
NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Site details
From: Gary LaPook
Date: 2008 Nov 30, 04:11 -0800
From: Gary LaPook
Date: 2008 Nov 30, 04:11 -0800
Gary adds: When reassembling the A-10 the easiest way to align the index prism is to use the sextant like a normal marine sextant. Set the counter to zero. Install the index prism and the fixed prism but don't tighten up the screw holding the index prism shaft, just hold the prism in the frame with your finger. Don't install the plates that close the inside of the the A-10 frame as they limit your ability to push the index prism out of engagement with the worm. Go outside and sight on a clear object in the distance, the farther the better, by looking around the left edge of the fixed prism. Then move the index prism up or down by moving it slightly to the left to disengage it from the worm so that it can be moved up or down. Let it drop into the worm when you have the same object lined up in the prism with the object as viewed around the lefthand edge of the fixed prism, then tighten up the screw to hold the index shaft in. When reassembling the index prism into the frame put grease not oil on the tapered shaft because the tapered shaft applies a great deal of pressure on the mating surface and oil is not strong enough to supply enough lubrication. If you use oil you will end up with a horrendous amount of backlash, say about a 30' difference when you bring a star up or down.. The trickiest thing about installing the index prism is installing the spring that goes around the index prism pivot to apply a constant pressure on the gear teeth against the worm to minimize backlash. You need a small forceps that lock to grasp the end of the spring and manoeuvre the end of the spring into the underside of the index prism, this is a frustrating exercise due to the very limited room for working but necessary. You might be a blt to use a piece of fishing line for this but I haven't tried it. gl On Nov 27, 7:08�pm, bruce hamiltonwrote: > All times GMT 27 Nov 2008 > > A-10 Sextant with 31.5' index error off the arc (horizon reading is lees > than zero in case if am mixed up) > Sextant has no other calibration. I frequently get LOP's within 2 miles > of my AP so I am happy. It has backlash so I try not to change > directions. �I suspect some other error as stars with higher altitudes > tend to give me bigger errors. > I am actually quite surprised that I am getting a fix that is close > enough to find the airport (or Bermuda) if I had do. I have an A-12 and > Mark IX, but I only drag out one an evening. > > Thanks > > I am presently using CelestNav 3.0 for the palm pilot to work out the > sites. I would appreciate any comments on the program. I like it for > everything but the fix calculation, but I think 3.0 is only a Beta. > > AP 49d �16.1 N �123d 7.1 W > > Pollux � 06:19:33 � 27d �59.3' > Vega � �06:16:31 � 13d � �0.3' > Betelg � 06:10:53 � 28d �44.3' > Altair � �03:56:11 � 22d �37.0' > Vega � �03:54:45 � 32d �06.9 > Capella 03:52:46 � 39d �35.7' --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To unsubscribe, email NavList-unsubscribe@fer3.com -~----------~----~----~----~------~----~------~--~---