Advanced search  
Pages: 1 ... 7 8 [9] 10   Go Down

Author Topic: Working the Flight backwards  (Read 110389 times)

Ric Gillespie

  • Executive Director
  • Administrator
  • *
  • Posts: 5428
  • "Do not try. Do or do not. There is no try" Yoda
Re: Working the Flight backwards
« Reply #120 on: September 11, 2011, 08:34:18 AM »

Noonan (as recorded by P.Mantz , see Hollywood Pilot by Dwiggins) let the offset track fly by time-distance DR on the ETA via direct course to destination...

I have no idea what that sentence means.  On page 100 of Hollywood Pilot, Dwiggins relates Mantz's of the flight from Oakland to Honolulu.  With guidance from Manning, Noonan and Mantz, Earhart used the Bendix loop to fly a straight-in course.  "For the first time, AE had a chance to try out the Bendix loop antenna direction finder. Noonan asked her to hold Makapu beacon 'ten degrees on the starboard bow' - a heading of 252 degrees.  She went about it calmly, professionally, rotating the antenna loop on top of the cockpit until the compass needle swung over to 10 degrees - ten degrees to the right of where the electra was pointed.  This, she knew, was a wind drift correction Noonan had figured out."

Dwiggins had that last bit screwed up.  The procedure he describes would be correct if Earhart had an Automatic Direction Finder (ADF) but the read-out for the Bendix RDF was a simple left-right needle.  Dwiggins had a lot of things screwed up.  He has Manning annoying Earhart by coming forward to take star sightings through the hatch above her head. There is no way the cockpit hatch could be opened in flight without it tearing off the airplane.
Logged

h.a.c. van asten

  • T4
  • ****
  • Posts: 322
Re: Working the Flight backwards
« Reply #121 on: September 11, 2011, 11:56:41 AM »

Mantz interrogated Noonan about the risks of flying to Howland Island . Noonan replied using the One Line Approach (calling it "deliberate error" , the term used by Chichester , 1931) by offset from an on course point , established by an LOP ("from a series of sun observations"), this to be advanced over destination . The offset should be , he said , " e.g. left or right 10 or 20 degrees" and then : "When your time comes turn left or right and fly until you find your  destination" .  Thence , so to see , he (usually ?) planned to fly the offset lane by DR to the turn off point without further celnav . (Hollywood Pilot , 1967 , p. 105) . If he so did in the road of Howland he may have easily hit a line westwards of the over Howland (erroneous position) line , if his offset lane initial point was actually further west than precomputed , having the island on the starboard now @ ETA , in lieu of running it in sight below the Aircraft Progression Line . This does btw not affect the possibility to eventually fly to the Phoenix Group by setting course from a point of the position line by terrestrial triangulation and compass .
Logged

Ric Gillespie

  • Executive Director
  • Administrator
  • *
  • Posts: 5428
  • "Do not try. Do or do not. There is no try" Yoda
Re: Working the Flight backwards
« Reply #122 on: September 11, 2011, 12:44:48 PM »

The offset should be , he said , " e.g. left or right 10 or 20 degrees" and then : "When your time comes turn left or right and fly until you find your  destination" .  Thence , so to see , he (usually ?) planned to fly the offset lane by DR to the turn off point without further celnav . (Hollywood Pilot , 1967 , p. 105)

In my copy of Hollywood Pilot (first edition) the conversation you describe is on page 118-119. According to Dwiggins, according to Mantz's recollection, Noonan did describe the offset method as the way to find your destination "when you only have one star, or only the sun, and you can't get a second line of position to intersect the first on and give you a fix."  That, of course, does not describe the situation Noonan expected to face on the flight to Howland.  The "second line of position to intersect the first one" was expected to be a radio bearing provided either by Itasca or by the aircraft's own radio direction finder.

Let's say, for the sake of argument, that Noonan used an offset to the left (north) just to be safe.  They hit the advanced LOP, turn right and fly until AE says "We must be on you but cannot see you."  An hour later, having still failed to get any help from RDF, she says, "We are on the line 157 337 ... we are running on line north and south."
The whole point of using an offset is to be sure which way you need to fly on the line to reach your destination. If they used an offset why were they flying north and south on the line?
Logged

h.a.c. van asten

  • T4
  • ****
  • Posts: 322
Re: Working the Flight backwards
« Reply #123 on: September 11, 2011, 02:01:01 PM »

I have the Dwiggins paperback . Assume that about sunrise the latitude error was expected 5% of 300 mls , and the longitude error was expected 7% (both figures for experienced navigator) , then the combined possible error was the square root of the sum of the squares : (25 + 49)^1/2 =  8.6% of 300 mls = 26 mls . The circle of uncertainty @ the position fix has a 26 miles radius . For a northwards offset you should take the southernmost turn off point within visibility range of destination , say 10 miles . Thence , the northernmost turn off point will be (10 mls + 2 x 26 mls) = 62 mls off your island on the position line , to acquire a secure approach operation . If consequently , your latitude @ fix was more than 26 mls northwards w.r.t. your DR , say 40 mls , then you will not see the island @ ETA , and you continue southwards . When no result you turn northwards to look if you were more than 26 mls southwards of DR latitude @ fix , which case you have left the island behind you when turning off . You can continue flying north and south as far as your fuel permits , or , alternatively , 2 evasion operations remain : 1. Fly a search pattern , 2 . Divert to another defined landpoint in your chart , both if fuel permits . If fuel is low : stay one the line so that rescue parties have a first target to find you .
Logged

Gary LaPook

  • T5
  • *****
  • Posts: 1624
Re: Working the Flight backwards
« Reply #124 on: September 11, 2011, 09:43:53 PM »

Noonan (as recorded by P.Mantz , see Hollywood Pilot by Dwiggins) let the offset track fly by time-distance DR on the ETA via direct course to destination...

I have no idea what that sentence means.  On page 100 of Hollywood Pilot, Dwiggins relates Mantz's of the flight from Oakland to Honolulu.  With guidance from Manning, Noonan and Mantz, Earhart used the Bendix loop to fly a straight-in course.  "For the first time, AE had a chance to try out the Bendix loop antenna direction finder. Noonan asked her to hold Makapu beacon 'ten degrees on the starboard bow' - a heading of 252 degrees.  She went about it calmly, professionally, rotating the antenna loop on top of the cockpit until the compass needle swung over to 10 degrees - ten degrees to the right of where the electra was pointed.  This, she knew, was a wind drift correction Noonan had figured out."

Dwiggins had that last bit screwed up.  The procedure he describes would be correct if Earhart had an Automatic Direction Finder (ADF) but the read-out for the Bendix RDF was a simple left-right needle.  Dwiggins had a lot of things screwed up.  He has Manning annoying Earhart by coming forward to take star sightings through the hatch above her head. There is no way the cockpit hatch could be opened in flight without it tearing off the airplane.
---------------------------

Are you sure about that Ric, I thought she had to listen for the null?

I have attached a copy of the 1941 Bendix catalog page that shows pictures of the components of the MN-13 Bendix RDF system, I don't see any left-right needle. It appears that this would have been the system installed in Earhart's plane since it could be used with the already installed radio receiver. There are other RDFs shown in this catalog that do have left- right indicators but those also have dedicated RDF radio receivers with outputs to drive the left-right indicator.

From the picture of Earhart mugging with the RDF loop, is is clear that she had the lower sensitivity nine inch loop, a poor choice for this flight.

I also notice that this RDF had provision for an input from a sense antenna to eliminate the 180 degree ambiguity. It is possible that the belly antenna was this sense antenna.

Hmmm, as I am typing this it just occurred to me that perhaps the loss of the belly sense antenna could have caused AE's RDF problem. The MN-13 has a frequency range up to 1500 kcs but that is probably a limit on the MN-13 loop amplifier but it apparently did work with the 7500 kcs signal but was only able to send a weaker signal to the radio receiver due to that signal being above the designed frequency range of the MN-13 loop amplifier.  Earhart's radio apparently was able to receive the 7500 kcs signal but she couldn't get a null. It is just possible, that although not optimized for 7500 kcs, that this loop might have had enough directivity to have provided a bearing to Itasca. The MN-13 has a switch which selects the sense antenna or leaves it out of the process. With the sense antenna connected and the selector switch set in the uni-directional position, this equipment eliminates the 180 degree ambiguity and produces only one null instead of the usual two nulls, spaced 180 degrees apart.

So what happens if Earhart sets the switch to the uni-directional position but there is no signal coming in on the sense antenna terminal because the antenna was lost? What would Earhart hear in her headphones? No null?  Two nulls? I don't know the answer to this question. I do know, that with an ADF, that without the sense antenna the needle just spins around and around, never settling on a bearing. I wonder now if Earhart could have been saved if only she had placed that switch back into the bi-directional position and used the normal procedure to manually eliminate the 180 degree ambiguity.

Ric, has Brandenburg looked into this?

gl
« Last Edit: September 11, 2011, 10:58:16 PM by Gary LaPook »
Logged

h.a.c. van asten

  • T4
  • ****
  • Posts: 322
Re: Working the Flight backwards
« Reply #125 on: September 12, 2011, 12:07:40 AM »

If the sense aerial is lost the RDF operator  "hears a null" , but ambiguity is not locked out and it can not be determined if the transmitting station is ahead of you , or behind , resp. to port or starboard . In WW II a B24 aircraft (Lady Be Good) ended up 600 mls in the North African Desert by the same failure . Earhart said to hear no null at all which thence must be attributed to other circumstances (transmitter too close , no sharply tuned receiver etc.) .
Logged

Gary LaPook

  • T5
  • *****
  • Posts: 1624
Re: Working the Flight backwards
« Reply #126 on: September 12, 2011, 01:24:53 AM »

Noonan (as recorded by P.Mantz , see Hollywood Pilot by Dwiggins) let the offset track fly by time-distance DR on the ETA via direct course to destination...

I have no idea what that sentence means.  On page 100 of Hollywood Pilot, Dwiggins relates Mantz's of the flight from Oakland to Honolulu.  With guidance from Manning, Noonan and Mantz, Earhart used the Bendix loop to fly a straight-in course.  "For the first time, AE had a chance to try out the Bendix loop antenna direction finder. Noonan asked her to hold Makapu beacon 'ten degrees on the starboard bow' - a heading of 252 degrees.  She went about it calmly, professionally, rotating the antenna loop on top of the cockpit until the compass needle swung over to 10 degrees - ten degrees to the right of where the electra was pointed.  This, she knew, was a wind drift correction Noonan had figured out."

Dwiggins had that last bit screwed up.  The procedure he describes would be correct if Earhart had an Automatic Direction Finder (ADF) but the read-out for the Bendix RDF was a simple left-right needle.  Dwiggins had a lot of things screwed up.  He has Manning annoying Earhart by coming forward to take star sightings through the hatch above her head. There is no way the cockpit hatch could be opened in flight without it tearing off the airplane.

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

Certainly one, and possibly three sextant observation were taken from the cockpit, if not through the hatch then through the windshield. The relative bearings of these shots were 320° (40° left of the nose, 341° (19° left of the nose,) and 36° right of the nose. These relative bearing are based on the azimuth of the stars shot and the track on the plane. They may very a  bit based on any wind correction angle being used.  The 341° relative bearing observation certainly was taken from the cockpit and the other two would have been easier from the cockpit than from the nav station aft.

I have attached a table showing the bearings of the fourteen celestial observations taken on the flight to Hawaii.

gl
Logged

Gary LaPook

  • T5
  • *****
  • Posts: 1624
Re: Working the Flight backwards
« Reply #127 on: September 12, 2011, 01:53:10 AM »

The offset should be , he said , " e.g. left or right 10 or 20 degrees" and then : "When your time comes turn left or right and fly until you find your  destination" .  Thence , so to see , he (usually ?) planned to fly the offset lane by DR to the turn off point without further celnav . (Hollywood Pilot , 1967 , p. 105)

In my copy of Hollywood Pilot (first edition) the conversation you describe is on page 118-119. According to Dwiggins, according to Mantz's recollection, Noonan did describe the offset method as the way to find your destination "when you only have one star, or only the sun, and you can't get a second line of position to intersect the first on and give you a fix."  That, of course, does not describe the situation Noonan expected to face on the flight to Howland.  The "second line of position to intersect the first one" was expected to be a radio bearing provided either by Itasca or by the aircraft's own radio direction finder.

Let's say, for the sake of argument, that Noonan used an offset to the left (north) just to be safe.  They hit the advanced LOP, turn right and fly until AE says "We must be on you but cannot see you."  An hour later, having still failed to get any help from RDF, she says, "We are on the line 157 337 ... we are running on line north and south."
The whole point of using an offset is to be sure which way you need to fly on the line to reach your destination. If they used an offset why were they flying north and south on the line?

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

Here are two links to illustrations of how celnav is actually done in fight. The first one ilustrates the landfall (offset) procedure and the second general in flight celnav also showing how wind is determined between two fixes.

https://sites.google.com/site/fredienoonan/other-flight-navigation-information/recent-landfall-approach

https://sites.google.com/site/fredienoonan/other-flight-navigation-information/in-flight-celestial-navigation

gl
Logged

h.a.c. van asten

  • T4
  • ****
  • Posts: 322
Re: Working the Flight backwards
« Reply #128 on: September 12, 2011, 02:41:40 AM »

You can not , btw , eliminate the ambiguity by manual intervention , that was why the B 24 went astray , the navigator made the wrong guess having his air base behind him north  instead of ahead south . The sense aerial together with the loop quenches signals from one direction by the interferention of two different electromagnetic field graphs .
Logged

Ric Gillespie

  • Executive Director
  • Administrator
  • *
  • Posts: 5428
  • "Do not try. Do or do not. There is no try" Yoda
Re: Working the Flight backwards
« Reply #129 on: September 12, 2011, 08:01:10 AM »

Are you sure about that Ric, I thought she had to listen for the null?

Yes, she had to listen for the null.  That's what she meant when she said "unable to get a minimum."

I have attached a copy of the 1941 Bendix catalog page that shows pictures of the components of the MN-13 Bendix RDF system, I don't see any left-right needle.

In the "Radio" section of the August 1937 issue of Aero Digest magazine - "Newest Developments in the Field of Aircraft Radio" - is an article entitled "Bendix D-Fs." I'll send you a PDF.  The article begins, " Proven in several years of service in military aeronautics, Bendix aircraft radio direction finders have recently been made available commercially, in four models - MN-1, MN-3, MN-5 and MN-7."  Earhart's appears to have been an MN-5. 
Unfortunately, there is no known photo of the instrument panel at the time of the second world flight attempt.  In The Miami Cockpit Photo I showed that the photo Elgen Long claimed was taken in Miami - wasn't.  It was probably taken in Burbank early in February or March 1937. There was a Bendix left-right needle on the panel at that time (immediately in front of the pilot and directly over the turn & bank).

I also notice that this RDF had provision for an input from a sense antenna to eliminate the 180 degree ambiguity. It is possible that the belly antenna was this sense antenna.

This dead horse has been flogged a hundred times. The starboard side belly antenna was on the airplane when it was delivered in July 1936 - long before it had any kind of direction finding system.  When the Hooven Radio Compass was installed in October 1936 a parallel second belly antenna appeared on the port side - almost certainly a sense antenna for the Hooven unit.  When the Bendix MN-5 replaced the Hooven Radio Compass immediately prior to the first world flight attempt, the port side belly antenna remained in place -possibly as a sense antenna for the new Bendix unit.  After the airplane was repaired following the Luke Field accident it had only the original starboard side antenna.

« Last Edit: September 12, 2011, 09:52:05 AM by Ric Gillespie »
Logged

Bob Brandenburg

  • TIGHAR member
  • *
  • Posts: 33
Re: Working the Flight backwards
« Reply #130 on: September 12, 2011, 09:11:38 AM »

LF/MF loop systems don't do well with skywave HF signals, which can have a high degree of horizontal polarization.   

As for directional ambiguity, that would be an issue only if the navigator didn't know the general direction of the signal source.  That would  not have been the case on the approach to Howland from the west -- before hitting the LOP.   Howland was somewhere forward of the aircraft. 

Bob

 
Logged

Gary LaPook

  • T5
  • *****
  • Posts: 1624
Re: Working the Flight backwards
« Reply #131 on: September 12, 2011, 02:49:23 PM »

LF/MF loop systems don't do well with skywave HF signals, which can have a high degree of horizontal polarization.   

As for directional ambiguity, that would be an issue only if the navigator didn't know the general direction of the signal source.  That would  not have been the case on the approach to Howland from the west -- before hitting the LOP.   Howland was somewhere forward of the aircraft. 

Bob
----------------------
Ric sent me that magazine article and it makes very interesting reading. To use the uni-directional feature the pilot must tune the loop amplifier in such a way that the loop output is equal to the sense antenna output which might be a complication beyond Earhart's abilities, Manning did this tuning for her on the approach to Hawaii. It is also possible, that because the 7500 kcs was so much higher than the design frequency band for the loop amplifier, than it would not even have been possible to equalize the two signals.

So Bob, my question is, what would she have heard in her earphones if she had the RDF set to uni-directional and :
1) she had not been able to equalize the two signals; 2) if the sense antenna was inoperative due to some damage or due to not being installed (any idea where the sense antenna is on the plane? I originally assumed that there was no sense antenna since they are not needed with a manual RDF.)

Same question if she switched it to bi-directional?  No signal received? we know this isn't the case since she reported receiving the signal. Equal signal all around the dial? one null? two nulls? one strong null and one weak null?

Any ideas?

gl

If she had the RDF set to uni-directional








-
Logged

Bob Brandenburg

  • TIGHAR member
  • *
  • Posts: 33
Re: Working the Flight backwards
« Reply #132 on: September 12, 2011, 03:33:14 PM »

If she was hearing 7500, which would be a skywave signal, the horizontal polarization component of the downcoming field could dominate, preventing her from getting a null.   She could hear the signal regardless of what sense mode she selected, but would be unable to get a null.  There's a reason why loop direction finder bands were in the low- and medium-frequency regions  -- signals there are vertically polarized, and tend to be that way when received within groundwave range. 

Another possibility is that the signal duration was too short for her to get a null.

Bob



Logged

Gary LaPook

  • T5
  • *****
  • Posts: 1624
Re: Working the Flight backwards
« Reply #133 on: September 15, 2011, 12:35:11 AM »

If she was hearing 7500, which would be a skywave signal, the horizontal polarization component of the downcoming field could dominate, preventing her from getting a null.   She could hear the signal regardless of what sense mode she selected, but would be unable to get a null.  There's a reason why loop direction finder bands were in the low- and medium-frequency regions  -- signals there are vertically polarized, and tend to be that way when received within groundwave range. 

Another possibility is that the signal duration was too short for her to get a null.

Bob
------------------------------
Hooven criticizes the Bendix equipment and claims that Earhart was lost because of the 180 degree ambiguity. Either he didn't realize that the Bendix equipment incorporated a sense antenna or he knew, that even though the Bendix could be equipped with a sense antenna, that this particular installation didn't.

Did the plane have a sense antenna installed for the RDF?

gl
Logged

Ric Gillespie

  • Executive Director
  • Administrator
  • *
  • Posts: 5428
  • "Do not try. Do or do not. There is no try" Yoda
Re: Working the Flight backwards
« Reply #134 on: September 15, 2011, 07:56:52 AM »

Did the plane have a sense antenna installed for the RDF?

There was only one belly antenna on the airplane during the second world flight attempt and it looks like the same antenna that had been on the airplane since it was delivered in 1936 - so no, I don't think there was a sense antenna for the RDF at the time of the Lae/Howland flight.
Logged
Pages: 1 ... 7 8 [9] 10   Go Up
 

Copyright 2018 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