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    Re: Amelia Earhart's aerial navigation
    From: Gary LaPook
    Date: 2009 Nov 19, 09:37 -0800

    Drift sights were improved over time. Chichester in 1931 didn't use any
    drift sight, he just estimated his drift on three different headings.
    See his chart to Norfolk island:
    He plotted the arcs and rays as his method of determining drift on three
    I have attached a photo of a pelorus/drift sight used in an open cockpit
    plane in 1930. It was mounted behind the cockpit looking aft.
    I have previously uploaded an excerpt of AFM 51-40 which discusses drift
    meters including the B-3 and the B-5 which is located here:
    The B-3 looked straight down and was more sophisticated than the B-5, it
    was gyro stabilized, but it is a very large instrument about 4 or 5 feet
    long. The B-5 looked slightly off to the side instead of straight down.
    If you examine WW 2 bombers you will often find the hole in the side of
    the plane at the nav station where the B-5 was mounted with its
    periscope tube extending through the side of the plane.
    I am also attaching several pictures of my B-5. The rotating computer
    dial on the left was used to compute ground speed by timing the movement
    of the surface object past two reticle lines but this was limited by the
    need to know your precise altitude.
    Ken Gebhart wrote:
    > Gary,  the drift sight I used in P2s looked directly below the
    > airplane, not toward the rear.  It had a capability to look rearward,
    > but that was to align it with the airplane.  Looking down, a rotatable
    > grid was aligned with white caps or waves, and the drift angle read.
    >  Looking rearward to any extent would introduce an error.
    > Ken Gebhart
    > On Nov 19, 2009, at 12:44 AM, Gary LaPook wrote:
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