In rec.aviation.piloting Mxsmanic wrote:
writes:

You are talking about a gyro compass.

No, I'm not.

Yes, you are.

A gyro compass is huge, expensive and heavy.

But there is none inside an inertial reference platform. An IRS uses laser
gyros.

They are still big, heavy, and expensive.

They can take hours to settle on a usable reading.

An IRS can find true north in a few minutes, depending on latitude.

An INS system can NOT find true north and requries an external input
to tell it where north is.

You are clueless.

An INS system has to be initialized with it's current position and just
tells you where you have moved relative to the starting position.

But it also finds true north on its own, without any need for external data.
It simply detects the rotation of the Earth, and that gives it an east-west
reference, to which true north is perpendicular.

No, INS can not find true north, only a gyro compass can find true
north.

A gyrocompass doesn't work at airplane speeds.

You have no idea what you are talking about.

Google for it. You'll be surprised.

Lets sum up reality versus your babbling ignorance:

Only a gyrocompass can find true north.

A gyrocompass won't work at all at airplane speeds and is problematic
at fast, modern ship speeds.

Because a gyrocompass uses the precession caused by the Earth's rotation
to find north and the Earth rotates so slowly, it can take several
hours for a gyrocompass to settle when first turned on.

An INS is a collection of gyros and accelerometers that sense movement.

An INS does not contain a gyrocompass.

An INS requires an external input to tell it where north is.

An INS has to be initialized to tell it it's current position.

Once an INS is initialized, it can tell you how far you have moved.

An INS has to be periodically updated with it's true position because
the gyros, including laser gyros, drift.

No GA aircraft and few transport aircraft have INS installed.

For how gyrocompasses work:

http://en.wikipedia.org/wiki/Gyrocompass

http://www.navis.gr/navaids/gyro.htm

http://tpub.com/content/administrati...s/14221_74.htm

For how INS works:

http://en.wikipedia.org/wiki/Inertial_guidance_system

--
Jim Pennino

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