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Old 17th Jul 2013, 17:05
  #4037 (permalink)  
Danny42C
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Danny finds things going from bad to worse.

Your tormentor now had three more arrows in his quiver: he could let you have the lot if so inclined. The first was "No Compass". This was really quite unrealistic, how can a Compass go u/s unless you hit it with a hammer ? (Lightning strike ? - not all that common, now is it ?)

The antediluvian aircraft of those times had a "Directional Gyro" on the panel. This was, in effect, a compass with no north-seeking function (clearly an Irish idea in the first place). You waited till your magnetic compass settled down, then set your D.G. in accordance with it. (Many people routinely set the exact runway heading on the D.G. each time when lined up for T.O.)

The D.G. did not jiggle about like a compass needle, and it was much easier to hold a heading on it. The ATC practice assumed that the D.G. had not been so set before you found your compass u/s, so it was no use to you. Of course, the answer now was to orientate it some other way. Where is North ?

Any scornful cub scout will now tell you, that in GMT, and in the Northern Hemisphere, if you point the hour hand of your watch at the Sun, half way between that hand and 12 is South, near enough (no, you do not have to find the moss on the trees). To make it easier for the pilot, and to cover the occasions when he had no watch, or had forgotten to wind it up, ATC had Tables of Sun's Azimuth, corrected for date and latitude. Bloggs headed into Sun, and set the figure you gave him on his D.G. Easy.

By night ? - Pole Star. Can't see Sun or Polaris ? - tricky now, but there was a "one-and-two" method, I vaguely recall. This involved instructing your man to fly S&L at constant speed, then taking successive bearings on him at (say) exactly zero, +30 and +90 seconds. You plotted these, marked a ruler at the 1 and 3 inch points, and wiggled it on the plot until you got a perfect "match". It'll only fit in one position: now you know his track (roughly, but good enough). Tell him to put it on his D.G. Bob's your uncle.

This, of course, was so time-comsuming that it was a one-to-one business; it was really only an ATC tour-de-force to keep us on our toes.

But enough already. There was worse to come.

'Night, all,

Danny42C


Do not bite off more than you can chew.