. Noonan makes no mention of using an offset and I don't recall any reference to Pan Am using offsets in various books (i.e. The Chosen Instrument, Bender/Altschul, 1982; Pan American's Pacific Pioneers, Krupnick, 2000; etc.)
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OK one final stupid question and thanks for your patience.
On foot i walk and if i stray to my left as is common i can use my compass to see this? Why not see the arrow in my compass on a plane move?
Because the compass in the plane does not move. It tells us the direction the nose of the plane is pointed not the actual movement of the plane relative to the ground. In an extreme example the plane would appear from the ground to be flying with its nose rotated left or right from its actual movement. See "crabbing" = To direct (an aircraft) partly into a crosswind to eliminate drift.
In the hiking example I see two possibilities. One takes place in clear conditions. A sight is taken on a landmark. The hiker follows the azimuth. Ground conditions may obscure the landmark at times. Each time the landmark is viewed a new sight is taken and the corrected new azimuth is followed. In the second case the landmark is not in view. The azimuth is taken from a map. The hiker follows that bearing. He may stray off course due to conditions such as heavy brush or fog. If there is any significant distance to traverse my guess is he would not reach his destination straight on. Once he has gone the requisite distance hopefully he will recognize a terrain feature or road that will lead him to the goal. Think of the straying off course as analogous to wind drift.
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OK one final stupid question and thanks for your patience.
On foot i walk and if i stray to my left as is common i can use my compass to see this? Why not see the arrow in my compass on a plane move?
There's a subtle but important difference between two different ways of "straying to your left."
Imagine yourself on a football field. Stand in the center of one goal and note that the other goal is directly South of you. Hold a compass down by your waist. Now put a large bucket over your head so that you can look down and see the compass, but you can't look around and see any of the field at all. There are no painted lines and that the turf is very smooth and even so it gives you no visual cues. All you can see is the compass.
Start walking straight ahead, keeping the compass needle on 'S'. You will eventually reach the middle of the other goal, or within a couple of feet.
Next, imagine that every 5 steps, I say "Stop", and instruct you to close your eyes while I pick you up, shake you around a little bit, and put you back down, at which point you can open your eyes again and resume walking. Let's say it takes 50 steps to cross the field, so I do this ten times.
- If what I did while I picked you up was simply turn you, say, 10 degrees to the left, then when I put you back down and you open your eyes again, the compass needle won't be pointing at 'S' any more, and all you need to do is turn to the right until the compass needle points to 'S' again and resume walking. You'll get to the other goal just fine.
- On the other hand, what if what I did while I picked you up was not to turn you at all, but instead to carry you five feet to your left and put you back down. (remember, I'm shaking you so you can't really tell by the feel if I'm turning your or displacing you). Now, when I put you back down and you open your eyes, the compass will still be pointing to 'S', so you'll just resume walking. But, after doing this ten times, by the time you reach the other end of the field you won't be at the goal at all, you'll be 50 feet to the left of it. Your compass won't have helped you at all.
Dealing with wind (in aircraft) or current (in boats) is like the second case, not the first.
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OK one final stupid question and thanks for your patience.
On foot i walk and if i stray to my left as is common i can use my compass to see this? Why not see the arrow in my compass on a plane move?
There's a subtle but important difference between two different ways of "straying to your left."
Imagine yourself on a football field. Stand in the center of one goal and note that the other goal is directly South of you. Hold a compass down by your waist. Now put a large bucket over your head so that you can look down and see the compass, but you can't look around and see any of the field at all. There are no painted lines and that the turf is very smooth and even so it gives you no visual cues. All you can see is the compass.
Start walking straight ahead, keeping the compass needle on 'S'. You will eventually reach the middle of the other goal, or within a couple of feet.
Next, imagine that every 5 steps, I say "Stop", and instruct you to close your eyes while I pick you up, shake you around a little bit, and put you back down, at which point you can open your eyes again and resume walking. Let's say it takes 50 steps to cross the field, so I do this ten times.
- If what I did while I picked you up was simply turn you, say, 10 degrees to the left, then when I put you back down and you open your eyes again, the compass needle won't be pointing at 'S' any more, and all you need to do is turn to the right until the compass needle points to 'S' again and resume walking. You'll get to the other goal just fine.
- On the other hand, what if what I did while I picked you up was not to turn you at all, but instead to carry you five feet to your left and put you back down. (remember, I'm shaking you so you can't really tell by the feel if I'm turning your or displacing you). Now, when I put you back down and you open your eyes, the compass will still be pointing to 'S', so you'll just resume walking. But, after doing this ten times, by the time you reach the other end of the field you won't be at the goal at all, you'll be 50 feet to the left of it. Your compass won't have helped you at all.
Dealing with wind (in aircraft) or current (in boats) is like the second case, not the first.
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Or,
While you are walking with your head in the bucket looking at your compass, the grounds crew is pulling the astroturf that you are walkin on off to the west. When you have walked your estimated hundred yards and you look straight ahead again, no goal posts.
gl
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Thanks guys for humoring a land lubber :D
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Another good analogy to illustrate the difference between heading and course is to visualize crossing a river in a boat.
You could just point the bow at the dock across the river and as the current carried you downstream, keep turning and pointing the bow at the dock and you will get there, but your course will be a French Curved arc and not a straight line. (In radio navigation of an aircraft, this would be called "homing".)
Now if you want the boat to follow a straight course across that river, you would just aim your bow upstream to cancel the current's effect (or drift) and have a straight line across the river for your course.
The degree of correction depends on both the speed of the boat and speed of the current. In computing the heading and ground speed for your aircraft, you draw a "Wind Triangle" and for a flight with a ten mile-an-hour wind; you would first draw a ten mile offset from your starting point in the direction of the wind. Now you draw the third leg of your triangle from that point to a point one hour flight time (zero-wind) up your course line and you can measure on that line the heading you will need and the length of that line will give you your ground speed (or how far through the moving air you will need to fly to cover that distance).
In 1937 you would have used a simple 'slide-rule' type calculator and pencil to do that 'wind-triangle' for you.
Art Johnson ATP/AGI/CFII
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Well then , in document "Francis Chichester , 1922 Portuguese flight , Navigator , p. 238 , we read : "April 12 , 1922 . At 1815 navigator found plane to be on a LOP which , extended to the left , cut through the tiny rocky objective. Pilot changed course accordingly and objection was attained" . And on p. 239 : " Pan American World Airways later made island landfalls on transoceanic flights by using the same technique" .
Is that a book or an article? Who wrote it? Please provide a proper citation.
Francis Millet Rogers, “Precision astrolabe: Portuguese navigators and transoceanic aviation,” Academia Internacional da Cultura Portuguesa; [distributed in the U.S.A. by W. S. Sullwold, Taunton, Mass.], 1971, 397 pages
Google digitized it in 2008 from a copy at the library of the University of California -- Davis, but only snippets can be seen online with Google Books.
From page 238,
Realizing that the late-afternoon LOP's were trending ever more toward a NS stance, navigator at 1715 recommended to pilot that he turn right and start to cut across the LOP's. At 1815 navigator found plane to be on an LOP which, extended to the left, cut through the tiny rocky objective. Pilot changed course accordingly and objective was attained.
The second quote given by Mr. van Asten is shown to be at the top of page 239, with what appears to be a footnote number of "8". To see from whom that statement about Pan American's use of the technique came will probably require a visit to a library. Copies of the book are said to be in the vicinity of Washington, DC, at the Library of Congress, the Smithsonian, NOAA (in Silver Spring, MD), and in the Nimitz Library at the U.S. Naval Academy.
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You don't have to visit a library since I have the book, see: https://sites.google.com/site/fredienoonan/resources/precision-astrolabe-rogers-1971
It is confusing trying to figure out that footnote. After flipping back and forth through the book and looking at the bibliography it appears that footnote 8 cites to Avigation, by Bradley Jones. The problem though is that Avigation was written in 1931, long before Pan Am starting flying the Pacific. It appears that the footnote was the basis for other statements in the paragraph about Coutinho and is not related to the statement about Pan Am. The author must have had some reason to state that Pan Am used the landfall method to find islands but, unfortunately, he doesn't document what his source was for that statement.
gl
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The author must have had some reason to state that Pan Am used the landfall method to find islands but, unfortunately, he doesn't document what his source was for that statement.
He obviously thought it was true but that doesn't make it true. His statement is therefore an undocumented secondary source. Can't use it.
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Well then , in document "Francis Chichester , 1922 Portuguese flight , Navigator , p. 238 , we read : "April 12 , 1922 . At 1815 navigator found plane to be on a LOP which , extended to the left , cut through the tiny rocky objective. Pilot changed course accordingly and objection was attained" . And on p. 239 : " Pan American World Airways later made island landfalls on transoceanic flights by using the same technique" .
Is that a book or an article? Who wrote it? Please provide a proper citation.
Francis Millet Rogers, “Precision astrolabe: Portuguese navigators and transoceanic aviation,” Academia Internacional da Cultura Portuguesa; [distributed in the U.S.A. by W. S. Sullwold, Taunton, Mass.], 1971, 397 pages
Google digitized it in 2008 from a copy at the library of the University of California -- Davis, but only snippets can be seen online with Google Books.
From page 238,
Realizing that the late-afternoon LOP's were trending ever more toward a NS stance, navigator at 1715 recommended to pilot that he turn right and start to cut across the LOP's. At 1815 navigator found plane to be on an LOP which, extended to the left, cut through the tiny rocky objective. Pilot changed course accordingly and objective was attained.
The second quote given by Mr. van Asten is shown to be at the top of page 239, with what appears to be a footnote number of "8". To see from whom that statement about Pan American's use of the technique came will probably require a visit to a library. Copies of the book are said to be in the vicinity of Washington, DC, at the Library of Congress, the Smithsonian, NOAA (in Silver Spring, MD), and in the Nimitz Library at the U.S. Naval Academy.
-------------------------------------------------------------------
You don't have to visit a library since I have the book, see: https://sites.google.com/site/fredienoonan/resources/precision-astrolabe-rogers-1971
It is confusing trying to figure out that footnote. After flipping back and forth through the book and looking at the bibliography it appears that footnote 8 cites to Avigation, by Bradley Jones. The problem though is that Avigation was written in 1931, long before Pan Am starting flying the Pacific. It appears that the footnote was the basis for other statements in the paragraph about Coutinho and is not related to the statement about Pan Am. The author must have had some reason to state that Pan Am used the landfall method to find islands but, unfortunately, he doesn't document what his source was for that statement.
gl
-----------------------------------------------------------
"The author must have had some reason to state that Pan Am used the landfall method to find islands but, unfortunately, he doesn't document what his source was for that statement."
The author was a professional historian and a professor at Harvard and wrote at least twenty books so it seems unlikely that he would have written that statement without some authority for it. Unfortunately we can't ask him because he died in 1989.
See: http://www.nps.gov/history/history/online_books/npswapa/extContent/usmc/pcn-190-003125-00/sec5a.htm
gl
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The author was a professional historian and a professor at Harvard and wrote at least twenty books so it seems unlikely that he would have written that statement without some authority for it. Unfortunately we can't ask him because he died in 1989.
We run into reputable sources who are dead wrong all the time. Harry Maude and Eric Bevington knew Gallagher personally and were distinguished Colonial Service officers intimately familiar with the Phoenix Islands Settlement Scheme (it was Maude's idea). Both were absolutely certain that no bones had ever been found on Gardner Island.
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The author was a professional historian and a professor at Harvard and wrote at least twenty books so it seems unlikely that he would have written that statement without some authority for it. Unfortunately we can't ask him because he died in 1989.
We run into reputable sources who are dead wrong all the time. Harry Maude and Eric Bevington knew Gallagher personally and were distinguished Colonial Service officers intimately familiar with the Phoenix Islands Settlement Scheme (it was Maude's idea). Both were absolutely certain that no bones had ever been found on Gardner Island.
--------------------------
He might have been wrong about this but I doubt that it just came to him in a dream one night. He must have heard it from somebody or read it somewhere and his sources might have gotten it wrong, or they might have gotten it right, but we can't tell from this book.
gl
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He must have heard it from somebody or read it somewhere and his sources might have gotten it wrong, or they might have gotten it right, but we can't tell from this book.
Agreed, but if Pan Am did use offsets to find the islands on their trans-Pacific route (Oahu, Midway, Wake) there should be mention of it somewhere. They weren't flying in secret.
This was scheduled passenger service and there is an extensive literature about it.
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Mr.Campbell ,
By the sunset fix you can see that Noonan precompted for checking position by celnav which was normal operating practice. For sunrise , due the on first leg delay , Noonan had to recompute en route since sunrise o/b would originally have occurred at the Turn Off Point before going inbound for Howland. If having gone astray , Itasca would have been long before 1912 GMT be warned by radio , but on the contrary : before 1912 GMT there was not any sign of distress. That holds Noonan precisely knowing where he was when commencing the approach procedure. Do we have any indication about this statement in terms of air navigation ? Yes we have : without exact initial calibration of latitude , the sunrise point of time having been precomputed , we know that the precise LHA of sun was 90-03-50 , computed by H.O.208 , Tab. II by navigator himself. @ 175453 GMT sunrise time the GHA of sun was [(175453) x 15] - 180 deg = 88-43-15. Thence, @ observed sunrise the longitude was : 88-43-15-W + 90-03-50-W = 178-47-05-W. The latitude was already contained in the precomputation by homework. Whatever pre-sunrise track was flown , great circle , rhumb line , any other initial point , From sunrise Noonan knew exactly where he was , given some decline from observation error. I do btw not comment for "make point" , if a computation is good you can safely follow I.Newton : Non fingo hypothesis.
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Mr.Campbell ,
By the sunset fix you can see that Noonan precompted for checking position by celnav which was normal operating practice. For sunrise , due the on first leg delay , Noonan had to recompute en route since sunrise o/b would originally have occurred at the Turn Off Point before going inbound for Howland. If having gone astray , Itasca would have been long before 1912 GMT be warned by radio , but on the contrary : before 1912 GMT there was not any sign of distress. That holds Noonan precisely knowing where he was when commencing the approach procedure. Do we have any indication about this statement in terms of air navigation ? Yes we have : without exact initial calibration of latitude , the sunrise point of time having been precomputed , we know that the precise LHA of sun was 90-03-50 , computed by H.O.208 , Tab. II by navigator himself. @ 175453 GMT sunrise time the GHA of sun was [(175453) x 15] - 180 deg = 88-43-15. Thence, @ observed sunrise the longitude was : 88-43-15-W + 90-03-50-W = 178-47-05-W. The latitude was already contained in the precomputation by homework. Whatever pre-sunrise track was flown , great circle , rhumb line , any other initial point , From sunrise Noonan knew exactly where he was , given some decline from observation error. I do btw not comment for "make point" , if a computation is good you can safely follow I.Newton : Non fingo hypothesis.
-------------------------------------------------
This is for you guys that may have been following this discussion and scratching your heads about what is going on. This post by Mr. van Austen provides the opportunity to show that his methodology is wrong by demonstrating a basic error that anybody should be able to understand.
Basic to all computations for celestial navigation is knowing the position of the body being observed, in this case the sun. Celestial positions are specified like locations on earth. On earth the position north and south of the equator is called latitude and the location east and west of the Greenwich Meridian is called longitude. For celestial bodies, the position north and south of the equator is called declination and the position west of the Greenwich Meridian is called Greenwich Hour Angle (GHA.) Since the earth turns, the GHA of the sun increases at the rate of fifteen degrees every hour, one degree every four minutes and one minute of GHA every four seconds. This is why accurate time is so important because if your chronometer is wrong by just four seconds you will take out a value for GHA from the Nautical Almanac that is wrong by one minute of longitude which will make the derived position in error by one nautical mile.
In his post, Mr. van Asten states that at 17:54:53 GMT the GHA of the sun was 88-43-15 (88 degrees 43 minutes and 15 seconds. This is the same as 88° 43.2', rounded to the nearest 0.1'.) We don't have to take his word for it since it is easy for us to figure it out for ourselves by using the nautical almanac.
Look at the 1937 Nautical Almanac for July 2nd, available here: https://sites.google.com/site/fredienoonan/resources/air-almanac-2009/sun-s-gha
Take out the value of the Sun's GHA for 1800 GMT (the closest tabulated value to Mr. van Asten's time of 17:54:53) which is 89° 02.5'. Since this is the location of the Sun 5 minutes and 7 seconds after Mr. van Asten's time, we must make a correction for this difference. To do this we go to the Interpolation for the GHA of the Sun table available at the same site. Enter this table for the time difference of 5 minutes and 7 seconds and take out the amount the Sun moved in that time period which is 1° 16.8' of GHA. Since we are interested in finding the Sun's GHA for an earlier period, we must subtract this correction from the 1800 GMT tabulated value and find the GHA of the Sun, as tabulated in the 1937 Nautical Almanac (the almanac carried by Noonan), for 17:54:53 GMT was 87° 45.7'. Comparing this to Mr. van Asten's value of 88° 43.2' shows his in in error by 0° 57.5' equivalent to a 57.5 nautical mile error.
Check the math yourself:
GHA sun @ 1800 GMT = 89° 02.5'
Adjustment for 5:07 = - 1° 16.8'
GHA at 175453 GMT = 87° 45.7'
then:
van Asten's GHA = 88° 43.2'
Minus the correct GHA sun - 87° 45.7'
Deference = 0° 57.5'
This would also produce an error in the time of sunrise of 3 minutes and 50 seconds which we can also see by using the interpolation table to find the time interval that would produce the difference in GHA of 0° 57.5' .
Is that simple enough?
gl
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Mr.Campbell ,
By the sunset fix you can see that Noonan precompted for checking position by celnav which was normal operating practice. For sunrise , due the on first leg delay , Noonan had to recompute en route since sunrise o/b would originally have occurred at the Turn Off Point before going inbound for Howland. If having gone astray , Itasca would have been long before 1912 GMT be warned by radio , but on the contrary : before 1912 GMT there was not any sign of distress. That holds Noonan precisely knowing where he was when commencing the approach procedure. Do we have any indication about this statement in terms of air navigation ? Yes we have : without exact initial calibration of latitude , the sunrise point of time having been precomputed , we know that the precise LHA of sun was 90-03-50 , computed by H.O.208 , Tab. II by navigator himself. @ 175453 GMT sunrise time the GHA of sun was [(175453) x 15] - 180 deg = 88-43-15. Thence, @ observed sunrise the longitude was : 88-43-15-W + 90-03-50-W = 178-47-05-W. The latitude was already contained in the precomputation by homework. Whatever pre-sunrise track was flown , great circle , rhumb line , any other initial point , From sunrise Noonan knew exactly where he was , given some decline from observation error. I do btw not comment for "make point" , if a computation is good you can safely follow I.Newton : Non fingo hypothesis.
-------------------------------------------------
This is for you guys that may have been following this discussion and scratching your heads about what is going on. This post by Mr. van Austen provides the opportunity to show that his methodology is wrong by demonstrating a basic error that anybody should be able to understand.
Basic to all computations for celestial navigation is knowing the position of the body being observed, in this case the sun. Celestial positions are specified like locations on earth. On earth the position north and south of the equator is called latitude and the location east and west of the Greenwich Meridian is called longitude. For celestial bodies, the position north and south of the equator is called declination and the position west of the Greenwich Meridian is called Greenwich Hour Angle (GHA.) Since the earth turns, the GHA of the sun increases at the rate of fifteen degrees every hour, one degree every four minutes and one minute of GHA every four seconds. This is why accurate time is so important because if your chronometer is wrong by just four seconds you will take out a value for GHA from the Nautical Almanac that is wrong by one minute of longitude which will make the derived position in error by one nautical mile.
In his post, Mr. van Asten states that at 17:54:53 GMT the GHA of the sun was 88-43-15 (88 degrees 43 minutes and 15 seconds. This is the same as 88° 43.2', rounded to the nearest 0.1'.) We don't have to take his word for it since it is easy for us to figure it out for ourselves by using the nautical almanac.
Look at the 1937 Nautical Almanac for July 2nd, available here: https://sites.google.com/site/fredienoonan/resources/air-almanac-2009/sun-s-gha
Take out the value of the Sun's GHA for 1800 GMT (the closest tabulated value to Mr. van Asten's time of 17:54:53) which is 89° 02.5'. Since this is the location of the Sun 5 minutes and 7 seconds after Mr. van Asten's time, we must make a correction for this difference. To do this we go to the Interpolation for the GHA of the Sun table available at the same site. Enter this table for the time difference of 5 minutes and 7 seconds and take out the amount the Sun moved in that time period which is 1° 16.8' of GHA. Since we are interested in finding the Sun's GHA for an earlier period, we must subtract this correction from the 1800 GMT tabulated value and find the GHA of the Sun, as tabulated in the 1937 Nautical Almanac (the almanac carried by Noonan), for 17:54:53 GMT was 87° 45.7'. Comparing this to Mr. van Asten's value of 88° 43.2' shows his in in error by 0° 57.5' equivalent to a 57.5 nautical mile error.
Check the math yourself:
GHA sun @ 1800 GMT = 89° 02.5'
Adjustment for 5:07 = - 1° 16.8'
GHA at 175453 GMT = 87° 45.7'
then:
van Asten's GHA = 88° 43.2'
Minus the correct GHA sun - 87° 45.7'
Deference = 0° 57.5'
This would also produce an error in the time of sunrise of 3 minutes and 50 seconds which we can also see by using the interpolation table to find the time interval that would produce the difference in GHA of 0° 57.5' .
Is that simple enough?
gl
--------------------------------
GHA sun @ 1800 GMT = 89° 02.5'
Adjustment for 5:07 = - 1° 16.8'
GHA at 175453 GMT = 87° 45.7'
BTW, this is exactly the way that Noonan would calculate the GHA of the Sun for his celestial navigation so you can see there is nothing mysterious or complicated about it, it ain't rocket science.
gl
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G.Lpk No , this is not simple enough , on July 2 , 1937 , between 1700-1800 GMT two phenomena had equal values : the equation of time and the sun´s rising velocity per minute of time ,both amounting to 3m50s , or 00-57´-30" difference of LHA . If figures are not used in the correct sequence (first 3m50s rising sun , from 53´/13´.8 , then 3m50s equation) , the result is the 57´30" difference you notify . Start again with diagram 3 , p.27 of EJN-2008.
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G.Lpk . 57´30" . The error you make is that @ sunset the LHA is for the true sun´s centre in the horizon (bubble) , the sunrise LHA is for sun´s U.L. in the horizon (marine).
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G.Lpk No , this is not simple enough , on July 2 , 1937 , between 1700-1800 GMT two phenomena had equal values : the equation of time and the sun´s rising velocity per minute of time ,both amounting to 3m50s , or 00-57´-30" difference of LHA . If figures are not used in the correct sequence (first 3m50s rising sun , from 53´/13´.8 , then 3m50s equation) , the result is the 57´30" difference you notify . Start again with diagram 3 , p.27 of EJN-2008.
---------------------------------
Mr van Asten, it appears that you are you claiming that the GHA data for the Sun listed in the 1937 Nautical Almanac is wrong so you must be smarter than the people at the U.S. Naval Observatory!
gl
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G.Lpk No , this is not simple enough , on July 2 , 1937 , between 1700-1800 GMT two phenomena had equal values : the equation of time and the sun´s rising velocity per minute of time ,both amounting to 3m50s , or 00-57´-30" difference of LHA . If figures are not used in the correct sequence (first 3m50s rising sun , from 53´/13´.8 , then 3m50s equation) , the result is the 57´30" difference you notify . Start again with diagram 3 , p.27 of EJN-2008.
---------------------------------
Mr van Asten, it appears that you are you claiming that the GHA data for the Sun listed in the 1937 Nautical Almanac is wrong so you must be smarter than the people at the U.S. Naval Observatory!
gl
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You wrote:
"175453 GMT sunrise time the GHA of sun was [(175453) x 15] - 180 deg = 88-43-15. " (88° 43.2')
The GHA from the Nautical Almanac for the same time is 87° 45.7. These are two different numbers, they can't both be right. You claim you are right so you are claiming that the Nautical Almanac is wrong.
gl
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G.Lpk. 88-43-15 vs 87-45-40 LHA . The 88-43-15 LHA is for 175453 GMT centre of true sun in the horizon as seen by bubble sextant ; at this same point of time , U.L.of visible sun is in the horizon , with centre altitude minus 53´ . At 175453 GMT , observing by marine sextant , you actually look at the sun for 175103 GMT , centre 53´below. When sun´s centre comes in the horizon consequently , the mean sun has traveled to 175453 GMT + 3m50s = 175843 GMT . So , if you observe by marine instead of bubble you see the sun come up 175853 - 175453 = 3m50s too early , and you go 3m50s too early on the offset course. That is (in one session) the mechanism of the probable observation error commited.
The typical (air) navigator´s short method to obtain sunrise time after having fixed position @ sunset Is : (round arcseconds)
178-47 - 159-07 df lon due E 22-06
LHA @ sunset / centre 88-03
LHA @ visible sun U.L. 90-04
_____
200-13
subract from 360-00
______
Travel of true sun @ flight 157-47
Divide by 15 deg / hr 10h39m08s
Add to 07h15m45s
_________
GMT of sunrise U.L. 150 off Hwl 17h54m53s
========
Thereof : A/c´s speed was 1326´ = 1,528.7 mls @ 10h39m08s = 143.5 mph due eastward between sunset / sunrise coordinates. If A/c´s great circle due east speed declines from this figure , other tracking than via great circle was taken.
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H. A. C. van Asten, I'm having an awfully hard time following the thread here. Could you give a summary of the position that you are trying to support (or to refute,) and what the evidence is that you are bringing forth in support of (or in refutation of) that position? I'm completely lost in the weeds here.
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To Chris
The one absolutely clear thing I'm reading in this threataos that if you really are in the weeds Chris then you need a weed whacker before you can get that sextant to work! :D
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G.Lpk. 88-43-15 vs 87-45-40 LHA . The 88-43-15 LHA is for 175453 GMT centre of true[/i] sun in the horizon as seen by bubble sextant ; at this same point of time , U.L.of visible sun is in the horizon , with centre altitude minus 53´ . At 175453 GMT , observing by marine sextant , you actually look at the sun for 175103 GMT , centre 53´below. When sun´s centre comes in the horizon consequently , the mean sun has traveled to 175453 GMT + 3m50s = 175843 GMT . So , if you observe by marine instead of bubble you see the sun come up 175853 - 175453 = 3m50s too early , and you go 3m50s too early on the offset course. That is (in one session) the mechanism of the probable observation error commited.
The typical (air) navigator´s short method to obtain sunrise time after having fixed position @ sunset Is : (round arcseconds)
178-47 - 159-07 df lon due E 22-06
LHA @ sunset / centre 88-03
LHA @ visible sun U.L. 90-04
_____
200-13
subract from 360-00
______
Travel of true sun @ flight 157-47
Divide by 15 deg / hr 10h39m08s
Add to 07h15m45s
_________
GMT of sunrise U.L. 150 off Hwl 17h54m53s
========
Thereof : A/c´s speed was 1326´ = 1,528.7 mls @ 10h39m08s = 143.5 mph due eastward between sunset / sunrise coordinates. If A/c´s great circle due east speed declines from this figure , other tracking than via great circle was taken.
-------------------------------
Mr. van Asten, you wrote:
"G.Lpk. 88-43-15 vs 87-45-40 LHA . The 88-43-15 LHA is for 175453 GMT "
Are you are now claiming that the GHAs (Greenwich Hour Angles) that don't agree are actually LHAs (Local Hour Angles) which is an entirely different thing and, again, your computation of what the LHAs were is obviously in error.
gl
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G.Lpk. 88-43-15 vs 87-45-40 LHA . The 88-43-15 LHA is for 175453 GMT centre of true sun in the horizon as seen by bubble sextant ; at this same point of time , U.L.of visible sun is in the horizon , with centre altitude minus 53´ . At 175453 GMT , observing by marine sextant , you actually look at the sun for 175103 GMT , centre 53´below. When sun´s centre comes in the horizon consequently , the mean sun has traveled to 175453 GMT + 3m50s = 175843 GMT . So , if you observe by marine instead of bubble you see the sun come up 175853 - 175453 = 3m50s too early , and you go 3m50s too early on the offset course. That is (in one session) the mechanism of the probable observation error commited.
The typical (air) navigator´s short method to obtain sunrise time after having fixed position @ sunset Is : (round arcseconds)
178-47 - 159-07 df lon due E 22-06
LHA @ sunset / centre 88-03
LHA @ visible sun U.L. 90-04
_____
200-13
subract from 360-00
______
Travel of true sun @ flight 157-47
Divide by 15 deg / hr 10h39m08s
Add to 07h15m45s
_________
GMT of sunrise U.L. 150 off Hwl 17h54m53s
========
Thereof : A/c´s speed was 1326´ = 1,528.7 mls @ 10h39m08s = 143.5 mph due eastward between sunset / sunrise coordinates. If A/c´s great circle due east speed declines from this figure , other tracking than via great circle was taken.
----------------------------------
Mr. van Asten,
You now show us an entirely new method (this must be the third or fourth) that you have invented for computing the time of sunrise that is different than the last method you showed to us. You now claim that this is " The typical (air) navigator´s short method (it doesn't look that short to me) to obtain sunrise time" but your original posts, and your two published articles, stated with certainty that Noonan used a much shorter method than this one to compute the time of sunrise, that of a simple interpolation in the Nautical Almanac sunrise table. So which one of all of the methods were most "typical"? Do you have any evidence that Noonan had ever heard of any of your "typical" methods?
gl
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"There are three kinds of lies - lies, damned lies, and statistics." Benjamin Disraeli
Maybe we should amend that and add, "fun with numbers."? Just a thought.
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G.Lpk. 88-43-15 vs 87-45-40 LHA . The 88-43-15 LHA is for 175453 GMT centre of true sun in the horizon as seen by bubble sextant ; at this same point of time , U.L.of visible sun is in the horizon , with centre altitude minus 53´ . At 175453 GMT , observing by marine sextant , you actually look at the sun for 175103 GMT , centre 53´below. When sun´s centre comes in the horizon consequently , the mean sun has traveled to 175453 GMT + 3m50s = 175843 GMT . So , if you observe by marine instead of bubble you see the sun come up 175853 - 175453 = 3m50s too early , and you go 3m50s too early on the offset course. That is (in one session) the mechanism of the probable observation error commited.
The typical (air) navigator´s short method to obtain sunrise time after having fixed position @ sunset Is : (round arcsecond...
----------------------------------
Mr. van Asten,
You now show us an entirely new method (this must be the third or fourth) that you have invented for computing the time of sunrise that is different than the last method you showed to us. You now claim that this is " The typical (air) navigator´s short method (it doesn't look that short to me) to obtain sunrise time" but your original posts, and your two published articles, stated with certainty that Noonan used a much shorter method than this one to compute the time of sunrise, that of a simple interpolation in the Nautical Almanac sunrise table. So which one of all of the methods were most "typical"? Do you have any evidence that Noonan had ever heard of any of your "typical" methods?
gl
---------------------------------------------
Mr. van Asten,
Something I still remember from the logic course that I took way back in college is that "a contradiction is necessarily false." You stated:
"175453 GMT centre of true sun in the horizon as seen by bubble sextant ; at this same point of time , U.L.of visible sun is in the horizon..."
If the U.L (upper limb, the very top of the sun) is just appearing above the horizon, which you can see with the marine sextant (or with just the unaided eye), how can you, "at this same point of time", see the center of the sun by use of a bubble sextant? Even Superman with his x-ray vision looking through a bubble sextant could not see the center of the sun "at this same point of time" because it is below the horizon and the planet earth is in the way. This is an obvious contradiction so it must necessarily be false.
gl
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Mr. Lapook ,
There is no contradiction at all : the time of optical sunrise U.L. is 3m50s earlier than the time of sunrise true sun central . As a result , the observation being by marine sextant , at 175453 GCT , navigator looks at the sun for 175453 - 3m50s = 175103 apparent time , that is , the visible sun´s U.L. flashes the horizon. By the last posted calculation of sunrise from the sunset fix I demonstrated that Noonan had at his disposal a variety of simple methods to precompute phenomena he needed. Which method he actually made use of is of zero importance for consistency , it may very well have been a listing like in the N.A. , but with always identical outcomes as shown. If navigator , for the sunrise fix , had used the bubble sextant , the crew would , technically , with certainty have found the island without any other aid than celnav. The 3m50s time lag (not equation) existed for the entire 1700-1815 period , that renders the navigation error independend of the precise position of A/c within the limits of reasonable air/groundspeed.
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Mr. Lapook ,
There is no contradiction at all : the time of optical sunrise U.L. is 3m50s earlier than the time of sunrise true sun central . As a result , the observation being by marine sextant , at 175453 GCT , navigator looks at the sun for 175453 - 3m50s = 175103 apparent time , that is , the visible sun´s U.L. flashes the horizon. By the last posted calculation of sunrise from the sunset fix I demonstrated that Noonan had at his disposal a variety of simple methods to precompute phenomena he needed. Which method he actually made use of is of zero importance for consistency , it may very well have been a listing like in the N.A. , but with always identical outcomes as shown. If navigator , for the sunrise fix , had used the bubble sextant , the crew would , technically , with certainty have found the island without any other aid than celnav. The 3m50s time lag (not equation) existed for the entire 1700-1815 period , that renders the navigation error independend of the precise position of A/c within the limits of reasonable air/groundspeed.
---------------------------
You did not explain how a navigator, using a bubble sextant, can look through the earth to see the center of the sun when only the upper limb is actually above the horizon and you said these two observations are made "at this same point of time ."
gl
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Gary, you've heard the one about trying to nail Jell-O to the wall? Same thing as trying to have a reasoned discourse with Mr. Van Asten. He is right. Regardless of anything remotely resembling logic that anyone else may try to apply to the discussion at hand.
Except for the tiny little fact that neither he nor anyone else in this discussion was there on that fateful day. The only two people who were are dead. So trying to recreate what happened on that day, using math, a seance, a Cray supercomputer, God or the Great Pumpkin, is nothing more than an intellectual exercise. In the end, it proves nothing - and it still doesn't put Amelia and Fred on Howland Island, unfortunately. My (http://home.earthlink.net/~mymodels2/icon_smile_2cents.gif)
-
Except for the tiny little fact that neither he nor anyone else in this discussion was there on that fateful day. The only two people who were are dead.
Ahh.. So you're part of the "they're dead" cover-up conspiracy as well. :P
-
Mr. Lapook ,
According to your replies I would not have explained "looking at the same time by two sextant types" , etc. The key to overcome the misunderstanding is the following : the N.A. or any other source gives GMT of sunrise U.L. @ 175453 GMT . It here concerns the visible (also named ´apparent´-) sun , for which the true sun must be 53´below the horizon . Hence , if you go to look to sunrise U.L. with the marine sextant , you actually see the sun for @ GMT 175453 - 3m50s = 175103 Greenwich Apparent Time . The sun rises with 13´8 / time minute , so 53´/ 13´.8 = 3m50s after 175103 GAT , sun´s centre is in the horizon , elevation zero . Now you have 2 alternatives : I . @ 175453 GMT you observe with the marine sextant . You now see the sun with a LHA which is 57´.5 larger than it would be @ 175453 GAT. It will last 3m50s (53´/ 13´.8) before the true sun (centre) is in the horizon , the LHA having diminished with 57´.5 . II . @ 175453 GAT you observe with the bubble sextant , the LHA has the correct opening since you view the true sun . During the time lag 175103 GAT to 175453 GAT however , the MEAN sun traveled from 175453 GAT to 175843 GMT by the time equation , equally being 3m50s . Balance : since you fly on GMT schedule , given that you observe by marine sextant , whereas you used the bubble sextant @ sunset last evening , you will seemingly arrive at precomptud Zulu time at your next initial point . However , actually , you will be there 3m50s early. If the initial point is at the "alter to offset course" place , you will consequently arrive 3m50s short of the precomputed Turn-Off-Point on the from sunrise advanced LOP .
I from experience know that this reasoning about time lags is a dreadful blackbox , inscrutable and demanding for many hours of study , but that´s just how it is.
-
G.Lpk. Yes , alternatively with marine / bubble sextant .
-
G.Lpk . Yes I can , and not through earth , since 3m50s rise time after 175103 GAT the true sun is in the (celestial) horizon , 3m50s equation slow on the mean sun , to see it by bubble sextant @ 175843 GMT.
-
Mt.Fwr . What do you think about "Fun with hypotheses" ?
-
Mr. Lapook ,
Excuse , I went vertigo for a while , the correct term for both cases is : Greenwich Hour Angle.
-
Chr.Ows . Not in a few words . Plse see EJN 2008-2011 and follow comments to/from mr.Lapook who is a sharp referee.
-
Mr.Lapook ,
No . A sparrow is a bird , but not all birds are sparrows . Precision analysis shows GHA 88-43-10 sunrise central 175453 GAT to be interconnected with LHA 88-03-18 sunset central 071545 GAT : both GAT since it concerns the bubble sextant observation(s) , one facultative (@ rise), one real (@ down) . Draw the angles circle and you will see.
-
Chr.Owns . in very short terms : Noonan established position @ sunrise near Nukumanu , high altitude , by the bubble sextant . He thereof precomputed sunrise next morning to be @ 175453 GMT in position 178-47-W : 00-09´-N , 150 mls off Howland. For accuracy he now used , low flying 1,000 ft , the marine sextant . The bubble sextant registers on the true sun . The marine sextant registers on the visible sun , upper limb @ sunrise. Between the visib. sun in the horizon and te true sun in the horizon existed an astronomical time difference of 3m50s. Henceforth , by not again using the bubble sextant @ sunrise he saw U.L. 3m50s too early , although the watch hands stood 175453 , thereof estimating to be 150 mls off , but actually they were 3m50s x 150 mph = 9.6 mls more , i.e. 160 mls off . Steering on the offset course for the island (100 mls out) was also 3m50s early and an erroneous Turn Off Point taken on a line 10 mls west of Howland on chart . At 1912 GMT (fuel reserves for 1h05m) the inbound flight , course 157T , was completed , but the island did not run up below the A/c progression line , since it was 16 mls (10 + 6 chart error) on the port bow. As a result Howland remained beyond visual range , RDF exercitions failed , and A/c proceeded (337T) until fuel ran out.
-
G.Lpk. No computation in navigation was " very short" , therefore navigators precomputed by homework , mostly before flight , sometimes during flight . All short methods (Pinto , Dreisonstok , Lieuwen , Ageton , H.O.214 , H.O.249) are for practical air navigation only time saving if precomputation before flight is accomplished.
-
Chr.Owns . in very short terms : Noonan established position @ sunrise near Nukumanu , high altitude , by the bubble sextant . He thereof precomputed sunrise next morning to be @ 175453 GMT in position 178-47-W : 00-09´-N , 150 mls off Howland. For accuracy he now used , low flying 1,000 ft , the marine sextant . The bubble sextant registers on the true sun . The marine sextant registers on the visible sun , upper limb @ sunrise. Between the visib. sun in the horizon and te true sun in the horizon existed an astronomical time difference of 3m50s. Henceforth , by not again using the bubble sextant @ sunrise he saw U.L. 3m50s too early , although the watch hands stood 175453 , thereof estimating to be 150 mls off , but actually they were 3m50s x 150 mph = 9.6 mls more , i.e. 160 mls off . Steering on the offset course for the island (100 mls out) was also 3m50s early and an erroneous Turn Off Point taken on a line 10 mls west of Howland on chart . At 1912 GMT (fuel reserves for 1h05m) the inbound flight , course 157T , was completed , but the island did not run up below the A/c progression line , since it was 16 mls (10 + 6 chart error) on the port bow. As a result Howland remained beyond visual range , RDF exercitions failed , and A/c proceeded (337T) until fuel ran out.
In other words, what you're saying is that - Noonan was planning to use the offset method to intercept Howland,
- At the time he was deciding when to turn off, they were flying at 1,000 feet,
- He used the marine sextant rather than the bubble sextant to take a sunrise sight, but failed to apply the refraction correction, which put him ~10 miles West of where he thought he was.
- Noonan was using charts that had Howland's position off by 6 miles.
- Combined error of chart + failure to correct for refraction put him 16 miles W of where he wanted to be at the point they turned and began flying the 337T course
- They flew down the 337T course until they ran out of fuel, at which point they ditched and sank.
Thank you. I suspect that if you had laid out this theory beforehand, you would have had less resistance from people on this forum.
The theory is internally consistent, as far as I can tell, but it does depend on a large number of assumptions that are untestable.
-
"... but it does depend on a large number of assumptions that are untestable." Bingo.
One of the main assumptions, to me, being that Noonan got stupid and sloppy near the end, knowing that his own life was on the line. I'm sorry, Mr. Van Asten, you can throw all the numbers up against the wall and hope some of them stick, but that just doesn't compute, as they say.
-
Chr.Owns . in very short terms : Noonan established position @ sunrise near Nukumanu , high altitude , by the bubble sextant . He thereof precomputed sunrise next morning to be @ 175453 GMT in position 178-47-W : 00-09´-N , 150 mls off Howland. For accuracy he now used , low flying 1,000 ft , the marine sextant . The bubble sextant registers on the true sun . The marine sextant registers on the visible sun , upper limb @ sunrise. Between the visib. sun in the horizon and te true sun in the horizon existed an astronomical time difference of 3m50s. Henceforth , by not again using the bubble sextant @ sunrise he saw U.L. 3m50s too early , although the watch hands stood 175453 , thereof estimating to be 150 mls off , but actually they were 3m50s x 150 mph = 9.6 mls more , i.e. 160 mls off . Steering on the offset course for the island (100 mls out) was also 3m50s early and an erroneous Turn Off Point taken on a line 10 mls west of Howland on chart . At 1912 GMT (fuel reserves for 1h05m) the inbound flight , course 157T , was completed , but the island did not run up below the A/c progression line , since it was 16 mls (10 + 6 chart error) on the port bow. As a result Howland remained beyond visual range , RDF exercitions failed , and A/c proceeded (337T) until fuel ran out.
Your posterior conclusions are correct (not "refraction correction" , but that is detail) . The sunset fix parameters deliver the time-coordinates group for the sunrise fix , hence the uncertainties are possibly less than you suggest.
In other words, what you're saying is that - Noonan was planning to use the offset method to intercept Howland,
- At the time he was deciding when to turn off, they were flying at 1,000 feet,
- He used the marine sextant rather than the bubble sextant to take a sunrise sight, but failed to apply the refraction correction, which put him ~10 miles West of where he thought he was.
- Noonan was using charts that had Howland's position off by 6 miles.
- Combined error of chart + failure to correct for refraction put him 16 miles W of where he wanted to be at the point they turned and began flying the 337T course
- They flew down the 337T course until they ran out of fuel, at which point they ditched and sank.
Thank you. I suspect that if you had laid out this theory beforehand, you would have had less resistance from people on this forum.
The theory is internally consistent, as far as I can tell, but it does depend on a large number of assumptions that are untestable.
-
"... but it does depend on a large number of assumptions that are untestable." Bingo.
One of the main assumptions, to me, being that Noonan got stupid and sloppy near the end, knowing that his own life was on the line. I'm sorry, Mr. Van Asten, you can throw all the numbers up against the wall and hope some of them stick, but that just doesn't compute, as they say.
To quote A.Einstein : if only one sticks that will do (and it does).
-
Chr.Owns . in very short terms : Noonan established position @ sunrise near Nukumanu , high altitude , by the bubble sextant . He thereof precomputed sunrise next morning to be @ 175453 GMT in position 178-47-W : 00-09´-N , 150 mls off Howland. For accuracy he now used , low flying 1,000 ft , the marine sextant . The bubble sextant registers on the true sun . The marine sextant registers on the visible sun , upper limb @ sunrise. Between the visib. sun in the horizon and te true sun in the horizon existed an astronomical time difference of 3m50s. Henceforth , by not again using the bubble sextant @ sunrise he saw U.L. 3m50s too early , although the watch hands stood 175453 , thereof estimating to be 150 mls off , but actually they were 3m50s x 150 mph = 9.6 mls more , i.e. 160 mls off . Steering on the offset course for the island (100 mls out) was also 3m50s early and an erroneous Turn Off Point taken on a line 10 mls west of Howland on chart . At 1912 GMT (fuel reserves for 1h05m) the inbound flight , course 157T , was completed , but the island did not run up below the A/c progression line , since it was 16 mls (10 + 6 chart error) on the port bow. As a result Howland remained beyond visual range , RDF exercitions failed , and A/c proceeded (337T) until fuel ran out.
In other words, what you're saying is that - Noonan was planning to use the offset method to intercept Howland,
- At the time he was deciding when to turn off, they were flying at 1,000 feet,
- He used the marine sextant rather than the bubble sextant to take a sunrise sight, but failed to apply the refraction correction, which put him ~10 miles West of where he thought he was.
- Noonan was using charts that had Howland's position off by 6 miles.
- Combined error of chart + failure to correct for refraction put him 16 miles W of where he wanted to be at the point they turned and began flying the 337T course
- They flew down the 337T course until they ran out of fuel, at which point they ditched and sank.
Thank you. I suspect that if you had laid out this theory beforehand, you would have had less resistance from people on this forum.
The theory is internally consistent, as far as I can tell, but it does depend on a large number of assumptions that are untestable.
Yes , I possibly started at the intricate side however , making statements is one thing , but delivering unconditional proof is another and not child´s play.
-
G.Lpk. No computation in navigation was " very short" , therefore navigators precomputed by homework , mostly before flight , sometimes during flight . All short methods (Pinto , Dreisonstok , Lieuwen , Ageton , H.O.214 , H.O.249) are for practical air navigation only time saving if precomputation before flight is accomplished.
---------------------------
This is just one more illustration that you don't know what your are talking about. I have done it many times, (and any Air Force navigator will say the same thing), it is easy to do the precomputations IN FLIGHT for a three fix in only nine or ten minutes.
gl
-
Mr. Lapook ,
According to your replies I would not have explained "looking at the same time by two sextant types" , etc. The key to overcome the misunderstanding is the following : the N.A. or any other source gives GMT of sunrise U.L. @ 175453 GMT . It here concerns the visible (also named ´apparent´-) sun , for which the true sun must be 53´below the horizon . Hence , if you go to look to sunrise U.L. with the marine sextant , you actually see the sun for @ GMT 175453 - 3m50s = 175103 Greenwich Apparent Time . The sun rises with 13´8 / time minute , so 53´/ 13´.8 = 3m50s after 175103 GAT , sun´s centre is in the horizon , elevation zero . Now you have 2 alternatives : I . @ 175453 GMT you observe with the marine sextant . You now see the sun with a LHA which is 57´.5 larger than it would be @ 175453 GAT. It will last 3m50s (53´/ 13´.8) before the true sun (centre) is in the horizon , the LHA having diminished with 57´.5 . II . @ 175453 GAT you observe with the bubble sextant , the LHA has the correct opening since you view the true sun . During the time lag 175103 GAT to 175453 GAT however , the MEAN sun traveled from 175453 GAT to 175843 GMT by the time equation , equally being 3m50s . Balance : since you fly on GMT schedule , given that you observe by marine sextant , whereas you used the bubble sextant @ sunset last evening , you will seemingly arrive at precomptud Zulu time at your next initial point . However , actually , you will be there 3m50s early. If the initial point is at the "alter to offset course" place , you will consequently arrive 3m50s short of the precomputed Turn-Off-Point on the from sunrise advanced LOP .
I from experience know that this reasoning about time lags is a dreadful blackbox , inscrutable and demanding for many hours of study , but that´s just how it is.
--------------------------------------
Imagine...you have taken your wife, or girlfriend (probably not both at the same time) on a dream
vacation of a lifetime to Hawaii. You are alone with her now at a very romantic and secluded
spot, sitting on a blanket, high up on a cliff on the Napali coast on the west coast of Kauai
waiting for sunset. You are sipping a fine french wine with the woman you love the most. The
sun is slowly sinking towards the horizon and you have hopes of seeing that elusive “green flash”
when the sun sets. The sun is slipping behind the edge of the earth, and then, just as the last sliver
of the sun disappears into the sea, you see it, the green flash! You take your lover into your arms,
kiss her gently, and then.. you are.. one.
Meanwhile, on another cliff a couple of miles away, Mr. van Asten is doing the same thing with
the woman he loves. Suddenly, he jams the cork back into the wine bottle and says to his wife,
“get up it’s time to go.”
She is shocked and says “wait a minute, I thought we were here to watch the sunset and I can still
see the whole sun, it isn’t even close to setting.”
He says to his disappointed wife. “You are mistaken, my dear, the sun has already set.”
Noticing the confused look on her face he goes on “we are about a thousand feet above sea level
so when we are looking at the sea horizon we are actually looking downward, below the level
horizontal plane. The sun, even though we can still see the entire disk, is actually below the
horizontal level so it has already set. Now get up, we’re leaving.”
This illustrates just one of the many problems with Mr. van Asten’s theories, he has his own idea
of what “sunset” is that doesn’t comport with anybody else’s understanding of that word! (Let’s
call it “van Asten sunset”.) And he is right about this, as observed from an altitude of a thousand
feet, the entire sun will be visible above the natural horizon when it is actually below the true
horizontal. What this actually means, to everyone else, is that sunset will occur at a later time for
an observer up on the cliff than for a person standing on the beach, down at the sea shore,
directly below the cliff. The sun will have to go down even further to be hidden behind the sea
horizon and this takes a little bit of time.
Basically, this weird idea of what sunset or sunrise is, (which is different than everybody else’s
and is not found in any dictionary or navigation manual) leads to all of Mr. van Asten’s theories,
methods and conclusions.
I actually understand his theories and methodology and even his complex computations, which
he does in the most complicated way possible, there are much easier ways to do the same
computations. Noonan would not have used his method of computation and we know this
because Noonan said so in his letter to Weems
see page 425 here:
https://sites.google.com/site/fredienoonan/resources/weems/weems-424-425.JPG?attredirects=0
where he praises the “Greenwich hour-angle idea” which is the simple way the calculation of
GHA is done that I showed you in a prior post. Even though Mr. van Asten has developed
formulas that end up producing correct answers (for his theories), these formulas are not found in
navigation manuals, were not used by navigators in Noonan’s time, and have no purpose in
navigation except to support Mr. van Asten’s theories.
Based on his idea of sunrise/sunset, he comes up with a unique way to use a marine sextant
(which would work for the “van Asten sunset”) that is not found in any navigation text. He also
has described to me, off list, his method of using a bubble sextant which is just plain wrong. I do
not want to get back into the weeds of the complex computations and this is not necessary to
show that Mr. van Asten is wrong since we can look at basic, easily understood, problems with
his methodology.
We will start with his idea that Noonan measured the point of “van Asten sunrise” with a marine
sextant and not with his bubble sextant. This is critical to his theory since he blames Noonan for
using the wrong technique with the marine sextant and that the error (that he believes led to the
loss) would not have occurred if Noonan had used his bubble sextant tor the “van Asten sunrise”
observation. He gets this idea from Noonan’s letter saying that a marine sextant was carried on a
Pan Am Clipper even though there is no evidence ( Ric’s sextant box is a theory, not evidence)
that a marine sextant was carried on the Earhart flight. If there was no marine sextant on board
then no way to make this error. He read a standard navigation textbook, Navigation and Nautical
Astronomy by Dutton, 1928 edition, which is devoted almost entirely to marine navigation with
just one short chapter on the, then new, field of “Aerial Navigation.” Mr. van Asten referred me
to a paragraph in this chapter that describes how to measure the sun’s altitude that recommended
that flight navigators use marine sextants because they were more accurate than bubble sextants. I
reviewed my library and pointed out to him that that wording had been removed from the same
paragraph in the 1934 edition of the book due to the rapid improvements in bubble sextants in
the intervening years. There is no reason to believe that Noonan would have used a marine
sextant (even if he had one available) for taking any observations from the Electra. Noonan said
himself, that even though a marine sextant had been carried in the Pan Am Clipper as a
“preventer” (a backup), that all observations had been made with the Pioneer bubble sextant.
See page 423:
https://sites.google.com/site/fredienoonan/resources/weems/weems-422-423.JPG?attredirects=0
Making it even more obvious that bubble sextants had reached the level of required accuracy is
the fact that marine sextants were NOT issued to navigators during WW2, they were all given
bubble sextants.
Mr. van Asten refuses to accept these facts.
Enough for now.
gl
-
G.Lpk. No computation in navigation was " very short" , therefore navigators precomputed by homework , mostly before flight , sometimes during flight . All short methods (Pinto , Dreisonstok , Lieuwen , Ageton , H.O.214 , H.O.249) are for practical air navigation only time saving if precomputation before flight is accomplished.
---------------------------
This is just one more illustration that you don't know what your are talking about. I have done it many times, (and any Air Force navigator will say the same thing), it is easy to do the precomputations IN FLIGHT for a three fix in only nine or ten minutes.
gl
---------------------------------
Here are some links showing how the computations are done IN FLIGHT
http://www.oceannavigator.com/content/celestial-air
http://www.avweb.com/news/avtraining/IFR_bySunAndStars_200781-1.html
https://sites.google.com/site/fredienoonan/other-flight-navigation-information/in-flight-celestial-navigation
They all show that Mr. van Asten is wrong again.
gl
-
G.Lpk. No computation in navigation was " very short" , therefore navigators precomputed by homework , mostly before flight , sometimes during flight . All short methods (Pinto , Dreisonstok , Lieuwen , Ageton , H.O.214 , H.O.249) are for practical air navigation only time saving if precomputation before flight is accomplished.
---------------------------
This is just one more illustration that you don't know what your are talking about. I have done it many times, (and any Air Force navigator will say the same thing), it is easy to do the precomputations IN FLIGHT for a three fix in only nine or ten minutes.
gl
---------------------------------
Here are some links showing how the computations are done IN FLIGHT
http://www.oceannavigator.com/content/celestial-air
http://www.avweb.com/news/avtraining/IFR_bySunAndStars_200781-1.html
https://sites.google.com/site/fredienoonan/other-flight-navigation-information/in-flight-celestial-navigation
They all show that Mr. van Asten is wrong again.
gl
-----------------------
Noonan himself wrote that the average time needed to compute and plot a fix was only six minutes.
gl
-
Mr. Lapook ,
According to your replies I would not have explained "looking at the same time by two sextant types" , etc. The key to overcome the misunderstanding is the following : the N.A. or any other source gives GMT of sunrise U.L. @ 175453 GMT . It here concerns the visible (also named ´apparent´-) sun , for which the true sun must be 53´below the horizon . Hence , if you go to look to sunrise U.L. with the marine sextant , you actually see the sun for @ GMT 175453 - 3m50s = 175103 Greenwich Apparent Time . The sun rises with 13´8 / time minute , so 53´/ 13´.8 = 3m50s after 175103 GAT , sun´s centre is in the horizon , elevation zero . Now you have 2 alternatives : I . @ 175453 GMT you observe with the marine sextant . You now see the sun with a LHA which is 57´.5 larger than it would be @ 175453 GAT. It will last 3m50s (53´/ 13´.8) before the true sun (centre) is in the horizon , the LHA having diminished with 57´.5 . II . @ 175453 GAT you observe with the bubble sextant , the LHA has the correct opening since you view the true sun . During the time lag 175103 GAT to 175453 GAT however , the MEAN sun traveled from 175453 GAT to 175843 GMT by the time equation , equally being 3m50s . Balance : since you fly on GMT schedule , given that you observe by marine sextant , whereas you used the bubble sextant @ sunset last evening , you will seemingly arrive at precomptud Zulu time at your next initial point . However , actually , you will be there 3m50s early. If the initial point is at the "alter to offset course" place , you will consequently arrive 3m50s short of the precomputed Turn-Off-Point on the from sunrise advanced LOP .
I from experience know that this reasoning about time lags is a dreadful blackbox , inscrutable and demanding for many hours of study , but that´s just how it is.
--------------------------------------
Imagine...you have taken your wife, or girlfriend (probably not both at the same time) on a dream
vacation of a lifetime to Hawaii. You are alone with her now at a very romantic and secluded
spot, sitting on a blanket, high up on a cliff on the Napali coast on the west coast of Kauai
waiting for sunset. You are sipping a fine french wine with the woman you love the most. The
sun is slowly sinking towards the horizon and you have hopes of seeing that elusive “green flash”
when the sun sets. The sun is slipping behind the edge of the earth, and then, just as the last sliver
of the sun disappears into the sea, you see it, the green flash! You take your lover into your arms,
kiss her gently, and then.. you are.. one.
Meanwhile, on another cliff a couple of miles away, Mr. van Asten is doing the same thing with
the woman he loves. Suddenly, he jams the cork back into the wine bottle and says to his wife,
“get up it’s time to go.”
She is shocked and says “wait a minute, I thought we were here to watch the sunset and I can still
see the whole sun, it isn’t even close to setting.”
He says to his disappointed wife. “You are mistaken, my dear, the sun has already set.”
Noticing the confused look on her face he goes on “we are about a thousand feet above sea level
so when we are looking at the sea horizon we are actually looking downward, below the level
horizontal plane. The sun, even though we can still see the entire disk, is actually below the
horizontal level so it has already set. Now get up, we’re leaving.”
This illustrates just one of the many problems with Mr. van Asten’s theories, he has his own idea
of what “sunset” is that doesn’t comport with anybody else’s understanding of that word! (Let’s
call it “van Asten sunset”.) And he is right about this, as observed from an altitude of a thousand
feet, the entire sun will be visible above the natural horizon when it is actually below the true
horizontal. What this actually means, to everyone else, is that sunset will occur at a later time for
an observer up on the cliff than for a person standing on the beach, down at the sea shore,
directly below the cliff. The sun will have to go down even further to be hidden behind the sea
horizon and this takes a little bit of time.
Basically, this weird idea of what sunset or sunrise is, (which is different than everybody else’s
and is not found in any dictionary or navigation manual) leads to all of Mr. van Asten’s theories,
methods and conclusions.
I actually understand his theories and methodology and even his complex computations, which
he does in the most complicated way possible, there are much easier ways to do the same
computations. Noonan would not have used his method of computation and we know this
because Noonan said so in his letter to Weems
see page 425 here:
https://sites.google.com/site/fredienoonan/resources/weems/weems-424-425.JPG?attredirects=0
where he praises the “Greenwich hour-angle idea” which is the simple way the calculation of
GHA is done that I showed you in a prior post. Even though Mr. van Asten has developed
formulas that end up producing correct answers (for his theories), these formulas are not found in
navigation manuals, were not used by navigators in Noonan’s time, and have no purpose in
navigation except to support Mr. van Asten’s theories.
Based on his idea of sunrise/sunset, he comes up with a unique way to use a marine sextant
(which would work for the “van Asten sunset”) that is not found in any navigation text. He also
has described to me, off list, his method of using a bubble sextant which is just plain wrong. I do
not want to get back into the weeds of the complex computations and this is not necessary to
show that Mr. van Asten is wrong since we can look at basic, easily understood, problems with
his methodology.
We will start with his idea that Noonan measured the point of “van Asten sunrise” with a marine
sextant and not with his bubble sextant. This is critical to his theory since he blames Noonan for
using the wrong technique with the marine sextant and that the error (that he believes led to the
loss) would not have occurred if Noonan had used his bubble sextant tor the “van Asten sunrise”
observation. He gets this idea from Noonan’s letter saying that a marine sextant was carried on a
Pan Am Clipper even though there is no evidence ( Ric’s sextant box is a theory, not evidence)
that a marine sextant was carried on the Earhart flight. If there was no marine sextant on board
then no way to make this error. He read a standard navigation textbook, Navigation and Nautical
Astronomy by Dutton, 1928 edition, which is devoted almost entirely to marine navigation with
just one short chapter on the, then new, field of “Aerial Navigation.” Mr. van Asten referred me
to a paragraph in this chapter that describes how to measure the sun’s altitude that recommended
that flight navigators use marine sextants because they were more accurate than bubble sextants. I
reviewed my library and pointed out to him that that wording had been removed from the same
paragraph in the 1934 edition of the book due to the rapid improvements in bubble sextants in
the intervening years. There is no reason to believe that Noonan would have used a marine
sextant (even if he had one available) for taking any observations from the Electra. Noonan said
himself, that even though a marine sextant had been carried in the Pan Am Clipper as a
“preventer” (a backup), that all observations had been made with the Pioneer bubble sextant.
See page 423:
https://sites.google.com/site/fredienoonan/resources/weems/weems-422-423.JPG?attredirects=0
Making it even more obvious that bubble sextants had reached the level of required accuracy is
the fact that marine sextants were NOT issued to navigators during WW2, they were all given
bubble sextants.
Mr. van Asten refuses to accept these facts.
Enough for now.
gl
Mr.Lapook ,
I see , by many words , that you try to undermine the theory in question , which is good since any theory needs a testbench before it can be generally accepted . However , you continuously bring into discussion the relevancy rate of it , all your comments have , so far , no influence on the internal consistency . P.e. you write about the "van Asten sunset", whereas it is clear and explained that only a "Frederick Noonan sunset" is on record , communicated @ 0720 GMT for 159-07-E ; 04-33-30-S coordinates . You also bring into discussion bubble sextants , not marine sextants , given to WW-II air navigators because of the assumed amelioration of the instrument , whereas it is trivial that in war time , aircraft fly necessarily at high altitudes with sky and local horizon blended so that marine sextants failed their reference line. In all your comments stating "mr.van Asten is wrong again" and "You don´t know what you are talking about" , not one sentence concerning supposed inconsistency finds a good argument . It is , other example , not new to me that precomputation took place during flight : since the turn-off point after sunrise would have been originally reached at sunrise , Noonan had to recompute in flight for ephemeris of another coordinates pair. The exact algorithms used for his calculations indeed remain unknown , but that is no argument for the statement that mine would be too long , too intricate , upside down , etc. , it is for e.g. sunset clear that Noonan acquired the same outcomes , and that is unconditionall , one step and more forward in the field of quantitative research for the incident.
-
Mr. Lapook ,
According to your replies I would not have explained "looking at the same time by two sextant types" , etc. The key to overcome the misunderstanding is the following : the N.A. or any other source gives GMT of sunrise U.L. @ 175453 GMT . It here concerns the visible (also named ´apparent´-) sun , for which the true sun must be 53´below the horizon . Hence , if you go to look to sunrise U.L. with the marine sextant , you actually see the sun for @ GMT 175453 - 3m50s = 175103 Greenwich Apparent Time . The sun rises with 13´8 / time minute , so 53´/ 13´.8 = 3m50s after 175103 GAT , sun´s centre is in the horizon , elevation zero . Now you have 2 alternatives : I . @ 175453 GMT you observe with the marine sextant . You now see the sun with a LHA which is 57´.5 larger than it would be @ 175453 GAT. It will last 3m50s (53´/ 13´.8) before the true sun (centre) is in the horizon , the LHA having diminished with 57´.5 . II . @ 175453 GAT you observe with the bubble sextant , the LHA has the correct opening since you view the true sun . During the time lag 175103 GAT to 175453 GAT however , the MEAN sun traveled from 175453 GAT to 175843 GMT by the time equation , equally being 3m50s . Balance : since you fly on GMT schedule , given that you observe by marine sextant , whereas you used the bubble sextant @ sunset last evening , you will seemingly arrive at precomptud Zulu time at your next initial point . However , actually , you will be there 3m50s early. If the initial point is at the "alter to offset course" place , you will consequently arrive 3m50s short of the precomputed Turn-Off-Point on the from sunrise advanced LOP .
I from experience know that this reasoning about time lags is a dreadful blackbox , inscrutable and demanding for many hours of study , but that´s just how it is.
--------------------------------------
Imagine...you have taken your wife, or girlfriend (probably not both at the same time) on a dream
vacation of a lifetime to Hawaii. You are alone with her now at a very romantic and secluded
spot, sitting on a blanket, high up on a cliff on the Napali coast on the west coast of Kauai
waiting for sunset. You are sipping a fine french wine with the woman you love the most. The
sun is slowly sinking towards the horizon and you have hopes of seeing that elusive “green flash”
when the sun sets. The sun is slipping behind the edge of the earth, and then, just as the last sliver
of the sun disappears into the sea, you see it, the green flash! You take your lover into your arms,
kiss her gently, and then.. you are.. one.
Meanwhile, on another cliff a couple of miles away, Mr. van Asten is doing the same thing with
the woman he loves. Suddenly, he jams the cork back into the wine bottle and says to his wife,
“get up it’s time to go.”
She is shocked and says “wait a minute, I thought we were here to watch the sunset and I can still
see the whole sun, it isn’t even close to setting.”
He says to his disappointed wife. “You are mistaken, my dear, the sun has already set.”
Noticing the confused look on her face he goes on “we are about a thousand feet above sea level
so when we are looking at the sea horizon we are actually looking downward, below the level
horizontal plane. The sun, even though we can still see the entire disk, is actually below the
horizontal level so it has already set. Now get up, we’re leaving.”
This illustrates just one of the many problems with Mr. van Asten’s theories, he has his own idea
of what “sunset” is that doesn’t comport with anybody else’s understanding of that word! (Let’s
call it “van Asten sunset”.) And he is right about this, as observed from an altitude of a thousand
feet, the entire sun will be visible above the natural horizon when it is actually below the true
horizontal. What this actually means, to everyone else, is that sunset will occur at a later time for
an observer up on the cliff than for a person standing on the beach, down at the sea shore,
directly below the cliff. The sun will have to go down even further to be hidden behind the sea
horizon and this takes a little bit of time.
Basically, this weird idea of what sunset or sunrise is, (which is different than everybody else’s
and is not found in any dictionary or navigation manual) leads to all of Mr. van Asten’s theories,
methods and conclusions.
I actually understand his theories and methodology and even his complex computations, which
he does in the most complicated way possible, there are much easier ways to do the same
computations. Noonan would not have used his method of computation and we know this
because Noonan said so in his letter to Weems
see page 425 here:
https://sites.google.com/site/fredienoonan/resources/weems/weems-424-425.JPG?attredirects=0
where he praises the “Greenwich hour-angle idea” which is the simple way the calculation of
GHA is done that I showed you in a prior post. Even though Mr. van Asten has developed
formulas that end up producing correct answers (for his theories), these formulas are not found in
navigation manuals, were not used by navigators in Noonan’s time, and have no purpose in
navigation except to support Mr. van Asten’s theories.
Based on his idea of sunrise/sunset, he comes up with a unique way to use a marine sextant
(which would work for the “van Asten sunset”) that is not found in any navigation text. He also
has described to me, off list, his method of using a bubble sextant which is just plain wrong. I do
not want to get back into the weeds of the complex computations and this is not necessary to
show that Mr. van Asten is wrong since we can look at basic, easily understood, problems with
his methodology.
We will start with his idea that Noonan measured the point of “van Asten sunrise” with a marine
sextant and not with his bubble sextant. This is critical to his theory since he blames Noonan for
using the wrong technique with the marine sextant and that the error (that he believes led to the
loss) would not have occurred if Noonan had used his bubble sextant tor the “van Asten sunrise”
observation. He gets this idea from Noonan’s letter saying that a marine sextant was carried on a
Pan Am Clipper even though there is no evidence ( Ric’s sextant box is a theory, not evidence)
that a marine sextant was carried on the Earhart flight. If there was no marine sextant on board
then no way to make this error. He read a standard navigation textbook, Navigation and Nautical
Astronomy by Dutton, 1928 edition, which is devoted almost entirely to marine navigation with
just one short chapter on the, then new, field of “Aerial Navigation.” Mr. van Asten referred me
to a paragraph in this chapter that describes how to measure the sun’s altitude that recommended
that flight navigators use marine sextants because they were more accurate than bubble sextants. I
reviewed my library and pointed out to him that that wording had been removed from the same
paragraph in the 1934 edition of the book due to the rapid improvements in bubble sextants in
the intervening years. There is no reason to believe that Noonan would have used a marine
sextant (even if he had one available) for taking any observations from the Electra. Noonan said
himself, that even though a marine sextant had been carried in the Pan Am Clipper as a
“preventer” (a backup), that all observations had been made with the Pioneer bubble sextant.
See page 423:
https://sites.google.com/site/fredienoonan/resources/weems/weems-422-423.JPG?attredirects=0
Making it even more obvious that bubble sextants had reached the level of required accuracy is
the fact that marine sextants were NOT issued to navigators during WW2, they were all given
bubble sextants.
Mr. van Asten refuses to accept these facts.
Enough for now.
gl
Mr.Lapook ,
I see , by many words , that you try to undermine the theory in question , which is good since any theory needs a testbench before it can be generally accepted . However , you continuously bring into discussion the relevancy rate of it , all your comments have , so far , no influence on the internal consistency . P.e. you write about the "van Asten sunset", whereas it is clear and explained that only a "Frederick Noonan sunset" is on record , communicated @ 0720 GMT for 159-07-E ; 04-33-30-S coordinates . You also bring into discussion bubble sextants , not marine sextants , given to WW-II air navigators because of the assumed amelioration of the instrument , whereas it is trivial that in war time , aircraft fly necessarily at high altitudes with sky and local horizon blended so that marine sextants failed their reference line. In all your comments stating "mr.van Asten is wrong again" and "You don´t know what you are talking about" , not one sentence concerning supposed inconsistency finds a good argument . It is , other example , not new to me that precomputation took place during flight : since the turn-off point after sunrise would have been originally reached at sunrise , Noonan had to recompute in flight for ephemeris of another coordinates pair. The exact algorithms used for his calculations indeed remain unknown , but that is no argument for the statement that mine would be too long , too intricate , upside down , etc. , it is for e.g. sunset clear that Noonan acquired the same outcomes , and that is unconditionall , one step and more forward in the field of quantitative research for the incident.
On hilltop no.3 , 1,000 ft above sea near sunset , sits a mr. L with a Gibson Girl , kite in the air , to contact his airline company at sunset time for checking the company´s new sunset tables. At precomputed sunset time , he looks to .. a disc and sees it largely and complete above the horizon through his marine sextant telescope . He calls the company , shouting : "your tables are wrong , with my calibrated sextant I still see the sun after sunrise , your Greenwich Hour Angle notation is adverse , I am sure I corrected for dip !"
shouts the company executive back : "You are fired , Sir , you should have turned up your horizon 53 additional arcminutes .. the knob at the underside" .
-
... he has his own idea
of what “sunset” is that doesn’t comport with anybody else’s understanding of that word! ...
Basically, this weird idea of what sunset or sunrise is, (which is different than everybody else’s
and is not found in any dictionary or navigation manual) leads to all of Mr. van Asten’s theories,
methods and conclusions.
I actually understand his theories and methodology and even his complex computations ...
Thanks for clarifying the nature of the argument. Much appreciated!
We will start with his idea that Noonan measured the point of “van Asten sunrise” with a marine
sextant and not with his bubble sextant. This is critical to his theory since he blames Noonan for
using the wrong technique with the marine sextant and that the error (that he believes led to the
loss) would not have occurred if Noonan had used his bubble sextant tor the “van Asten sunrise”
observation.
Thanks for untangling that.
If there was no marine sextant on board
then no way to make this error.
Even if there was a marine sextant on board (with or without the bubble modification used on many Brandis instruments (http://tighar.org/wiki/Sextant)), there is no reason to think that Fred would have chosen to use it rather than the Pioneer instrument that was designed for use in aerial navigation.
Oh, reading further along, I see that we are already in agreement on that score:
... There is no reason to believe that Noonan would have used a marine
sextant (even if he had one available) for taking any observations from the Electra. Noonan said
himself, that even though a marine sextant had been carried in the Pan Am Clipper as a
“preventer” (a backup), that all observations had been made with the Pioneer bubble sextant.
Van Asten's bottom line appears in Figure 6 of "Where to Search for the Earhart Lockheed Electra." (http://davidkbowman.com/Search_For_Earhart_Lockheed.pdf) Using his system, he calculates that the plane came down in an area roughly 85 miles NNW of Howland Island--the area immediately searched by the Itasca on 2 July 1937 (http://tighar.org/wiki/Coast_Guard_search). I'm not sure how close this is to Elgen Long's calculations (http://tighar.org/wiki/Long) or whether the two Nauticos searches (http://tighar.org/wiki/Nauticos) have covered that area.
-
... he has his own idea
of what “sunset” is that doesn’t comport with anybody else’s understanding of that word! ...
Basically, this weird idea of what sunset or sunrise is, (which is different than everybody else’s
and is not found in any dictionary or navigation manual) leads to all of Mr. van Asten’s theories,
methods and conclusions.
I actually understand his theories and methodology and even his complex computations ...
Thanks for clarifying the nature of the argument. Much appreciated!
We will start with his idea that Noonan measured the point of “van Asten sunrise” with a marine
sextant and not with his bubble sextant. This is critical to his theory since he blames Noonan for
using the wrong technique with the marine sextant and that the error (that he believes led to the
loss) would not have occurred if Noonan had used his bubble sextant tor the “van Asten sunrise”
observation.
Thanks for untangling that.
If there was no marine sextant on board
then no way to make this error.
Even if there was a marine sextant on board (with or without the bubble modification used on many Brandis instruments (http://tighar.org/wiki/Sextant)), there is no reason to think that Fred would have chosen to use it rather than the Pioneer instrument that was designed for use in aerial navigation.
Oh, reading further along, I see that we are already in agreement on that score:
... There is no reason to believe that Noonan would have used a marine
sextant (even if he had one available) for taking any observations from the Electra. Noonan said
himself, that even though a marine sextant had been carried in the Pan Am Clipper as a
“preventer” (a backup), that all observations had been made with the Pioneer bubble sextant.
Van Asten's bottom line appears in Figure 6 of "Where to Search for the Earhart Lockheed Electra." (http://davidkbowman.com/Search_For_Earhart_Lockheed.pdf) Using his system, he calculates that the plane came down in an area roughly 85 miles NNW of Howland Island--the area immediately searched by the Itasca on 2 July 1937 (http://tighar.org/wiki/Coast_Guard_search). I'm not sure how close this is to Elgen Long's calculations (http://tighar.org/wiki/Long) or whether the two Nauticos searches (http://tighar.org/wiki/Nauticos) have covered that area.
I do not know about Nauticos searches , Waitt discoveries searched along E.Long´s ´circles of uncertainty´ , southwards of 1 deg 49 - N . That the area would have been visited by Itasca confirms nothing : there have been numerous aircraft on sea accidents without trace.
-
The problem I see with the concept of making this flight by the offset method is based in the uncertainty associated with flight parameters and the accumulated errors produced by them.
Offsets only make sense if they don't add more risk or error than they compensate for. For example, if you're flying from Havana to Key West (roughly 020T) and for some reason don't have enough fuel to continue on to mainland Florida if you miss to the west, it makes sense to shade your course to the right (say 030T) and turn west when you see the Keys. The Keys are fixed, visible to the naked eye, they lead to Key West and you have a very high probabliity of finding them, so you're not introducing new error or uncertainty. You are, however, guaranteeing a longer flight.
Doing the same thing based on a DR track buys you very little, and at quite a price in terms of risk and uncertainty. For simplicitys sake, consider a flight from a point on the equator to a small island 1000 nm east on the equator. If you think an offset is a good idea, go ahead and fly to a spot in the ocean (not an island, coastline, depth contour or lighted range, just a random-looking patch of ocean) exactly 100 nm south of the island, then hang a left. The island will be exactly 100 nm ahead of you. Piece of cake.
If: You were able to hit the correct longitude. At night. No identifiable landmarks. No decent winds aloft data. Maybe a single LOP a couple hours before ETA.
If AE and FN intended to try this, it would require that they not home in on the RDF bearings they intended to be picking up. As Itasca and/or Howland came into range, they would have to watch the bearing move from almost dead ahead to straight off the port wing and then and only then only then turn at that point. Then fly into their destination from a direction 90 degrees from their origin.
Without telling the people that would be looking for them that they would be coming in from the south.
Seems a bit of a stretch to me.
-----------------------------
Except that the two methods to use to find the island are not mutually exclusive. The RDF should have picked up the Itasca's signals several hundred miles out. They used radio bearings that were more than 600 NM on the flight to Hawii. So there is no problem aiming directly towards Howland expecting to be able to get radio bearings when within 200 NM. When they didn't get a signal there is no problem with turning off to start the landfall since that procedure is accurate enough to get them to Howland in case they never do get the radio signal. If, on the way to the offset point they do start receiving the signals then they would not have to continue all the way to the sun line LOP but would turn to head directly toward Howland as soon as they got the signals.
This is common when flying an instrument approach. You follow a routing to the initial approach fix at which point you will turn away from the destination airport to fly a procedure turn and only after completing the procedure turn are you then heading towards the airport. This "full instrument procedure" adds 9 or 10 minutes to the flight time so you don't want to do it you do not have to. So, if you are flying toward the IAF and you happen to be below the clouds and you see the airport, say off to your left, then you tell the controller "airport in sight" and he then clears you for a "visual approach" which then allows you, at that point, to turn directly towards the airport. There is no reason to complete the full approach and waste all that time.
Same thing with a landfall approach.
See:
https://sites.google.com/site/fredienoonan/topics/landfall-procedure
https://sites.google.com/site/fredienoonan/discussions/navigation-to-howland-island
gl
-
Mr. Lapook ,
According to your replies I would not have explained "looking at the same time by two sextant types" , etc. The key to overcome the misunderstanding is the following : the N.A. or any other source gives GMT of sunrise U.L. @ 175453 GMT . It here concerns the visible (also named ´apparent´-) sun , for which the true sun must be 53´below the horizon . Hence , if you go to look to sunrise U.L. with the marine sextant , you actually see the sun for @ GMT 175453 - 3m50s = 175103 Greenwich Apparent Time . The sun rises with 13´8 / time minute , so 53´/ 13´.8 = 3m50s after 175103 GAT , sun´s centre is in the horizon , elevation zero . Now you have 2 alternatives : I . @ 175453 GMT you observe with the marine sextant . You now see the sun with a LHA which is 57´.5 larger than it would be @ 175453 GAT. It will last 3m50s (53´/ 13´.8) before the true sun (centre) is in the horizon , the LHA having diminished with 57´.5 . II . @ 175453 GAT you observe with the bubble sextant , the LHA has the correct opening since you view the true sun . During the time lag 175103 GAT to 175453 GAT however , the MEAN sun traveled from 175453 GAT to 175843 GMT by the time equation , equally being 3m50s . Balance : since you fly on GMT schedule , given that you observe by marine sextant , whereas you used the bubble sextant @ sunset last evening , you will seemingly arrive at precomptud Zulu time at your next initial point . However , actually , you will be there 3m50s early. If the initial point is at the "alter to offset course" place , you will consequently arrive 3m50s short of the precomputed Turn-Off-Point on the from sunrise advanced LOP .
I from experience know that this reasoning about time lags is a dreadful blackbox , inscrutable and demanding for many hours of study , but that´s just how it is.
--------------------------------------
Imagine...you have taken your wife, .....
Enough for now.
gl
Mr.Lapook ,
I see , by many words , that you try to undermine the theory in question , which is good since any theory needs a testbench before it can be generally accepted . However , you continuously bring into discussion the relevancy rate of it , all your comments have , so far , no influence on the internal consistency . P.e. you write about the "van Asten sunset", whereas it is clear and explained that only a "Frederick Noonan sunset" is on record , communicated @ 0720 GMT for 159-07-E ; 04-33-30-S coordinates . You also bring into discussion bubble sextants , not marine sextants , given to WW-II air navigators because of the assumed amelioration of the instrument , whereas it is trivial that in war time , aircraft fly necessarily at high altitudes with sky and local horizon blended so that marine sextants failed their reference line. In all your comments stating "mr.van Asten is wrong again" and "You don´t know what you are talking about" , not one sentence concerning supposed inconsistency finds a good argument . It is , other example , not new to me that precomputation took place during flight : since the turn-off point after sunrise would have been originally reached at sunrise , Noonan had to recompute in flight for ephemeris of another coordinates pair. The exact algorithms used for his calculations indeed remain unknown , but that is no argument for the statement that mine would be too long , too intricate , upside down , etc. , it is for e.g. sunset clear that Noonan acquired the same outcomes , and that is unconditionall , one step and more forward in the field of quantitative research for the incident.
On hilltop no.3 , 1,000 ft above sea near sunset , sits a mr. L with a Gibson Girl , kite in the air , to contact his airline company at sunset time for checking the company´s new sunset tables. At precomputed sunset time , he looks to .. a disc and sees it largely and complete above the horizon through his marine sextant telescope . He calls the company , shouting : "your tables are wrong , with my calibrated sextant I still see the sun after sunrise , your Greenwich Hour Angle notation is adverse , I am sure I corrected for dip !"
shouts the company executive back : "You are fired , Sir , you should have turned up your horizon 53 additional arcminutes .. the knob at the underside" .
------------------------------------------------------------------------------
(Continuing on with our romantic vignette.)
...
“Noticing the confused look on her face he goes on ‘we are about a thousand feet above sea level
so when we are looking at the sea horizon we are actually looking downward, below the level
horizontal plane. The sun, even though we can still see the entire disk, is actually below the
horizontal level so it has already set. Now get up, we’re leaving.’”
“But wait, I wanted to see a romantic sunset, this sucks. How do you even know that the sun is
below the true horizontal?” she asks.
“Because I figured out a way to determine it without help from anybody else, and I am pretty
proud of myself, I looked in lots of navigation manuals and this method is not in any of them! I
did find in these manuals that navigators have to allow for the fact that the visible horizon is
actually below the true horizontal when taking sights with their marine sextants. Since it is below
zero and it is used as the reference for the measurements, all altitudes measured with a marine
sextant are too large so navigators must subtract the amount that the visible horizon is below the
true horizontal from all of their sextant readings. They call this the “dip” correction and it varies
according to the height the observer’s eye is above sea level. They find this correction tabulated
in the “dip correction table” in the Nautical Almanac. I looked in the dip table and found that for
our height above the sea, one thousand feet, the dip correction is a little more than half a degree,
thirty-one minutes of arc, actually. So, I just set the index arm on my marine sextant to thirty-one
minutes, looked at the horizon through the horizon mirror on the sextant and waited until the
upper limb of the sun, that I was viewing in the index mirror, sank down until it appeared to be
lined up with the visible horizon reference in the sextant mirror so I then knew that the upper
limb was at the true horizontal and so the sun had set.”
She says “OK, that’s great. So that’s what you were doing over there by yourself, I thought... oh
never mind.”
“You’re RIGHT, it is great, I FIGURED IT OUT, nobody else had ever discovered this method
for finding the true horizontal!” he replied.
“O.K. but can we please wait a little while longer so I can actually see the sun disappear behind
the horizon, I’d like to see the green flash” she begs.
“No!, I know when the true sunset is, so we are leaving now.”
(We will now leave this couple to work our their “issues.”)
In fact, this method would work if anybody needed to find the point of “van Asten
sunset/sunrise” which no navigator has yet to discover the need to do.
I communicated with Mr. van Asten about this and asked him how Noonan would have known
his height above the sea so that he could look in the dip table to determine the correct value of
dip to place on his sextant. He responded that Earhart said that she was at a thousand feet and
that she knew that from her altimeter.
On May 16th I wrote to Mr. van Asten:
“To have an accurate altitude from a barometric altimeter you need to have a local altimeter
setting (QNH) for a reporting station within 50 nm of your location and Earhart had set her
altimeter on the ground in Lae, 2222 nm away and had not received any altimeter setting since
then. Over such a great distance it is possible for an altimeter to be off by a 1000 feet since the
change in atmospheric pressure for the different locations will cause the altimeter to read
incorrectly.
Just to give you an example, I just checked the weather at Minneapolis, Minnesota and at
Billings, Montana, two airports separated by only 644 nm. At 0600 Z the altimeter setting at
Minneapolis is 31.18 inches of hg and at Billings the altimeter setting is only 29.72 inches of hg.
With this difference in altimeter settings, a pilot taking off from Minneapolis and flying only 644
nm to Billings without getting the local Billings altimeter setting (QNH) would end up 460 feet
lower than what his altimeter is indicating, and this in only 644 nm. A pilot flying in the opposite
direction would find himself 460 feet too high. Noonan would not have used a mariner's sextant
because he would know of the uncertainty in the altitude and the resulting uncertainty in the
correct dip correction to use. Since Noonan did not have a current altimeter setting then his
height could easily have been off by plus or minus 500 feet so the dip might be anywhere
between 22' and 38' giving the marine sextant altitude 16' of uncertainty But using the
methodology that you laid out of setting the marine sextant to 31' (the dip at 1000 feet) and then
waiting for the upper limb of the sun to come up into alignment with the visible horizon seen in
the marine sextant then causes you to see the upper limb of the sun aligned with the true
horizontal . Then you said to subtract 53' (37' refraction and 16' of semi-diameter) from this zero
altitude to arrive at the true altitude of the center of the sun of minus 53'.
But if they were only at 500 feet instead of 1000 feet then the dip correction is only 22' so setting
the sextant as you said would not cause it to define the true horizontal but would actually set the
reference at 9' above the true horizontal so the observation would be in error by the same 9'
meaning that the true altitude of the center of the sun would be minus 44' not the minus 53' of
your computation, resulting in a 9 nm error in the line of position which would eventually place
them 9 nm east of Howland.
If, instead, they were actually at 1500 feet then the dip correction would have been 38' instead of
the 31' that you have set your marine sextant to which would then result in a 7' error, placing
them 7 nm west of Howland. There is 16' of uncertainty from this possible altimetery error
causing 16' of uncertainty in the correct dip correction to use. This results in a 16 nm uncertainty
in the derived position of the aircraft. Noonan would have gotten a more accurate LOP using the
bubble sextant which doesn't require a correction for dip. This would also cause the “van Asten
sunrise” to occur up to 36 seconds early or late compared to your computations.”
(You can see the dip correction table at:
https://sites.google.com/site/fredienoonan/resources/nautical-almanac-1937/almanac-1937-277.J
PG?attredirects=0
You can also read about the dip and refraction corrections in the American Practical Navigator,
1888 and 1914 editions here:
https://sites.google.com/site/fredienoonan/resources/american-practical-navigator-1888
and
https://sites.google.com/site/fredienoonan/resources/american-practical-naigator-h-o-9-1914
These excerpts also contain the complete sections on the methods of determining longitude and
you can review them and you will find no mention of the “van Asten’s sunrise” method.)
Mr. van Asten’s response actually made me laugh out loud. He said Noonan could just use his
bubble sextant to measure the dip of the visible horizon to place on his marine sextant and then
look in the dip table for that amount of dip and so determine the altitude of the plane.
I responded:
“You come up with an interesting use for the dip table. But if they used the bubble sextant to
measure the dip then there would have been no need to determine dip at all since they would just
use the bubble sextant for taking the observations.”
Mr. van Asten has a bubble sextant and plays with it while standing on the ground so he doesn’t
understand the use of a bubble sextant in the air. Due to the constant accelerations a plane feels,
the bubble is in constant motion even if the air feels smooth to the occupants. In turbulence it
really moves around. So when taking an observation you are constantly turning the altitude knob
on the sextant to chase the bubble with the image of the sun. The extreme readings might actually
differ from the true reading by more than a full degree (60'). You must take many sights over a
short period and average the readings to get any kind of accuracy at all and you must accept an
uncertainty of plus and minus 7'. This would also apply to a measurement of the dip of the visible
horizon, so this uncertainty would then be transmitted to the marine sextant and would carry
through to the horizontal established by the “van Asten method..” The uncertainty introduced this
way is just about the same as that introduced by lack of a current altimeter setting.
Mr. van Asten also doesn’t allow for the uncertainty in the readings from a marine sextant.
Various statistical studies have been made using data from thousands of observations by
hundreds of observers and the standard deviation is about 1.6' so the uncertainty is twice this,
3.2'. This would be added to the uncertainty in determining the dip setting to be used so the total
uncertainty, if Noonan wanted to use a marine sextant to determine “van Asten sunrise”, would
be 10' or 11' which is worse than just using the bubble sextant alone.
I also pointed out to Mr. van Asten:
“She did not report being at 1000 feet until 1912 Z, 78 minutes after you believed that they were
observing sunrise at 1000 feet as part of their “must be on you” transmission when they believed
that they were already at Howland. They would have traveled approximately 170 nm in that time
interval. There is no reason to assume that they descended from their cruising altitude as soon as
you believe. Flying higher provided better fuel economy and better opportunities for celestial
observations. Clouds are often in layers at different altitudes. So, for example, if there was a
scattered layer at 15,000 feet and a broken layer at 8,000 feet then flying at 10,000 feet would
provide very good observation conditions with only a small part of the heavens obstructed.
Flying below 8,000 feet would produce possibly complete obstructions to observations as the two
layers (each having large openings) could overlap.”
Mr. van Asten wrote back:
“2. Besides mentions in biographies , why would Noonan have the plane going down to 1,000 ft ,
an unfavorable altitude for seeing a small island , if it was not necessary to have the horizon
sharply within visual range ?”
-To which I responded:
“Most people believe that they were down at 1000 feet when they thought they were near the
island and at that point (and not before) they had been compelled to descend below a low cloud
layer in order to search for Howland. “
(to be continued)
gl
-
Mr. Lapook ,
Mr. van Asten also doesn’t allow for the uncertainty in the readings from a marine sextant.
Various statistical studies have been made using data from thousands of observations by
hundreds of observers and the standard deviation is about 1.6' so the uncertainty is twice this,
3.2'. This would be added to the uncertainty in determining the dip setting to be used so the total
uncertainty, if Noonan wanted to use a marine sextant to determine “van Asten sunrise”, would
be 10' or 11' which is worse than just using the bubble sextant alone.
---------------------------------
I forgot to say that the accuracy of marine sextant sights was determined for observations taken on shipboard where the height of eye above sea level was measured so there was no uncertainty in the dip correction to be use. There is no reason to believe that an in-flight marine sextant observation would be more accurate than a shipboard observation and would probably be less accurate but there are no statistics on that BECAUSE NO ONE USES A MARINE SEXTANT IN FLIGHT!
gl
-
... If they used the bubble sextant to
measure the dip then there would have been no need to determine dip at all since they would just
use the bubble sextant for taking the observations. ...
Does the Pioneer bubble sextant obviate the need to know one's altitude when drawing a LOP based on an observation?
Or does the potential error introduced by not being able to calibrate their altimeter to a local barometric reference affect both kinds of instruments equally?
-
... If they used the bubble sextant to
measure the dip then there would have been no need to determine dip at all since they would just
use the bubble sextant for taking the observations. ...
Does the Pioneer bubble sextant obviate the need to know one's altitude when drawing a LOP based on an observation?
Or does the potential error introduced by not being able to calibrate their altimeter to a local barometric reference affect both kinds of instruments equally?
A marine sextant measures the angle between
- A line between your eye and the observed object, and
- A line between your eye and the observed horizon
The higher up you are, the lower the observed horizon is, and so the angle will change based upon your altitude.
The bubble sextant measures the angle between
- A line between your eye and the observed object, and
- The horizontal plane, as measured by what is essentially a very precise refinement of a carpenter's level.
In this case, ascending or descending doesn't change anything, so your altitude doesn't need to be taken into consideration, except for the special case when the observed object is very close to the horizon and subject to atmospheric refraction.
-
The bubble sextant measures the angle between
- A line between your eye and the observed object, and
- The horizontal plane, as measured by what is essentially a very precise refinement of a carpenter's level.
In this case, ascending or descending doesn't change anything, so your altitude doesn't need to be taken into consideration, except for the special case when the observed object is very close to the horizon and subject to atmospheric refraction.
I'll take your word for this that this works.
The fact that the altitude of the observer makes no difference in the calculation of the LOP derived from an observation must be due to the inability of the instrument to detect the tiny difference in altitude compared to the vast distance from the celestial object. It must be a difference that makes no difference. If, instead of measuring the eye angle from the observer to a stars we were measuring the eye angle from the observers to a weather balloon, the difference in altitude between the observers would make a difference in the angles measured--wouldn't it?
To put it the other way around, looking at the situation from the standpoint of the star being observed, the two different observers are, for all practical purposes, at the same altitude (?).
-
Mr. Lapook ,
According to your replies I would not have explained "looking at the same time by two sextant types" , etc. The key to overcome the misunderstanding is the following : the N.A. or any other source gives GMT of sunrise U.L. @ 175453 GMT . It here concerns the visible (also named ´apparent´-) sun , for which the true sun must be 53´below the horizon . Hence , if you go to look to sunrise U.L. with the marine sextant , you actually see the sun for @ GMT 175453 - 3m50s = 175103 Greenwich Apparent Time . The sun rises with 13´8 / time minute , so 53´/ 13´.8 = 3m50s after 175103 GAT , sun´s centre is in the horizon , elevation zero . Now you have 2 alternatives : I . @ 175453 GMT you observe with the marine sextant . You now see the sun with a LHA which is 57´.5 larger than it would be @ 175453 GAT. It will last 3m50s (53´/ 13´.8) before the true sun (centre) is in the horizon , the LHA having diminished with 57´.5 . II . @ 175453 GAT you observe with the bubble sextant , the LHA has the correct opening since you view the true sun . During the time lag 175103 GAT to 175453 GAT however , the MEAN sun traveled from 175453 GAT to 175843 GMT by the time equation , equally being 3m50s . Balance : since you fly on GMT schedule , given that you observe by marine sextant , whereas you used the bubble sextant @ sunset last evening , you will seemingly arrive at precomptud Zulu time at your next initial point . However , actually , you will be there 3m50s early. If the initial point is at the "alter to offset course" place , you will consequently arrive 3m50s short of the precomputed Turn-Off-Point on the from sunrise advanced LOP .
I from experience know that this reasoning about time lags is a dreadful blackbox , inscrutable and demanding for many hours of study , but that´s just how it is.
--------------------------------------
Imagine...you have taken your wife, .....
Enough for now.
gl
Mr.Lapook ,
I see , by many words , that you try to undermine the theory in question , which is good since any theory needs a testbench before it can be generally accepted . However , you continuously bring into discussion the relevancy rate of it , all your comments have , so far , no influence on the internal consistency . P.e. you write about the "van Asten sunset", whereas it is clear and explained that only a "Frederick Noonan sunset" is on record , communicated @ 0720 GMT for 159-07-E ; 04-33-30-S coordinates . You also bring into discussion bubble sextants , not marine sextants , given to WW-II air navigators because of the assumed amelioration of the instrument , whereas it is trivial that in war time , aircraft fly necessarily at high altitudes with sky and local horizon blended so that marine sextants failed their reference line. In all your comments stating "mr.van Asten is wrong again" and "You don´t know what you are talking about" , not one sentence concerning supposed inconsistency finds a good argument . It is , other example , not new to me that precomputation took place during flight : since the turn-off point after sunrise would have been originally reached at sunrise , Noonan had to recompute in flight for ephemeris of another coordinates pair. The exact algorithms used for his calculations indeed remain unknown , but that is no argument for the statement that mine would be too long , too intricate , upside down , etc. , it is for e.g. sunset clear that Noonan acquired the same outcomes , and that is unconditionall , one step and more forward in the field of quantitative research for the incident.
On hilltop no.3 , 1,000 ft above sea near sunset , sits a mr. L with a Gibson Girl , kite in the air , to contact his airline company at sunset time for checking the company´s new sunset tables. At precomputed sunset time , he looks to .. a disc and sees it largely and complete above the horizon through his marine sextant telescope . He calls the company , shouting : "your tables are wrong , with my calibrated sextant I still see the sun after sunrise , your Greenwich Hour Angle notation is adverse , I am sure I corrected for dip !"
shouts the company executive back : "You are fired , Sir , you should have turned up your horizon 53 additional arcminutes .. the knob at the underside" .
------------------------------------------------------------------------------
(Continuing on with our romantic vignette.)
...
“Noticing the confused look on her face he goes on ‘we are about a thousand feet above sea level
so when we are looking at the sea horizon we are actually looking downward, below the level
horizontal plane. The sun, even though we can still see the entire disk, is actually below the
horizontal level so it has already set. Now get up, we’re leaving.’”
“But wait, I wanted to see a romantic sunset, this sucks. How do you even know that the sun is
below the true horizontal?” she asks.
“Because I figured out a way to determine it without help from anybody else, and I am pretty
proud of myself, I looked in lots of navigation manuals and this method is not in any of them! I
did find in these manuals that navigators have to allow for the fact that the visible horizon is
actually below the true horizontal when taking sights with their marine sextants. Since it is below
zero and it is used as the reference for the measurements, all altitudes measured with a marine
sextant are too large so navigators must subtract the amount that the visible horizon is below the
true horizontal from all of their sextant readings. They call this the “dip” correction and it varies
according to the height the observer’s eye is above sea level. They find this correction tabulated
in the “dip correction table” in the Nautical Almanac. I looked in the dip table and found that for
our height above the sea, one thousand feet, the dip correction is a little more than half a degree,
thirty-one minutes of arc, actually. So, I just set the index arm on my marine sextant to thirty-one
minutes, looked at the horizon through the horizon mirror on the sextant and waited until the
upper limb of the sun, that I was viewing in the index mirror, sank down until it appeared to be
lined up with the visible horizon reference in the sextant mirror so I then knew that the upper
limb was at the true horizontal and so the sun had set.”
She says “OK, that’s great. So that’s what you were doing over there by yourself, I thought... oh
never mind.”
“You’re RIGHT, it is great, I FIGURED IT OUT, nobody else had ever discovered this method
for finding the true horizontal!” he replied.
“O.K. but can we please wait a little while longer so I can actually see the sun disappear behind
the horizon, I’d like to see the green flash” she begs.
“No!, I know when the true sunset is, so we are leaving now.”
(We will now leave this couple to work our their “issues.”)
In fact, this method would work if anybody needed to find the point of “van Asten
sunset/sunrise” which no navigator has yet to discover the need to do.
I communicated with Mr. van Asten about this and asked him how Noonan would have known
his height above the sea so that he could look in the dip table to determine the correct value of
dip to place on his sextant. He responded that Earhart said that she was at a thousand feet and
that she knew that from her altimeter.
On May 16th I wrote to Mr. van Asten:
“To have an accurate altitude from a barometric altimeter you need to have a local altimeter
setting (QNH) for a reporting station within 50 nm of your location and Earhart had set her
altimeter on the ground in Lae, 2222 nm away and had not received any altimeter setting since
then. Over such a great distance it is possible for an altimeter to be off by a 1000 feet since the
change in atmospheric pressure for the different locations will cause the altimeter to read
incorrectly.
Just to give you an example, I just checked the weather at Minneapolis, Minnesota and at
Billings, Montana, two airports separated by only 644 nm. At 0600 Z the altimeter setting at
Minneapolis is 31.18 inches of hg and at Billings the altimeter setting is only 29.72 inches of hg.
With this difference in altimeter settings, a pilot taking off from Minneapolis and flying only 644
nm to Billings without getting the local Billings altimeter setting (QNH) would end up 460 feet
lower than what his altimeter is indicating, and this in only 644 nm. A pilot flying in the opposite
direction would find himself 460 feet too high. Noonan would not have used a mariner's sextant
because he would know of the uncertainty in the altitude and the resulting uncertainty in the
correct dip correction to use. Since Noonan did not have a current altimeter setting then his
height could easily have been off by plus or minus 500 feet so the dip might be anywhere
between 22' and 38' giving the marine sextant altitude 16' of uncertainty But using the
methodology that you laid out of setting the marine sextant to 31' (the dip at 1000 feet) and then
waiting for the upper limb of the sun to come up into alignment with the visible horizon seen in
the marine sextant then causes you to see the upper limb of the sun aligned with the true
horizontal . Then you said to subtract 53' (37' refraction and 16' of semi-diameter) from this zero
altitude to arrive at the true altitude of the center of the sun of minus 53'.
But if they were only at 500 feet instead of 1000 feet then the dip correction is only 22' so setting
the sextant as you said would not cause it to define the true horizontal but would actually set the
reference at 9' above the true horizontal so the observation would be in error by the same 9'
meaning that the true altitude of the center of the sun would be minus 44' not the minus 53' of
your computation, resulting in a 9 nm error in the line of position which would eventually place
them 9 nm east of Howland.
If, instead, they were actually at 1500 feet then the dip correction would have been 38' instead of
the 31' that you have set your marine sextant to which would then result in a 7' error, placing
them 7 nm west of Howland. There is 16' of uncertainty from this possible altimetery error
causing 16' of uncertainty in the correct dip correction to use. This results in a 16 nm uncertainty
in the derived position of the aircraft. Noonan would have gotten a more accurate LOP using the
bubble sextant which doesn't require a correction for dip. This would also cause the “van Asten
sunrise” to occur up to 36 seconds early or late compared to your computations.”
(You can see the dip correction table at:
https://sites.google.com/site/fredienoonan/resources/nautical-almanac-1937/almanac-1937-277.J
PG?attredirects=0
You can also read about the dip and refraction corrections in the American Practical Navigator,
1888 and 1914 editions here:
https://sites.google.com/site/fredienoonan/resources/american-practical-navigator-1888
and
https://sites.google.com/site/fredienoonan/resources/american-practical-naigator-h-o-9-1914
These excerpts also contain the complete sections on the methods of determining longitude and
you can review them and you will find no mention of the “van Asten’s sunrise” method.)
Mr. van Asten’s response actually made me laugh out loud. He said Noonan could just use his
bubble sextant to measure the dip of the visible horizon to place on his marine sextant and then
look in the dip table for that amount of dip and so determine the altitude of the plane.
I responded:
“You come up with an interesting use for the dip table. But if they used the bubble sextant to
measure the dip then there would have been no need to determine dip at all since they would just
use the bubble sextant for taking the observations.”
Mr. van Asten has a bubble sextant and plays with it while standing on the ground so he doesn’t
understand the use of a bubble sextant in the air. Due to the constant accelerations a plane feels,
the bubble is in constant motion even if the air feels smooth to the occupants. In turbulence it
really moves around. So when taking an observation you are constantly turning the altitude knob
on the sextant to chase the bubble with the image of the sun. The extreme readings might actually
differ from the true reading by more than a full degree (60'). You must take many sights over a
short period and average the readings to get any kind of accuracy at all and you must accept an
uncertainty of plus and minus 7'. This would also apply to a measurement of the dip of the visible
horizon, so this uncertainty would then be transmitted to the marine sextant and would carry
through to the horizontal established by the “van Asten method..” The uncertainty introduced this
way is just about the same as that introduced by lack of a current altimeter setting.
Mr. van Asten also doesn’t allow for the uncertainty in the readings from a marine sextant.
Various statistical studies have been made using data from thousands of observations by
hundreds of observers and the standard deviation is about 1.6' so the uncertainty is twice this,
3.2'. This would be added to the uncertainty in determining the dip setting to be used so the total
uncertainty, if Noonan wanted to use a marine sextant to determine “van Asten sunrise”, would
be 10' or 11' which is worse than just using the bubble sextant alone.
I also pointed out to Mr. van Asten:
“She did not report being at 1000 feet until 1912 Z, 78 minutes after you believed that they were
observing sunrise at 1000 feet as part of their “must be on you” transmission when they believed
that they were already at Howland. They would have traveled approximately 170 nm in that time
interval. There is no reason to assume that they descended from their cruising altitude as soon as
you believe. Flying higher provided better fuel economy and better opportunities for celestial
observations. Clouds are often in layers at different altitudes. So, for example, if there was a
scattered layer at 15,000 feet and a broken layer at 8,000 feet then flying at 10,000 feet would
provide very good observation conditions with only a small part of the heavens obstructed.
Flying below 8,000 feet would produce possibly complete obstructions to observations as the two
layers (each having large openings) could overlap.”
Mr. van Asten wrote back:
“2. Besides mentions in biographies , why would Noonan have the plane going down to 1,000 ft ,
an unfavorable altitude for seeing a small island , if it was not necessary to have the horizon
sharply within visual range ?”
-To which I responded:
“Most people believe that they were down at 1000 feet when they thought they were near the
island and at that point (and not before) they had been compelled to descend below a low cloud
layer in order to search for Howland. “
(to be continued)
gl
Is any document available on low cloud area westward of Howland ?
-
The bubble sextant measures the angle between
- A line between your eye and the observed object, and
- The horizontal plane, as measured by what is essentially a very precise refinement of a carpenter's level.
In this case, ascending or descending doesn't change anything, so your altitude doesn't need to be taken into consideration, except for the special case when the observed object is very close to the horizon and subject to atmospheric refraction.
I'll take your word for this that this works.
The fact that the altitude of the observer makes no difference in the calculation of the LOP derived from an observation must be due to the inability of the instrument to detect the tiny difference in altitude compared to the vast distance from the celestial object. It must be a difference that makes no difference. If, instead of measuring the eye angle from the observer to a stars we were measuring the eye angle from the observers to a weather balloon, the difference in altitude between the observers would make a difference in the angles measured--wouldn't it?
To put it the other way around, looking at the situation from the standpoint of the star being observed, the two different observers are, for all practical purposes, at the same altitude (?).
The horizon for a bubble sextant is the celestial horizon which is parallel to the ´equator´of the observer since the extension of the equator and the celestial horizon point to infinity .
-
... If they used the bubble sextant to
measure the dip then there would have been no need to determine dip at all since they would just
use the bubble sextant for taking the observations. ...
Does the Pioneer bubble sextant obviate the need to know one's altitude when drawing a LOP based on an observation?
Or does the potential error introduced by not being able to calibrate their altimeter to a local barometric reference affect both kinds of instruments equally?
Altitude is of no importance for any artificial horizon sextant since the bubble is in line with the celestial horizon which is parallel with the observer´s "equator" , both pointing to infinity.
Altimeter and b-sextant have no interconnection in the given sense . If no QNH is available and the altimeter off scale , the possibility to assess low altitude remains by consulting the table for dip in H.O.208 , giving 00-31´ for 1,000 ft. If you turn up a mariner´s sextant to 31´ and you see the optical horizon in the reference line , you are @ 1,000 ft altitude.
-
Mr. Lapook ,
Mr. van Asten also doesn’t allow for the uncertainty in the readings from a marine sextant.
Various statistical studies have been made using data from thousands of observations by
hundreds of observers and the standard deviation is about 1.6' so the uncertainty is twice this,
3.2'. This would be added to the uncertainty in determining the dip setting to be used so the total
uncertainty, if Noonan wanted to use a marine sextant to determine “van Asten sunrise”, would
be 10' or 11' which is worse than just using the bubble sextant alone.
---------------------------------
I forgot to say that the accuracy of marine sextant sights was determined for observations taken on shipboard where the height of eye above sea level was measured so there was no uncertainty in the dip correction to be use. There is no reason to believe that an in-flight marine sextant observation would be more accurate than a shipboard observation and would probably be less accurate but there are no statistics on that BECAUSE NO ONE USES A MARINE SEXTANT IN FLIGHT!
gl
Chichester , and a variety of ocean pilots used marine sextants to establish A/c´s position w.r.t. lines of position in the One Line Approach operation , they all were succesful in finding their destiination this way , there is no record of any miscarriage by using the method. Hegenburger/Maitland (on a completely precomputed navigation plan to Hawaii) even carried a single telescope to be able observing objects of which elevation was of no importance , p.e. for sunset/sunrise not any instrument besides the unarmed eye and facultatively a green filter is needed , since only the point of time @ U.L. appearance is of importance , to match it with the running list figures for latitude/longitude. If p.e. mr. Noonan used the mariner´s sextant (for it´s green filter) or not , that has zero influence on the error he possibly/probably committed by not using the bubble sextant like @ sunset . The only second condition for observing sunrise from an A/c is : fly low to avoid seeing the sun earlier than @ sea level which is the lower reference for elevation of heavenly bodies. It is for these reasons of no use to bring yes or no marine sextants in the field of discussion , for any navtable or navformula if computed elevation is zero .
.
-
Mr. Lapook ,
According to your replies I would not have explained "looking at the same time by two sextant types" , etc. The key to overcome the misunderstanding is the following : the N.A. or any other source gives GMT of sunrise U.L. @ 175453 GMT . It here concerns the visible (also named ´apparent´-) sun , for which the true sun must be 53´below the horizon . Hence , if you go to look to sunrise U.L. with the marine sextant , you actually see the sun for @ GMT 175453 - 3m50s = 175103 Greenwich Apparent Time . The sun rises with 13´8 / time minute , so 53´/ 13´.8 = 3m50s after 175103 GAT , sun´s centre is in the horizon , elevation zero . Now you have 2 alternatives : I . @ 175453 GMT you observe with the marine sextant . You now see the sun with a LHA which is 57´.5 larger than it would be @ 175453 GAT. It will last 3m50s (53´/ 13´.8) before the true sun (centre) is in the horizon , the LHA having diminished with 57´.5 . II . @ 175453 GAT you observe with the bubble sextant , the LHA has the correct opening since you view the true sun . During the time lag 175103 GAT to 175453 GAT however , the MEAN sun traveled from 175453 GAT to 175843 GMT by the time equation , equally being 3m50s . Balance : since you fly on GMT schedule , given that you observe by marine sextant , whereas you used the bubble sextant @ sunset last evening , you will seemingly arrive at precomptud Zulu time at your next initial point . However , actually , you will be there 3m50s early. If the initial point is at the "alter to offset course" place , you will consequently arrive 3m50s short of the precomputed Turn-Off-Point on the from sunrise advanced LOP .
I from experience know that this reasoning about time lags is a dreadful blackbox , inscrutable and demanding for many hours of study , but that´s just how it is.
--------------------------------------
Imagine...you have taken your wife, .....
Enough for now.
gl
Mr.Lapook ,
I see , by many words , that you try to undermine the theory in question , which is good since any theory needs a testbench before it can be generally accepted . However , you continuously bring into discussion the relevancy rate of it , all your comments have , so far , no influence on the internal consistency . P.e. you write about the "van Asten sunset", whereas it is clear and explained that only a "Frederick Noonan sunset" is on record , communicated @ 0720 GMT for 159-07-E ; 04-33-30-S coordinates . You also bring into discussion bubble sextants , not marine sextants , given to WW-II air navigators because of the assumed amelioration of the instrument , whereas it is trivial that in war time , aircraft fly necessarily at high altitudes with sky and local horizon blended so that marine sextants failed their reference line. In all your comments stating "mr.van Asten is wrong again" and "You don´t know what you are talking about" , not one sentence concerning supposed inconsistency finds a good argument . It is , other example , not new to me that precomputation took place during flight : since the turn-off point after sunrise would have been originally reached at sunrise , Noonan had to recompute in flight for ephemeris of another coordinates pair. The exact algorithms used for his calculations indeed remain unknown , but that is no argument for the statement that mine would be too long , too intricate , upside down , etc. , it is for e.g. sunset clear that Noonan acquired the same outcomes , and that is unconditionall , one step and more forward in the field of quantitative research for the incident.
On hilltop no.3 , 1,000 ft above sea near sunset , sits a mr. L with a Gibson Girl , kite in the air , to contact his airline company at sunset time for checking the company´s new sunset tables. At precomputed sunset time , he looks to .. a disc and sees it largely and complete above the horizon through his marine sextant telescope . He calls the company , shouting : "your tables are wrong , with my calibrated sextant I still see the sun after sunrise , your Greenwich Hour Angle notation is adverse , I am sure I corrected for dip !"
shouts the company executive back : "You are fired , Sir , you should have turned up your horizon 53 additional arcminutes .. the knob at the underside" .
------------------------------------------------------------------------------
(Continuing on with our romantic vignette.)
...
“Noticing the confused look on her face he goes on ‘we are about a thousand feet above sea level
so when we are looking at the sea horizon we are actually looking downward, below the level
horizontal plane. The sun, even though we can still see the entire disk, is actually below the
horizontal level so it has already set. Now get up, we’re leaving.’”
“But wait, I wanted to see a romantic sunset, this sucks. How do you even know that the sun is
below the true horizontal?” she asks.
“Because I figured out a way to determine it without help from anybody else, and I am pretty
proud of myself, I looked in lots of navigation manuals and this method is not in any of them! I
did find in these manuals that navigators have to allow for the fact that the visible horizon is
actually below the true horizontal when taking sights with their marine sextants. Since it is below
zero and it is used as the reference for the measurements, all altitudes measured with a marine
sextant are too large so navigators must subtract the amount that the visible horizon is below the
true horizontal from all of their sextant readings. They call this the “dip” correction and it varies
according to the height the observer’s eye is above sea level. They find this correction tabulated
in the “dip correction table” in the Nautical Almanac. I looked in the dip table and found that for
our height above the sea, one thousand feet, the dip correction is a little more than half a degree,
thirty-one minutes of arc, actually. So, I just set the index arm on my marine sextant to thirty-one
minutes, looked at the horizon through the horizon mirror on the sextant and waited until the
upper limb of the sun, that I was viewing in the index mirror, sank down until it appeared to be
lined up with the visible horizon reference in the sextant mirror so I then knew that the upper
limb was at the true horizontal and so the sun had set.”
She says “OK, that’s great. So that’s what you were doing over there by yourself, I thought... oh
never mind.”
“You’re RIGHT, it is great, I FIGURED IT OUT, nobody else had ever discovered this method
for finding the true horizontal!” he replied.
“O.K. but can we please wait a little while longer so I can actually see the sun disappear behind
the horizon, I’d like to see the green flash” she begs.
“No!, I know when the true sunset is, so we are leaving now.”
(We will now leave this couple to work our their “issues.”)
In fact, this method would work if anybody needed to find the point of “van Asten
sunset/sunrise” which no navigator has yet to discover the need to do.
I communicated with Mr. van Asten about this and asked him how Noonan would have known
his height above the sea so that he could look in the dip table to determine the correct value of
dip to place on his sextant. He responded that Earhart said that she was at a thousand feet and
that she knew that from her altimeter.
On May 16th I wrote to Mr. van Asten:
“To have an accurate altitude from a barometric altimeter you need to have a local altimeter
setting (QNH) for a reporting station within 50 nm of your location and Earhart had set her
altimeter on the ground in Lae, 2222 nm away and had not received any altimeter setting since
then. Over such a great distance it is possible for an altimeter to be off by a 1000 feet since the
change in atmospheric pressure for the different locations will cause the altimeter to read
incorrectly.
Just to give you an example, I just checked the weather at Minneapolis, Minnesota and at
Billings, Montana, two airports separated by only 644 nm. At 0600 Z the altimeter setting at
Minneapolis is 31.18 inches of hg and at Billings the altimeter setting is only 29.72 inches of hg.
With this difference in altimeter settings, a pilot taking off from Minneapolis and flying only 644
nm to Billings without getting the local Billings altimeter setting (QNH) would end up 460 feet
lower than what his altimeter is indicating, and this in only 644 nm. A pilot flying in the opposite
direction would find himself 460 feet too high. Noonan would not have used a mariner's sextant
because he would know of the uncertainty in the altitude and the resulting uncertainty in the
correct dip correction to use. Since Noonan did not have a current altimeter setting then his
height could easily have been off by plus or minus 500 feet so the dip might be anywhere
between 22' and 38' giving the marine sextant altitude 16' of uncertainty But using the
methodology that you laid out of setting the marine sextant to 31' (the dip at 1000 feet) and then
waiting for the upper limb of the sun to come up into alignment with the visible horizon seen in
the marine sextant then causes you to see the upper limb of the sun aligned with the true
horizontal . Then you said to subtract 53' (37' refraction and 16' of semi-diameter) from this zero
altitude to arrive at the true altitude of the center of the sun of minus 53'.
But if they were only at 500 feet instead of 1000 feet then the dip correction is only 22' so setting
the sextant as you said would not cause it to define the true horizontal but would actually set the
reference at 9' above the true horizontal so the observation would be in error by the same 9'
meaning that the true altitude of the center of the sun would be minus 44' not the minus 53' of
your computation, resulting in a 9 nm error in the line of position which would eventually place
them 9 nm east of Howland.
If, instead, they were actually at 1500 feet then the dip correction would have been 38' instead of
the 31' that you have set your marine sextant to which would then result in a 7' error, placing
them 7 nm west of Howland. There is 16' of uncertainty from this possible altimetery error
causing 16' of uncertainty in the correct dip correction to use. This results in a 16 nm uncertainty
in the derived position of the aircraft. Noonan would have gotten a more accurate LOP using the
bubble sextant which doesn't require a correction for dip. This would also cause the “van Asten
sunrise” to occur up to 36 seconds early or late compared to your computations.”
(You can see the dip correction table at:
https://sites.google.com/site/fredienoonan/resources/nautical-almanac-1937/almanac-1937-277.J
PG?attredirects=0
You can also read about the dip and refraction corrections in the American Practical Navigator,
1888 and 1914 editions here:
https://sites.google.com/site/fredienoonan/resources/american-practical-navigator-1888
and
https://sites.google.com/site/fredienoonan/resources/american-practical-naigator-h-o-9-1914
These excerpts also contain the complete sections on the methods of determining longitude and
you can review them and you will find no mention of the “van Asten’s sunrise” method.)
Mr. van Asten’s response actually made me laugh out loud. He said Noonan could just use his
bubble sextant to measure the dip of the visible horizon to place on his marine sextant and then
look in the dip table for that amount of dip and so determine the altitude of the plane.
I responded:
“You come up with an interesting use for the dip table. But if they used the bubble sextant to
measure the dip then there would have been no need to determine dip at all since they would just
use the bubble sextant for taking the observations.”
Mr. van Asten has a bubble sextant and plays with it while standing on the ground so he doesn’t
understand the use of a bubble sextant in the air. Due to the constant accelerations a plane feels,
the bubble is in constant motion even if the air feels smooth to the occupants. In turbulence it
really moves around. So when taking an observation you are constantly turning the altitude knob
on the sextant to chase the bubble with the image of the sun. The extreme readings might actually
differ from the true reading by more than a full degree (60'). You must take many sights over a
short period and average the readings to get any kind of accuracy at all and you must accept an
uncertainty of plus and minus 7'. This would also apply to a measurement of the dip of the visible
horizon, so this uncertainty would then be transmitted to the marine sextant and would carry
through to the horizontal established by the “van Asten method..” The uncertainty introduced this
way is just about the same as that introduced by lack of a current altimeter setting.
Mr. van Asten also doesn’t allow for the uncertainty in the readings from a marine sextant.
Various statistical studies have been made using data from thousands of observations by
hundreds of observers and the standard deviation is about 1.6' so the uncertainty is twice this,
3.2'. This would be added to the uncertainty in determining the dip setting to be used so the total
uncertainty, if Noonan wanted to use a marine sextant to determine “van Asten sunrise”, would
be 10' or 11' which is worse than just using the bubble sextant alone.
I also pointed out to Mr. van Asten:
“She did not report being at 1000 feet until 1912 Z, 78 minutes after you believed that they were
observing sunrise at 1000 feet as part of their “must be on you” transmission when they believed
that they were already at Howland. They would have traveled approximately 170 nm in that time
interval. There is no reason to assume that they descended from their cruising altitude as soon as
you believe. Flying higher provided better fuel economy and better opportunities for celestial
observations. Clouds are often in layers at different altitudes. So, for example, if there was a
scattered layer at 15,000 feet and a broken layer at 8,000 feet then flying at 10,000 feet would
provide very good observation conditions with only a small part of the heavens obstructed.
Flying below 8,000 feet would produce possibly complete obstructions to observations as the two
layers (each having large openings) could overlap.”
Mr. van Asten wrote back:
“2. Besides mentions in biographies , why would Noonan have the plane going down to 1,000 ft ,
an unfavorable altitude for seeing a small island , if it was not necessary to have the horizon
sharply within visual range ?”
-To which I responded:
“Most people believe that they were down at 1000 feet when they thought they were near the
island and at that point (and not before) they had been compelled to descend below a low cloud
layer in order to search for Howland. “
(to be continued)
gl
When mr. A Einstein heard a journalist comment : "Sir , hundreds of people can deliver proof that your theory is conflicting" , he replied : "If so , one would had been enough" .
-
If, instead of measuring the eye angle from the observer to a stars we were measuring the eye angle from the observers to a weather balloon, the difference in altitude between the observers would make a difference in the angles measured--wouldn't it?
Yes... consider the extreme case where, to the observer on the ground, the weather balloon is directly overhead (altitude of 90 degrees); to an observer at the same altitude as the weather balloon, the balloon would be at an altitude of zero.
To put it the other way around, looking at the situation from the standpoint of the star being observed, the two different observers are, for all practical purposes, at the same altitude (?).
Yes. the star is, for all practical purposes in celestial navigation, infinitely far away.
-
... he has his own idea
of what “sunset” is that doesn’t comport with anybody else’s understanding of that word! ...
Basically, this weird idea of what sunset or sunrise is, (which is different than everybody else’s
and is not found in any dictionary or navigation manual) leads to all of Mr. van Asten’s theories,
methods and conclusions.
I actually understand his theories and methodology and even his complex computations ...
Thanks for clarifying the nature of the argument. Much appreciated!
We will start with his idea that Noonan measured the point of “van Asten sunrise” with a marine
sextant and not with his bubble sextant. This is critical to his theory since he blames Noonan for
using the wrong technique with the marine sextant and that the error (that he believes led to the
loss) would not have occurred if Noonan had used his bubble sextant tor the “van Asten sunrise”
observation.
Thanks for untangling that.
If there was no marine sextant on board
then no way to make this error.
Even if there was a marine sextant on board (with or without the bubble modification used on many Brandis instruments (http://tighar.org/wiki/Sextant)), there is no reason to think that Fred would have chosen to use it rather than the Pioneer instrument that was designed for use in aerial navigation.
Oh, reading further along, I see that we are already in agreement on that score:
... There is no reason to believe that Noonan would have used a marine
sextant (even if he had one available) for taking any observations from the Electra. Noonan said
himself, that even though a marine sextant had been carried in the Pan Am Clipper as a
“preventer” (a backup), that all observations had been made with the Pioneer bubble sextant.
Van Asten's bottom line appears in Figure 6 of "Where to Search for the Earhart Lockheed Electra." (http://davidkbowman.com/Search_For_Earhart_Lockheed.pdf) Using his system, he calculates that the plane came down in an area roughly 85 miles NNW of Howland Island--the area immediately searched by the Itasca on 2 July 1937 (http://tighar.org/wiki/Coast_Guard_search). I'm not sure how close this is to Elgen Long's calculations (http://tighar.org/wiki/Long) or whether the two Nauticos searches (http://tighar.org/wiki/Nauticos) have covered that area.
I do not know about Nauticos searches , Waitt discoveries searched along E.Long´s ´circles of uncertainty´ , southwards of 1 deg 49 - N . That the area would have been visited by Itasca confirms nothing : there have been numerous aircraft on sea accidents without trace.
On your remark abt. E.Long : remarkably and fully independent of each other , supposed that mr.Long could not have read my contribution on fuel supplies & management of 1996 in the magazine of R.Neth.A.F. museum , Soesterberg , we register the 1845 GMT fuel reserves @ 45 US . In his book published after 1996 , Long gives just the figure ,no calculation .
In the course of 2008 mr.D.Jourdan handed over to mr.Long a copy of my EJN-2008 article . On receiving it he replied that , after thirty years research on the subject , he could no more afford the time and energy for studying other vistas .
-
Mr.Lapook ,
You write " We will start with his idea that Noonan measured the point of "van Asten sunrise" with a marine sextant .." mr.Noonan´s assumed observation error did not occur due to using the mariner´s sextant , but on the contrary : it occurred by not using the bubble sextant like @ sunset. At best the m-sextant delivered an easy means of establishing A/c´s exact altitude above ocean´s surface (via the dip table of H.O.no.208) , whereas also the dark green filter was a feature . Sunrise point of time could be established by observing with the unarmed eye (but : see filter) , with a telescope , binoculars , etc. since sunrise time is not a measurement , it is an observation only to match time with the preomputed running fix graph , or time-position group listing . Also the short period between 071930 GMT sunset & the 0720 position report delivers proof that a running fix table , or graph , had been precomputed.
The possibly only direct irrelevancy of the navigation model is that on the error-offset lane the sun´s altitude (16 deg) @ the erroneous turn-off-point differed considerably from the elevation (21 deg) @ the correct t-o-point , normally Noonan would have seen this . I can evade the complication (1) since when steering on the offset course the sun was below elevation (04--21) for reliable corrected sextant altitude , up to about halfway and (2) by estimating the 102 mls offset having been flown on D.R. , this last by preference . But it remains the more or less a flaw on the step of internal inconsistency . With the correct offset initial point the elevation difference was negligible (04-26 vs 04-21) for low sun given.
-
... If they used the bubble sextant to
measure the dip then there would have been no need to determine dip at all since they would just
use the bubble sextant for taking the observations. ...
Does the Pioneer bubble sextant obviate the need to know one's altitude when drawing a LOP based on an observation?
Or does the potential error introduced by not being able to calibrate their altimeter to a local barometric reference affect both kinds of instruments equally?
Altitude is of no importance for any artificial horizon sextant since the bubble is in line with the celestial horizon which is parallel with the observer´s "equator" , both pointing to infinity.
Altimeter and b-sextant have no interconnection in the given sense . If no QNH is available and the altimeter off scale , the possibility to assess low altitude remains by consulting the table for dip in H.O.208 , giving 00-31´ for 1,000 ft. If you turn up a mariner´s sextant to 31´ and you see the optical horizon in the reference line , you are @ 1,000 ft altitude.
--------------------------------------------------
It only works if you already know your altitude accurately. If you set your marine sextant to 31' and you are not actually at 1,000 feet then the sextant will define a false horizontal and all of your reading will be wrong. You have come up with a circular argument. If you measured the angle between the visible horizon and the "optical horizon" (that's a new term that you just came up with, I take it you meant the true horizontal) and the measurement was 31' you're right, you would be at 1,000. The problem is there is no reference out in the air somewhere showing where the true horizontal is so there is no way to make this measurement.
See the dip table at: https://sites.google.com/site/fredienoonan/resources/air-almanc-1982/AirAlmanac1982%2Cdiptable.jpg?attredirects=0
and you will see that if your true altitude is just 33 feet different from 1,000 feet then your horizontal will be off by 1'. If off by 500 feet then your horizontal will be off by 8'.
gl
-
Mr. Lapook ,
Mr. van Asten also doesn’t allow for the uncertainty in the readings from a marine sextant.
Various statistical studies have been made using data from thousands of observations by
hundreds of observers and the standard deviation is about 1.6' so the uncertainty is twice this,
3.2'. This would be added to the uncertainty in determining the dip setting to be used so the total
uncertainty, if Noonan wanted to use a marine sextant to determine “van Asten sunrise”, would
be 10' or 11' which is worse than just using the bubble sextant alone.
---------------------------------
I forgot to say that the accuracy of marine sextant sights was determined for observations taken on shipboard where the height of eye above sea level was measured so there was no uncertainty in the dip correction to be use. There is no reason to believe that an in-flight marine sextant observation would be more accurate than a shipboard observation and would probably be less accurate but there are no statistics on that BECAUSE NO ONE USES A MARINE SEXTANT IN FLIGHT!
gl
Chichester , and a variety of ocean pilots used marine sextants to establish A/c´s position w.r.t. lines of position in the One Line Approach operation , they all were succesful in finding their destiination this way , there is no record of any miscarriage by using the method. Hegenburger/Maitland (on a completely precomputed navigation plan to Hawaii) even carried a single telescope to be able observing objects of which elevation was of no importance , p.e. for sunset/sunrise not any instrument besides the unarmed eye and facultatively a green filter is needed , since only the point of time @ U.L. appearance is of importance , to match it with the running list figures for latitude/longitude. If p.e. mr. Noonan used the mariner´s sextant (for it´s green filter) or not , that has zero influence on the error he possibly/probably committed by not using the bubble sextant like @ sunset . The only second condition for observing sunrise from an A/c is : fly low to avoid seeing the sun earlier than @ sea level which is the lower reference for elevation of heavenly bodies. It is for these reasons of no use to bring yes or no marine sextants in the field of discussion , for any navtable or navformula if computed elevation is zero .
.
------------------------------------------------
Chichester, Coutinho and several other early pioneering aviators did use marine sextant but this was only because bubble sextants had not yet been perfected. During the 1910's and 1920' rapid progress was made in improving and perfecting bubble sextants, with many false paths until it all came together, the right lenses and, most importantly, the right curvature to the top of the bubble chamber.
You can read about these developments here: http://www.fer3.com/arc/imgx/Bubble-sextants-Precision-Astrolabe.pdf
By the early 1930's the bubble sextant had been perfected so no one used a marine sextant after that to take observations from airplanes.
I sent this to him before:
"It is interesting that you list some early aviators implying that they used your sunrise method, do
you have any sources for this claim? Ellsworth used a bubble sextant, Lindbergh used a Pioneer
bubble sextant (there is a photo of his navigation equipment in Weems, 1938). They all used the standard Line Of Position computation, not your "van Asten sunrise" method. I have analyzed
Chichester’s navigation extensively and he used a marine sextant to take five sextant
observations on the New Zealand to Norfolk Island flight in 1931, all were in the range of 23° 12' to 50°
50'. On the next leg to Lord Howe Island he also took five observations, all in the range of 23° 48'
to 53° 42'. So contrary to your claim, none of his observations were anywhere near a zero altitude
or a sunrise sight. "
Coutinho in 1922 took 40 observations with a mariner's sextant but the lowest altitude he measured was 16° 15', nowhere near the "van Asten horizon."
Mr van Asten also mentioned that these early aviators precomputed their sights and although that may be true what they precomputed were the normal "computed altitudes" used for the normal Line Of Position navigation method, not for the "van Austen sunset/sunrise" method. It appears that Mr. van Austen doesn't understand how these precomputations were done. Here is link to many flight navigation manuals that explain this procedure and he might get some value from reading them.
https://sites.google.com/site/fredienoonan/topics/precomputed-altitude-curves
I have asked Mr. van Austen repeatedly to produce any proof that he might have that anybody ever used his method and he has never produced a thing.
gl
-
Mr van Asten also mentioned that these early aviators precomputed their sights and although that may be true what they precomputed were the normal "computed altitudes" used for the normal Line Of Position navigation method, not for the "van Austen sunset/sunrise" method. It appears that Mr. van Austen doesn't understand how these precomputations were done. Here is link to many flight navigation manuals that explain this procedure and he might get some value from reading them.
https://sites.google.com/site/fredienoonan/topics/precomputed-altitude-curves
--------------------------------------------------------------
Here is a link to a recent example of precomputation :
http://www.fer3.com/arc/m2.aspx?i=116311&y=201104
gl
-
Chichester , and a variety of ocean pilots used marine sextants to establish A/c´s position w.r.t. lines of position in the One Line Approach operation , they all were succesful in finding their destiination this way , there is no record of any miscarriage by using the method. Hegenburger/Maitland (on a completely precomputed navigation plan to Hawaii) even carried a single telescope to be able observing objects of which elevation was of no importance , p.e. for sunset/sunrise not any instrument besides the unarmed eye and facultatively a green filter is needed , since only the point of time @ U.L. appearance is of importance , to match it with the running list figures for latitude/longitude. If p.e. mr. Noonan used the mariner´s sextant (for it´s green filter) or not , that has zero influence on the error he possibly/probably committed by not using the bubble sextant like @ sunset . The only second condition for observing sunrise from an A/c is : fly low to avoid seeing the sun earlier than @ sea level which is the lower reference for elevation of heavenly bodies. It is for these reasons of no use to bring yes or no marine sextants in the field of discussion , for any navtable or navformula if computed elevation is zero .
Mr. van Asten,
It would be an error to use the marine sextant only if he had computed data for use with a bubble sextant and then only if he were using the "van Asten sunset/sunrise" method which you have never produced any proof whatsoever that it was ever used by anybody, and this includes you, since you have never used it either.
gl
-
Mr.Lapook ,
You write " We will start with his idea that Noonan measured the point of "van Asten sunrise" with a marine sextant .." mr.Noonan´s assumed observation error did not occur due to using the mariner´s sextant , but on the contrary : it occurred by not using the bubble sextant like @ sunset. At best the m-sextant delivered an easy means of establishing A/c´s exact altitude above ocean´s surface (via the dip table of H.O.no.208) , whereas also the dark green filter was a feature . Sunrise point of time could be established by observing with the unarmed eye (but : see filter) , with a telescope , binoculars , etc. since sunrise time is not a measurement , it is an observation only to match time with the preomputed running fix graph , or time-position group listing . Also the short period between 071930 GMT sunset & the 0720 position report delivers proof that a running fix table , or graph , had been precomputed.
The possibly only direct irrelevancy of the navigation model is that on the error-offset lane the sun´s altitude (16 deg) @ the erroneous turn-off-point differed considerably from the elevation (21 deg) @ the correct t-o-point , normally Noonan would have seen this . I can evade the complication (1) since when steering on the offset course the sun was below elevation (04--21) for reliable corrected sextant altitude , up to about halfway and (2) by estimating the 102 mls offset having been flown on D.R. , this last by preference . But it remains the more or less a flaw on the step of internal inconsistency . With the correct offset initial point the elevation difference was negligible (04-26 vs 04-21) for low sun given.
---------------------------------
Yep, that is a pretty amazing performance by Noonan and Earhart. Since he took the sextant reading (according to van Austen) at 07:19:30 GMT and the message was received at Lae at 07:20:00 GMT. This means that in only 30 seconds Noonan read the sextant, compared his reading with his precomputed table, wrote the position on a piece of paper, stuck that paper on the end of a fishing pole, slid the pole across the fuel tanks to the cockpit, Earhart removed the note from the fishing pole, read the message, picked up the microphone and sent that message! I wonder how many times they had to practice those maneuvers in order to get their time down to only 30 seconds. But wait, in keeping with Mr. van Austen's level of precision in his computations, we must allow for the time it took for the radio signals to travel all the way to Lae. From that position is was 1,384,820 meters to Lae and radio waves travel only at the speed of light, 299,792,458 meters per second so it took 0.00461962 seconds for the message to get to Lae, so Earhart must have started transmitting at 7:19:59.995380738 GMT. This means that all these action had to have been completed in less than 30 seconds, in only 29.995380738 seconds. I am really impressed now.
Of course, what makes this performance even more amazing is that the message was received in Lae at 0718 GMT, a minute and half before Noonan took the sextant reading (according to Mr. van Austens's theory) so the radio signals must have traveled faster than the speed of light and traveled back in time by one and a half minutes. See the Chatter report.
Basically, this proves that Mr. van Austen was wrong about his "sunset running fix" in his published paper and his theory relies on this "sunset running fix" for proof that Noonan was attempting a "sunrise fix" the next morning. He also relies on the distance traveled from this earlier "sunset running fix" as a basis for the "sunrise fix". Neither of these fixes were precomputed or measured by Noonan.
gl
-
... he has his own idea
of what “sunset” is that doesn’t comport with anybody else’s understanding of that word! ...
On your remark abt. E.Long : remarkably and fully independent of each other , supposed that mr.Long could not have read my contribution on fuel supplies & management of 1996 in the magazine of R.Neth.A.F. museum , Soesterberg , we register the 1845 GMT fuel reserves @ 45 US . In his book published after 1996 , Long gives just the figure ,no calculation .
In the course of 2008 mr.D.Jourdan handed over to mr.Long a copy of my EJN-2008 article . On receiving it he replied that , after thirty years research on the subject , he could no more afford the time and energy for studying other vistas .
I hate to admit that Elgin Long is smarter than I am but he was smart enough to ignore Mr. van Austen and his weird theories and did not waste a lot of his time, as I have, in responding to Mr. van Austen.
gl
-
... The only second condition for observing sunrise from an A/c is : fly low to avoid seeing the sun earlier than @ sea level which is the lower reference for elevation of heavenly bodies.
The only way to fly low enough to "to avoid seeing the sun earlier than @ sea level" is to be in a submarine, since you would have to be below sea level.
gl
-
... he has his own idea
of what “sunset” is that doesn’t comport with anybody else’s understanding of that word! ...
On your remark abt. E.Long : remarkably and fully independent of each other , supposed that mr.Long could not have read my contribution on fuel supplies & management of 1996 in the magazine of R.Neth.A.F. museum , Soesterberg , we register the 1845 GMT fuel reserves @ 45 US . In his book published after 1996 , Long gives just the figure ,no calculation .
In the course of 2008 mr.D.Jourdan handed over to mr.Long a copy of my EJN-2008 article . On receiving it he replied that , after thirty years research on the subject , he could no more afford the time and energy for studying other vistas .
I hate to admit that Elgin Long is smarter than I am but he was smart enough to ignore Mr. van Austen and his weird theories and did not waste a lot of his time, as I have, in responding to Mr. van Austen.
gl
Mr. Long´s reply was not to me , he replied to mr. Jourdan , who later said to me that it was mr.Long´s getting on in years , that kept him from studying the 2008 article .
-
Chichester , and a variety of ocean pilots used marine sextants to establish A/c´s position w.r.t. lines of position in the One Line Approach operation , they all were succesful in finding their destiination this way , there is no record of any miscarriage by using the method. Hegenburger/Maitland (on a completely precomputed navigation plan to Hawaii) even carried a single telescope to be able observing objects of which elevation was of no importance , p.e. for sunset/sunrise not any instrument besides the unarmed eye and facultatively a green filter is needed , since only the point of time @ U.L. appearance is of importance , to match it with the running list figures for latitude/longitude. If p.e. mr. Noonan used the mariner´s sextant (for it´s green filter) or not , that has zero influence on the error he possibly/probably committed by not using the bubble sextant like @ sunset . The only second condition for observing sunrise from an A/c is : fly low to avoid seeing the sun earlier than @ sea level which is the lower reference for elevation of heavenly bodies. It is for these reasons of no use to bring yes or no marine sextants in the field of discussion , for any navtable or navformula if computed elevation is zero .
Mr. van Asten,
It would be an error to use the marine sextant only if he had computed data for use with a bubble sextant and then only if he were using the "van Asten sunset/sunrise" method which you have never produced any proof whatsoever that it was ever used by anybody, and this includes you, since you have never used it either.
gl
mr.Noonan actually computed data for using the bubble sextant , namely for the sunset fix . Later @ sunrise he accidentally maintained them , but did not continue the use of the b-sextant , replacing it for observation by unarmed eye , telescope , marine sextant , or whatever it may have been . In EJN 2008 I suggested the marine sextant having been used because of it´s green filter against dazzle .
-
... If they used the bubble sextant to
measure the dip then there would have been no need to determine dip at all since they would just
use the bubble sextant for taking the observations. ...
Does the Pioneer bubble sextant obviate the need to know one's altitude when drawing a LOP based on an observation?
Or does the potential error introduced by not being able to calibrate their altimeter to a local barometric reference affect both kinds of instruments equally?
Altitude is of no importance for any artificial horizon sextant since the bubble is in line with the celestial horizon which is parallel with the observer´s "equator" , both pointing to infinity.
Altimeter and b-sextant have no interconnection in the given sense . If no QNH is available and the altimeter off scale , the possibility to assess low altitude remains by consulting the table for dip in H.O.208 , giving 00-31´ for 1,000 ft. If you turn up a mariner´s sextant to 31´ and you see the optical horizon in the reference line , you are @ 1,000 ft altitude.
--------------------------------------------------
It only works if you already know your altitude accurately. If you set your marine sextant to 31' and you are not actually at 1,000 feet then the sextant will define a false horizontal and all of your reading will be wrong. You have come up with a circular argument. If you measured the angle between the visible horizon and the "optical horizon" (that's a new term that you just came up with, I take it you meant the true horizontal) and the measurement was 31' you're right, you would be at 1,000. The problem is there is no reference out in the air somewhere showing where the true horizontal is so there is no way to make this measurement.
See the dip table at: https://sites.google.com/site/fredienoonan/resources/air-almanc-1982/AirAlmanac1982%2Cdiptable.jpg?attredirects=0
and you will see that if your true altitude is just 33 feet different from 1,000 feet then your horizontal will be off by 1'. If off by 500 feet then your horizontal will be off by 8'.
gl
Optical (= ´by vision´) horizon is another word for visible horizon , therefore , taking into account the horizon dip of 00-31´ for 1,000 ft from table in H.O.no.208 will assure you to be @ 1,000 ft altitude if you use a mariner´s sextant . A few days ago you mentioned , by comment , to consider this a method of interest in case of an off-scale altimeter.
-
... The only second condition for observing sunrise from an A/c is : fly low to avoid seeing the sun earlier than @ sea level which is the lower reference for elevation of heavenly bodies.
The only way to fly low enough to "to avoid seeing the sun earlier than @ sea level" is to be in a submarine, since you would have to be below sea level.
gl
Plse explain , I do not follow this.
-
G.Lapk . btw , @ 1912 GMT A/c was reported to be @ 1,000 ft altitude , very good that you do not believe me , but why don´t you believe the pilot herself ?
-
Chichester , and a variety of ocean pilots used marine sextants to establish A/c´s position w.r.t. lines of position in the One Line Approach operation , they all were succesful in finding their destiination this way , there is no record of any miscarriage by using the method. Hegenburger/Maitland (on a completely precomputed navigation plan to Hawaii) even carried a single telescope to be able observing objects of which elevation was of no importance , p.e. for sunset/sunrise not any instrument besides the unarmed eye and facultatively a green filter is needed , since only the point of time @ U.L. appearance is of importance , to match it with the running list figures for latitude/longitude. If p.e. mr. Noonan used the mariner´s sextant (for it´s green filter) or not , that has zero influence on the error he possibly/probably committed by not using the bubble sextant like @ sunset . The only second condition for observing sunrise from an A/c is : fly low to avoid seeing the sun earlier than @ sea level which is the lower reference for elevation of heavenly bodies. It is for these reasons of no use to bring yes or no marine sextants in the field of discussion , for any navtable or navformula if computed elevation is zero .
Mr. van Asten,
It would be an error to use the marine sextant only if he had computed data for use with a bubble sextant and then only if he were using the "van Asten sunset/sunrise" method which you have never produced any proof whatsoever that it was ever used by anybody, and this includes you, since you have never used it either.
gl
mr.Noonan actually computed data for using the bubble sextant , namely for the sunset fix . Later @ sunrise he accidentally maintained them , but did not continue the use of the b-sextant , replacing it for observation by unarmed eye , telescope , marine sextant , or whatever it may have been . In EJN 2008 I suggested the marine sextant having been used because of it´s green filter against dazzle .
---------------------------
Mr. van Asten,
Now you are changing your story and talking about a normal sunrise LOP which can be taken with the naked eye by simply observing the upper limb of the sun appear above the visible horizon which, as viewed from an airplane, the sun's altitude is actually below zero. The problem with this is that Noonan did not have a refraction table that showed the refraction correction for altitudes less than 6 degrees above horizontal so would not have been able to make the necessary corrections so as to derive an accurate LOP. The lowest altitude of 6 degrees in his refraction table shows a correction of 8' but for a zero altitude we know that it is 34.5' (you claim 37') He would have been aware of this problem so would not have attempted this. See the refraction correction table in the 1937 edition of H.O. 208 that Noonan was using here:
https://sites.google.com/site/fredienoonan/resources/navigation-tables-for-mariners-and-aviators-h-o-208-dreisonstok-1937/HO208%281937%29.pdf?attredirects=0
It is because you realized that Noonan's refraction table did not allow a "sunrise" observation that you invented the "van Asten" sunrise" concept since you thought it could be computed with the Nautical Almanac's sunrise table which already incorporated refraction in the computation of the times of sunrise and sunset. Now that you have admitted that you couldn't use the sunrise table to compute an accurate time of sunrise, you are back to trying to have Noonan guess at a refraction correction without a table showing corrections for low altitudes.
You wrote in you 2008 paper:
"The Observation Error Translates to a Virtual
Time Error
Figure 3 represents the situation for 1754:53 GMT
when Noonan, coming from the Nukumanu-Nikunau
night flight, observes sunrise, U.L.H., with the
marine sextant preset (+25'.2 arcmin for 1,000 ft
altitude, green filter) for dip and dazzle."
You have the marine sextant set to allow for dip, which is in "van Asten sunrise/sunset" method through which to observe the sun. You did not say that Noonan simply watched the sun appear above the visible horizon.
You can't wiggle out of it now because you have posted way too many times that the problem was caused by Noonan taking the sunrise observation with the marine sextant.
You posted on May 8th on the "Dateline" thread:
"we follow H.O.208 the marine sextant setting for a sunrise observation @ 1,000 ft should be : I. set the index screw to (+) 31´ by which II. the horizon will show up ahead with the instrument held horizontally"
and there are a plethora of other examples where you clearly wrote that he observed the sunrise with the marine sextant preset to 31'.
Another reason that you can't change your story now is that your computations would have shown Noonan more than 28 nautical miles further to the west if he had actually just observed a real sunrise at the time you stated because the sun rises sooner to an observer at altitude. The time you give, 17:54:53 GMT, is the time an observer at 0° 09' north, 178° 47' west at sea level would have observed the upper limb of the sun appear above the visible sea horizon. An observer one thousand feet directly above this spot on earth would have observed the sun appear above the visible sea horizon 1 minute and 52 seconds earlier at 17:53:01 GMT. If you had been claiming that Noonan actually observed the sun rise above the visible sea horizon without using a sextant, just his naked eyeballs, then you would have told us his longitude was 178° 19' west, 28 nautical miles further west than you have constantly claimed in all of your posts and in your 2008 article. The only way to make an observer flying at 1,000 feet note the time of sunrise as being the same time as the observer at sea level directly below him notes the time of sunrise is to use the "van Asten sunrise/sunset" method with the flying observer using a marine sextant set to 31'.
Nice try.
gl
-
... The only second condition for observing sunrise from an A/c is : fly low to avoid seeing the sun earlier than @ sea level which is the lower reference for elevation of heavenly bodies.
The only way to fly low enough to "to avoid seeing the sun earlier than @ sea level" is to be in a submarine, since you would have to be below sea level.
gl
Plse explain , I do not follow this.
-------------------------
-------------------------------------------
OK. An observer above sea level, either on a cliff or in an airplane, will see the sun rise earlier than an observer directly below him at sea level. At the location and time that you claim, an observer at 1,000 feet above sea level will see the upper limb of the sun appear above the visible sea horizon one minute and fifty two seconds before the observer directly below him at sea level will see the sun appear. The only way to see the sun rise after the observer at sea level sees the sun rise is to be at a lower altitude than sea level, hence the need for a submarine.
gl
-
G.Lapk . btw , @ 1912 GMT A/c was reported to be @ 1,000 ft altitude , very good that you do not believe me , but why don´t you believe the pilot herself ?
------------------------------------------
I answered this question in a prior post.
“She did not report being at 1000 feet until 1912 Z, 78 minutes after you believed that they were
observing sunrise at 1000 feet as part of their “must be on you” transmission when they believed
that they were already at Howland. They would have traveled approximately 170 nm in that time
interval. There is no reason to assume that they descended from their cruising altitude as soon as
you believe. Flying higher provided better fuel economy and better opportunities for celestial
observations. Clouds are often in layers at different altitudes. So, for example, if there was a
scattered layer at 15,000 feet and a broken layer at 8,000 feet then flying at 10,000 feet would
provide very good observation conditions with only a small part of the heavens obstructed.
Flying below 8,000 feet would produce possibly complete obstructions to observations as the two
layers (each having large openings) could overlap.”
Mr. van Asten wrote back:
“2. Besides mentions in biographies , why would Noonan have the plane going down to 1,000 ft ,
an unfavorable altitude for seeing a small island , if it was not necessary to have the horizon
sharply within visual range ?”
-To which I responded:
“Most people believe that they were down at 1000 feet when they thought they were near the
island and at that point (and not before) they had been compelled to descend below a low cloud
layer in order to search for Howland. “
gl
-
Mr.Lapook ,
The possibly only direct irrelevancy of the navigation model is that on the error-offset lane the sun´s altitude (16 deg) @ the erroneous turn-off-point differed considerably from the elevation (21 deg) @ the correct t-o-point , normally Noonan would have seen this . I can evade the complication (1) since when steering on the offset course the sun was below elevation (04--21) for reliable corrected sextant altitude , up to about halfway and (2) by estimating the 102 mls offset having been flown on D.R. , this last by preference . But it remains the more or less a flaw on the step of internal inconsistency . With the correct offset initial point the elevation difference was negligible (04-26 vs 04-21) for low sun given.
_________________________________
Mr. van Asten,
Your diagram in your article shows that they reached the turnoff point at 1859 GMT at which point the sun's altitude was 16° 04.5' (not the 21 ° that you stated) for an observer at Howland and anywhere else on the correct LOP through Howland. This was plenty high enough for accurate sextant sights.
Anytime after 1815 GMT the sun's altitude was above the six degree minimum needed by Noonan's refraction correction table so he would have been taking sights of the sun for 44 minutes prior to the interception and would not have relied on dead reckoning for 102 miles which would have introduced an uncertainty of 10 miles in the turn off point onto the LOP. You apparently do not understand the basic idea behind the landfall procedure, that you take sights as you approach the LOP so that it is an accurate interception and then you take additional sights to ensure staying on the LOP to the destination. You do not DR for a long leg to the interception. If you were going to DR for 102 miles then there would be no reason to do the landfall procedure.
Try reading the flight manuals that explain this procedure that I have posted here:
https://sites.google.com/site/fredienoonan/topics/landfall-procedure
gl
-
Chichester , and a variety of ocean pilots used marine sextants to establish A/c´s position w.r.t. lines of position in the One Line Approach operation , they all were succesful in finding their destiination this way , there is no record of any miscarriage by using the method. Hegenburger/Maitland (on a completely precomputed navigation plan to Hawaii) even carried a single telescope to be able observing objects of which elevation was of no importance , p.e. for sunset/sunrise not any instrument besides the unarmed eye and facultatively a green filter is needed , since only the point of time @ U.L. appearance is of importance , to match it with the running list figures for latitude/longitude. If p.e. mr. Noonan used the mariner´s sextant (for it´s green filter) or not , that has zero influence on the error he possibly/probably committed by not using the bubble sextant like @ sunset . The only second condition for observing sunrise from an A/c is : fly low to avoid seeing the sun earlier than @ sea level which is the lower reference for elevation of heavenly bodies. It is for these reasons of no use to bring yes or no marine sextants in the field of discussion , for any navtable or navformula if computed elevation is zero .
Mr. van Asten,
It would be an error to use the marine sextant only if he had computed data for use with a bubble sextant and then only if he were using the "van Asten sunset/sunrise" method which you have never produced any proof whatsoever that it was ever used by anybody, and this includes you, since you have never used it either.
gl
mr.Noonan actually computed data for using the bubble sextant , namely for the sunset fix . Later @ sunrise he accidentally maintained them , but did not continue the use of the b-sextant , replacing it for observation by unarmed eye , telescope , marine sextant , or whatever it may have been . In EJN 2008 I suggested the marine sextant having been used because of it´s green filter against dazzle .
---------------------------
Mr. van Asten,
Now you are changing your story and talking about a normal sunrise LOP which can be taken with the naked eye by simply observing the upper limb of the sun appear above the visible horizon which, as viewed from an airplane, the sun's altitude is actually below zero. The problem with this is that Noonan did not have a refraction table that showed the refraction correction for altitudes less than 6 degrees above horizontal so would not have been able to make the necessary corrections so as to derive an accurate LOP. The lowest altitude of 6 degrees in his refraction table shows a correction of 8' but for a zero altitude we know that it is 34.5' (you claim 37') He would have been aware of this problem so would not have attempted this. See the refraction correction table in the 1937 edition of H.O. 208 that Noonan was using here:
https://sites.google.com/site/fredienoonan/resources/navigation-tables-for-mariners-and-aviators-h-o-208-dreisonstok-1937/HO208%281937%29.pdf?attredirects=0
It is because you realized that Noonan's refraction table did not allow a "sunrise" observation that you invented the "van Asten" sunrise" concept since you thought it could be computed with the Nautical Almanac's sunrise table which already incorporated refraction in the computation of the times of sunrise and sunset. Now that you have admitted that you couldn't use the sunrise table to compute an accurate time of sunrise, you are back to trying to have Noonan guess at a refraction correction without a table showing corrections for low altitudes.
You wrote in you 2008 paper:
"The Observation Error Translates to a Virtual
Time Error
Figure 3 represents the situation for 1754:53 GMT
when Noonan, coming from the Nukumanu-Nikunau
night flight, observes sunrise, U.L.H., with the
marine sextant preset (+25'.2 arcmin for 1,000 ft
altitude, green filter) for dip and dazzle."
You have the marine sextant set to allow for dip, which is in "van Asten sunrise/sunset" method through which to observe the sun. You did not say that Noonan simply watched the sun appear above the visible horizon.
You can't wiggle out of it now because you have posted way too many times that the problem was caused by Noonan taking the sunrise observation with the marine sextant.
You posted on May 8th on the "Dateline" thread:
"we follow H.O.208 the marine sextant setting for a sunrise observation @ 1,000 ft should be : I. set the index screw to (+) 31´ by which II. the horizon will show up ahead with the instrument held horizontally"
and there are a plethora of other examples where you clearly wrote that he observed the sunrise with the marine sextant preset to 31'.
Another reason that you can't change your story now is that your computations would have shown Noonan more than 28 nautical miles further to the west if he had actually just observed a real sunrise at the time you stated because the sun rises sooner to an observer at altitude. The time you give, 17:54:53 GMT, is the time an observer at 0° 09' north, 178° 47' west at sea level would have observed the upper limb of the sun appear above the visible sea horizon. An observer one thousand feet directly above this spot on earth would have observed the sun appear above the visible sea horizon 1 minute and 52 seconds earlier at 17:53:01 GMT. If you had been claiming that Noonan actually observed the sun rise above the visible sea horizon without using a sextant, just his naked eyeballs, then you would have told us his longitude was 178° 19' west, 28 nautical miles further west than you have constantly claimed in all of your posts and in your 2008 article. The only way to make an observer flying at 1,000 feet note the time of sunrise as being the same time as the observer at sea level directly below him notes the time of sunrise is to use the "van Asten sunrise/sunset" method with the flying observer using a marine sextant set to 31'.
Nice try.
gl
@ 1,000 ft , 305 m altitude the horiron dips 00-31´ whereas the sun rises @ 13´.8 per time minute . Sun will appear 31´/13´.8 = 2m15s earlier (yours 1m50s) @ 1,000 ft than @ zero ft. Subtract from 175453 GMT and find 175238 GMTthe instant mr.Noonan saw sunrise . By addition of 2m15s he knew to be 150 mls off Howland . Sea navigators were much more familiar with calculation of angles etc. since they had not from the beginning of their career the "short methods" to their disposal . You p.e. have mentioned that the paragraph on sunrise fix for aircraft has been deleted from ´Dutton´ since 1934 . For that year Noonan was 41 with a 20 years seaman´s career behind . Within that era , sea liners captains ordered
two , sometimes three navigators on deck to separately shoot sun , moon or stars , after which , below deck , they computed for 20 minutes to establish position of ship . It is in short , reasonable that mr. Noonan exactly knew what he was doing.
I consequently jump to your critics on the 0720 GMT announced position near Nukumanu . Your statement about the time point having been 0718 GMT (before GMT sunrise 071930) does not hold . The figure is from a citation of the "Chater´s report" document and concerns tranmissions Lae to Earhart for weather updates @ 18 minutes past the hour. The figure is repeated (0418 , 0519 , 0718) through the report . The figure , not from radio logbook (there was none) , does not at all represent an agreement with the Earhart crew themselves.
Third : there have been comments stating that the departure time from Lae , 0000 GMT , concerned an @ random decision etc. etc. It was not : @ 6 a.m. 7/1 Earhart to Black radiogram reads in part "PLAN LEAVE BY TEN THIS MORNING NEW GUINEA TIME" . Later @ 7/01 followed , in part : "BLACK ITASCA DUE LOCAL CONDITIONS TAKE OFF DELAYED UNTIL 2130 GMT JULY SECOND" . Eventually , 7/2 : "URGENT BLACK ITASCA AMELIA EARHART LEFT LAE TEN AM LOCAL TIME JULY 2ND DUE HOWLAND ISLAND 18 HOURS TIME" . it is at least a reasonable supposition that the crew tuned departure time to mr.Noonan´s precomputed flight data .
-
Mr.Lapook ,
The possibly only direct irrelevancy of the navigation model is that on the error-offset lane the sun´s altitude (16 deg) @ the erroneous turn-off-point differed considerably from the elevation (21 deg) @ the correct t-o-point , normally Noonan would have seen this . I can evade the complication (1) since when steering on the offset course the sun was below elevation (04--21) for reliable corrected sextant altitude , up to about halfway and (2) by estimating the 102 mls offset having been flown on D.R. , this last by preference . But it remains the more or less a flaw on the step of internal inconsistency . With the correct offset initial point the elevation difference was negligible (04-26 vs 04-21) for low sun given.
_________________________________
Mr. van Asten,
Your diagram in your article shows that they reached the turnoff point at 1859 GMT at which point the sun's altitude was 16° 04.5' (not the 21 ° that you stated) for an observer at Howland and anywhere else on the correct LOP through Howland. This was plenty high enough for accurate sextant sights.
Anytime after 1815 GMT the sun's altitude was above the six degree minimum needed by Noonan's refraction correction table so he would have been taking sights of the sun for 44 minutes prior to the interception and would not have relied on dead reckoning for 102 miles which would have introduced an uncertainty of 10 miles in the turn off point onto the LOP. You apparently do not understand the basic idea behind the landfall procedure, that you take sights as you approach the LOP so that it is an accurate interception and then you take additional sights to ensure staying on the LOP to the destination. You do not DR for a long leg to the interception. If you were going to DR for 102 miles then there would be no reason to do the landfall procedure.
Try reading the flight manuals that explain this procedure that I have posted here:
https://sites.google.com/site/fredienoonan/topics/landfall-procedure
gl
You may safely assume that in the course of 23 years I have consulted all representative flght manuals . When commencing the 055 T offset @ 1815 for the correct longitude sun´s altitude was 04-26 , at the end @ 1859 it was 21-00 . On the erroneous offset the respective elevations were 04-21 and 16-00 , all figures rounded to arcmin. I already mentioned by comment that the 16-00 / 21-00 difference may be a weakness of determination , also since textbooks prescriptions ask for repeated observation like you say . Because for the article I had to do the work alone (no old style navigators available , no readers) , and against deadlines , combined with the menace of making the treatise unreadable due to too many details , I decided for the text & diagrams as published . I have worked for 20 years in the sciences during my professional career , there is not any reason for which I would venture to " wiggle out" (as you call it) from a problem . There is namely , a possibility (not yet computed) that the offset entire track was longer than 132 mls because instead of having made good 348 mls @ 175453 GMT , only 337 mls had been made good , this has influence on the ETA time-position groups .
-
G.Lapk . btw , @ 1912 GMT A/c was reported to be @ 1,000 ft altitude , very good that you do not believe me , but why don´t you believe the pilot herself ?
------------------------------------------
I answered this question in a prior post.
“She did not report being at 1000 feet until 1912 Z, 78 minutes after you believed that they were
observing sunrise at 1000 feet as part of their “must be on you” transmission when they believed
that they were already at Howland. They would have traveled approximately 170 nm in that time
interval. There is no reason to assume that they descended from their cruising altitude as soon as
you believe. Flying higher provided better fuel economy and better opportunities for celestial
observations. Clouds are often in layers at different altitudes. So, for example, if there was a
scattered layer at 15,000 feet and a broken layer at 8,000 feet then flying at 10,000 feet would
provide very good observation conditions with only a small part of the heavens obstructed.
Flying below 8,000 feet would produce possibly complete obstructions to observations as the two
layers (each having large openings) could overlap.”
Mr. van Asten wrote back:
“2. Besides mentions in biographies , why would Noonan have the plane going down to 1,000 ft ,
an unfavorable altitude for seeing a small island , if it was not necessary to have the horizon
sharply within visual range ?”
-To which I responded:
“Most people believe that they were down at 1000 feet when they thought they were near the
island and at that point (and not before) they had been compelled to descend below a low cloud
layer in order to search for Howland. “
gl
The "low cloud cover" appears in every unquantified story , as well as the 200 mph fiction , the one for flying low , the other to make up for lost time etc. etc. Both phenomena did not exist and about the first : there was no cloud cover in the Howland region that day.
-
... The only second condition for observing sunrise from an A/c is : fly low to avoid seeing the sun earlier than @ sea level which is the lower reference for elevation of heavenly bodies.
The only way to fly low enough to "to avoid seeing the sun earlier than @ sea level" is to be in a submarine, since you would have to be below sea level.
gl
Plse explain , I do not follow this.
-------------------------
-------------------------------------------
OK. An observer above sea level, either on a cliff or in an airplane, will see the sun rise earlier than an observer directly below him at sea level. At the location and time that you claim, an observer at 1,000 feet above sea level will see the upper limb of the sun appear above the visible sea horizon one minute and fifty two seconds before the observer directly below him at sea level will see the sun appear. The only way to see the sun rise after the observer at sea level sees the sun rise is to be at a lower altitude than sea level, hence the need for a submarine.
gl
Nice joke . Only : from the higher position one sees the sun come up earlier due to the horizon dip , for which aviators can as well compensate as seamen from the deck , either by directlly applying the dip from table , or by applying a time difference from simple computation like shown earlier . As a general result , all comments up to now have not injured consistency , and not displaced the erroneous position line for one inch .
-
Mr.Lapook ,
You write " We will start with his idea that Noonan measured the point of "van Asten sunrise" with a marine sextant .." mr.Noonan´s assumed observation error did not occur due to using the mariner´s sextant , but on the contrary : it occurred by not using the bubble sextant like @ sunset. At best the m-sextant delivered an easy means of establishing A/c´s exact altitude above ocean´s surface (via the dip table of H.O.no.208) , whereas also the dark green filter was a feature . Sunrise point of time could be established by observing with the unarmed eye (but : see filter) , with a telescope , binoculars , etc. since sunrise time is not a measurement , it is an observation only to match time with the preomputed running fix graph , or time-position group listing . Also the short period between 071930 GMT sunset & the 0720 position report delivers proof that a running fix table , or graph , had been precomputed.
The possibly only direct irrelevancy of the navigation model is that on the error-offset lane the sun´s altitude (16 deg) @ the erroneous turn-off-point differed considerably from the elevation (21 deg) @ the correct t-o-point , normally Noonan would have seen this . I can evade the complication (1) since when steering on the offset course the sun was below elevation (04--21) for reliable corrected sextant altitude , up to about halfway and (2) by estimating the 102 mls offset having been flown on D.R. , this last by preference . But it remains the more or less a flaw on the step of internal inconsistency . With the correct offset initial point the elevation difference was negligible (04-26 vs 04-21) for low sun given.
---------------------------------
Yep, that is a pretty amazing performance by Noonan and Earhart. Since he took the sextant reading (according to van Austen) at 07:19:30 GMT and the message was received at Lae at 07:20:00 GMT. This means that in only 30 seconds Noonan read the sextant, compared his reading with his precomputed table, wrote the position on a piece of paper, stuck that paper on the end of a fishing pole, slid the pole across the fuel tanks to the cockpit, Earhart removed the note from the fishing pole, read the message, picked up the microphone and sent that message! I wonder how many times they had to practice those maneuvers in order to get their time down to only 30 seconds. But wait, in keeping with Mr. van Austen's level of precision in his computations, we must allow for the time it took for the radio signals to travel all the way to Lae. From that position is was 1,384,820 meters to Lae and radio waves travel only at the speed of light, 299,792,458 meters per second so it took 0.00461962 seconds for the message to get to Lae, so Earhart must have started transmitting at 7:19:59.995380738 GMT. This means that all these action had to have been completed in less than 30 seconds, in only 29.995380738 seconds. I am really impressed now.
Of course, what makes this performance even more amazing is that the message was received in Lae at 0718 GMT, a minute and half before Noonan took the sextant reading (according to Mr. van Austens's theory) so the radio signals must have traveled faster than the speed of light and traveled back in time by one and a half minutes. See the Chatter report.
Basically, this proves that Mr. van Austen was wrong about his "sunset running fix" in his published paper and his theory relies on this "sunset running fix" for proof that Noonan was attempting a "sunrise fix" the next morning. He also relies on the distance traveled from this earlier "sunset running fix" as a basis for the "sunrise fix". Neither of these fixes were precomputed or measured by Noonan.
gl
What , properly , was Noonan doing o/b of that aircraft , play at cards ?
-
Mr. Lapook ,
Mr. van Asten also doesn’t allow for the uncertainty in the readings from a marine sextant.
Various statistical studies have been made using data from thousands of observations by
hundreds of observers and the standard deviation is about 1.6' so the uncertainty is twice this,
3.2'. This would be added to the uncertainty in determining the dip setting to be used so the total
uncertainty, if Noonan wanted to use a marine sextant to determine “van Asten sunrise”, would
be 10' or 11' which is worse than just using the bubble sextant alone.
---------------------------------
I forgot to say that the accuracy of marine sextant sights was determined for observations taken on shipboard where the height of eye above sea level was measured so there was no uncertainty in the dip correction to be use. There is no reason to believe that an in-flight marine sextant observation would be more accurate than a shipboard observation and would probably be less accurate but there are no statistics on that BECAUSE NO ONE USES A MARINE SEXTANT IN FLIGHT!
gl
Chichester , and a variety of ocean pilots used marine sextants to establish A/c´s position w.r.t. lines of position in the One Line Approach operation , they all were succesful in finding their destiination this way , there is no record of any miscarriage by using the method. Hegenburger/Maitland (on a completely precomputed navigation plan to Hawaii) even carried a single telescope to be able observing objects of which elevation was of no importance , p.e. for sunset/sunrise not any instrument besides the unarmed eye and facultatively a green filter is needed , since only the point of time @ U.L. appearance is of importance , to match it with the running list figures for latitude/longitude. If p.e. mr. Noonan used the mariner´s sextant (for it´s green filter) or not , that has zero influence on the error he possibly/probably committed by not using the bubble sextant like @ sunset . The only second condition for observing sunrise from an A/c is : fly low to avoid seeing the sun earlier than @ sea level which is the lower reference for elevation of heavenly bodies. It is for these reasons of no use to bring yes or no marine sextants in the field of discussion , for any navtable or navformula if computed elevation is zero .
.
------------------------------------------------
Chichester, Coutinho and several other early pioneering aviators did use marine sextant but this was only because bubble sextants had not yet been perfected. During the 1910's and 1920' rapid progress was made in improving and perfecting bubble sextants, with many false paths until it all came together, the right lenses and, most importantly, the right curvature to the top of the bubble chamber.
You can read about these developments here: http://www.fer3.com/arc/imgx/Bubble-sextants-Precision-Astrolabe.pdf
By the early 1930's the bubble sextant had been perfected so no one used a marine sextant after that to take observations from airplanes.
I sent this to him before:
"It is interesting that you list some early aviators implying that they used your sunrise method, do
you have any sources for this claim? Ellsworth used a bubble sextant, Lindbergh used a Pioneer
bubble sextant (there is a photo of his navigation equipment in Weems, 1938). They all used the standard Line Of Position computation, not your "van Asten sunrise" method. I have analyzed
Chichester’s navigation extensively and he used a marine sextant to take five sextant
observations on the New Zealand to Norfolk Island flight in 1931, all were in the range of 23° 12' to 50°
50'. On the next leg to Lord Howe Island he also took five observations, all in the range of 23° 48'
to 53° 42'. So contrary to your claim, none of his observations were anywhere near a zero altitude
or a sunrise sight. "
Coutinho in 1922 took 40 observations with a mariner's sextant but the lowest altitude he measured was 16° 15', nowhere near the "van Asten horizon."
Mr van Asten also mentioned that these early aviators precomputed their sights and although that may be true what they precomputed were the normal "computed altitudes" used for the normal Line Of Position navigation method, not for the "van Austen sunset/sunrise" method. It appears that Mr. van Austen doesn't understand how these precomputations were done. Here is link to many flight navigation manuals that explain this procedure and he might get some value from reading them.
https://sites.google.com/site/fredienoonan/topics/precomputed-altitude-curves
I have asked Mr. van Austen repeatedly to produce any proof that he might have that anybody ever used his method and he has never produced a thing.
gl
[/quote
Never produced a thing ? Read EJN-2011 for mr.Noonan´s own sunset fix with same fashion as for sunrise.
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... If they used the bubble sextant to
measure the dip then there would have been no need to determine dip at all since they would just
use the bubble sextant for taking the observations. ...
Does the Pioneer bubble sextant obviate the need to know one's altitude when drawing a LOP based on an observation?
Or does the potential error introduced by not being able to calibrate their altimeter to a local barometric reference affect both kinds of instruments equally?
Altitude is of no importance for any artificial horizon sextant since the bubble is in line with the celestial horizon which is parallel with the observer´s "equator" , both pointing to infinity.
Altimeter and b-sextant have no interconnection in the given sense . If no QNH is available and the altimeter off scale , the possibility to assess low altitude remains by consulting the table for dip in H.O.208 , giving 00-31´ for 1,000 ft. If you turn up a mariner´s sextant to 31´ and you see the optical horizon in the reference line , you are @ 1,000 ft altitude.
--------------------------------------------------
It only works if you already know your altitude accurately. If you set your marine sextant to 31' and you are not actually at 1,000 feet then the sextant will define a false horizontal and all of your reading will be wrong. You have come up with a circular argument. If you measured the angle between the visible horizon and the "optical horizon" (that's a new term that you just came up with, I take it you meant the true horizontal) and the measurement was 31' you're right, you would be at 1,000. The problem is there is no reference out in the air somewhere showing where the true horizontal is so there is no way to make this measurement.
See the dip table at: https://sites.google.com/site/fredienoonan/resources/air-almanc-1982/AirAlmanac1982%2Cdiptable.jpg?attredirects=0
and you will see that if your true altitude is just 33 feet different from 1,000 feet then your horizontal will be off by 1'. If off by 500 feet then your horizontal will be off by 8'.
gl
Nonsense , if you preset 31´ and you are not @ 1,000 feet the local horizon line does not match the instrument´s horizon mirror line , and you must ascend / descend .
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“Most people believe that they were down at 1000 feet when they thought they were near the
island and at that point (and not before) they had been compelled to descend below a low cloud
layer in order to search for Howland. “
I believe that the 1912 GMT transmission (http://tighar.org/wiki/Transmission_timeline) gives their altitude as 1000 feet. No motive is given in the transmission for the descent.
The splendid article, "Log Jam," (http://tighar.org/Publications/TTracks/12_2/logjam.html) records this as 07:42 a.m. Itasca time.
Previous altitude reports were all from early in the flight: 7000, 10000, 8000.
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Nonsense , if you preset 31´ and you are not @ 1,000 feet the local horizon line does not match the instrument´s horizon mirror line , and you must ascend / descend .
Except that there is no such thing as the "instrument´s horizon mirror line" so you have nothing to compare with the local horizon (the visible sea horizon.) Mr. van Asten, have you never looked through a marine sextant?
That is the purpose of the bubble in the bubble sextant, to provide a level reference independent of the sea horizon and marine sextants do not have such a reference. Find someone who has a marine sextant and take a look through it.
gl
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@ 1,000 ft , 305 m altitude the horiron dips 00-31´ whereas the sun rises @ 13´.8 per time minute . Sun will appear 31´/13´.8 = 2m15s earlier (yours 1m50s) @ 1,000 ft than @ zero ft. Subtract from 175453 GMT and find 175238 GMTthe instant mr.Noonan saw sunrise . By addition of 2m15s he knew to be 150 mls off Howland . Sea navigators were much more familiar with calculation of angles etc. since they had not from the beginning of their career the "short methods" to their disposal . You p.e. have mentioned that the paragraph on sunrise fix for aircraft has been deleted from ´Dutton´ since 1934 . For that year Noonan was 41 with a 20 years seaman´s career behind . Within that era , sea liners captains ordered
two , sometimes three navigators on deck to separately shoot sun , moon or stars , after which , below deck , they computed for 20 minutes to establish position of ship . It is in short , reasonable that mr. Noonan exactly knew what he was doing.
I consequently jump to your critics on the 0720 GMT announced position near Nukumanu . Your statement about the time point having been 0718 GMT (before GMT sunrise 071930) does not hold . The figure is from a citation of the "Chater´s report" document and concerns tranmissions Lae to Earhart for weather updates @ 18 minutes past the hour. The figure is repeated (0418 , 0519 , 0718) through the report . The figure , not from radio logbook (there was none) , does not at all represent an agreement with the Earhart crew themselves.
Third : there have been comments stating that the departure time from Lae , 0000 GMT , concerned an @ random decision etc. etc. It was not : @ 6 a.m. 7/1 Earhart to Black radiogram reads in part "PLAN LEAVE BY TEN THIS MORNING NEW GUINEA TIME" . Later @ 7/01 followed , in part : "BLACK ITASCA DUE LOCAL CONDITIONS TAKE OFF DELAYED UNTIL 2130 GMT JULY SECOND" . Eventually , 7/2 : "URGENT BLACK ITASCA AMELIA EARHART LEFT LAE TEN AM LOCAL TIME JULY 2ND DUE HOWLAND ISLAND 18 HOURS TIME" . it is at least a reasonable supposition that the crew tuned departure time to mr.Noonan´s precomputed flight data .
1. There never was a "sunrise" paragraph in any edition of Dutton, you only cited to a sentence within one paragraph that you found in the 1928 edition that recommended using a marine sextant, nothing about a "sunrise" fix and this sentence was removed from the 1934 and subsequent editions.
2. Read the Chater report again. It says the position report was received at 5:18 p.m. (0718 GMT). Nor can you claim that Chater was merely writing down the scheduled times for communications with Earhart of 18 minutes after each hour because Chater recorded the prior report from Earhart as being received at 3:19 p.m. (0319 GMT.) So contrary to your claim, the figure was NOT repeated. Nor was there any report at 0418, there are only three transmissions from Earhart recorded, 2:18 p.m., 3:19 p.m. and 5:18 p.m. (0218, 0319 and 0518 GMT.)
3. They did not take off at the time that they had planned as stated in her radiograms.
gl
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You may safely assume that in the course of 23 years I have consulted all representative flght manuals . When commencing the 055 T offset @ 1815 for the correct longitude sun´s altitude was 04-26 , at the end @ 1859 it was 21-00 . On the erroneous offset the respective elevations were 04-21 and 16-00 , all figures rounded to arcmin. I already mentioned by comment that the 16-00 / 21-00 difference may be a weakness of determination , also since textbooks prescriptions ask for repeated observation like you say . Because for the article I had to do the work alone (no old style navigators available , no readers) , and against deadlines , combined with the menace of making the treatise unreadable due to too many details , I decided for the text & diagrams as published . I have worked for 20 years in the sciences during my professional career , there is not any reason for which I would venture to " wiggle out" (as you call it) from a problem . There is namely , a possibility (not yet computed) that the offset entire track was longer than 132 mls because instead of having made good 348 mls @ 175453 GMT , only 337 mls had been made good , this has influence on the ETA time-position groups .
-----------------------------------------------------
Mr. van Asten,
If there really was a difference between the 16 degree altitude of the sun at the erroneous interception that you claim compared to the 21 degree altitude that you calculate for the correct LOP then the difference between them, 5 degrees, would produce an error of 300 NM, pretty hard for Noonan to be that wrong! AS I posted before, the correct altitude at the turn off point onto the correct LOP was 16° 04.5' at 1859 GMT.
There is something wrong with your computations of these altitudes.
Here is link to the U.S. Naval Observatory site that will do the computations for you so you won't get the wrong answers.
http://aa.usno.navy.mil/data/docs/celnavtable.php
Readers of these posts can go to that site themselves and check Mr. van Asten's computations themselves. Just put in the date, time, and the coordinates for Howland (0° 48' N, 176° 38' W) to calculate the sun's altitude at Howland and any place along the correct LOP through Howland. Look at the column marked "Hc" which is the standard abbreviation for "computed altitude." "Zn" = azimuth and "GHA is Greenwich Hour Angle. While you are at it you can check out Mr. van Asten's calculation of GHA of the sun for 175453 GMT, just enter in that time and look at the GHA column. Mr. van Asten said in his prior posts that the GHA of the sun at that time was 88° 43.2', did he get it right? I said the GHA at 175453 GMT was 87° 45.7', did I get it right?
And no, I do not assume that you have consulted all representative flght manuals since you have failed to cite to any of them in your posts or in our other correspondence.
gl
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Never produced a thing ? Read EJN-2011 for mr.Noonan´s own sunset fix with same fashion as for sunrise.
Well, since we do not have Mr. Noonan"s work papers, we have only your theoretical computations of them, how about producing at least one other example of anybody other than Noonan using your "sunrise/sunset" methodology or a cite to a navigation text describing your method?
gl
I will in due time find such back in my handbooks/textbooks .
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And no, I do not assume that you have consulted all representative flght manual[/b][/i]s since you have failed to cite to any of them in your posts or in our other correspondence.
No , I just do not remember where I found the fashion , like I told you I am not at home now and must postpone consulting the books. I will recompute the altitudes , the coordinates are : correct turn-off point 176-53-W ; 01-13-N . Erroneous turn-off point 177-01-W ; 01-10-N .
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Never produced a thing ? Read EJN-2011 for mr.Noonan´s own sunset fix with same fashion as for sunrise.
Well, since we do not have Mr. Noonan"s work papers, we have only your theoretical computations of them, how about producing at least one other example of anybody other than Noonan using your "sunrise/sunset" methodology or a cite to a navigation text describing your method?
gl
-
No , I just do not remember where I found the fashion , like I told you I am not at home now and must postpone consulting the books. I will recompute the altitudes , the coordinates are : correct turn-off point 176-53-W ; 01-13-N . Erroneous turn-off point 177-01-W ; 01-10-N .
Mr. van Asten,
Using your coordinates for what you believe was the correct turn off point at 1859 GMT produces an altitude for the sun of 16° 00.8' so it was not the correct turn off point because the altitude is not equal to the altitude at Howland for the same time which was 16° 04.5'. and this is the essential requirement for the LOP. However, I see that the altitude at the erroneous coordinates used by Williams, 0° 49' N, 176° 43' W produces an altitude of 16° 00.3' so your turn off coordinates are within half a mile of the LOP through the Williams coordinates so this is accurate enough. The difference between the altitudes at the Williams coordinates and the correct coordinates for Howland would have caused the LOP through the Williams coordinates to be parallel to the correct LOP and offset by 4.2 nautical miles, not enough to cause them to miss the island. Notice, none of these altitudes are anywhere near the 21 degrees that you claimed.
The altitude of the sun at 1859 at the point you identify as the erroneous turn off point was 15° 52.2' a difference of 8.1 nautical miles from your correct turn off point onto the Williams LOP and 12.3 NM short of the actual LOP through Howland.
I can't believe that you didn't notice your error in claiming that the altitudes were 16 and 21 degrees, a difference of 5 degrees, since THE BASIC PREMISE behind all celestial navigation is that a difference of 1 degree produces an error, or difference, of 60 nautical miles. Your calculated altitudes produced an error of 300 NM!
Tsk, tsk.
Such an obvious error calls into question all of your other calculations.
gl
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Such an obvious error calls into question all of your other calculations.
Yes I made some arithmatic error somewhere here , but not in the other calculations . See corrections posted (diff. error vs correct -28´)
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Mr. Long´s reply was not to me , he replied to mr. Jourdan , who later said to me that it was mr.Long´s getting on in years , that kept him from studying the 2008 article .
Mr. van Asten,
It seems likely that Mr. Jurdan was just trying to spare your feelings.
gl
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Mr.Lapook ,
The possibly only direct irrelevancy of the navigation model is that on the error-offset lane the sun´s altitude (16 deg) @ the erroneous turn-off-point differed considerably from the elevation (21 deg) @ the correct t-o-point , normally Noonan would have seen this . I can evade the complication (1) since when steering on the offset course the sun was below elevation (04--21) for reliable corrected sextant altitude , up to about halfway and (2) by estimating the 102 mls offset having been flown on D.R. , this last by preference . But it remains the more or less a flaw on the step of internal inconsistency . With the correct offset initial point the elevation difference was negligible (04-26 vs 04-21) for low sun given.
_________________________________
Mr. van Asten,
Your diagram in your article shows that they reached the turnoff point at 1859 GMT at which point the sun's altitude was 16° 04.5' (not the 21 ° that you stated) for an observer at Howland and anywhere else on the correct LOP through Howland. This was plenty high enough for accurate sextant sights.
Anytime after 1815 GMT the sun's altitude was above the six degree minimum needed by Noonan's refraction correction table so he would have been taking sights of the sun for 44 minutes prior to the interception and would not have relied on dead reckoning for 102 miles which would have introduced an uncertainty of 10 miles in the turn off point onto the LOP. You apparently do not understand the basic idea behind the landfall procedure, that you take sights as you approach the LOP so that it is an accurate interception and then you take additional sights to ensure staying on the LOP to the destination. You do not DR for a long leg to the interception. If you were going to DR for 102 miles then there would be no reason to do the landfall procedure.
Try reading the flight manuals that explain this procedure that I have posted here:
https://sites.google.com/site/fredienoonan/topics/landfall-procedure
gl
---------------------------------
Mr. van Asten,
You wrote in your 2011 published paper:
"Usually the Offset
Track was fiown by OR, especially with low sun giving
less reliable position outcomes due to difficult
assess of refraction."
You correctly point out that at the point that you believe that they turned to 55° T at 1815 GMT to intercept the LOP, 102 statute miles short of your "erroneous turn off point", that the altitude of the sun was only 4° 21' which was below the minimum 6° in Noonan's refraction table so he could not take a normal sun sight at this point. You then claim that because of this that the sun continued to be too low to allow additional sights as he approached the LOP and this is, obviously, incorrect since we know the sun was 16° high at the point of interception so its altitude had to rise above 6° at some place along this leg. Even at the initial point where the turn was made to 55° T the sun rose above 6° at 1823 GMT so allowed at least 36 minutes for Noonan to take additional sights. In this period Noonan should have been able to take 5 or 6 additional sights. See: http://www.fer3.com/arc/m2.aspx?i=116311
Your theory is that due to Noonan using a marine sextant instead of the bubble sextant to determine the 175453 GMT fix that he introduced an error that caused them to be 11 NM west of where they thought they were. Your theory goes on to claim that they then dead reckoned the rest of the way to where they believed Howland was located which maintained that 11 NM error in all subsequent DR positions. This shows that you do not understand that the whole purpose of the landfall procedure is to cure any existing errors in the DR by taking additional sights while nearing the LOP and then taking additional sights while flying on the LOP to ensure staying on the LOP. Even just one sight taken after 175453 GMT would have cured the problem that you complain about since Noonan would then have a correct reading and a correct fix. Your entire DR leg, 102 SM to the turn off point plus 30 SM along the LOP is a total of 132 SM, would cause an uncertainty, due to the these DR segments, of plus and minus 13.2 SM. In addition to this uncertainty you must add the uncertainty in the original 175453 fix which is, according to all flight navigation texts and the Federal Aviation Regulations, considered to be 10 NM, 11.5 SM, making the total uncertainty, when in the vicinity of Howland, of plus and minus 24.7 SM. Nobody, in his right mind, would ever try to find this island with this level of uncertainty which is why you must take additional sights when flying the landfall procedure.
You don't have to take my word for this, you can read the standard flight navigation manuals that describe the landfall procedure here:
https://sites.google.com/site/fredienoonan/topics/landfall-procedure
gl
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You don't have to take my word for this, you can read the standard flight navigation manuals that describe the landfall procedure here:
https://sites.google.com/site/fredienoonan/topics/landfall-procedure
Yes , I certainly take your word , it is however , not so that I said that the entire offset lane would have a too low sun ; I estimated it , without specific computation , to about halfway , with the bubble sextant for observation . I do not think that using the marine sextant would for this event give other results w.r.t. the elevation differences @ the two turn off coordinates pairs , I will check nevertheless . I did not take the elevation of sun for Howland , but for the T.O.P.`s themselves (as by F.Chichester) . The entire OLA tracking 132 mls , mr.Noonan may have ventured DR only , you reckon 10% deviation , 13 mls , but @ nearly still air his abberation would certainly have been less , say 5% or 7 mls . In 1996 I have sent the pre-article to the chairman of Royal Institute of Navigation , Great Britain . In a letter he admitted that basically , accumulation of errors I described , probably was cause of the incident . He btw added that I should best contact The Institute of Navigation (USA) since Amelia Earhart was a typical American pioneer. In 2007 I so did , but received answer to appoint 3 referees myself : they did not find a referee for the of the era science of navigation . The answer came with a remark : "Why not distances measured in nautical miles as usual" (the manuscript was read through by a retired sea navigator) .
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Yes , I certainly take your word , it is however , not so that I said that the entire offset lane would have a too low sun ; I estimated it , without specific computation , to about halfway , with the bubble sextant for observation . I do not think that using the marine sextant would for this event give other results w.r.t. the elevation differences @ the two turn off coordinates pairs , I will check nevertheless . I did not take the elevation of sun for Howland , but for the T.O.P.`s themselves (as by F.Chichester) . The entire OLA tracking 132 mls , mr.Noonan may have ventured DR only , you reckon 10% deviation , 13 mls , but @ nearly still air his abberation would certainly have been less , say 5% or 7 mls . In 1996 I have sent the pre-article to the chairman of Royal Institute of Navigation , Great Britain . In a letter he admitted that basically , accumulation of errors I described , probably was cause of the incident . He btw added that I should best contact The Institute of Navigation (USA) since Amelia Earhart was a typical American pioneer. In 2007 I so did , but received answer to appoint 3 referees myself : they did not find a referee for the of the era science of navigation . The answer came with a remark : "Why not distances measured in nautical miles as usual" (the manuscript was read through by a retired sea navigator) .
Mr. van Asten,
When doing a landfall the navigator uses the destination as the assumed position for the calculation of the Hc for the LOP. He calculates a series of sun altitudes at 20 minute intervals and plots the altitudes on a graph against time. The altitude at the destination determines the LOP through the destination so the altitude must be exactly the same at the turn off point as at the destination. The navigator does not care about the exact latitude and longitude of the turn off point, he doesn't even determine it. He just flies toward the LOP and takes altitudes and compares them to the graph of plotted altitudes until his measured altitude is the same as it would be at the destination for the time of observation which tells him that he has arrived at the LOP so he then turns to follow it.
See: Air Navigation, Weems; the Navigator's Information File; and Celestial Air Navigation, TM 1-206 available here:
https://sites.google.com/site/fredienoonan/topics/landfall-procedure
The air was not still but had strong winds out of the eastern quarter. Sometimes you might get lucky and have your DR error be only 5% but most times it is not that good. If you were in Noonan's position would you assume that this is the day that your will have really good DR accuracy, since you are betting your life on it. A prudent navigator assumes a maximum possible error when working out a landfall procedure to ensure that he arrives at the island. For normal flight he might expect a 10% uncertainty but for such a critical flight he would have allowed for an even larger possible error. No flight navigator would DR for 132 SM in this situation.
You needed a flight navigator, not a sea navigator, to review your papers. Flight navigation is much different than surface navigation because the wind speed and its variations are such a large proportion of the the speed of the aircraft. A 30 knot wind is almost one-quarter the speed of Earhart's plane and a variation in speed of 10 knots is normal and 20 knots is not unusual as is the change of direction by 20 or 30 degrees. In the open ocean it is very unusual to find a current of even one knot which is only one-twentieth the speed of most ships and ocean currents are very constant, it is hard to get all that water to change direction. So DR in the air has a much greater uncertainty than sea navigation. I have copies of Mr. Noonan's charts for the Natal to Dakar flight and for the California to Hawaii flight. On the flight to Dakar the plane was off course by 125 nautical miles at one point. On the flight to Hawaii there were fixes 35, 65, 85 and 125 nautical miles off course. You have not appreciated in your papers and posts this fact of life for flight navigators.
gl
-
The air was not still but had strong winds out of the eastern quarter. Sometimes you might get lucky and have your DR error be only 5% but most times it is not that good. If you were in Noonan's position would you assume that this is the day that your will have really good DR accuracy, since you are betting your life on it. A prudent navigator assumes a maximum possible error when working out a landfall procedure to ensure that he arrives at the island. For normal flight he might expect a 10% uncertainty but for such a critical flight he would have allowed for an even larger possible error. No flight navigator would DR for 132 SM in this situation.
You needed a flight navigator, not a sea navigator, to review your papers. Flight navigation is much different than surface navigation because the wind speed and its variations are such a large proportion of the the speed of the aircraft. A 30 knot wind is almost one-quarter the speed of Earhart's plane and a variation in speed of 10 knots is normal and 20 knots is not unusual as is the change of direction by 20 or 30 degrees. In the open ocean it is very unusual to find a current of even one knot which is only one-twentieth the speed of most ships and ocean currents are very constant, it is hard to get all that water to change direction. So DR in the air has a much greater uncertainty than sea navigation. I have copies of Mr. Noonan's charts for the Natal to Dakar flight and for the California to Hawaii flight. On the flight to Dakar the plane was off course by 125 nautical miles at one point. On the flight to Hawaii there were fixes 35, 65, 85 and 125 nautical miles off course. You have not appreciated in your papers and posts this fact of life for flight navigators.
gl
Yes , I agree on the necessity of continuous celnav check of your DR , also @ relatively short distances off destination . For the OLA , according to prescriptions by Weems et al , the over destination sun´s elevation is taken as the reference hc for turning off if compliance with your sextant reading is acquired . Now proceed as follows : take the sun´s elevation @ the erroneous TOP for ETA 1859 GMT, this being hc(e) = 16-00 @ 177-01-W ; 01-10-N . Then , compute sun´s elevation for Howland @ 176-43-W ; 00-49-N (the C.Williams in mr.Noonan´s chart specified coordinates) . You will find hc(c) = 16-00 . Thence mr. Noonan , coming from the erroneous offset lane initial point (181453 GMT , 178-14-W ; 00-13-N) , will have found ho = hc @ 1859 GMT [with any sextant type] , upon which he ordered the A/c to steer 157 T on the erroneous position line , having Howland (176-38-W ; 00-48-N) @ 16 mls on the port beam , instead of below the APL , at 1912 GMT : everything with exactness to the second for arc & time according to text & diagrams of article EJN-2008 .
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The air was not still but had strong winds out of the eastern quarter. Sometimes you might get lucky and have your DR error be only 5% but most times it is not that good. If you were in Noonan's position would you assume that this is the day that your will have really good DR accuracy, since you are betting your life on it. A prudent navigator assumes a maximum possible error when working out a landfall procedure to ensure that he arrives at the island. For normal flight he might expect a 10% uncertainty but for such a critical flight he would have allowed for an even larger possible error. No flight navigator would DR for 132 SM in this situation.
You needed a flight navigator, not a sea navigator, to review your papers. Flight navigation is much different than surface navigation because the wind speed and its variations are such a large proportion of the the speed of the aircraft. A 30 knot wind is almost one-quarter the speed of Earhart's plane and a variation in speed of 10 knots is normal and 20 knots is not unusual as is the change of direction by 20 or 30 degrees. In the open ocean it is very unusual to find a current of even one knot which is only one-twentieth the speed of most ships and ocean currents are very constant, it is hard to get all that water to change direction. So DR in the air has a much greater uncertainty than sea navigation. I have copies of Mr. Noonan's charts for the Natal to Dakar flight and for the California to Hawaii flight. On the flight to Dakar the plane was off course by 125 nautical miles at one point. On the flight to Hawaii there were fixes 35, 65, 85 and 125 nautical miles off course. You have not appreciated in your papers and posts this fact of life for flight navigators.
gl
Yes , I agree on the necessity of continuous celnav check of your DR , also @ relatively short distances off destination . For the OLA , according to prescriptions by Weems et al , the over destination sun´s elevation is taken as the reference hc for turning off if compliance with your sextant reading is acquired . Now proceed as follows : take the sun´s elevation @ the erroneous TOP for ETA 1859 GMT, this being hc(e) = 16-00 @ 177-01-W ; 01-10-N . Then , compute sun´s elevation for Howland @ 176-43-W ; 00-49-N (the C.Williams in mr.Noonan´s chart specified coordinates) . You will find hc(c) = 16-00 . Thence mr. Noonan , coming from the erroneous offset lane initial point (181453 GMT , 178-14-W ; 00-13-N) , will have found ho = hc @ 1859 GMT [with any sextant type] , upon which he ordered the A/c to steer 157 T on the erroneous position line , having Howland (176-38-W ; 00-48-N) @ 16 mls on the port beam , instead of below the APL , at 1912 GMT : everything with exactness to the second for arc & time according to text & diagrams of article EJN-2008 .
------------------------------------
Well, you almost have it right. At 1859 GMT Noonan takes an observation of the sun and measures 16° 00'. He then looks at his precomputed curve of the sun's altitude for 1859 GMT and sees that the precomputed altitude at the Williams coordinates at 1859 GMT is also 16° 00'. He then knows that he has intercepted the LOP through the Williams coordinates because every point on that LOP will have the same altitude for the sun as at the Williams coordinates. Nonnan then turns to 157°. See graph of precomputed altitudes available here:
https://sites.google.com/site/fredienoonan/topics/precomputed-altitude-curves/Howlandprecomputation.jpg?attredirects=0
(The red line is the line of precomputed altitudes for the incorrect Williams coordinates and the blue line is the curve for the correct coordinates for Howland. You will notice that the spacing between the two curves remains constant, 4', which is the same as the 4 NM distance between Howland and the Williams coordinates. Noonan did not have the correct coordinates for Howland so his graph would only have the red line. This is just a sample covering the period of 1858 to 1916 GMT. Noonan would have prepared a graph like this covering the period from 1815 to the estimated time of fuel exhaustion.)
If, at 1859 GMT Noonan had measured only 15° 52' he would see the difference between his measurement and the expected measurement of 16° 00' found on the red curve equals 8' so he would know that he had not yet reached his turn off point but that he still had an additional 8 nautical miles to go. Any altitude measurement that plots below the curve means that the plane has not yet reached the LOP and must continue toward the northeast. Any sextant altitude measurement that plots above the curve means that the plane has overshot the LOP so the plane must correct its heading back toward the southwest.
After he has turned to 157° he continues to take sextant readings. For example, if he takes a reading at 1907 GMT and finds an altitude of 17° 52' and he compares it to the red line for the same time and reads out 17° 50' he would see that the difference is 2' indicating that he is 2 NM to the left of course since his reading is greater than the correct altitude. He could then make a slight heading change to the right or just ignore it since a 2' difference is very small and well within the expected scatter of the sextant readings. This shows him tracking closely to the LOP that leads to the Williams coordinates. The LOP through the Williams coordinates runs parallel to the correct LOP through Howland, offset to the southwest by 4 NM.
Then at 1912 GMT he takes another sextant shot of the sun and measures 18° 58' and comparing it to the precomputed altitude on the red line for the same time and takes out the same number, 18° 58' which shows he is on the LOP through the Williams coordinates. Staying on this LOP will take the plane over the Williams coordinates.
Since the Williams coordinates are only 4 NM from Howland the plane will pass within 4 NM of Howland not the 16 miles that you stated. He will not have turned off too soon because his sextant reading has cured the error in the 175453 fix.
gl
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It seems to me that Gary is making an awful lot of sense, not to mention his Been There, Done That level of experience that he brings to the discussion.
Which, again to me, carries a whole lot more weight than repeatedly throwing numbers against the wall to see which ones stick. My 2 cents.
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I'm going to ask Marty to chime in due to his superior knowledge of Jesuit teachings, but if I recall correctly they teach you in middle school that this type of discussion can make you go blind.
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Well, you almost have it right. At 1859 GMT Noonan takes an observation of the sun and measures 16° 00'. He then looks at his precomputed curve of the sun's altitude for 1859 GMT and sees that the precomputed altitude at the Williams coordinates at 1859 GMT is also 16° 00'. He then knows that he has intercepted the LOP through the Williams coordinates because every point on that LOP will have the same altitude for the sun as at the Williams coordinates. Nonnan then turns to 157°. See graph of precomputed altitudes available here:
https://sites.google.com/site/fredienoonan/topics/precomputed-altitude-curves/Howlandprecomputation.jpg?attredirects=0
(The red line is the line of precomputed altitudes for the incorrect Williams coordinates and the blue line is the curve for the correct coordinates for Howland. You will notice that the spacing between the two curves remains constant, 4', which is the same as the 4 NM distance between Howland and the Williams coordinates. Noonan did not have the correct coordinates for Howland so his graph would only have the red line.)
If, at 1859 GMT Noonan had measured only 15° 52' he would see the difference between his measurement and the expected measurement of 16° 00' found on the red curve equals 8' so he would know that he had not yet reached his turn off point but that he still had an additional 8 nautical miles to go. Any altitude measurement that plots below the curve means that the plane has not yet reached the LOP and must continue toward the northeast. Any sextant altitude measurement that plots above the curve means that the plane has overshot the LOP so the plane must correct its heading back toward the southwest.
After he has turned to 157° he continues to take sextant readings. For example, if he takes a reading at 1907 GMT and finds an altitude of 17° 52' and he compares it to the red line for the same time and reads out 17° 50' he would see that the difference is 2' indicating that he is 2 NM to the left of course since his reading is greater than the correct altitude. He could then make a slight heading change to the right or just ignore it since a 2' difference is very small and well within the expected scatter of the sextant readings. This shows him tracking closely to the LOP that leads to the Williams coordinates. The LOP through the Williams coordinates runs parallel to the correct LOP through Howland, offset to the southwest by 4 NM.
Then at 1912 GMT he takes another sextant shot of the sun and measures 18° 58' and comparing it to the precomputed altitude on the red line for the same time and takes out the same number, 18° 58' which shows he is on the LOP through the Williams coordinates. Staying on this LOP will take the plane over the Williams coordinates.
Since the Williams coordinates are only 4 NM from Howland the plane will pass within 4 NM of Howland not the 16 miles that you stated. He will not have turned off too soon because his sextant reading has cured the error in the 175453 fix.
The correct TOP was @ 176-53 ; 01-13 , the erroneous TOP was @ 177-01 ; 01-10 according to EJN-2008 . With H.O.208 we find for 1859 GMT / Hwl. ass.posn. hc = 15-12´.0 . For the error TOP we also find 15-12´.0 , which says that mr.Noonan observed ho = hc @ 1859 GMT to alter to 157 T on the erroneous LOP . There is however , more : when approaching for the TOP on the correct offset lane , A/c also met the error LOP @ a point X, slightly southeastward of the error TOP . Elevation of sun on that point will be close to 15-12´ and it is therefore possible that the island was missed since the computations for elevation had been made by H.O.208 in combination with the erroneous Howland chart coordinates. I will for X-point additionally compute with H.O.208 , if elevation of sun is close to 15-12´ these outcomes may open new vistas in accordance with Occam´s razor : with observance of all in and outs : simplest solution.
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Well, since we do not have Mr. Noonan"s work papers, we have only your theoretical computations of them, how about producing at least one other example of anybody other than Noonan using your "sunrise/sunset" methodology or a cite to a navigation text describing your method?
Not needed , Noonan himself is the example , by his sunset fix 071930 GMT .
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PLEASE can someone apart from GLP or HVA give us an update as to where this thread is going!
:) i'm not a navigator but the word circule (sp) comes to mind :)
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....if I recall correctly they teach you in middle school that this type of discussion can make you go blind.
At the very least, go deaf. :P After a year, this thread with its 215 replies and 6,591 views has only become more and more convoluted. It would seem we've squeezed out all the goodness that's in here; maybe, we should leave the dead horse in peace. :'(
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R.I.P. dead horse. :'(
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....if I recall correctly they teach you in middle school that this type of discussion can make you go blind.
Stuff happens!
At the very least, go deaf. :P After a year, this thread with its 215 replies and 6,591 views has only become more and more convoluted. It would seem we've squeezed out all the goodness that's in here; maybe, we should leave the dead horse in peace. :'(
I gave up on participating in this discussion in detail a couple of weeks ago after someone provided links to Van Asten's two articles.
Gary's posts have been illuminating. I suppose at some point we could lock the thread and ask them to carry on the rest of the argument in private.
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....if I recall correctly they teach you in middle school that this type of discussion can make you go blind.
Stuff happens!
At the very least, go deaf. :P After a year, this thread with its 215 replies and 6,591 views has only become more and more convoluted. It would seem we've squeezed out all the goodness that's in here; maybe, we should leave the dead horse in peace. :'(
I gave up on participating in this discussion in detail a couple of weeks ago after someone provided links to Van Asten's two articles.
Gary's posts have been illuminating. I suppose at some point we could lock the thread and ask them to carry on the rest of the argument in private.
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You don't have to, I'm done. I thought I was finally making some progress, but it's clear I wasn't.
I first communicated with Mr. van Asten after I read his two articles that are just full errors. I was making a friendly effort to help him understand how this navigation really works. I think that it is obvious to everyone that he is not interested in learning anything. He always goes back to his 0719:30 observation, the one that led to the position report that was received in Lae one minute and a half prior to that observation! I was always taught that time goes in only one direction, from earlier to later. Apparently in Mr. van Asten's parallel universe time can run in the opposite direction. Don't try to confuse him with the facts.
So, I give up, he will have to carry on without my help.
gl
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You don't have to, I'm done.
I first communicated with Mr. van Asten after I read his two articles that are just full errors. I was making a friendly effort to help him understand how this navigation really works. I think that it is obvious to everyone that he is not interested in learning anything. He always goes back to his 0719:30 observation, the one that lead to the position report that was received in Lae one minute and a half prior to that observation! I was always taught that time goes in only one direction, from earlier to later. Apparently in Mr. van Asten's parallel universe time can run in the opposite direction. Don't try to confuse him with the facts.
So, I give up, he will have to carry on without my help.
I appreciate your efforts very much, Gary. Thanks!
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You don't have to, I'm done.
I first communicated with Mr. van Asten after I read his two articles that are just full errors. I was making a friendly effort to help him understand how this navigation really works. I think that it is obvious to everyone that he is not interested in learning anything. He always goes back to his 0719:30 observation, the one that lead to the position report that was received in Lae one minute and a half prior to that observation! I was always taught that time goes in only one direction, from earlier to later. Apparently in Mr. van Asten's parallel universe time can run in the opposite direction. Don't try to confuse him with the facts.
So, I give up, he will have to carry on without my help.
I appreciate your efforts very much, Gary. Thanks!
------------------------------
I hope that it wasn't a complete waste of my time. Hopefully my long explanations have served to demystify the process for other readers of these posts so that they can see now that it isn't voodoo or even rocket science. It has some complications but it is a rational process when you see how it all works.
gl
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You don't have to, I'm done.
I first communicated with Mr. van Asten after I read his two articles that are just full errors. I was making a friendly effort to help him understand how this navigation really works. I think that it is obvious to everyone that he is not interested in learning anything. He always goes back to his 0719:30 observation, the one that lead to the position report that was received in Lae one minute and a half prior to that observation! I was always taught that time goes in only one direction, from earlier to later. Apparently in Mr. van Asten's parallel universe time can run in the opposite direction. Don't try to confuse him with the facts.
So, I give up, he will have to carry on without my help.
I appreciate your efforts very much, Gary. Thanks!
------------------------------
I hope that it wasn't a complete wasted of my time. Hopefully my long explanations have served to demystify the process for other readers of these posts so that they can see now that it isn't voodoo or even rocket science. It has some complications but it is a rational process when you see how it all works.
gl
The 0718 time point is not from a radio logbook and nowhere cited , unless in the Chater report . It is even possible if not probable , for the case that the announce was made @ 0718 in lieu of 0720 , that mr.Noonan saw his series of observations before sunrise nearing the precomputed hc-ho graph or listing upon which he messaged to the pilot in advance . I do not believe this scenario , but the possibility remains.
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You don't have to, I'm done.
I first communicated with Mr. van Asten after I read his two articles that are just full errors. I was making a friendly effort to help him understand how this navigation really works. I think that it is obvious to everyone that he is not interested in learning anything. He always goes back to his 0719:30 observation, the one that lead to the position report that was received in Lae one minute and a half prior to that observation! I was always taught that time goes in only one direction, from earlier to later. Apparently in Mr. van Asten's parallel universe time can run in the opposite direction. Don't try to confuse him with the facts.
I highly appreciated your professional comments & inputs really of great value but , i.m.h.o. they are not convincing in the field of the deployed theory . Too bad that no other quantitative inquiry exists for comparison .
So, I give up, he will have to carry on without my help.
I appreciate your efforts very much, Gary. Thanks!
------------------------------
I hope that it wasn't a complete wasted of my time. Hopefully my long explanations have served to demystify the process for other readers of these posts so that they can see now that it isn't voodoo or even rocket science. It has some complications but it is a rational process when you see how it all works.
gl
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The air was not still but had strong winds out of the eastern quarter. Sometimes you might get lucky and have your DR error be only 5% but most times it is not that good. If you were in Noonan's position would you assume that this is the day that your will have really good DR accuracy, since you are betting your life on it. A prudent navigator assumes a maximum possible error when working out a landfall procedure to ensure that he arrives at the island. For normal flight he might expect a 10% uncertainty but for such a critical flight he would have allowed for an even larger possible error. No flight navigator would DR for 132 SM in this situation.
You needed a flight navigator, not a sea navigator, to review your papers. Flight navigation is much different than surface navigation because the wind speed and its variations are such a large proportion of the the speed of the aircraft. A 30 knot wind is almost one-quarter the speed of Earhart's plane and a variation in speed of 10 knots is normal and 20 knots is not unusual as is the change of direction by 20 or 30 degrees. In the open ocean it is very unusual to find a current of even one knot which is only one-twentieth the speed of most ships and ocean currents are very constant, it is hard to get all that water to change direction. So DR in the air has a much greater uncertainty than sea navigation. I have copies of Mr. Noonan's charts for the Natal to Dakar flight and for the California to Hawaii flight. On the flight to Dakar the plane was off course by 125 nautical miles at one point. On the flight to Hawaii there were fixes 35, 65, 85 and 125 nautical miles off course. You have not appreciated in your papers and posts this fact of life for flight navigators.
gl
Yes , I agree on the necessity of continuous celnav check of your DR , also @ relatively short distances off destination . For the OLA , according to prescriptions by Weems et al , the over destination sun´s elevation is taken as the reference hc for turning off if compliance with your sextant reading is acquired . Now proceed as follows : take the sun´s elevation @ the erroneous TOP for ETA 1859 GMT, this being hc(e) = 16-00 @ 177-01-W ; 01-10-N . Then , compute sun´s elevation for Howland @ 176-43-W ; 00-49-N (the C.Williams in mr.Noonan´s chart specified coordinates) . You will find hc(c) = 16-00 . Thence mr. Noonan , coming from the erroneous offset lane initial point (181453 GMT , 178-14-W ; 00-13-N) , will have found ho = hc @ 1859 GMT [with any sextant type] , upon which he ordered the A/c to steer 157 T on the erroneous position line , having Howland (176-38-W ; 00-48-N) @ 16 mls on the port beam , instead of below the APL , at 1912 GMT : everything with exactness to the second for arc & time according to text & diagrams of article EJN-2008 .
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Well, you almost have it right. At 1859 GMT Noonan takes an observation of the sun and measures 16° 00'. He then looks at his precomputed curve of the sun's altitude for 1859 GMT and sees that the precomputed altitude at the Williams coordinates at 1859 GMT is also 16° 00'. He then knows that he has intercepted the LOP through the Williams coordinates because every point on that LOP will have the same altitude for the sun as at the Williams coordinates. Nonnan then turns to 157°. See graph of precomputed altitudes available here:
https://sites.google.com/site/fredienoonan/topics/precomputed-altitude-curves/Howlandprecomputation.jpg?attredirects=0
(The red line is the line of precomputed altitudes for the incorrect Williams coordinates and the blue line is the curve for the correct coordinates for Howland. You will notice that the spacing between the two curves remains constant, 4', which is the same as the 4 NM distance between Howland and the Williams coordinates. Noonan did not have the correct coordinates for Howland so his graph would only have the red line. This is just a sample covering the period of 1858 to 1916 GMT. Noonan would have prepared a graph like this covering the period from 1815 to the estimated time of fuel exhaustion.)
If, at 1859 GMT Noonan had measured only 15° 52' he would see the difference between his measurement and the expected measurement of 16° 00' found on the red curve equals 8' so he would know that he had not yet reached his turn off point but that he still had an additional 8 nautical miles to go. Any altitude measurement that plots below the curve means that the plane has not yet reached the LOP and must continue toward the northeast. Any sextant altitude measurement that plots above the curve means that the plane has overshot the LOP so the plane must correct its heading back toward the southwest.
After he has turned to 157° he continues to take sextant readings. For example, if he takes a reading at 1907 GMT and finds an altitude of 17° 52' and he compares it to the red line for the same time and reads out 17° 50' he would see that the difference is 2' indicating that he is 2 NM to the left of course since his reading is greater than the correct altitude. He could then make a slight heading change to the right or just ignore it since a 2' difference is very small and well within the expected scatter of the sextant readings. This shows him tracking closely to the LOP that leads to the Williams coordinates. The LOP through the Williams coordinates runs parallel to the correct LOP through Howland, offset to the southwest by 4 NM.
Then at 1912 GMT he takes another sextant shot of the sun and measures 18° 58' and comparing it to the precomputed altitude on the red line for the same time and takes out the same number, 18° 58' which shows he is on the LOP through the Williams coordinates. Staying on this LOP will take the plane over the Williams coordinates.
Since the Williams coordinates are only 4 NM from Howland the plane will pass within 4 NM of Howland not the 16 miles that you stated. He will not have turned off too soon because his sextant reading has cured the error in the 175453 fix.
gl
No , the ho values acquired are the same H.O.no.208 hc = 15-12´ for as well the LOP over Howland T.P. , Howland A.P. and TOP-error , the last having been met first by A/c . Thence @ 1912 GMT A/c passed 16 mls west of Howland T.P.
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Nonsense , if you preset 31´ and you are not @ 1,000 feet the local horizon line does not match the instrument´s horizon mirror line , and you must ascend / descend .
Except that there is no such thing as the "instrument´s horizon mirror line" so you have nothing to compare with the local horizon (the visible sea horizon.) Mr. van Asten, have you never looked through a marine sextant?
That is the purpose of the bubble in the bubble sextant, to provide a level reference independent of the sea horizon and marine sextants do not have such a reference. Find someone who has a marine sextant and take a look through it.
gl
Instrument horizon mirror line is the horizon as reflected in the field of vision , coming from the variable inclination reflector.
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“Most people believe that they were down at 1000 feet when they thought they were near the
island and at that point (and not before) they had been compelled to descend below a low cloud
layer in order to search for Howland. “
I believe that the 1912 GMT transmission (http://tighar.org/wiki/Transmission_timeline) gives their altitude as 1000 feet. No motive is given in the transmission for the descent.
The splendid article, "Log Jam," (http://tighar.org/Publications/TTracks/12_2/logjam.html) records this as 07:42 a.m. Itasca time.
Previous altitude reports were all from early in the flight: 7000, 10000, 8000.
In Log Jam we read that @ 1912 the fuel reserves were for 1/2 hour and @ 2013 they amounted to 150 gallons (?)
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You don't have to, I'm done.
I first communicated with Mr. van Asten after I read his two articles that are just full errors. I was making a friendly effort to help him understand how this navigation really works. I think that it is obvious to everyone that he is not interested in learning anything. He always goes back to his 0719:30 observation, the one that lead to the position report that was received in Lae one minute and a half prior to that observation! I was always taught that time goes in only one direction, from earlier to later. Apparently in Mr. van Asten's parallel universe time can run in the opposite direction. Don't try to confuse him with the facts.
So, I give up, he will have to carry on without my help.
I appreciate your efforts very much, Gary. Thanks!
All representative sources , the Hooven report included , let know that the position tranmission 159-07-E ; 04-33.5-S was received 0720 GMT @ Lae ; some sources mention "0520 p.m." , evidently local time congruent with 0720 GMT .
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... Hopefully my long explanations have served to demystify the process for other readers of these posts so that they can see now that it isn't voodoo or even rocket science. It has some complications but it is a rational process when you see how it all works.
You've helped me a lot.
Celestial navigation is awesome. It is an example of "standing on the shoulders of giants." Our amazing GPS units use the same kind of spatial logic along with the added precision that comes from astonishingly accurate clocks and clever databases. What a great achievement!
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... Hopefully my long explanations have served to demystify the process for other readers of these posts so that they can see now that it isn't voodoo or even rocket science. It has some complications but it is a rational process when you see how it all works.
You've helped me a lot.
Celestial navigation is awesome. It is an example of "standing on the shoulders of giants." Our amazing GPS units use the same kind of spatial logic along with the added precision that comes from astonishingly accurate clocks and clever databases. What a great achievement!
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Thanks for that.
gl
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You may safely assume that in the course of 23 years I have consulted all representative flght manuals . When commencing the 055 T offset @ 1815 for the correct longitude sun´s altitude was 04-26 , at the end @ 1859 it was 21-00 . On the erroneous offset the respective elevations were 04-21 and 16-00 , all figures rounded to arcmin. I already mentioned by comment that the 16-00 / 21-00 difference may be a weakness of determination , also since textbooks prescriptions ask for repeated observation like you say . Because for the article I had to do the work alone (no old style navigators available , no readers) , and against deadlines , combined with the menace of making the treatise unreadable due to too many details , I decided for the text & diagrams as published . I have worked for 20 years in the sciences during my professional career , there is not any reason for which I would venture to " wiggle out" (as you call it) from a problem . There is namely , a possibility (not yet computed) that the offset entire track was longer than 132 mls because instead of having made good 348 mls @ 175453 GMT , only 337 mls had been made good , this has influence on the ETA time-position groups .
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Mr. van Asten,
If there really was a difference between the 16 degree altitude of the sun at the erroneous interception that you claim compared to the 21 degree altitude that you calculate for the correct LOP then the difference between them, 5 degrees, would produce an error of 300 NM, pretty hard for Noonan to be that wrong! AS I posted before, the correct altitude at the turn off point onto the correct LOP was 16° 04.5' at 1859 GMT.
There is something wrong with your computations of these altitudes.
Here is link to the U.S. Naval Observatory site that will do the computations for you so you won't get the wrong answers.
http://aa.usno.navy.mil/data/docs/celnavtable.php
Readers of these posts can go to that site themselves and check Mr. van Asten's computations themselves. Just put in the date, time, and the coordinates for Howland (0° 48' N, 176° 38' W) to calculate the sun's altitude at Howland and any place along the correct LOP through Howland. Look at the column marked "Hc" which is the standard abbreviation for "computed altitude." "Zn" = azimuth and "GHA is Greenwich Hour Angle. While you are at it you can check out Mr. van Asten's calculation of GHA of the sun for 175453 GMT, just enter in that time and look at the GHA column. Mr. van Asten said in his prior posts that the GHA of the sun at that time was 88° 43.2', did he get it right? I said the GHA at 175453 GMT was 87° 45.7', did I get it right?
And no, I do not assume that you have consulted all representative flght manuals since you have failed to cite to any of them in your posts or in our other correspondence.
gl
88-03-14 is GHA-mean sun ; 87-45-45 is GHA-true sun , the latter used for determining LHA , nothing wrong with this .