Advanced search  
Pages: 1 2 3 [4] 5 6 ... 16   Go Down

Author Topic: Navigating the LOP with the offset method.  (Read 198492 times)

h.a.c. van asten

  • T4
  • ****
  • Posts: 322
Re: Navigating the LOP with the offset method.
« Reply #45 on: April 25, 2011, 11:38:14 PM »

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.
Logged

Ric Gillespie

  • Executive Director
  • Administrator
  • *
  • Posts: 5543
  • "Do not try. Do or do not. There is no try" Yoda
Re: Navigating the LOP with the offset method.
« Reply #46 on: April 26, 2011, 05:04:18 AM »

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.
Logged

h.a.c. van asten

  • T4
  • ****
  • Posts: 322
Re: Navigating the LOP with the offset method.
« Reply #47 on: April 26, 2011, 01:37:09 PM »

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.
Logged

h.a.c. van asten

  • T4
  • ****
  • Posts: 322
Re: Navigating the LOP with the offset method.
« Reply #48 on: April 27, 2011, 01:14:26 AM »

...  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" 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.
Logged

Ric Gillespie

  • Executive Director
  • Administrator
  • *
  • Posts: 5543
  • "Do not try. Do or do not. There is no try" Yoda
Re: Navigating the LOP with the offset method.
« Reply #49 on: April 27, 2011, 08:23:15 AM »

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.

Logged

h.a.c. van asten

  • T4
  • ****
  • Posts: 322
Re: Navigating the LOP with the offset method.
« Reply #50 on: April 27, 2011, 10:40:24 AM »

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.
Logged

Ric Gillespie

  • Executive Director
  • Administrator
  • *
  • Posts: 5543
  • "Do not try. Do or do not. There is no try" Yoda
Re: Navigating the LOP with the offset method.
« Reply #51 on: April 27, 2011, 11:10:34 AM »

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.
Logged

h.a.c. van asten

  • T4
  • ****
  • Posts: 322
Re: Navigating the LOP with the offset method.
« Reply #52 on: April 27, 2011, 03:26:58 PM »

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.
Logged

Ric Gillespie

  • Executive Director
  • Administrator
  • *
  • Posts: 5543
  • "Do not try. Do or do not. There is no try" Yoda
Re: Navigating the LOP with the offset method.
« Reply #53 on: April 27, 2011, 06:46:10 PM »

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.
Logged

Ashley Such

  • T3
  • ***
  • Posts: 119
Re: Navigating the LOP with the offset method.
« Reply #54 on: April 27, 2011, 07:01:45 PM »

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? ???
Logged

h.a.c. van asten

  • T4
  • ****
  • Posts: 322
Re: Navigating the LOP with the offset method.
« Reply #55 on: April 27, 2011, 09:56:08 PM »

R.G. At 2014 GMT she additionally said : "..We are running north and south .. "
Logged

h.a.c. van asten

  • T4
  • ****
  • Posts: 322
Re: Navigating the LOP with the offset method.
« Reply #56 on: April 27, 2011, 10:28:30 PM »

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.
Logged

Thom Boughton

  • T2
  • **
  • Posts: 89
  • Infinite Rider on The Big Dogma
Re: Navigating the LOP with the offset method.
« Reply #57 on: April 28, 2011, 01:01:29 AM »

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
TIGHAR #3159R
 
Logged

h.a.c. van asten

  • T4
  • ****
  • Posts: 322
Re: Navigating the LOP with the offset method.
« Reply #58 on: April 28, 2011, 02:26:00 AM »

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.
Logged

h.a.c. van asten

  • T4
  • ****
  • Posts: 322
Re: Navigating the LOP with the offset method.
« Reply #59 on: April 28, 2011, 02:51:14 AM »

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.
Logged
Pages: 1 2 3 [4] 5 6 ... 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