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    Re: Lean And Mean Bubble Sextant Sun Sight
    From: Paul Dolkas
    Date: 2013 Mar 11, 20:07 -0700

    Greg-

     

    The Link A-12 doesn’t have any cross hairs (at least mine doesn’t). Nor would you want any. The cool thing about how they matched the radius of curvature in the cell to the geometry is that as you move the sextant, both sun image and the bubble move at the same rate, just like how a nautical sextant has the horizon & sun move together.  Makes taking a shot while the plane or boat is bouncing around.

     

    -Paul

     

    Paul Dolkas

    From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of Greg Rudzinski
    Sent: Monday, March 11, 2013 2:00 PM
    To: paul{at}dolkas.net
    Subject: [NavList] Re: Lean And Mean Bubble Sextant Sun Sight

     


    Paolo,

    I'm assuming that you have cross hairs in your field of view. It is not a good idea to mark an observation that is too far left or right of center as this puts the body off vertical. When viewing the body adjacent to the bubble try to always use the same side of the bubble for consistency. To simulate observations of actual flight try using the octant from the passenger seat of a car with a friend driving (no auto pilot ;-)

    Greg Rudzinski

    P.S. Generally I'm not happy with individual bubble intercepts over 9'. You should be able to improve on the 15' intercept.

    Lean And Mean Bubble Sextant Sun Sight
    From: Paolo Borchetta
    Date: Mar 11, 13:19 -0700
    Today I did a little experiment on finding the accuracy of a quick raw set of sun sights taken with my Link A-12 bubble octant to simulate actual in flight conditions when we might have to live with just keeping the sun and the bubble somewhere in the middle of the chamber without too much of a chance of perfect collimation.
    I shot two sun lines at two hours distance from the same position marked with GPS, purposely it was a no frill, quick sight reduction, time of start of the session, time of end, averaged, same for the 12-13 or so sights for the first sun line and 6-7 for the second. Purposely I didn't apply any correction for T/P although today was a bit hot.
    Target was a very quick time of the manual sight reduction and a quick plotting.
    Bottom line the cel. fix was 15 nmi from the GPS fix with bearing 119.7degT.
    BAD or NOT? One thing I noticed is that the second LOP was a bit more off then the first (checking with the USNO data).
    One initial observation that I can empirically make is that it appears that the more sights you take, the likely errors can offset each other, that could be the reason for the first LOP to be very precise as compared to the second.
    However I'd like to hear some more opinion on the whole exercise.
    Paolo


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