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Author Topic: LOP-Possible stupid question  (Read 45529 times)

Harry Howe, Jr.

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Re: LOP-Possible stupid question
« Reply #30 on: August 22, 2011, 09:10:46 PM »


I didn't mean to imply that George was Perfect and could have flown from Howland to Gardner gy himself, certainly not,  but, with proper flying AE and Ceorge could easily have flown the distance and spotted Gardner.  I believe that is what they did, landing at Gardner at about 2400 (GCT) Noon Howland time.  Too bad that AE didn't let the Itasca in on her intentions.  If she had then Cmdr Thompson would have known which quadrant to steam off to, the SE,  which heading to take, 157 degrees, and would have arrived at Gardner in 20 hours or so to find AE and  FN standing next to their plane waving vigorously.  Alas, that/s not what she did.  Saying "Running north and south on 157/337" is meaningless.  "Running north to south on 337 to 157"would have passed on critical info.  To have said "diverting to Cardner Island" would also have been helpful.
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John Kada

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Re: LOP-Possible stupid question
« Reply #31 on: August 22, 2011, 10:22:26 PM »

As long as we're asking possibly stupid questions,  I'm curious whether variations in magnetic declination might have played a role in the failure of AE and FN to find Howland. Just as there was incorrect information circulating about the exact coordinates of Howland, is it possible that the correct information about magnetic declination in the vicinity of Howland was not provided to AE and FN? 

If my crude understanding of their navigation procedure is correct, after the last position determination by celestial navigation was made they would have had to rely on compass readings to stay on course and then to stay on the LOP for the last part of the flight. If the correction for magnetic declination was in error, this would have led to a systematic navigational error; whether this could have been a significant systematic error I leave for the likes of the estimable Mr. LaPook to shed light on.

If a magnetic declination correction error could conceivably have been a significant source of error on the flight, then I wonder if a record exists somewhere of the information that FN and AE had when they left Lae.

By the way, NOAA has an online magnetic declination calculator, which gives a magnetic declination of 5 degrees 26 minutes East for Lae and 9 degrees 29 minutes East at Howland in 1937...

« Last Edit: August 22, 2011, 10:45:48 PM by John Kada »
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Gary LaPook

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Re: LOP-Possible stupid question
« Reply #32 on: August 23, 2011, 02:11:23 AM »

As long as we're asking possibly stupid questions,  I'm curious whether variations in magnetic declination might have played a role in the failure of AE and FN to find Howland. Just as there was incorrect information circulating about the exact coordinates of Howland, is it possible that the correct information about magnetic declination in the vicinity of Howland was not provided to AE and FN? 

If my crude understanding of their navigation procedure is correct, after the last position determination by celestial navigation was made they would have had to rely on compass readings to stay on course and then to stay on the LOP for the last part of the flight. If the correction for magnetic declination was in error, this would have led to a systematic navigational error; whether this could have been a significant systematic error I leave for the likes of the estimable Mr. LaPook to shed light on.

If a magnetic declination correction error could conceivably have been a significant source of error on the flight, then I wonder if a record exists somewhere of the information that FN and AE had when they left Lae.

By the way, NOAA has an online magnetic declination calculator, which gives a magnetic declination of 5 degrees 26 minutes East for Lae and 9 degrees 29 minutes East at Howland in 1937...

----------------------------------------

Surveyors call it "declination" while navigators call it "variation." The NOAA computer modeling of the Earth's magnetic field computes the variation at Howland in July 1937 as 9° 29' east, nine and a half degrees east. This means the magnetic field of the Earth at that location was shifted 9.5° east of true north so if you turned to "magnetic north" using a perfect compass you would actually be heading 009.5° true. Williams (and presumably Noonan) used the value of 9° east, one half a degree different than the NOAA value, and this assumes that the NOAA prediction is correct. Williams listed 6° east for Lae, again a half degree difference. In a perfect world this half a degree difference could make a half NM error after flying 60 NM, not enough to make them miss Howland while flying the LOP but would grow to about 3 NM on a flight to Gardner, but nobody can maintain a heading to a one degree accuracy anyway. Noonan would have made the normal correction for this easterly variation by subtracting 9° from the 157° true course, determining the magnetic course to be 148°. Since the compass installed in the plane was also affected by the magnetic fields of components in the plane itself an additional correction needed to be made for this "deviation." I have attached a photo of the "compass correction card" showing the deviation on various headings. The deviation on a course of 150° is 2° "west" so Earhart would have added this 2° to the magnetic course of 148° to arrive at the compass course of 150°. Remember the mnenomic for making these corrections: "True Virgins Make Dull Companions." To this Noonan would have added or subtracted the wind correction angle to determine the heading to keep them on the LOP.

-------------------------------------------------------------------------

Errors can creep in at many places in this process and these accumulate to cause the cross track uncertainty in the dead reckoning, so the dead reckoning must be corrected from time to time by taking addition sights of the sun. In computing the compass heading needed to maintain the true course of 157°, Noonan had to add three numbers that had been rounded to one degree accuracy even though they were not exactly at an even degree. For example, 9.5° variation was rounded to 9° even. The azimuth of the Sun was rounded to 067° T while the actual azimuth varied from 66.9° at 1745 Z to 66.5° at 1845 Z and 62.8° at 2013 Z. The compass correction card showed a correction for a heading of 120° of + 1° and for 150° of + 2° so the correction for the magnetic heading of 148° is somewhere in between. (And the correction card itself was not perfect since it was derived by swinging the compass and that is not a perfect process.) Adding three quantities, each of which were rounded to one degree precision, introduces a 3° uncertainty in the result.

Then, to this, Noonan had to allow a wind correction angle to counteract the cross-wind. The WCA is also rounded to one degree so the uncertainty in the calculation increases to 4° . The WCA itself has an even greater uncertainty since it was derived by calculating the wind from drift observations or by "wind between fixes" and each of these procedures have their own levels of uncertainty.

So, the half a degree discrepancy between the Williams variation value and the NOAA variation is the least of the problems. These uncertainties add up and this is the reason that you have to allow for a 10% uncertainty in dead reckoning. If Noonan knew that he was over Howland (and the one thing he knew for sure was that he was NOT over Howland) and he wanted to go to Gardner, then he would have to take into consideration that his DR position, after flying 350 NM to Gardner, could be as much as 35 NM in error and he could miss that island by passing 35 NM east or 35 NM west. With 20 NM visibility his chance of finding Gardner was 40/70, or only 57%, the odds were only 4 to 3, barely better than even money. Would you bet your life at these odds?

Or, since their lives were on the line, in making their to abandon the search for Howland and to attempt to find Gardner, Noonan and Earhart might have used something more conservative like the estimate of DR accuracy contained in the U.S. Navy Flight Navigation Manual, H.O. 216, of 20 NM per hour plus 1% of the distance. Using this formulation you find the uncertainty to be 63 NM meaning that they could have passed up to 63 NM east or west of Gardner, a total of 126 NM. Since they would only be able to see the island for 20 NM from either side, a total detection diameter of 40 NM, the probability of seeing Gardner was only 40/126, 32%, making the odds 40 to 86, or more that 2 to 1 against saving their lives. Would you make that bet? And Noonan had to know that he was at least 20 NM from Howland, since he did not see that island, and he had no way to determine exactly where so he would have known that his actual odds were much worse.

See: https://sites.google.com/site/fredienoonan/topics/accuracy-of-dead-reckoning

and:

 https://sites.google.com/site/fredienoonan/topics/measureing-and-determining-wind-speed-and-direction-while-in-flight

gl
« Last Edit: August 23, 2011, 08:03:34 PM by Gary LaPook »
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Harry Howe, Jr.

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Re: LOP-Possible stupid question
« Reply #33 on: August 23, 2011, 11:46:08 AM »


I was wondering how long it would take for someone to ask about variations in the compass headings relative to true north.
There were two pilots aboard, AE and FN, one of whom was an expert navigator as well who we can assume knew about corrections necessary on trips that span large east/west directions.  Presumably the necessary declination "lines" were marked on their chart and corrections made to  the compass as the trip progressed, but we really don't know what information they had prior to takeoff and during flight.

I can only  say by experience as a pilot that, on every cross-country flight without fail,  I made it a practice to adjust my magnetic compass for declination as marked on my chart and for variatioins due to plane components from the planes card prior to takeoff and periodically during the flight.  That practice got me in the habit of doing it regularly and to check it as I flew the course.  It is essential to develope good habits early on in one's flying experience so that these things become "second nature".  Whether AE and FN had developed such habits is not known.  I have a personnel opinion.
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Gary LaPook

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Re: LOP-Possible stupid question
« Reply #34 on: August 23, 2011, 03:26:25 PM »


I was wondering how long it would take for someone to ask about variations in the compass headings relative to true north.
There were two pilots aboard, AE and FN, one of whom was an expert navigator as well who we can assume knew about corrections necessary on trips that span large east/west directions.  Presumably the necessary declination "lines" were marked on their chart and corrections made to  the compass as the trip progressed, but we really don't know what information they had prior to takeoff and during flight.

I can only  say by experience as a pilot that, on every cross-country flight without fail,  I made it a practice to adjust my magnetic compass for declination as marked on my chart and for variatioins due to plane components from the planes card prior to takeoff and periodically during the flight.  That practice got me in the habit of doing it regularly and to check it as I flew the course.  It is essential to develope good habits early on in one's flying experience so that these things become "second nature".  Whether AE and FN had developed such habits is not known.  I have a personnel opinion.

----------------------------------------------


It has been posted on the TIGHAR forum that the several islands of the Phoenix Island group provided a "catcher's mitt" ensuring that Noonan would be certain to stumble onto at least one of these islands, that they were impossible to miss. This also is not true as these islands are spread very far apart from each other and the plane could fly through the entire island group without being close enough to any of the islands to be certain of seeing land. See chart ONC M-17, (each square on this chart is 60 nautical miles on a side, 69 statute miles.)

https://sites.google.com/site/fredienoonan/resources/trial/onc-m-17-1.JPG?attredirects=0
https://sites.google.com/site/fredienoonan/resources/trial/onc-m-17-4.JPG?attredirects=0

The Phoenix islands consist of McKean island which is 50 NM to the left of the course to
Gardner, Hull is 140 NM, Sydney is 180 NM, Birnie is 190 NM, Canton is 200, Enderbery is
230 and Phoenix island is 250 NM. There are no islands to the right of the course. Most
are at greater distances from Howland than Gardner and there is a lot of water in between.
It is not a sure thing like turning till the compass says "E for Europe" like Lindbergh did.


Here is an analogy to help make this clear.

You are walking down a street. A black limousine pulls up next to you. Two big guys jump out, rough you up and throw you into the trunk. After a long drive the car finally stops and you are pulled out of the trunk. It is now dark. You look around and you realize you are standing in Yankee Stadium.

Vito Corleone walks up to you and says. "I've got a little proposition for you."
"What kind of a proposition, " you ask nervously.
"See the outfielders out there, right, center and left field?"
"Yes" you say.
"Here is my proposition" says the Godfather. "I will have my pitcher pitch one ball to you. You hit it, and if it is caught on the fly by any of the outfielders, I will give you a hundred thousand dollars."
"And if they don't catch it, what do I have to pay you?" you reply.
"Oh, nothing" say the Godfather, "My boys will just shoot you in the head and dump your body in the river where you can sleep with the fishes. Oh, I forgot to mention, the outfielders are not allowed to move."
"Gee, do I have any other options?" you ask.
"Tell you what" the Godfather goes on, "since I am such a nice guy I will make you another proposition but you will have to choose between just these two. I will have the pitcher pitch you three balls and you hit them back to the pitcher or to the shortstop and if either the pitcher or the shortstop catches one of the balls on the fly I will give you a million dollars."
"And if they don't catch one of the balls..." your voice trails off.
"Same deal, my boys shoot you in the head."

So which proposition do you choose?

This is the true "catcher's mitt" situation.

If you take the first proposition you have only one chance to hit the ball and the non-moving outfielders present very small targets to hit that are far away. Even if the ball is caught you only get one hundred thousand bucks. If the ball is not caught you sleep with the fishes.

If you take the second proposition you get three chances to hit the ball and the pitcher and shortstop have three chances to catch the ball and they are much closer and make much bigger targets to hit at this close range. If one of them catches the ball you get a million dollars, ten times more than the first proposition. If they don't catch the ball you are no worse off than with the first proposition, you still end up sleeping with the fishes.

So would Noonan and Earhart have decided to fly 350 nautical miles across the sea, hoping to find several small island which are spread so far apart that even with 20 mile visibility they could fly between them without seeing any of them, knowing that they would have only one chance since they would burn up all of their fuel on the way leaving nothing left to fly a search pattern with? And even if they are successful in finding one of the islands, there they are, barely alive, with no water or food, the airplane destroyed, no round the world flight, AE and Putnam bankrupt. If not successful they sleep with the fishes.

Or would they turn around and fly a standard search pattern with three hours of fuel on board to allow a long search, with Howland and Baker, with twenty mile visibility, presenting a target 80 miles wide and only 50 to a hundred miles away, a target hard to miss. And if successful they win the big prize, the airplane is refueled and the round the world flight is completed, accolades and money roll in and AE and Putnam have fame and wealth. If not successful they are no worse off than if missing the Phoenix islands, they still sleep with the fishes.

What choice would you make?

gl
« Last Edit: August 25, 2011, 04:02:02 PM by Gary LaPook »
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Gary LaPook

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Re: LOP-Possible stupid question
« Reply #35 on: August 23, 2011, 04:20:41 PM »

Thanks Gary! Think I may still flunk this class but at least i'm trying.

I see how a LOP works and understand that without reference points then yes you would more than likely struggle to stay on the line.  It wouldn't stop you from getting there with some good fortune and luck though.

In simple terms why do the lines change from 157 to 153, 148 and finaly 126? re read again and had a light bulb moment.

Can you not navigate a LOP and take into account the counter clockwise rotate centred on Howland? Thus keeping along the LOP. Otherwise by the looks of it TIGHAR should be looking on Kanton not Niku  ;)

---------------------------------------------

The LOP is plotted at right angles to the azimuth of the Sun. From 1745 Z to 1845 Z the azimuth of the Sun was 067° plus 90° makes 157°. As the earth turns the sun moves across the sky and the azimuth changes during the day. But the LOP didn't stop at 126° since the sun kept moving.  At noon the azimuth of the sun at Howland was straight north so an LOP taken at that time would have run 090/270°. The azimuth was changing in a counter-clockwise direction which may be confusing you since you are probably used to seeing the direction of the sun changing in a clockwise direction. But from a position south of the sun, the sun moves in the opposite direction and noon occurs with the sun to the north while for the U.S. and Europe the sun is south at noon.

gl
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Harry Howe, Jr.

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Re: LOP-Possible stupid question
« Reply #36 on: August 23, 2011, 05:45:40 PM »



AE/FN probably knew exactly where Gardner was relative to Howland before they took off and had it in mind as a possible alternative forced landing  place.

That is my belief.

They also probably had places to the NW in the Marshalls for the same purpose but also knew that they were close to twice as far away as Gardner. .  They also would have known that the Japanese were in control of the Marshalls.  Their choice would have been to the SSE  to Baker, McKean, and Gardner, Common Sense.
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John Kada

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Re: LOP-Possible stupid question
« Reply #37 on: August 23, 2011, 09:33:26 PM »

Gary,

Thanks for answering my question.

I assume that Williams is the standard navigational reference that FN would have used, and apparently the value for the magnetic variation at Gardner given in Williams matches the NOAA value for all practical purposes, so we have no reason to think that a magnetic variation correction error was a factor in the loss of the flight.
« Last Edit: August 23, 2011, 09:47:53 PM by John Kada »
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Harry Howe, Jr.

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Re: LOP-Possible stupid question
« Reply #38 on: August 24, 2011, 11:41:39 AM »


John Kada
The magnetic declination and variation of the compass probably did not play a part in the failure of the flight from Lae to Howland, however we really don't know what went on in that cockpit.  Only AE and FN knew and they aren't with us.

Whether they adjusted their compass for magnetic declination and variation at takeoff and periodically during the long west to east flight, I do not know.  Their failure to find Howland and/or to be rescued at Gardner was a result of many errors, the moist egregious of which was to take off without knowing that their RDF (Radio Direction Finder) was working properly and that they knew and understood the limitations of the RDFs at Howland and on the Itasca.
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Gary LaPook

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Re: LOP-Possible stupid question
« Reply #39 on: August 24, 2011, 06:16:43 PM »

Gary,

Thanks for answering my question.

I assume that Williams is the standard navigational reference that FN would have used, and apparently the value for the magnetic variation at Gardner given in Williams matches the NOAA value for all practical purposes, so we have no reason to think that a magnetic variation correction error was a factor in the loss of the flight.

------------------------
Williams had the variation for Lae, Howland and some places in between but not Gardner.

gl
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John Kada

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Re: LOP-Possible stupid question
« Reply #40 on: August 24, 2011, 06:31:53 PM »

Oops--I meant to say Howland, not Gardner/Nikumaroro...
« Last Edit: August 24, 2011, 06:34:00 PM by John Kada »
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Chris Johnson

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Re: LOP-Possible stupid question
« Reply #41 on: August 25, 2011, 12:15:21 PM »

OK slight thread drift (should have called the thread Chris's dumb questions on navigation) but can anyone explain this to me?

Quote
Recent research has indicated that on July 2, 1937, Earhart´s aircraft was not (contrary to current literature) flown over the great circle New Guinea-to-Howland.
From Wikipedia sourced from
Quote
European Journal of Navigation, Vol. 9, no. 1, 2011.
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Edgard Engelman

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Re: LOP-Possible stupid question
« Reply #42 on: August 25, 2011, 02:07:12 PM »

In fact you can download the entire artice at http://davidkbowman.com/wagner_noonan.pdf.
It was written by H.A.C.van Asten. It would be interesting to have Gary LaPook's opinion on this paper.
« Last Edit: August 25, 2011, 02:12:00 PM by Edgard Engelman »
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Chris Johnson

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Re: LOP-Possible stupid question
« Reply #43 on: August 25, 2011, 02:21:55 PM »

In fact you can download the entire artice at http://davidkbowman.com/wagner_noonan.pdf.
It was written by H.A.C.van Asten. It would be interesting to have Gary LaPook's opinion on this paper.

Thanks :)
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Gary LaPook

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Re: LOP-Possible stupid question
« Reply #44 on: August 25, 2011, 02:32:21 PM »

OK slight thread drift (should have called the thread Chris's dumb questions on navigation) but can anyone explain this to me?

Quote
Recent research has indicated that on July 2, 1937, Earhart´s aircraft was not (contrary to current literature) flown over the great circle New Guinea-to-Howland.
From Wikipedia sourced from
Quote
European Journal of Navigation, Vol. 9, no. 1, 2011.

---------------------
There is nothing magic about the great circle course. Compared to the rhumb line course a great circle course may be significantly shorter depending mainly on the latitude of the departure and the destination. Near the equator there is virtually no difference between them, the rhumb line from Lae to Howland is less than 0.2 SM longer than the great circle, the course is just 1.4 degrees different at the start and it is never more than 10 SM offset to the side of the great circle. Prior to GPS it would not have been possible for any navigator to determine whether he was flying the rhumb line or flying the great circle on this flight.

On a long flight even large deviations to the side do not appreciably lengthen the flight. On the fight from Lae to Howland he plane could have been off course 100 SM at the midpoint and this would add only 8 SM to the total distance.

gl

gl
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