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    Re: Bubble horizon
    From: Robert Eno
    Date: 2002 Dec 17, 01:09 -0500

    Hello Paul,
    
    I had a look at the C.Plath bubble attachments in the Celestaire catalogue.
    I am very, very surprised and delighted to see that Ken managed to find
    some. I bought my first one (a used model) from Ken in the early nineties
    and never regretted the purchase.
    
    So, I strongly suggest that if you are serious about having the best marine
    sextant bubble attachment ever made, you buy this one; more so because the
    catalogue indicates that they've never been used. If I had some extra $$, I
    would buy another one for myself. It should also be noted these attachments
    lend themselves to repairs. I had a machinist friend fabricate special
    wrenches to remove the fluid re-fill cap and the sight glass nuts. You
    seldom have to re-fill the fluid by the way, if the unit is sealed properly.
    $950 is steep but it is not an unreasonable price to pay for this instrument
    when you consider that models of lesser quality go for more. Ken is not
    giving me a commission for salesmanship by the way.
    
    I have tried the Kollsman - bought one for $65 US several years ago. It's a
    very nice sextant, however, it is hard to hold without the mount. I have it
    in my collection simply for bragging rights (and it is a nice example of
    aircraft sextant technology). I used one in a C130 Hercules transport in the
    mid nineties whilst I was winging my way from Greenland to south Baffin
    Island. It didn't take much to get the navigator to let me have a crack at
    it. It was a neat experience, albeit a humbling one. Came out of it with a
    new respect for air navigators. No more turning my nose up at the flyboys.
    
    The biggest drawback to the Kollsman is the reflective "pellicle" which is
    situated inside of the body of the unit which transmits the image of the
    celestial body to the eyepiece. Once it starts to absorb moisture it
    wrinkles and spoils the view. For this reason, the Kollsman is fitted with a
    removable cylinder which contains a desiccant to keep the pellicle dry and
    taut. Every once in a while, you must remove this cylinder, dry out the
    desiccant and replace it. Unfortunately for me, I left it for to long and
    the pellicle self-destructed. I have not made much of an effort to find a
    replacement so if you ever come across a supply of them, let me know.
    
    The Mark IX is simply the best bubble sextant ever made. The bubble unit
    inside, by itself is the best system that I have ever seen. If one could rig
    a marine sextant bubble attachment using the Mark IX system, it would
    surpass even the C.Plath. What is really nice about the MK IX and which sets
    it apart from other bubble sextants and bubble attachments is that it can be
    used for even dim stars. There is a Lucite ring around the bubble chamber
    which, when the electric illumination system is activated, produces a halo
    effect around the sight view and the bubble. In this way the illumination
    system does not wash out the light from dim stars such as Polaris. The MK IX
    bubble system is adjustable.
    
    The only drawback to this instrument is that you cannot easily determine
    things like index and instrument errors, save for taking hundred of sights
    from a known location and then graphing the results. They do not lend
    themselves well to operator repairs. The only person I know of who know/knew
    how to fix these things was a fellow in Australia who may or may not be with
    us anymore. He was over 80 years of age ten years ago. I have not heard from
    him in a while. Celestaire use to carry the MK IX and used to have the
    equipment to calibrate it, but I do not know if they still have this stuff.
    Perhaps Mr. Gebhart can tell us.
    
    In the final analysis, and considering all factors (accuracy, ease of use,
    reparability, calibration etc.) my vote is with the C.Plath bubble
    attachment. If you can get one, snap it up post haste. They are getting
    rarer and rarer although I have a strong suspicion that the US military has
    a warehouse full of surplus Plaths somewhere in a secret location...
    
    Hope this helps.
    
    
    Robert
    
    
    
    ----- Original Message -----
    From: Paul Hirose 
    To: 
    Sent: Monday, December 16, 2002 11:42 PM
    Subject: Re: Bubble horizon
    
    
    > Robert Eno wrote:
    > >
    > > This bubble attachment did not have a provision for adjusting the size
    of
    > > the bubble. In my estimation, it was not worth the price. It appears to
    me,
    >
    > Come on, don't be coy. Who made that poorly designed bubble horizon?
    > Cassens & Plath?
    >
    > > Contrast this to a C.Plath bubble attachment which does have a provision
    for
    > > adjusting the size of the bubble. One can obtain very accurate
    positioning
    > > data when using this device. Unfortunately, they are relics of the past.
    I
    > > don't think that they have been manufactured since the early 1960's but
    are
    > > still available from time to time, from antique and used sextant
    dealers.
    >
    > The 2003 Celestaire catalog has C. Plath bubble horizons for $950.
    > They are German military surplus, never issued.
    >
    > > best, the most accurate and the easiest to use, ever, is the RAE Mark IX
    > > aircraft sextant. It wins hands down in all categories.
    >
    > I would like to hear about the good and bad points of the bubble
    > sextants you've tried. Recently I won a Kollsman periscopic on eBay
    > for about $100. Hasn't arrived yet. Back when I was in the USAF I
    > played with these a couple times but never dreamed I'd own one.
    >
    > Thinking about buying an AN-5851 (Navy Mark V) bubble sextant as well.
    > There are plenty on eBay and the prices are good.
    >
    > I've seen British Mark IXs from time to time but know little about
    > them. If they are the cat's meow like you say, maybe I ought to get
    > one too.
    >
    > In an article I saw on the Web, one old air navigator said he found
    > the Kollsman periscopic sextants a real breakthrough. No more
    > scratched, dirty astrodomes with their refraction corrections and
    > blowout hazard in pressurized planes. The periscopic sextant tube
    > slipped into a mount in the top of the cockpit and was held securely
    > and conveniently for the navigator. The mount had an azimuth scale
    > which was visible through the sextant. You could use that to help find
    > stars, or get an accurate true heading.
    >
    > Unfortunately I won't have the luxury of a mount, so I'll have to get
    > used to freehand use or set it on a support. At least I've handled
    > these sextants before, so I know what to expect.
    >
    > KC-135s used to have flat windows on top of the plane near the bubble
    > sextant port. I heard they were replaced with metal plates after an
    > accident in the 80s (?) in which a nav got sucked out to his death.
    > Such stories are often apocryphal, but there may be some truth to this
    > one. The one -135 I worked on in my career, in the 1990s, did have the
    > window openings plated over. In fact, I heard the story of the nav
    > from one of the crew chiefs on that bird, after he noticed me playing
    > with the periscopic sextant. What a way to die.
    >
    >
    
    
    

       
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