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    Re: problems with artifical horizons
    From: Gary LaPook
    Date: 2012 Mar 20, 14:22 -0700
    Precompute the altitude of the sun or simply use a H.O. 2102- D.

    gl

    --- On Tue, 3/20/12, Randall.F.Morrow{at}kp.org <Randall.F.Morrow{at}kp.org> wrote:

    From: Randall.F.Morrow{at}kp.org <Randall.F.Morrow{at}kp.org>
    Subject: [NavList] Re: problems with artifical horizons
    To: NavList@fer3.com
    Date: Tuesday, March 20, 2012, 2:03 PM


    Alan,
       I use a mirror AH exclusively and have experienced the same issue you mention.   In every case it has turned out that the sextant was off vertical so the path of the sun's reflection in the AH did not cross my field of view.   Some exploratory "rocking" is often needed.    It is also helpful to take a guess at the altitude and pre-set the angle of the index arm to twice this guess.   That allows you to rock without having to combine rocking with turning the micrometer drum.    Even if your guess is just close, it may bring the glow of the sun's reflection into view, allowing you to 'dial it in'.  
       Just some general mirror AH advice; you must have a very accurate level to get good results.   The string levels you mention are not nearly accurate enough.  They are probably in the neighborhood of several tens of minutes and you need fractions of a single minute.    There have been many posts about this issue.   In addition, you may need to add some extra filtering in front of the horizon glass to decrease the sun's brilliance.   The normal horizon shades are not intended too look directly at a reflection of the sun.   There are films for this purpose, again mentioned in previous posts.
    Good hunting, Randy


    Randall F Morrow PT
    Kern County - Bakersfield


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    "Alan S" <alan202---.net>
    Sent by: navlist-bounce@fer3.com

    03/20/2012 01:29 PM

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    [NavList] problems with artifical horizons







    I have two of the things, one being the Davis AH, people here are likely familiar with this device.

    I also have a home made AH, first surface mirror, 10" x 10", on a levelable base. I level the assembly using a couple of string levels and reasonably fine leveling screws 120 degrees apart.

    This afternoon, I'm in the Pittsburgh area, I did a couple of sun shots with the Davis AH sitting on the ground. IE was 1.8 Min On Arc. Measured angles were 90 D 48 Min, and 90 D 25 Min, without correction. Time was around 1430, Eastern Daylight Savings Time. Nothing further wad done, that is the sights were not reduced.

    I next brought the mirror AH out for an airing. Setting is on the ground, leveling the unit, I saw reflected sun, but could not find sextant sun, that would be the sun that moves when the index arm is swung.

    I next tried setting the mirror ah on an elevated surface, using an ironing board, which is about 40" high. After leveling the assembly, I tried a sun shot, rocking the sextant while swinging the index arm. Reflected sun was visible, but alas could not find the sextant sun.

    I assume that I'm doing something wrong, but cannot figure out what that might be. Anyone here got any bright ideas or suggestions?

    Thanks in advance for same.

    Alan

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