Sun's True Bearing

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photofly
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Re: Sun's True Bearing

Post by photofly »

Worth remembering that at the north pole, civil polar night lasts for weeks!
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Re: Sun's True Bearing

Post by photofly »

Spandau’s method is based on assuming the sun’s azimuth angle varies linearly with time of day, at 15 degrees per hour.

Some though will convince you that’s not true anywhere except at two spots, one in the polar region of each hemisphere, on any day. It may be “good enough” at high latitudes but it’s not even slightly true at the equator: if you’re on the equator (at one of the equinox days, to make things easy) the sun rises in the east, and stays in the east, switching instantly to west as it passes overhead at noon. It’s never anything other than directly east, overhead, or west.

So while the sun sweeps out 15 degrees of longitude per hour at the pole as it trundles around the horizon (again, let’s assume on one of the equinoxes) this is less and less true when you move away from the pole.

In general the sun’s azimuth angle changes fastest at culmination, when it’s highest in the sky. At the equator the azimuth rate is zero the whole day except for the instant when the sun is exactly overhead when it sweeps infinitely fast, 180 degrees from east to west in no time at all.

There’s an equation for the azimuth angle on wikipedia: it’s not something you can do in your head:
https://en.m.wikipedia.org/wiki/Solar_azimuth_angle

More generally this is the difficulty in converting from azimuth/altitude coordinates (easy to measure by observation) to hour-angle/declination coordinates (easy to coordinate to solar time).
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Re: Sun's True Bearing

Post by Spandau »

While that may be true, one generally does not operate in True in the vicinity of the equator, it's more of a fairly northern (or southern) latitude thing. But for the sake of argument, you are correct.
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Re: Sun's True Bearing

Post by Spandau »

pelmet wrote: Tue Apr 03, 2018 1:55 pm
Spandau wrote: Tue Apr 03, 2018 1:08 pm You're right, in that kind of scenario up at the pole you can't really do it "from the hip". Let me blow some dust off the books when I go back to work next week, dig out an astro compass and I'll try and explain the math. I haven't thought about this in quite awhile. Even when I was doing it often we just GPS'd it to our best guess as to where the fuel cache should be (it moves) and then headed for Eureka.
Actually, just use the position of the sun to figure out what track to fly. At 12Z, it is over 0 degrees longitude(or very close to it) which is 60 degrees to your left as you fly toward Alert(it is actually at 65 degrees W but you should pick up the NDB as you get closer). Four hours later, the sun will have moved 60 degrees(15 per hour) so adjust it to be 15 degrees further to the right per hour as you head toward Alert. The guy starting at 16Z can head toward the sun initially. Maybe make a mark on the window every half hour and keep a shadow in place for that time period to prevent wandering. The resultant leg will be a series of straight lines with a heading change every 30 minutes that generally heads toward your destination. Hopefully you had enough fuel for Eureka anyways with....shhhhhhh....in-flight refueling and the false logbook entry that you stopped somewhere enroute and refueled for a ;)"max gross weight" ;) takeoff. Well, I heard that used to happen on occasion.

Of course one might say...but what about on a cloudy day or at night but who goes to the north pole at night and who goes on a cloudy day when you don't have proper lighting to analyze the icepack for landing.

All subject to confirmation by others....otherwise, I might be the one to end up in Russia.

That would work, I suppose - I see where you're going with it.

We did generally have a fuel cache around 88 north, but it was usually continuously making about two or three knots. During the last few seasons there was often a (brave) guy staying there and relaying his position back to Resolute every few hours so we'd usually have a position update via HF. I think he'd get moved back "upstream" with every new cache. The homer in the Twin Otter would only pick up the beeper at the cache from about twenty miles or so (when it worked) as I recall. I think the tourist trips to the pole have basically stopped now as there's just no way to even remotely make it look legal. On wheel-skis with bellies and tips we were probably fifteen and change if we were an ounce.

You can't go to the pole when the light is flat, it is strictly a VERY vfr operation. The pressure ridges there are monstrous in places. It really makes you appreciate pavement.
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Re: Sun's True Bearing

Post by North Shore »

So why is this even a thing?
It seems to be a dusty, little used corner of aviation knowledge with a very specific target audience. And, if you do need it, it's more than likely that you'll be taught it as OJT by an experienced vet.
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photofly
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Re: Sun's True Bearing

Post by photofly »

Spandau wrote: Tue Apr 03, 2018 5:56 pm While that may be true, one generally does not operate in True in the vicinity of the equator, it's more of a fairly northern (or southern) latitude thing. But for the sake of argument, you are correct.
We could check the error for a suitable choice of lattitude if we had a copy of TP784E. Anyone know where to get one? :whistle:
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Re: Sun's True Bearing

Post by Spandau »

Just out of curiosity, who did you fly for in the arctic?
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pelmet
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Re: Sun's True Bearing

Post by pelmet »

North Shore wrote: Tue Apr 03, 2018 6:20 pm So why is this even a thing?
It seems to be a dusty, little used corner of aviation knowledge with a very specific target audience. And, if you do need it, it's more than likely that you'll be taught it as OJT by an experienced vet.
Just a continuation of a thread that someone else started. Besides, doesn't TC still want you to know this kind of stuff on the exams? Plus, as a moderator, I'm sure that interesting(even if mostly useless info) can make a thread more interesting. I would have thought you would want that kind of thing.

Besides....what if you end up disappearing in your 777(like that Malaysian one)right at the north pole, survive and discover a long range ultralight as part of the cargo. I used to watch the A-Team and think that I might be able to pull off a Howling Mad Murdoch stunt and save the day by reaching Alert or Station Nord.
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Re: Sun's True Bearing

Post by North Shore »

Sure, I guess, pelmet. My comment was more aimed at TC and their exams than the interesting, yet esoteric, stuff in the thread - couldn't they come up with material that's a little more applicable to a wider selection of modern pilots?

777?! Somedays I wish that I'd gone down that road...
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Re: Sun's True Bearing

Post by Spandau »

I wrote an AME exam not long ago that asked about how Omega worked. Gave me a good laugh, anyway!
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photofly
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Re: Sun's True Bearing

Post by photofly »

According to the US Naval Observatory's website, the azimuth of the sun today at 1400Z at Pangnirtung, NU, at 66.14N, 65.72W was 139.5 degrees.

According to the Spandau method, the approximate azimuth at Greenwich at that time was 210°T, and at Pang therefore 210-65.72 = 144.3 degrees. Which is pretty close.
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Re: Sun's True Bearing

Post by Spandau »

photofly wrote: Tue Apr 03, 2018 10:46 pm According to the US Naval Observatory's website, the azimuth of the sun today at 1400Z at Pangnirtung, NU, at 66.14N, 65.72W was 139.5 degrees.

According to the Spandau method, the approximate azimuth at Greenwich at that time was 210°T, and at Pang therefore 210-65.72 = 144.3 degrees. Which is pretty close.
It's certainly not a replacement for having an astro compass and an almanac and two extra hands to be able to use them while you're trying to fly, but prowling around on the arctic coast in a Beaver or something and having nothing else, it will work reasonably well, at least well enough to get you home. I expect the almanac is even likely available as an App somewhere now. I'll have to look for it.
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photofly
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Re: Sun's True Bearing

Post by photofly »

When I get a chance I'll try to put some limits on the error to this method; it would be interesting to know, for instance, the latitude above which it always gives you a heading correct to within say 10 degrees.
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Re: Sun's True Bearing

Post by Spandau »

That would be useful information. It's just a simpler way of expressing GMT in decimals x 15 - west longitude, which has been around forever. I should have prefaced it with "this should put you within about five degrees of the actual LHA".
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willan anable
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Re: Sun's True Bearing

Post by willan anable »

For the North Pole: Cage your DG BEFORE shutting one down - before Gen offline. Then after spooled up, BEFORE moving, un-cage. DG will know only one South. ... Just to be safe, should learn some Russian!
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