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AuthorTopic: LOP-Possible stupid question  (Read 67595 times)

Chris Johnson

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LOP-Possible stupid question
« on: August 18, 2011, 05:44:01 AM »

I hold my hands up and admit that I am no navigator but have a question regarding the LOP that I hope doesn’t become another theory battle between our esteemed navigational colleagues.

I may have asked something similar before so be patient.

FN and AE miss Howland Island but FN’s observations and calculations say he has reached the LOP 157 – 337.  How wide/broad is this line for them to fly up/down?  Could AE not just watch a compass to stay on the LOP with FN then taking shots to adjust for wind etc?
In this way could they then not reach the ‘catchers mitt’ of the Phoenix island?
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Martin X. Moleski, SJ

• Posts: 3006
Re: LOP-Possible stupid question
« Reply #1 on: August 18, 2011, 07:25:41 AM »

FN and AE miss Howland Island but FN’s observations and calculations say he has reached the LOP 157 – 337.  How wide/broad is this line for them to fly up/down?

A line, considered as a mathematical abstraction, has no width.

A line of position, considered as "the amount of territory visible from the aircraft" has a width that is variable, depending on weather, altitude, and the field of view from the aircraft.

Did you miss the discussion of how to visualize the LOP?

Quote
Could AE not just watch a compass to stay on the LOP with FN then taking shots to adjust for wind etc?
In this way could they then not reach the ‘catchers mitt’ of the Phoenix island?

Gary LaPook has given several links to his website where he argues that a navigator would have to continually revise position estimates in order to end up in the vicinity of Nikumaroro.

All that we know about what Fred did or did not do ends with the final received transmission: "We are on the line 157 337.  Will repeat the message.  We will repeat this on 6210 kcs.  Wait.  We are running [on] line [north and south]."

We do not know how long they stayed on that line.

We do not know how far east or west of Howland that line was, in fact.

We may surmise that Fred thoughtthat that line ran through Howland (there was no other reason for them to have identified that line or to have turned on it unless this was the case).

We can see that that line points down toward the vicinity of Niku.

We don't know what other position information Fred might have derived from later observations.

We don't know what other headings he might have told Amelia to fly.

If Earhart and Noonan ended up on Niku, we don't know exactly how they got there--on purpose or by accident.  In 1937, the Navy thought it was worthwhile to search there.  In 1988, a couple of seasoned military navigators, Tom Gannon and Tom Willi (the "two Toms"), persuaded TIGHAR that Niku was worth exploring.  Stuff happened, and here we are today, still wondering whether the Niku hypothesis is correct.

Finding the aircraft in Gary LaPook's search area would disprove the Niku hypothesis.  Finding the aircraft on or near Niku would disprove Gary's hypothesis that they splashed and sank near Howland.
LTM,

Marty
TIGHAR #2359A

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Chris Johnson

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• Trying to give a fig but would settle for \$100,000
Re: LOP-Possible stupid question
« Reply #2 on: August 18, 2011, 07:53:41 AM »

Thanks Marty

Missed the 'visualise' discussion, might just answer my questions.

Its Reading Mr LaPooks site that makes me ask these questions to try and understand the whole argument.
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Harry Howe, Jr.

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• Nuclear Physicist(Ret) Pilot(Ret) Scuba(Ret)
Re: LOP-Possible stupid question
« Reply #3 on: August 18, 2011, 11:39:45 AM »

Chris
I don't think there are any "stupid" questions, except the question not asked.

I have one of my own.  If I am not mistaken the plane was equipped with a Sperry AutoGyro Autopilot.  Anyone have any info on its capabilities??  Surely, it would have been used to maintain course on the long journey.

It also had a drift indicator which, I assume, would give info relative to wind drift and allow corrections to be made.  Then, how in the world did they miss Howland?  Maybe Howland was mislocated on the chart FN used for his course planning?
No Worries Mates
LTM   Harry (TIGHAR #3244R)

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h.a.c. van asten

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Re: LOP-Possible stupid question
« Reply #4 on: August 18, 2011, 12:04:19 PM »

First and evidently the recorded aircraft progression line did not by far cover the sun line as advanced over Howland´s true coordinates , secondly an on board compass pointing flight in any direction including north gives no resolution of the coordinates you are over .
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Chris Johnson

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Re: LOP-Possible stupid question
« Reply #5 on: August 18, 2011, 12:34:04 PM »

First and evidently the recorded aircraft progression line did not by far cover the sun line as advanced over Howland´s true coordinates , secondly an on board compass pointing flight in any direction including north gives no resolution of the coordinates you are over .

I'll use an example from compass navigation on land.  In poor visability and using a map where I have some idea (like FN said with his LOP) I can follow a bearing that gets me to my destination or there abouts!

If the LOP was correct then why not just fly along the line?

Good question about the auto pilot, nether thought of that.
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Gary LaPook

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Re: LOP-Possible stupid question
« Reply #6 on: August 18, 2011, 02:08:53 PM »

First and evidently the recorded aircraft progression line did not by far cover the sun line as advanced over Howland´s true coordinates , secondly an on board compass pointing flight in any direction including north gives no resolution of the coordinates you are over .

I'll use an example from compass navigation on land.  In poor visability and using a map where I have some idea (like FN said with his LOP) I can follow a bearing that gets me to my destination or there abouts!

If the LOP was correct then why not just fly along the line?

Good question about the auto pilot, nether thought of that.

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

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

You cannot determine if you are staying on the course line that would take you to Niku because the azimuth of the line changes as the sun moves (the LOP  pivots on Howland island) and doesn't go anywhere near Niku later in the day.

gl
« Last Edit: August 18, 2011, 07:13:51 PM by Gary LaPook »
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Chris Johnson

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Re: LOP-Possible stupid question
« Reply #7 on: August 18, 2011, 02:37:01 PM »

Ok simplistic idea here!

You think you are on the LOP and will either fly over the Howland area or the Phoenix area.  You fly North South in the hope its Howland, Baker, Jervis but its not its Gardner er al.  Possible? I don't know but could it have been?
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Gary LaPook

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Re: LOP-Possible stupid question
« Reply #8 on: August 18, 2011, 07:05:50 PM »

I hold my hands up and admit that I am no navigator but have a question regarding the LOP that I hope doesn’t become another theory battle between our esteemed navigational colleagues.

I may have asked something similar before so be patient.

FN and AE miss Howland Island but FN’s observations and calculations say he has reached the LOP 157 – 337.  How wide/broad is this line for them to fly up/down?  Could AE not just watch a compass to stay on the LOP with FN then taking shots to adjust for wind etc?
In this way could they then not reach the ‘catchers mitt’ of the Phoenix island?

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

You have to allow for the possibility of up to a 7 NM uncertainty in an LOP derived from a sextant observation.  This means you may be up to 7 NM to the right or to the left of the LOP that you believe should take you to Howland so the possible error band in 14 NM wide. However, you are much more likely to be closer to the center of the error band than to either edge but you must allow for that maximum possible error in planning your approach. If they did perfect navigation then following the LOP should have taken Noonan directly over Howland. If, at the moment they were passing Howland, the error was at maximum then they might have passed up to 7 NM east or west of the island, so Howland would have been easily visible with 20 NM visibility.

There is the possibility that Noonan was using coordinates for a point about 5 NM west- north west of he island and this would have produced an LOP that was offset from the proper LOP by 4 NM. Following this erroneous LOP would cause the plane to fly by Howland within a 14 NM error band centered 4 NM to the west of the island. So looking at the worst case, flying the 4 NM offset LOP and being at the furthest error to the west, another 7 NM, then the plane could have been passing the island offset by, at most, 11 NM, again well within visibility range.

gl
« Last Edit: August 21, 2011, 01:18:54 AM by Gary LaPook »
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Gary LaPook

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Re: LOP-Possible stupid question
« Reply #9 on: August 18, 2011, 07:23:40 PM »

Ok simplistic idea here!

You think you are on the LOP and will either fly over the Howland area or the Phoenix area.  You fly North South in the hope its Howland, Baker, Jervis but its not its Gardner er al.  Possible? I don't know but could it have been?

gl
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h.a.c. van asten

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Re: LOP-Possible stupid question
« Reply #10 on: August 19, 2011, 12:36:13 AM »

From alt. 1,000 ft @ distance 11 nm the optical angle covering the west-east width of Howland is 2 arcminutes ; 1 arcmin is the minimum for resolution of an image by the eye , so island was for theory within visual range , but marginally for practice . That destination was GMT 1912 far on the port bow in lieu of head on as expected was a first reason to announce  A/c being over the latitude , but nevertheless not in sight . The 1 arcmin limit for observation lies @ 14 miles off for alt. 1,000 ft . Koepke in 1967 o/b the Pellegreno flight with Polhelmus navigator , saw Howland when 10-12 mls away after continued looking out by the entire crew .
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Chris Johnson

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Re: LOP-Possible stupid question
« Reply #11 on: August 19, 2011, 01:45:59 AM »

Ok simplistic idea here!

You think you are on the LOP and will either fly over the Howland area or the Phoenix area.  You fly North South in the hope its Howland, Baker, Jervis but its not its Gardner er al.  Possible? I don't know but could it have been?

gl

I read it before I posted my question, your Starbucks analogy is quite simple to understand in the context of you know exactly where you are starting from and going with plenty of land marks.  Makes sense then that you can’t use a LOP to hit your target dead on.
Wasn’t the purpose of FN’s LOP to get as close to Howland as possible then use RDF to lock onto the Itasca and thus Howland?
So for whatever reason they miss Howland or at least can’t see it but by FN’s calculations are on his stated LOP.  FN’s LOP isn’t as simple as your finding a Starbucks on a named street.  His LOP says islands somewhere within a radius, lets fly northward for X miles/time, if no landfall fly southward for Y miles/time, should find Howland, Baker or Jarvis.  What FN doesn’t know is he is off line (?) and thus more likely to hit the Phoenix Islands.
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Harry Howe, Jr.

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• Nuclear Physicist(Ret) Pilot(Ret) Scuba(Ret)
Re: LOP-Possible stupid question
« Reply #12 on: August 19, 2011, 10:42:52 AM »

Chris
Expand a bit on what you mean by FN being "off-line" (?)
No Worries Mates
LTM   Harry (TIGHAR #3244R)

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Chris Johnson

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Re: LOP-Possible stupid question
« Reply #13 on: August 19, 2011, 12:57:33 PM »

Chris
Expand a bit on what you mean by FN being "off-line" (?)

Thinking he was online with Howland but actualy off line and online with the Phoenix group if thats possible
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Gary LaPook

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Re: LOP-Possible stupid question
« Reply #14 on: August 20, 2011, 04:22:39 AM »

Ok simplistic idea here!

You think you are on the LOP and will either fly over the Howland area or the Phoenix area.  You fly North South in the hope its Howland, Baker, Jervis but its not its Gardner er al.  Possible? I don't know but could it have been?

gl

I read it before I posted my question, your Starbucks analogy is quite simple to understand in the context of you know exactly where you are starting from and going with plenty of land marks.  Makes sense then that you can’t use a LOP to hit your target dead on.
Wasn’t the purpose of FN’s LOP to get as close to Howland as possible then use RDF to lock onto the Itasca and thus Howland?
So for whatever reason they miss Howland or at least can’t see it but by FN’s calculations are on his stated LOP. FN’s LOP isn’t as simple as your finding a Starbucks on a named street.  His LOP says islands somewhere within a radius, lets fly northward for X miles/time, if no landfall fly southward for Y miles/time, should find Howland, Baker or Jarvis.  What FN doesn’t know is he is off line (?) and thus more likely to hit the Phoenix Islands.

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

Since you liked the Simi Valley example I will expand upon that one.

See first diagram:

In that example your friend told you to meet him at the Starbucks located on Cochran Street, east of First Avenue. Since you know that your destination is located on Cochran street you know that if you intercept Cochran street at First Avenue and follow Cochran to the east that you are assured of finding the Starbucks. Cochran Street in an LOP and the center line of the pavement and the curbs and the street signs allow you to check and make sure you are staying on course.

Let's change the scenario slightly. This time your friend just tells you that the Starbucks is located straight east from the intersection of Cochran and First. You know that there is also a Starbucks located in the town of Gardner that is also straight east of the intersection of Cochran and First in Simi Valley. You backup plan is that if you can't hook up with your buddy at that Starbucks then you will go to the one in Gardner and get a Latte.

So you start out as before and drive to the intersection of Cochran and First and then drive east on Cochran looking for the Starbucks. For some reason you fail to spot it and you then notice that Cochran is curving to the left and is no longer going straight east. You decide that you have missed the meeting place and you decide to go to your backup Starbucks in Gardner so you drive over the curb and head off across the trackless desert, still heading east. You have no guidance except your compass because the LOP you had been following (Cochran Street) has changed directions and no longer goes towards Gardner. You drive across the desert for half a mile and then, suddenly, you hit yourself on your forehead. "This is stupid" you say to yourself, "there is not a chance in the world that I will be able to maintain my course accurately enough, with just a compass, driving across this desert, having to go around rabbit holes, cactus, rocks and what not, for me to find Gardner. And, duh, I don't have much gas left, I could run out and end up dying in this desert with the vultures pecking my eyes out. I better turn around and go back and look thoroughly for that Starbucks that I missed, and besides, that's where my friend is waiting for me!"

"This is the situation at Howland after 2013 Z.

See attached revised Simi Valley diagram.

I have also attached two photos of the ONC chart for the area which is at 1,000,000 to 1 scale, one inch equals 14 NM. I have drawn in the Sun line LOP running 157° True that existed from 1745 Z to 1845 Z. I have also drawn in the LOP for 2013 Z by which time it had changed to 153°. The LOP continues to rotate counter-clockwise, pivoting on Howland and by 2240 Z (the approximate time that the plane would be arriving at Gardner) it has changed all the way to 126°.The second photo shows an aeronautical plotter laid on the chart with the beginning of the scale at Gardner and you can see by how many miles the plane would have missed Gardner while staying on the LOP. This would be just like staying on Cochran Street after it curved to the left which would also cause you to miss Gardner.

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

For Noonan, following his LOP to his destination IS as simple as following the street to Starbucks. There is no radius involved, he knows he is on that line plus or minus (at most, very unlikely to be more) 7 NM both sides of the line, following the line should bring him close enough to find Howland just like driving down Cochran should get you close enough to spot that Starbucks in the back of the shopping center parking lot.

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

For the rest of you question see my prior post at:

https://tighar.org/smf/index.php/topic,383.msg5120.html#msg5120

gl
« Last Edit: August 21, 2011, 01:20:59 AM by Gary LaPook »
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