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Re: Questions regarding the mirror artificial horizon.
From: Bruce J. Pennino
Date: 2013 Sep 7, 08:26 -0400

Hello Alan:

The 9 " Empire torpedo level is more than adequate. I use it all the time when I take sights with the AH. Regarding the mirror,when I built my AH a couple of years ago I bought an ordinary quality mirror and a front surface mirror. The ordinary mirror works so well I've never used the first surface mirror. I figure one of these days I'll break the ordinary mirror and will then use the other one. I just have not spent enough time using the AH, but I suspect the first surface mirror is better with stars and there would be no "ghosting", or whatever it is called. I decided not to use plywood for a base because of moisture issues, but it should be ok. I would paint it. I built a platform for the AH because I wanted to get it out of the grass and off the ground. Because of sloping terrain, the platform has a "rail" running along the top edge (perpendicular) to the sight line. This helps with leveling on irregular terrain. I always use the platform on even level ground or a deck. Just flip platform over so the" rail " edge is up. The procedure for leveling has been discussed before. Do left to right first, then front to back. Level to center bubble one way, reverse level and relevel bringing the bubble half way back. Very quick and good enough. I routinely get fix of 1.5 to 3 nm. Regarding the brightness with the sun, I can't help with that , but I learned to do moon sights and early rising stars with the mirror AH. I never had much success with a pool of liquid, but I have an old USN mercury AH which I will try one of these days and compare results.

Bruce

----- Original Message -----

From: Alan S

To: bpennino.ce@charter.net

Sent: Friday, September 06, 2013 7:40 PM

Subject: [NavList] Questions regarding the mirror artificial horizon.

All: I have a "home made" mirror type artificial horizon, composed of the following. The mirror is 10" x 10", and is, at least supposedly, that "first surface mirror" Said mirror is mounted on 3/4" thk. x 14.5" x 11.75" piece of plywood, the mirror held in place with masking tape strips in each corner. It appears secure so mounted. The assembly has 3 1/4" x 20 tpi leveling screws in "t" nuts, the screws are round headed machine bolts, heads down. I understand that leveling of a mirror horizon is critical. I use an Empire brand 9" long torpedo level, the maker claims is accurate to within .0005"/",would this be sufficiently accurate for leveling of the mirror assembly? I also use a Davis Artificial Horizon, filled with water, which which I get quite good results, my calculated fix is often inside 2 NM of a known position (GPS coordinates). Trying sun shots this AM, with the mirror assembly, after leveling, the sun appeared painfully bright, even with ALL sextant sun shades in. Seems like additional sun shields would be appropriate, but what sort and how to rig them? As memory serves, a dark film was, at one point, mentioned by a poster here, don't recall who. Do you think that a cardboard tent spanning the mirror, with blue and orange colored film shields might work. Colored plastic shields that were furnished with the Davis Artificial Horizon work quite well. Any guidance would be appreciated. Thanks Alan ---------------------------------------------------------------- NavList message boards and member settings: www.fer3.com/NavList Members may optionally receive posts by email. To cancel email delivery, send a message to NoMail[at]fer3.com ----------------------------------------------------------------

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