Why The Hell... (random rant)

In rec.aviation.piloting TheSmokingGnu wrote:
wrote:
An INS does not contain a gyrocompass.

I thought I read somewhere that certain INS do have a gyrocompass, for
setting the initial positional reference.

The compass (compii??? :P ) in question was erected much faster than a
ship-borne model by being held at magnetic north by a mag compass while
it spun up (so the calibration time was only that to correct for local
variation, and not to find the entire harmonic of the Earth).

In any case, it was useless when actually flying, and the system only
used the accelerometers thereafter.

Well, if you forced it to magnetic north on turn on, it would be
statistically faster than some random position, but still takes
a long time to settle; the Earth doesn't rotate that fast.

What a gyrocompass actually seeks is alignment of it's axis with the
axis of the Earth's rotation, so you would also have to throw in
a latitude initializer to do much good.

That's not saying no one ever tried to build such a thing, but the
laws of physics that make it work make it impractical for airplanes.

Plus, the initialization for INS has to set the position AND which
way is north.


--
Jim Pennino

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