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    Re: Making an artificial horizon, and leveling thereof
    From: Gary LaPook
    Date: 2011 Jan 24, 15:15 -0800
    A pendulous mirror  supplies the horizontal reference in the MA-1 Kollsman artificial horizon sextant. The small mirror is mounted at the apex of a small cone and perpendicular to the axis of the cone. The rim of the cone is weighted and the cone is mounted on a needle bearing inside the apex of the cone, the whole is inside a liquid filled compartment for dampening. When we discussed a floating mirror in the past I suggested something similar with a weight like a keel hanging below the float holding the mirror so that the mirror would be leveled by the action of the keel not by the float.

    gl

    --- On Mon, 1/24/11, hch <h.halboth---.com> wrote:

    From: hch <h.halboth---.com>
    Subject: [NavList] Re: Making an artificial horizon, and leveling thereof
    To: NavList@fer3.com
    Date: Monday, January 24, 2011, 1:00 PM

    George,

    You are, of course aware that this subject was rather exhaustively explored on this List some time ago, proving the old adage to the effect that ... "what goes around, comes around". It is my recollection that the consensus of opinion at that time favored a screw leveled dark colored glass or Plexiglas ah, assuming that sufficiently accurate spirit levels could be obtained - as I recall, several excellent designs were appended to posts then submitted. This was, of course, intended as a substitute for the liquid, or mercury, ah both of which appear superior to any leveled reflective surface device.

    I recall posting at the time the significant, though not insurmountable, problem of keeping the centers of buoyancy and gravity aligned exactly both transversely and longitudinally in a floating arrangement of composite construction, so as to insure perfect equilibrium of floatation. It does seem rather extraneous to me to float a reflective device when the medium of floatation itself provides an adequate horizontal reflective surface to begin with.

    I have searched in vain to find these postings.

    Regards,

    Henry

    --- On Sat, 1/22/11, George Huxtable <george{at}hux.me.uk> wrote:

    From: George Huxtable <george{at}hux.me.uk>
    Subject: [NavList] Re: Making an artificial horizon, and leveling thereof
    To: NavList@fer3.com
    Date: Saturday, January 22, 2011, 3:05 PM

    Pictures I've seen of using an artificial horizon show the observer
    squatting cross-legged with the trough placed close in front on the ground,
    or else the trough placed on some sort of stool or table or tripod to bring
    it nearly against the sextant of an observer who is standing or perhaps
    stooping close by. Such closeness does not affect the reading, and would
    allow a smaller trough to be employed.

    I agree with Jeremy that it would be interesting to see how good such a
    rafted mirror could be, and I would not wish to put anyone off from trying
    it out. My intention was just to point out the problems that might arise,
    which would need to be overcome.

    George.

    contact George Huxtable, at  george{at}hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ----- Original Message -----
    From: <Anabasis75---.com>
    To: <NavList@fer3.com>
    Sent: Saturday, January 22, 2011 4:02 PM
    Subject: [NavList] Re: Making an artificial horizon, and leveling thereof


    |I would think that it would be a nice experiment for someone to build a
    | rafted mirror and float it in a artificial horizon and see what kind of
    errors
    | result since they can be compared to the known position.  We can then get
    | a  good set of numbers that indicate the real result of errors that
    George
    | pointed  out.
    |
    | I suspect that standing close to a artificial horizon would require you
    to
    | be quite low to the ground for lower altitudes.  Standing further back
    | would allow for you to stand erect and still see the sun.  This is
    assuming
    | that you don't put it on a reasonably level table.
    |
    | Jeremy
    |
    |
    | In a message dated 1/22/2011 5:29:46 A.M. Central Asia Standard Time,
    | george{at}hux.me.uk writes:
    |
    | Alan  wrote-
    |
    | "In any event, re "leveling", if I remember correctly, I read  somewhere
    | that this was NOT critical barring setting the thing up on a  steep
    | hillside, as "water, I suppose ditto for oil and or mercury, seeks  it's
    | own
    | level". Is this, or is this not the case re using an artificial
    horizon?"
    |
    | Yes, that's correct.
    |
    | In guessing at how little Mercury  one might be able to get away with, I
    | wrote, on 20 Jan-
    | "Mercury is  VERY dense (over 13) so an ounce of the stuff won't go far;
    | occupying about  2 millilitres. My guess is that  around 10-15 ml would
    be
    | required in  the trough of a sensibly-sized art. horizon, to make it easy
    to
    | use without  having to be over-careful about levelling. That would
    | correspond to 5 to 8  ounces. Maybe it would be possible to penny-pinch
    and
    | get way with somewhat  less."
    |
    | Since then, Bill Morris has actually tried it out, to see how  much
    Mercury
    | is required to get uniform coverage over the floor of an  artificial
    | horizon, without the liquid gathering into blobs, and has  assessed it as
    | 750 grams. This is about 55ml, which is very much more than  my own guess
    | that 10-15 ml might suffice. I've no doubt that he is right,  and accept
    | that judgment. There's nothing like practical trial, to get a  reliable
    | result.
    |
    | And normally, the levelling of such an artificial  horizon is very
    | non-critical, just as Alan says. It's only if skimping on  the Mercury,
    | that
    | any tilt might result in the liquid gathering in one  part of the trough,
    | leaving another bare, or affected by  meniscus.
    |
    | Alan continued-
    |
    | "I've done sun shots with mine, in the  spring and summer, standing in a
    | reasonably level parking area at our  apartment complex, taking sun
    sights
    | several hours apart, that when  plotted show quite small displacement
    | between my calculated fix and   GPS coordinates."
    |
    | This list thrives on numbers, Alan. Without numbers,  even approximate
    | ones,
    | a statement such as "show quite small displacement"  has no meaning to
    | anyone other than you.
    |
    | "Seems that orienting the  ah properly is an important factor, as is
    being
    | able to stand far enough  away from the ah so as to be able to see the
    | reflected and sextant  suns."
    |
    | That's a surprise, to me. On what basis do you deduce that any  such
    | discrepancy is the result of mis-orientation? And why do you need to
    stand
    | back to see the two views? Surely, the closer you can get, the  larger is
    | the solid angle that's available in the liquid reflector. I see  no such
    | advantage in standing back, as long as the wind-shield isn't  interfering
    | with the direct view.
    |
    | George.
    |
    | contact George  Huxtable, at  george{at}hux.me.uk
    | or at +44 1865 820222 (from UK,  01865 820222)
    | or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    |
    |
    |
    |
    |
    |





       
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