A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2014 Nov 14, 12:12 -0800
“Since” is definitely the watchword Gary. I’ve just looked at my logbook. The last time I could possibly have shot a sandwich fix in earnest was
7 Shot Sandwich Fix – Vulcan Style: Pick two navigation stars A and B approximately 90 degrees apart, ideally fore and aft and athwart ships. Set one up on each sextant. 6.5 minutes before mid-time, shoot star A twice, then star B three times, then star A twice as one minute shots one minute apart. Work out the four intercepts for star A and calculate their average. Calculate the average heading and IAS changes for star A, and calculate a correction for acceleration error using a Mear’s slide http://i372.photobucket.com/albums/oo168/keg167l/OddSlide.jpg in place of the TAS slide in your flight computer (I can’t quite remember how). Apply this to the average intercept for star A, and plot the position line on your chart. Do the same for star B. By the time the fix is on the chart it’s ancient history, so the technique is really only suitable for monitoring a Doppler or inertial fed system with a “fix counters” facility. It’s hard work without two willing assistants, one to record the heights and plot the fix, and one to call the timing.
If someone will explain to me in detail how to place a photo on this site, I’ll try and send a photo of our calculation form. I’ll look at your site with interest Gary. I always think it’s a shame that everyone knows who Amelia Earhart was, but very few people recognise the name Fred Noonan. Steady for Astro. Dave