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Re: Did a precessing gyro lead to the loss of Earhart?
From: Jackie Ferrari
Date: 2010 Sep 16, 20:13 +0100
From: Jackie Ferrari
Date: 2010 Sep 16, 20:13 +0100
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 LaPookDate: 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 > ---------------------------------------------------------------- > NavList message boards and member settings: www.fer3.com/NavList > Members may optionally receive posts by email. > To cancel email delivery, send a message to NoMail[at]fer3.com > ---------------------------------------------------------------- > > >