Re: 747-400 Magnetic Detectors

From:         inet@intellisys.net (brian whatcott)
Organization: Telepath
Date:         13 Sep 96 03:03:36 
References:   1 2 3
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In article <airliners.1996.1817@ohare.Chicago.COM>, stuart@slaw.com
says...

>During the inertial alignment process, the processor assumes that it has
>been given the correct lattitude and that it is motionless (or knows its
>motion from somewhere else in the case of aircraft carrier operation,
>et.al.).  From the latitude it computes the rate at which the surface of
>the earth is rotating (360 degrees in 24 hours at the equator, 0 at the
>north pole).  It then "levels itself" to local gravity, takes a wild guess
>at North, and compensates for the earth rate movement.

This explanation has interesting parallels to the explanation for
latitude compensation in the common or garden direction (or heading)
indicator. This has a latitude rider nut set to counteract the
apparent drift (yaw) provided by earth rotation - it's given as 15
degrees * sin ( latitude) per hour - which you will notice goes to zero
at the equator and 15 deg/hr at the poles.

   The reason for this diametrically opposite type explanation, I
suppose, is that there are three axes of rotation, likewise translation
- and Stuart is describing what sounds like a vertical translation
sensor or a mix of pitch-roll rotation in the inertial frame.

brian whatcott <inet@intellisys.net>
Altus OK