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Author Topic: LOP nonsense  (Read 33914 times)

Ric Gillespie

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Re: LOP nonsense
« Reply #30 on: September 01, 2011, 02:25:10 PM »

I've got some more Irish Jokes to share if you want  :P

Probably need to start a new topic.  ::)
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Gary LaPook

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Re: LOP nonsense
« Reply #31 on: September 01, 2011, 06:30:23 PM »



The walking in the desert with a compass in the hand is not an applicable analogy of the AE/FN situation. 
They had two compasses, one magnetic one radio, a directional Gyroscope, and an autopilot.  Also a drift indicator.  To have set the autopilot to fly a course of 337 to  157 (with a wind correction of course) and maintain that course for 3 hours wouldn't be a monumental feat for a pilot, even one of limited skills as AE.  The ten percent error  in DR doesn't apply to an autopilot guided flight.  They wouldn't have missed Gardner by 35 miles or even close to that.

Please remember that the prime function of an autopilot is to detect and correct for small deviations from a preset heading in order to maintain that heading.  That is what "George" (the autopilot) did.  Fred and Amelia monitored their progress (altitude, speed, fuel, engine performance, etc.)

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Harry, I don't know where you got the idea that having an autopilot to maintain the plane's heading eliminated all the factors that causes errors in dead reckoning. The autopilot maintains heading by reference to the directional gyro and the autopilot's directional gyro is no more accurate than the pilot's directional gyro, they both drift. And each of these gyros need to be reset by the pilot from time to time to agree with the pilot's compass so the same inaccuracies from this compass and the inaccuracies of resetting the directional gyros are the same for Earhart and for the autopilot. The only factor addressed by by having "George" handle the controls is possible inattention of the pilot in maintaining the heading, which is a small factor in the overall dead reckoning accuracy equation. All the other factors remain the same, such as wind shifts and gusts and inaccuracy in determining the actual wind by use of the drift meter (see: https://sites.google.com/site/fredienoonan/topics/measureing-and-determining-wind-speed-and-direction-while-in-flight  Noonan had a MK II drift meter, not the more sophisticated gyro stabilized models) and the subsequent error in determining the wind correction angle. Do you remember back to your student pilot days when you worked out a wind correction angle on your E-6B and determined the heading to hold. Did your computed heading ever work out to be exactly right or did you have to adjust your heading to aim at land marks in order to stay on course? Same problem when flying over the ocean but with no land marks available to make heading adjustments to stay on course. Dead reckoning on land or on the sea can be much more accurate than in flight because the factors that affect such dead reckoning are smaller and can be more perfectly known. Attached is an excerpt from Navigation and Nautical Astronomy, the official navigation textbook at the U.S. Naval Academy, outlining these factors. In land navigation you do not have to stare at the compass but can pick out landmarks in the distance and aim for them which provides an accurate way to maintain your heading  and you also do this when flying over land using "pilotage" but there are no such landmarks at sea so you are required to rely only on your compass and on your directional gyro that your set by reference to your compass, and George can't see any landmarks either.

Air Force Manual 51-40 states the 10% estimate of DR accuracy and the formula in U.S. Navy Manual 216 gives the accuracy for a plane traveling at 130 knots, such as Earhart's Electra, as 17%. These estimates come from the Air Force and the Navy, and guess what, Air Force and Navy planes have autopilots! I don't know how much time you have spent flying over the ocean but it is a lot different than flying over land with pilotage. See: https://sites.google.com/site/fredienoonan/topics/accuracy-of-dead-reckoning

gl
« Last Edit: September 01, 2011, 06:35:40 PM by Gary LaPook »
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Harry Howe, Jr.

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Re: LOP nonsense
« Reply #32 on: September 01, 2011, 09:08:25 PM »


GARY
I don't recall having said that the autopilot "eliminated" the potential errors in flying P&DR, just that the autopilot is looking at and correcting for deviations from its set  heading on a continuous basis, thus easing the pilot's chore of hand-flying the plane to stay on course.  Of course the pilot must monitor for gyro drift and adjust it to the compass heading periodically  in order for the gyro and hence the autopilot to maintain a proper heading.

When I was studying for an inatrument rating my instructor was very strict.  I had to fly my course "under the Hood" by P&DR, using only the "Sacred Seven"(compass, directional gyro, attitudinal gyro, altimeter, vertical speed indicator, airspeed indicator. and turn coordinator) and watch .  All other instruments were covered over with camera lens covers until I was within range of my initial approach fix and could then use the VOR/DME/ILS. the ADF etc. to complete my landing.  I flew a three legged trip of over 600 nm and hit all three destinations on the money.  It was tense and stressful and my shirt was soaking wet but I made it.
No Worries Mates
LTM   Harry (TIGHAR #3244R)
 
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Gary LaPook

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Re: LOP nonsense
« Reply #33 on: September 06, 2011, 08:51:13 PM »



The walking in the desert with a compass in the hand is not an applicable analogy of the AE/FN situation. 
They had two compasses, one magnetic one radio, a directional Gyroscope, and an autopilot.  Also a drift indicator.  To have set the autopilot to fly a course of 337 to  157 (with a wind correction of course) and maintain that course for 3 hours wouldn't be a monumental feat for a pilot, even one of limited skills as AE.  The ten percent error  in DR doesn't apply to an autopilot guided flight.  They wouldn't have missed Gardner by 35 miles or even close to that.

Please remember that the prime function of an autopilot is to detect and correct for small deviations from a preset heading in order to maintain that heading.  That is what "George" (the autopilot) did.  Fred and Amelia monitored their progress (altitude, speed, fuel, engine performance, etc.)

--------------------------
I asked you before, Harry, how much time you had spent flying over the ocean, it's a lot different than flying over land. A pilot has a much more intimate relationship with the ocean, flying at five thousand feet and ninety knots than you do from the back seat of an airliner at 35,000 feet and 450 knots.

I have attached a photo of land about ten NM ahead, landfalls are always happy moments.

As a pilot you might appreciate a story I posted on a navigation website, here is the link:

http://www.fer3.com/arc/m2.aspx?i=108647&y=200906

gl


« Last Edit: September 07, 2011, 01:13:01 AM by Gary LaPook »
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