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    Re: Kollsman averagers
    From: Gary LaPook
    Date: 2009 Nov 25, 13:07 -0800
    That's interesting, I wonder why only the American ones have a one minute averager. I have attached the operating manual and paragraph 2-12 clearly states that it only runs for one minute.


    Werner wrote:
    All my Kollsman periscopic sextants with the pendulous mirror (made in Germany
    and UK, under Kollsman licence) have the two minutes averager.
    Am Mittwoch, 25. November 2009 20:24:22 schrieb Gary LaPook:
     Even if the individual sights within the average are more accurate with
    the MA-1 than with the bubble instruments the mirror is still subject to
    the same accelerations as the bubble. These are of two types, random,
    caused by turbulence, and periodic, caused by the normal oscillations of
    the aircraft about its three axes such as phugoid and  dutch roll, with
    are sinusoidal in nature.  To eliminate or minimize the random errors
    "more is better." Taking a greater number of sights will result in a
    better average so taking more sights during the two minute period works
    for both bubble and mirror artificial horizons. The natural oscillation
    period of large aircraft is about 40 seconds and to minimize the errors
    caused by them it is best if the averaging period matches the period of
    the aircraft or exact multiples of it.  Two minutes matches three such
    periods while one minute is only one and a half periods and so will
    leave an inherent error in the data and the bias will depend upon where
    in the cycle the observation starts.
    douglas.denny@btopenworld.com wrote:
    May I offer a possible explanation?  It is only a guess however.
    The pendulous reference is easier to use than a bubble, being an horizon
    indicator rather than a circle in which the star is placed.  This I
    believe gives simpler and greater accuracy of observation than a bubble
    where the observer has to estimate the centre placement of the star in
    the bubble, and hence would require less time to complete an assessment
    of the star alignment with the reference.
    The oscillation period of a large aircraft I would have expected to be
    within a minute anyway,  so anything above one minute is not necessarily
    going to increase accuracy on this count. The only increase in accuracy
    would be if there are longer term accelerations present (such as an
    unwanted inadvertent side-slip) corrected within the time period of
    The only answer must be ultimately that tests would have been carried out
    by Kollsman and they probably found little difference in results for the
    one minute as opposed to two minute observation periods.
    Douglas Denny.
    Chichester.  England.

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