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    Re: Kollsman averagers
    From: Ronald P Barrett
    Date: 2009 Nov 26, 13:09 -0800
    As a former 60s USAF Navigator & Bombardier I was initially trained in the T-29 using the MA-1 for some 200+ hours + all the ground schooling. From 1961 on the USAF used most of the time, the Kollsman Periscopic with a two-minute averager (flown on or in all planes with the D-1 periscopic compass-ring-heading mount).

    The MA-1/2 sextant series was left to be flown on the planes with astrodomes well into the late 60s (like the AC-47s in Viet Nam, C-119Gs and C-123s). The one minute clock-averagers were all replaced with two-minute averagers:which was a very simple thing to do. The C-130s all had D-1s as did the C-141s.

    The USAF Navigator schools (1950-1965) were Harlingen and James Connally AFBs in Texas for Undergraduate Nav Training (UNT) and Mather AFB California for RadarNav&Bombardier training. From apx 1951 through 1965 all of the UNT schools used the MA-1/2 as we could carry it around and take training observations anywhere on base or at quarters. And all of the T-29s had at least one astrodome at that time. In the mid 50s as the D-1 arrived, astrodomes were replaced with D-1 mounts; so on some T-29s we had both an astrodome and a D-1 mount (often four total).

    In the 50s the USAF line aircraft for navs were transports and/or bombers. Back-seaters were at that time Radar Operators (ROs) and often had no nav equipment (F-82, F-94, F-89, and F-101B). Some ROs were never trained as navs at all. Later they were.

    The B-45 and B-47s used early D-1s. Over 2,000 B-47s were in the USAF from 1950-1963. The B-36 used the MA-1/2 as it had an astrodome just aft of the pilots from apx 1950-1960.

    Later the B-52 used the D-1 and MA-1 astrotrackers through the Hound Dog missile platforms. Loran was also utilized, as were the bombing radars. The B-58 was all integrated/doppler/radar/MA-1 astrotracker, that printed out its logs as you flew! The B-66 was a medium range bomber and the navs therein were like on the B-47 Navigator/Bombardiers and had over time the greatest of mix of nav tools. The Recci versions were the worst for mixes.

    On the transport side: the tactical (C-119, C-123) used various sextants depending on if they had an astrodome or the flight was long or short. On the longer range transports the sextant used was mostly determined by the fact that they plane was pressurized or not. Non-pressurized planes could well use an astrodome. On the pressurized (higher speed and higher altitude) lent itself to the use 100% of the periscopic D-1.

    The longer range transports (C-54, C-87, C-118, C-121, C-124) all started out with astrodomes and over time were modified to operate with D-1 mounts.

    The tanker fleets (KC-97 and KC-135) all used D-1 sextants. Remember there were almost as many tankers in the USAF as there were bombers.

    TWA had an incident that sealed the deal for the astrodome, when in the late 40s on a Connie, a nav was blown out of the plane by astrodome failure into the night over the Atlantic. The fix immediatley was a harnass the nav was to wear in the astrodome. The Airline History Museum (AHM) located at the Kansas City downtown Missouri USA airport has an engineering drawing of this on display.

    AHM also has the only full up International Navigator's exhibit that I know of in the world. The Museum features a full line of sextants out for the public to look at and a D-1 you can handle all you want. Ref. www.airlinehistorymuseum.com

    As to the 1-minute -vs- the 2-minute time averager. The occilations of all the planes were random, seldom typical and had as much to do with the autopilot(coupling) and aircraft aerodynamics as it did with atmospherics. Acceleration induced errors, passing cloud layers-moisture-ice, thermal layers, and earth transport were all added observation factors the navs kept in his head as he was shooting. Good example: Note the OAT is going up, the radar altitude is changing, the bubble horizon is being effected. Hummm; we are going across a jet stream!

    So yes two minutes of observation are far better than one! The fact that the European MAs only had a one minute averager I take means they bought the early MA (non-periscope) Kollsman and by the time the 2-minute upgrade was produced we were into planes needing a periscopic sextant+mount. So the upgrade of the early MA-1 was just not necessary. The D-1 just came with a full 2-minute averager.

    Many changes over time were also done to the periscopic D-1 and in the end they were used on the B-52 to feed backup observations to the ASQ-38 bombnav system, by a direct connection of the sextant to the computer system. In this case it was the EWO on the upper deck of the B-52 that took the observation, ID'd the celestial body, pushed a big black button on the timer-case and the Height Observed at that moment was fed to the computer. The Nav and the Bombardier in the B-52 sit in the basement of the B-52:refered to as the "Black Hole." To read how this was all done, read the B-52 navs book, "Flying form the Black Hole" by Robert O. Harder  A really great aviators read.

    As a flight nav I much prefered the ring of the bubble to the line of the mirror as the 360 view allowed me to judge all the factors I knew and felt were to be take into account on the observation. I was after all moving in all 6-axis!

    For other flight navigator's remarks go to www.afnoa.org They can speak with you directly. Please correct me if i got any of this wrong. Thanks.

    Ron Barrett, USAF Ret Nav and President Air Force Navigators Observers Association

    --- On Wed, 11/25/09, Gary LaPook <glapook@pacbell.net> wrote:

    From: Gary LaPook <glapook@pacbell.net>
    Subject: Re: [NavList 10813] Kollsman averagers
    To: navlist@fer3.com
    Date: Wednesday, November 25, 2009, 3:07 PM

    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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