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Author Topic: LOP-Possible stupid question  (Read 39196 times)

Chris Johnson

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Re: LOP-Possible stupid question
« Reply #15 on: August 22, 2011, 06:37:08 AM »

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  ;)
« Last Edit: August 22, 2011, 06:41:24 AM by Chris Johnson »
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Martin X. Moleski, SJ

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Re: LOP-Possible stupid question
« Reply #16 on: August 22, 2011, 11:24:14 AM »

... Otherwise by the looks of it TIGHAR should be looking on Kanton not Niku  ;)

Canton was thoroughly occupied by both the British and Americans in 1937; they called the arrangement a "condominium."  I suppose you could write a new conspiracy theory beginning with the premise that AE and FN landed there ...
LTM,

           Marty
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Chris Johnson

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Re: LOP-Possible stupid question
« Reply #17 on: August 22, 2011, 12:13:08 PM »

... Otherwise by the looks of it TIGHAR should be looking on Kanton not Niku  ;)

Canton was thoroughly occupied by both the British and Americans in 1937; they called the arrangement a "condominium."  I suppose you could write a new conspiracy theory beginning with the premise that AE and FN landed there ...

Thats OK i'm persuing one about a cross dressing coastguard at the moment ;)
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Harry Howe, Jr.

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Re: LOP-Possible stupid question
« Reply #18 on: August 22, 2011, 01:02:11 PM »


cHRIS, gARY
Do not forget that the Lockheed was equipped with an autopilot (George).  When they , AE/FN passed over where they thought Howland was (at 0843 Howland time) and set a course for Gardner (337 to 157) they would have set George for that course (wind corrected of course) and monitored their progress by time and speed.  That would have got them to a point where they could spot Gardner (3 times as long, 2 times as wide, 6 times the area when compared with Howland ) with a distinctively colored lagoon.  George would have got them there, just like George got them to the "Charted Position" which, unfortunately was 5 nm west of where Howland "Truly" was.

Moral of this story,  Never trust your life to a chart provided by some governmental body!  Be damned sure that your information is correct and verified before taking off on a long voyage completely over water and be damned sure you know your DF is operating properly and you know how to use it.
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LTM   Harry (TIGHAR #3244R)
 
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h.a.c. van asten

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Re: LOP-Possible stupid question
« Reply #19 on: August 22, 2011, 01:26:56 PM »

Autopilot maintains (compass) course after it has been set . From an unknown departure position you cannot set any course to any place . In the other event it would have been best to program George (auto pilot but not auto navigator) for Howland ...
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Chris Johnson

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Re: LOP-Possible stupid question
« Reply #20 on: August 22, 2011, 02:09:28 PM »

Autopilot maintains (compass) course after it has been set . From an unknown departure position you cannot set any course to any place . In the other event it would have been best to program George (auto pilot but not auto navigator) for Howland ...

I thought that if FN thought he was on the LOP then yes set the autopilot for points North the South in search of land?
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Gary LaPook

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Re: LOP-Possible stupid question
« Reply #21 on: August 22, 2011, 02:21:56 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  ;)

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

On January 15, 2003 I posted this challenge to the navigation experts on the TIGHAR forum:

=========================================================================
Date:         Wed, 15 Jan 2003 13:39:33 EST
From:         Gary LaPook
Subject:      Re: Marshall Islands and LOP

You are right Alan, the line on his chart would not move.

However the only value of a LOP is that it represents a line on the surface of the earth. We both agree that there was no LOP painted on the water that Noonan could see and follow. It was not a terrestrial line of position like a railroad track, road, river or shore line that a pilot can follow to an airport located next to such LOPs.

The celestial LOP is useful for finding an island if the line on the chart passes through the island and so representing a line on the earth's surface that also passes through the island. Then, if you can determine that you are staying on the line on your chart you will also be determining that you are staying on the  line on the surface of the earth that goes to the island. You make this determination by taking additional observations of the sun and comparing the altitude that you measure  to the altitude you would  have measured (which you compute) if you were on the LOP. If they are the same you are on the LOP, if not you can determine how far off you are and which way to turn to regain the line.

The question I have about your response relates to your statement:

>He would check
>his position periodically in relation to the line he had drawn on
>his chart. A line that never moved.

I don't know how he does this after the sun's azimuth has changed, perhaps you can explain it to me. Use this example to check his position in relation to the line he had drawn on the chart:

It is now 2240 Z on July 2,1937, about two and a half hours after the last transmission, and the airplane has been maintaining a true heading of 157 degrees and an airspeed of 120 knots and so should be getting close to Gardner. Noonan uses his bubble sextant and measures the altitude of the center of the sun. After making corrections for refraction and index error his observed altitude (Ho) is 59 degrees 15 minutes.

Where is he in relation to the line he had drawn on the chart?

Is the plane still on the LOP drawn on the chart?

If the plane is not on the line on the chart then how far off the LOP is the airplane?

Is the plane still on course for Gardner?

If it is not on the line to Gardner then which way should he turn to get to Gardner?

Please explain how you reach you conclusions and include the math.

If you have a scanner available I would appreciate it if you could scan in the chart work you do to figure out this example and email it to me at : glapook@pacbell.net since I would like to see how you accomplish this.

gl
===================================================

It's been 8 years and 7 months and still no serious response.

So, to answer your question, no you can't just make some compensation for the change in the azimuth of the LOP and then use it to find Gardner.

gl
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Chris Johnson

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Re: LOP-Possible stupid question
« Reply #22 on: August 22, 2011, 02:32:43 PM »

Woohhh big home work for a year 7 student (uk education 11 year old).  Need to go and think about it!
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Gary LaPook

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Re: LOP-Possible stupid question
« Reply #23 on: August 22, 2011, 02:45:47 PM »


cHRIS, gARY
Do not forget that the Lockheed was equipped with an autopilot (George). When they , AE/FN passed over where they thought Howland was (at 0843 Howland time) and set a course for Gardner (337 to 157) they would have set George for that course (wind corrected of course) and monitored their progress by time and speed.  That would have got them to a point where they could spot Gardner (3 times as long, 2 times as wide, 6 times the area when compared with Howland ) with a distinctively colored lagoon.  George would have got them there, just like George got them to the "Charted Position" which, unfortunately was 5 nm west of where Howland "Truly" was.

Moral of this story,  Never trust your life to a chart provided by some governmental body!  Be damned sure that your information is correct and verified before taking off on a long voyage completely over water and be damned sure you know your DF is operating properly and you know how to use it.

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

But since they were not over Howland at the start, setting a course of 157° (actually it is 159°) to Gardner would not take them to Gardner. If I want to fly to Chicago and I think I am over New York I would set my autopilot to maintain a heading of 270°. But, if I were actually over New Orleans that 270° heading would take me to Texas, not even close to Chicago. A basic premise in navigation is that you can not dead reckon to a destination starting from an unknown spot. Your DR can never be more accurate than the accuracy of your starting position and then it degrades further as you proceed.

Having flown behind many autopilots for many years I know that they would not be accurate enough to keep the plane on heading for 350 NM. Remember, "George" was not coupled to any VOR or GPS signal so could not keep the plane on "course" it was simply on "heading hold" which means it could only maintain a fixed heading as determined by the directional gyro (DG). Since directional gyros drift over time, "George" would be able to maintain a heading only if Earhart constantly compared her compass with the DG and kept resetting the DG to agree with the compass. The directional gyro was not "slaved" to the compass. I am sure that a 1937 autopilot did not do a better job than much more modern autopilots.

In fact, I am not even sure that "George" even had a "heading hold" mode, it might have been the much simpler "wing leveler" which just holds the wings level, more or less, and gets no input about the actual heading of the aircraft. With this type of simple autopilot any time the plane wanders off course due to turbulence or due to the "wing leveler" gyro not being perfect, the autopilot then just maintains the new position with no tendency to return to any particular heading. With a wing leveler the plane can end up going around in circles and the autopilot is perfectly happy about it. Wing levelers were common in planes even 50 years after the Earhart flight so it would not be surprising if her's was just a wing leveler. (Does anybody know the answer to this question?)

gl
« Last Edit: August 27, 2011, 01:35:14 AM by Gary LaPook »
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Harry Howe, Jr.

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Re: LOP-Possible stupid question
« Reply #24 on: August 22, 2011, 03:05:26 PM »


Gary
Geez, you mean a good pilot would have to be told that the Gyroscopic Directional Indicator might "drift" periodically and thus affect the autopilot that is slaved to it, and therefore must periodically be compared with the compass and adjisted periodically, as necessary?

When I learned to fly, that was standard practice and noone had to tell me.  But I guess we have to make allowances for AE.  She wasn't anywhere near a good pilot, just a famed aviatrix, whatever that might have been.
No Worries Mates
LTM   Harry (TIGHAR #3244R)
 
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Chris Johnson

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Re: LOP-Possible stupid question
« Reply #25 on: August 22, 2011, 03:14:15 PM »

ok confussed question but I read that they were setting a course for Gardner? but wern't they looking for Howland in the first instance?
« Last Edit: August 22, 2011, 03:16:24 PM by Chris Johnson »
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Gary LaPook

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Re: LOP-Possible stupid question
« Reply #26 on: August 22, 2011, 04:28:45 PM »

ok confussed question but I read that they were setting a course for Gardner? but wern't they looking for Howland in the first instance?

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

You're right, they were looking for Howland. When they didn't arrive, some people jumped to the conclusion that they could just fly down the extended LOP to Gardner, if they had done the math they would have known it was not possible. See: https://sites.google.com/site/fredienoonan/discussions/navigation-to-howland-island


gl
« Last Edit: August 22, 2011, 04:43:27 PM by Gary LaPook »
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Gary LaPook

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Re: LOP-Possible stupid question
« Reply #27 on: August 22, 2011, 04:40:38 PM »


Gary
Geez, you mean a good pilot would have to be told that the Gyroscopic Directional Indicator might "drift" periodically and thus affect the autopilot that is slaved to it, and therefore must periodically be compared with the compass and adjisted periodically, as necessary?

When I learned to fly, that was standard practice and noone had to tell me.  But I guess we have to make allowances for AE.  She wasn't anywhere near a good pilot, just a famed aviatrix, whatever that might have been.

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

Certainly not a slam against Amelia, all pilots understand about resetting the DG, including Amelia. But most of the people reading these posts are not pilots and your post could give the mis-impression that "George" was perfect and could easily fly to Gardner even if Amelia couldn't, which couldn't be further from the facts.

gl
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Harry Howe, Jr.

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Re: LOP-Possible stupid question
« Reply #28 on: August 22, 2011, 05:40:12 PM »


Facts??  What facts??  Do you mean the last radio transmission heard on the Itasca from AE where she was running on the line North and South 157/337? but didn't give anyone a clue about her heading or intentions?  Those facts?  Not a very good pilot.
I remember learning early on as a flight student that radio transmissions needed to contain  PHACTI  (Position, Heading, Altitude, Communication and Time and most important  Intentions!  Perhaps AE should have spent more time becoming a pilot and less time trying to break records.
No Worries Mates
LTM   Harry (TIGHAR #3244R)
 
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Gary LaPook

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Re: LOP-Possible stupid question
« Reply #29 on: August 22, 2011, 07:10:22 PM »


Facts??  What facts??  Do you mean the last radio transmission heard on the Itasca from AE where she was running on the line North and South 157/337? but didn't give anyone a clue about her heading or intentions?  Those facts?  Not a very good pilot.
I remember learning early on as a flight student that radio transmissions needed to contain  PHACTI  (Position, Heading, Altitude, Communication and Time and most important  Intentions!  Perhaps AE should have spent more time becoming a pilot and less time trying to break records.

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

"mis-impression that "George" was perfect and could easily fly to Gardner even if Amelia couldn't, which couldn't be further from the facts."

You misinterpreted what I wrote and took my reference to "facts" as applying to Amelia when I was actually referring to what I had written about the imperfection of "George."



gl
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