Why are headings still magnetic?

Roy Smith wrote:
Mxsmanic wrote:

I certainly won't quarrel with using magnetic navigation as a back-up,
but I do question basing normal navigation on a compass, which is
relatively unreliable compared to more modern methods.


Unreliable? The magnetic compass is about as reliable is it gets. There's
one moving part, no power source, and the Earth's magnetic field is good
for another few thousand years. What's unreliable about that? Of the
cannonical "watch and compass" navigation kit, the watch is by far the less
reliable of the two.

I suspect he was talking about accuracy or precision more than
reliability. Although, if you are talking about finding a distance
point with a high degree of reliability, then that term might be
appropriate. The inherent lack of accuracy of dead reckoning as
compared to GPS means that you will be much less likely to find a
precise point in the distance, and thus you could consider the
reliability of consistently finding that point.

Matt

"Grumman-581" wrote in message
...
"Mxsmanic" wrote in message
...
Yes, but the ANS could recognize stars even from the taxiway in broad
daylight. I still don't know how it managed that.

http://www.sr-71.org/blackbird/manual/4/4-3.php



Did (or does) the U-2 employ a comparable ANS

Mxsmanic wrote:
From what I've read, the ANS looked specifically at stars, not
planets, but I may be wrong.

Planet, star, it's all the same. It's a point of light in the sky. The
ephemeris calculations are a little more complicated for a planet, but
that's only something you'd notice if you were working it out with pencil
and paper.

Roy Smith wrote:
Mxsmanic wrote:
From what I've read, the ANS looked specifically at stars, not
planets, but I may be wrong.

Planet, star, it's all the same. It's a point of light in the sky. The
ephemeris calculations are a little more complicated for a planet, but
that's only something you'd notice if you were working it out with pencil
and paper.

But aren't the stars stuck to the celestial sphere so that their motion
is fairly simple and easy to predict. Planets are zipping around the
sun, as is the Earth, and the Earth is turning on its own axis. Much
more complicated.

"Chuck Peterson" charles.petersonxxx@comcast(removethis and xxx).net
writes:

Did (or does) the U-2 employ a comparable ANS

The U-2 predates the ANS, I believe, and today I'd expect it to be
using GPS instead, which is much more accurate.

--
Transpose mxsmanic and gmail to reach me by e-mail.

Roy Smith writes:

Unreliable? The magnetic compass is about as reliable is it gets. There's
one moving part, no power source, and the Earth's magnetic field is good
for another few thousand years. What's unreliable about that?

Put a chunk of metal next to it, and you'll see. Turn the aircraft,
and see if the compass instantly changes position.

--
Transpose mxsmanic and gmail to reach me by e-mail.

Roy Smith wrote:
Mxsmanic wrote:
I certainly won't quarrel with using magnetic navigation as a back-up,
but I do question basing normal navigation on a compass, which is
relatively unreliable compared to more modern methods.

Unreliable? The magnetic compass is about as reliable is it gets. There's
one moving part, no power source, and the Earth's magnetic field is good
for another few thousand years. What's unreliable about that? Of the
cannonical "watch and compass" navigation kit, the watch is by far the less
reliable of the two.

I met a sea captain that piloted an old ship full of refugees from
Latvia to Nova Scotia in 1939 with only a sextant and magnetic compass.
And he said it was overcast most of the time.

writes:

Accuracy isn't the problem. Would it be as reliable?
Would it be affordable and workable in airplanes that lack
electrical systems? And would it work when those
electrical systems failed?

In modern aircraft, a failure of electrical systems brings a lot more
problems than mere navigation errors. No radio, no other navaids, no
control surfaces in some aircraft, no propulsion in some aircraft.

And while a compass shows magnetic north, that's all it shows. You
have no idea how far north or south you are, or which direction to fly
to your destination.

--
Transpose mxsmanic and gmail to reach me by e-mail.

In article ,
Mxsmanic wrote:

Roy Smith writes:

Unreliable? The magnetic compass is about as reliable is it gets. There's
one moving part, no power source, and the Earth's magnetic field is good
for another few thousand years. What's unreliable about that?

Put a chunk of metal next to it, and you'll see. Turn the aircraft,
and see if the compass instantly changes position.

All devices have failure modes. Of course there are things which will
interfere with a magnetic compass, but I'll still stand by my statement
that it's about as reliable as a piece of technology can get.

In article ,
Stubby wrote:

Roy Smith wrote:
Mxsmanic wrote:
From what I've read, the ANS looked specifically at stars, not
planets, but I may be wrong.

Planet, star, it's all the same. It's a point of light in the sky. The
ephemeris calculations are a little more complicated for a planet, but
that's only something you'd notice if you were working it out with pencil
and paper.

But aren't the stars stuck to the celestial sphere so that their motion
is fairly simple and easy to predict. Planets are zipping around the
sun, as is the Earth, and the Earth is turning on its own axis. Much
more complicated.

Depends on your definition of "Much more complicated".

If you're doing it the traditional way, working from the Air (or Nautical)
Almanac with paper and pencil, reducing a planet sight is a couple more
table lookups and a couple more additions or subtractions. Some hulking
mainframe did all the really messy math for you a year or two earlier, in
plenty of time for the tables to be typeset, printed, and bound.

If you're doing it all from scratch with a computer, all the formulas you
need can be found in Jean Meeus's "Astronomical Formulae For Calculators"
(http://www.willbell.com/math/mc3.htm). The book was published in 1979,
and gave formulas usable on the popular hand calculators of the day to
achieve accuracies exceeding any practical navigational need.