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    Re: Amelia Earhart's aerial navigation
    From: Ken Gebhart
    Date: 2009 Nov 19, 21:27 +0100

    Looking off to the side is still ok, but looking aft will give an
    error.  Flying 3 different headings was called a wind star.  It gave
    not only drift but the actual wind, thus enabling you to have a
    ground speed too.  We often simply estimated the ground level wind
    speed from the ocean state, and applied a 90 degree CW (or was it
    CCW?) correction for coriolis to get the actual wind affecting us.
    This was best done below 8000 feet alt.
    On Nov 19, 2009, at 6:37 PM, Gary LaPook wrote:
    > 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:
    > http://www.fer3.com/arc/img/110621.chart%20to%20norfolk.pdf
    > He plotted the arcs and rays as his method of determining drift on
    > three
    > headings.
    > 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:
    > http://www.fer3.com/arc/img/108625.afm%2051-40%20drift.pdf
    > 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.
    > gl
    > 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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