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    Re: A12 vs A8-A sextants
    From: David Pike
    Date: 2020 Apr 28, 03:41 -0700

    Geoffrey Kolbe you wrote: Dave P wrote: "Rather than stab in the dark, we can talk about this more when you tell us which sextant and which manual." Manual is dated 23 January 1946. It is for the types A-6, A-6A, A-8 and A-8A (Bauch & Lomb) aircraft sextants. "Published under joint authority of the Commanding General, Army Air Forces, the Chief of the Bureau of Aeronautics, and the Air Council of the United Kingdom."  


    In my enthusiasm to get locked onto your mention of RAF sextants, I omitted to congratulate you on your excellent analysis of the A8 vs the A12 sextants.  Well done!  I can’t comment on the A8, because I haven’t used one, but your experience with the A12 ties in with mine.  Attempting to take out index error by wiggling the bubble chamber locating screws doesn’t seem to do much, and investing in a very expensive set ‘Bristol’ keys (Officer’s Allen Keys!) to adjust the index mirror is likely to make matters worse rather than better.   

    My A12 bubble is a bit sad at the moment.  I stuck a tiny black spot on the top centre as a kind of fiduciary mark and made a mess of it.  I should have just tested the idea first with a spirit-based pen, but we live and learn.  I can’t top up the bubble chamber with Zippo fuel  either, because last time I did it, I put a spot of varnish over the screw to seal it, and it’s worked its way down onto the tiny ball bearing and glued it in (acetone to release it maybe?).  I’m coming to the conclusion that if you’ve got fingers like cold cooked sausages like me, the best technique with old aircraft sextants is to calibrate them as best you can without fiddling and accept what you get.  If you have to carry several minutes of index error, so be it, it doesn’t do any harm so long as you’ve got the nerve to apply it each time you use the sextant.  

    I’m looking into a possible RAF connection with the A8 and 12, but as I said, I feel sure that any A8s which might have been used by the RAF were probably strays or gifts in hope of a larger order.  In the meantime, Deborah Warner at the Smithsonian is a good source of information on US aircraft sextants including the rivalry between the US and the UK developers in the 1930s and 40’s http://www.artefactsconsortium.org/Publications/PDFfiles/Vol5Mil/5.07.Military-Warner,SextantsGr75ppiFFFWEBF%20-%20Copy.pdf.

    Also, if you can get hold of it, Jeff Jefford’s ‘Observers and Navigators and other Non-Pilot Aircrew in the RFC, RNAS and RAF’ is an excellent source of information on the training of RAF  Observers by Pan American Airways and the USN in 1940 and 41, where they definitely used US sextants and the training of Navigators (after O changed to N) in Canada later. (the Grub Street version ISBN 10: 1909808024 ISBN 13: 9781909808027 is best)  DaveP

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