NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Sights perpendicular to course
From: Gary LaPook
Date: 2014 Nov 14, 22:44 -0800
From: David Pike <NoReply_DavidPike@fer3.com>
To: garylapook@pacbell.net
Sent: Friday, November 14, 2014 12:16 PM
Subject: [NavList] Re: Sights perpendicular to course
From: Gary LaPook
Date: 2014 Nov 14, 22:44 -0800
Ah, I see the method to the madness!
The four shots on star A have an average time of "zero," the planned fix time as do the three shots on star B so no reason to do MOO or MOB, pretty clever.
For those marine navigators reading this, and scratching their heads, look for an explanation of what we are discussing here:
gl
From: David Pike <NoReply_DavidPike@fer3.com>
To: garylapook@pacbell.net
Sent: Friday, November 14, 2014 12:16 PM
Subject: [NavList] Re: Sights perpendicular to course
“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 25th March 1980, and it had nothing to do with munching flight rations.
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
