Advanced search  
Pages: 1 [2] 3 4 ... 16   Go Down

Author Topic: Navigating the LOP with the offset method.  (Read 201596 times)

Mark Petersen

  • T3
  • ***
  • Posts: 125
Re: Navigating the LOP with the offset method.
« Reply #15 on: June 30, 2010, 12:05:02 PM »

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 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. 
Logged

Erik

  • T3
  • ***
  • Posts: 185
Re: Navigating the LOP with the offset method.
« Reply #16 on: July 01, 2010, 02:25:15 PM »

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...




Logged

Alan Williams

  • inactive
  • *
  • Posts: 47
Re: Navigating the LOP with the offset method.
« Reply #17 on: July 02, 2010, 07:40:48 AM »

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?
Logged

Martin X. Moleski, SJ

  • Administrator
  • *
  • Posts: 2961
Re: Navigating the LOP with the offset method.
« Reply #18 on: July 02, 2010, 07:58:25 AM »

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: 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."
LTM,

           Marty
           TIGHAR #2359A
 
Logged

Alan Williams

  • inactive
  • *
  • Posts: 47
Re: Navigating the LOP with the offset method.
« Reply #19 on: July 02, 2010, 08:14:44 AM »


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?...
Logged

Martin X. Moleski, SJ

  • Administrator
  • *
  • Posts: 2961
Re: Navigating the LOP with the offset method.
« Reply #20 on: July 02, 2010, 08:21:05 AM »

Thanks much for the reply - yes, what a detailed study.

Randy does nice work.

Quote
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.  They were certainly doing their best to detect Howland.  If Baker was detectable, they seem not to have detected it.
LTM,

           Marty
           TIGHAR #2359A
 
Logged

Erik

  • T3
  • ***
  • Posts: 185
Re: Navigating the LOP with the offset method.
« Reply #21 on: July 03, 2010, 05:20:55 AM »


Do we know if the 157/337 LOP was based TRUE heading or MAGNETIC heading? 
Logged

Martin X. Moleski, SJ

  • Administrator
  • *
  • Posts: 2961
Re: Navigating the LOP with the offset method.
« Reply #22 on: July 03, 2010, 06:15:05 AM »

Do we know if the 157/337 LOP was based TRUE heading or MAGNETIC heading? 

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?"

Strictly speaking, a 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 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.
LTM,

           Marty
           TIGHAR #2359A
 
Logged

Mark Petersen

  • T3
  • ***
  • Posts: 125
Re: Navigating the LOP with the offset method.
« Reply #23 on: July 03, 2010, 11:27:25 AM »

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?
Logged

Martin X. Moleski, SJ

  • Administrator
  • *
  • Posts: 2961
Re: Navigating the LOP with the offset method.
« Reply #24 on: July 03, 2010, 12:03:29 PM »

... 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.
LTM,

           Marty
           TIGHAR #2359A
 
Logged

Mark Petersen

  • T3
  • ***
  • Posts: 125
Re: Navigating the LOP with the offset method.
« Reply #25 on: July 03, 2010, 01:12:46 PM »

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 :)
Logged

Erik

  • T3
  • ***
  • Posts: 185
Re: Navigating the LOP with the offset method.
« Reply #26 on: July 03, 2010, 02:31:44 PM »

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?"

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.

Quote
Strictly speaking, a 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? 

Quote
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 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.

Quote
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!...........
Logged

Martin X. Moleski, SJ

  • Administrator
  • *
  • Posts: 2961
Re: Navigating the LOP with the offset method.
« Reply #27 on: July 03, 2010, 05:41:48 PM »

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. 

Quote
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.

Quote
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 came well after the Monte Carlo simulation, I think.
LTM,

           Marty
           TIGHAR #2359A
 
Logged

Bill Lloyd

  • T3
  • ***
  • Posts: 105
Re: Navigating the LOP with the offset method.
« Reply #28 on: July 03, 2010, 09:34:40 PM »

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. 
Logged

Martin X. Moleski, SJ

  • Administrator
  • *
  • Posts: 2961
Re: Navigating the LOP with the offset method.
« Reply #29 on: July 03, 2010, 11:18:45 PM »

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.

Quote
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."

Quote
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.
LTM,

           Marty
           TIGHAR #2359A
 
Logged
Pages: 1 [2] 3 4 ... 16   Go Up
 

Copyright 2019 by TIGHAR, a non-profit foundation. No portion of the TIGHAR Website may be reproduced by xerographic, photographic, digital or any other means for any purpose. No portion of the TIGHAR Website may be stored in a retrieval system, copied, transmitted or transferred in any form or by any means, whether electronic, mechanical, digital, photographic, magnetic or otherwise, for any purpose without the express, written permission of TIGHAR. All rights reserved.

Contact us at: info@tighar.org • Phone: 610-467-1937 • Membership formwebmaster@tighar.org

Powered by MySQL SMF 2.0.15 | SMF © 2017, Simple Machines Powered by PHP