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    Re: Kollsman averagers
    From: Werner Luehmann
    Date: 2009 Nov 25, 21:36 +0100

    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.
    > gl
    > 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
    > > observation.
    > >
    > > 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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