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    Re: Bubble Sextants
    From: Gary LaPook
    Date: 2008 Dec 16, 09:55 -0800

    Yes you do NEED an averager.
    
    The most perfected bubble sextants are probably the Kollsman
    instruments. The periscopic  instruments are too large for use in a
    small cockpit but the hand held Kollsmans, the MA-2 and the pendulous
    mirror MA-1, work real well in a small cockpit and I have taken many
    sights with these in cockpits as small as a Cessna 172. The bubble type
    can be used for sun sights without the need of a battery to illuminate
    the bubble during the day but the mirror type needs electricity to light
    up the reference reticle even during the day. Most of these have
    avergers.which work off of a wind up clockwork mechanism and do not need
    electricity to operate but the most modern have an electronic averager
    that is better than the clockwork models but do need 28 volts to
    operate. These would probably work on an aircraft 24 volt system which
    are actually  28 volts, when the engine is running, but I haven't tried
    this.  Even the clockwork averagers are more sophisticated than those in
    other sextants. The electronic avergers were put on the periscopic
    models in the 1980s but not on the hand held models. It is very simple
    to swap out these averagers and put an electronic one on the handheld
    sextants only requiring removing 4 screws, takes about 5 minutes. I did
    this with the MA-1 mirror type since it required electricity anyway. I
    left the mechanical averager on my MA-2 since I like the fact  that it
    will operate during the day without a power connection. The light bulbs
    that come in these require 28 volts and it is simple to make a power
    supply out of three nine volt batteries. If you prefer to make a power
    supply for 12 or 6 volts there are replacement light bulbs in these
    voltages. For about $25 you can make a 28 volt supply that works off of
    a 12 volt source. For practice on the ground you can buy a lawn
    sprinkler power transformer which puts out 28 volts.
    
    I also like the A-10A and I have flown across the ocean using this type.
    Its averger is not as sophisticated as the Kollsman's but is easy to
    use. Some people have had problems with them due to lack of lubrication
    during 50 years of non use but they can be refurbished in a couple of
    hours.
    
    Check with Celestaire to see if they have reconditioned sextants available.
    
    gl
    Peter Fogg wrote:
    > Welome Garry
    >
    > As an initial step, try entering some of those terms, eg; "bubble
    > sextant", etc, into the Search box at:
    > http://www.fer3.com/arc/
    >
    > There has been much discussion of these devices on this List and you
    > will find a wealth of information there.  Then feel free to pose
    > further questions here, as quite a few members use and have restored
    > such machines (although I'm not one of them!).
    >
    > On Tue, Dec 16, 2008 at 1:40 AM, JODIE COST  > wrote:
    >
    >     I am a commercial pilot here in Alaska and just starting my
    >     education in celestial navigation and I have two questions for the
    >     group.
    >
    >     As I have yet to find anyone teaching celestial navigation in the
    >     Anchorage area what home study courses or text do you recommend ?
    >
    >     Since I plan on using these skills on land and from the cockpit I
    >     an interested in a good bubble sextant, but which one? From what
    >     I've read, the R.A.F. MK IX seems to be highly recommended but I
    >     have yet to find a reliable source for them ( I won't use ebay for
    >     the purchase precision instruments). The U.S.Navy MK 5 and the
    >     U.S.A.A.F. A-14 are available in overhauled condition but don't
    >     seem to be as highly recommended as the MK IX.
    >
    >     Since I plan to use this sextant for navigation in flight would an
    >     averaging device be useful?
    >
    >     Thank you in advance for your help.
    >
    >     Garry Cost
    >
    >
    >
    >
    >     >
    
    
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