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    Re: Wind Velocity from Three Drifts
    From: Brian Walton
    Date: 2021 Mar 13, 05:39 -0800

      Tony,

       The plates normally used to illustrate Chichester's Tasman flights were produced by photographing his strip maps well after the event.  They are heavily retouched, to the extent that the edges of the strip map are not visible. The plotting lines needed to find a wind, were redrawn after the event to make the image suitable for printing; this explains their neatness.  They were redone on the ground. Chichester often states that vibration was such that he could hardly write.

       The handwritten notes must have been done on the photographed image. Both flght charts have identical explanations blocks. If the handwriting was done on a one-to-one scale replica, I guess the block would be about 9" wide. This gives a scale of about 6" to 1° of latitude, and a strip size of maybe 7 ' or 8' long, by about 11" wide.  That is big, but a roller map would stow down the right side of a Moth cockpit, and would just fit on top of Chichester's knee, protruding under the compass. Clumsy, and dangerous, but anything smaller makes the written numbers very small for someone needing glasses.

      The PLs shown on the strips go straight through the DR square, and do not show intercept plotting. They could have just been pre- calculated.

       I see no signs of the arithmetic needed to extract Sun data, and form dec, lat and lha to load a Bygrave, to calculate Z and Hc.  Chichester must have had another scratch pad.  When I used a Bygrave whilst also flying an open biplane solo, I also found it necessary to write down all the intermediate steps to avoid losing control by keeping eyes in for too long, and to enable checking.

    Brian Walton

       
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