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    Re: Solstice Sun Lines
    From: David Pike
    Date: 2017 Dec 25, 15:31 -0800

    Antoine you wrote: Hence, as a final result, if the corrections linked to following a rhumb line are simply to be dropped as regards modern Airliners following "perfect" Great Circles, the Coriolis lateral displacement effects on apparent vertical always need to be accounted for. Do you agree ?

    Change of variation.  You’ll notice on our pre-comp form that there’s a box for change of variation, but I can’t ever remember using it. 
    This might be for one of three reasons.

    a.  We always used DG mode while observing.

    b.  We had a magic automatic variation setting unit which only a Brit could have designed.  It was like a plastic mould of the inside of someone’s ear, which rotated with longitude.  A little pecker, which moved with latitude, kept rattling against it and adjusted the variation sent to ‘the system’ as it sensed a change.

    c.  I sat in front of the radar; the Plotter had control of the compass switches. 
    I usually did the pre-computing, the sextant work, and the checking of his element of the maths after the event, but he put the lines on the chart.

    2.  Coriolis.  Yes that’s always everywhere from bath-tubs emptying to high speed aircraft, especially high speed aircraft.  It usually required moving the LOP 6nm right of track in the northern hemisphere at the speeds and latitudes we flew at.  I used to be able to prove the maths; I’ll see if I can remember.  I used to start by imagining an aircraft flying north up a meridian from the equator.  At the Equator it has the sideways component in space of the Earths rotation.  If it maintains the meridian, that sideways component in space has reduced, so it must have experienced a deceleration.  However, it applies to all headings.  There’re a lot of r omegas in it, and I can’t find omega on my laptop.  Bill Lionheart, or Robin Stuart could explain it better than me.  Don’t forget to look for the eclipsing wingtips.  DaveP

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