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Question For The Nav's Amongst Us!

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Question For The Nav's Amongst Us!

Old 12th Feb 2019, 18:34
  #41 (permalink)  
Join Date: Aug 2013
Location: Washington.
Age: 69
Posts: 455
Originally Posted by ICM View Post
Did many USAF aircraft get a fully automated astro system as that Wiki article seems to imply? I ask as the C-141A was, I believe, intended to have one, complete with Astro-Tracker but, in the event, only the Astro Computer element was fitted. Very useful it was too, but sights were taken by Navs with a Kollsman sextant in the normal way.

And does anyone recall using that Link Celestial Nav Trainer mentioned, either in RAF or US service? All I can recall from Nav School in 1965 (Hullavington) was having to get 100 star/planet shots with the Bubble Sextant, hoping that the resulting lines went through some part of Wiltshire.
The C-141A had wiring for an Astrotracker but the fleet was not so equipped. I was a Starlifter nav from 1974-1980. We had an ASN-35 analog along track-cross track computer fed by the Doppler radar, a digital ASN-24 nav computer, that could compute celestial (az/el), provide lag/long ppos, and capable of being fed by the Doppler radar, APN59b radar, LORAN C and TACAN. We used a periscopic sextant, so needed to know the approximate az/el of the body before shooting. Both computers could feed the autopilot. Usually I did not operate with the LORAN link to the ASN-24 because the sky wave/ground waves kept changing without warning. I used radar and TACAN updates, if available and range was not too large, prior to coast out. In good MAC form, I used all available aids overwater.

On one trip from Cape Verde to Kinshasa during the day, there was only a sun line to correct the computers which drifted considerably. I had learned about and borrowed copies of the tables for pressure pattern navigation using temperature changes for d-values instead of pressure changes. To do so, we had to use air tracking ( i.e., constant heading, constant air speed). Even though effectiveness is degraded near the equator, it worked great, and we coasted in on track every time. Thank you to the KC-135 nav who shared those tables with me. Had a bit of a dispute with the co-pilot who wanted to use the ASN-24 link to the autopilot, which would have screwed up the pressure pattern process. I insisted he fly the heading and airspeed I gave him. The aircraft commander told him to do what the Nav said, unless he wanted to do the navigation over the broad watery expanse. To make sure, I set up the computer to go from one waypoint to the same waypoint, therefore unable to drive the autopilot (which was still able to fly in heading hold mode).

My memory doesn’t serve me well now, but I do recall the “fun” of grid navigation, which I usually only used for currency, not for necessity. The only exception was going to Thule AB in Greenland, which I tried to avoid if possible. (Although we were told there’s a beautiful woman behind every tree up there.)

In the late 70’s we started equipping with a single Delco Carosel INS to improve our NAT Track performance. Kind of took all the fun out of it.
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Old 12th Feb 2019, 19:20
  #42 (permalink)  
Join Date: Oct 2012
Location: UK
Posts: 1,744
Originally Posted by SASless View Post
With the current shifting of the Earth's magnetic fields in the Arctic Regions....even if you know your position to the ever so small a margin....how do you determine the proper course to steer to arrive at your destination?
Unless I am misunderstanding your question, the situation with most INU or Sat Nav is that you (the system) Navigate in True, and the Mag element can be superimposed either through an automatic database or through manual input. However, using Mag in areas of high Variation is, at best, confusing and so sticking with True works well. The old problem for INU's of the Pole was sorted by the system using a false Pole, driven away a known amount from the real one and the computation factored accordingly. The specific Lat/Long of any position is partly a product of the mapping system that you are updated to.

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