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There's a good photo of one set into the chart table of the china clipper with 
Fred working. Would there have been room for a chart table in the Electra?
Jackie
-original message-
Subject: [NavList] Re: Did a precessing gyro lead to the loss of Earhart?
From: Gary LaPook 
Date: 16/09/2010 7:42 pm

  I am watching a History Channel show about the loss of the "Lady Be 
Good," a B-24 lost in the Libian desert due to a navigational error. 
They were  showing artifacts recovered from the plane and they just 
showed the aperiodic compass!

gl



On 9/13/2010 2:20 PM, Gary LaPook wrote:
>
> I was looking at the documents on the Purdue archive website last 
> night and came across a photo of Earhart in the cockpit which is 
> attached. After zooming in on it I found even more convincing evidence 
> showing that a precessing gyro did not not cause the disappearance. 
> Earhart is tuning the radio with her left hand. Below her hand you can 
> see a white card. Zooming in on that card reveals that it is a compass 
> correction card which lists the compass deviation on various headings 
> and lists the headings to fly to correct for the measured deviation. 
> For example, according to this card, on a heading of south the 
> deviation is 1 degree west so you would steer 181 on the compass to 
> accomplish a 180 degree magnetic heading. All compasses in airplanes 
> are required to have their deviation determined (by "swinging the 
> compass") and must have such compass cards prepared. What makes this 
> particular compass card significant on the issue of gyro precession is 
> that at the top of the card it is marked "APERIODIC." This proves that 
> an aperiodic compass was installed in the airplane. Such a compass is 
> not the normal type of compass installed in airplanes and is not the 
> compass seen above the Cambridge analyzer above the instrument panel. 
> An aperiodic compass is much larger and more accurate and are read 
> while looking down on them, not through a window on the side as with a 
> normal aircraft compass. They are "aperiodic" because they do not have 
> a "period" meaning that they do not oscillate when disturbed like the 
> usual aircraft compass but remain dead steady. They are also called 
> "dead beat" compasses. They are also known as the "navigator's 
> compass" as different from the "pilot's compass" and can be seen at 
> the navigation stations in WW 2 aircraft. So Noonan would have been 
> referring to this much more accurate compass when checking the 
> headings that Earhart was flying and would not be looking at a 
> directional gyro.
>
> An aperiodic compass is read differently than the pilot's compass. In 
> order to eliminate the oscillating tendency, the mass of the compass 
> card was eliminated and instead there is just a compass needle. There 
> is rotating bezel with two lines across the face over the top of the 
> compass card that you set to the desired heading and you then turn the 
> airplane until the compass needle lines up with the lines on the 
> bezel. This is just like using a "marching" compass or a scuba diving 
> compass and it makes it easier to check that you are maintaining the 
> correct heading, no numbers to think about, just be sure the needle is 
> lined up.
>
> In addition, there is no reason to believe that a duplicate DG was 
> installed at the navigation station for Noonan's use and this would 
> have been unlikely since the purpose of a DG is for the pilot to use 
> it while making turns as the normal compass exhibits many errors when 
> the airplane is not flying straight and level at a constant speed. DGs 
> were powered by vacuum from a vacuum pump mounted on the engine so it 
> would have required running a vacuum line back to the nav station. I 
> have been through many WW 2 aircraft and have seen many aperiodic 
> compasses at the nav stations but I have never seen a DG there.
>
> gl
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