NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Gyroscope vs. Fluxgate compass
From: Brian Whatcott
Date: 2002 Feb 5, 17:40 -0600
From: Brian Whatcott
Date: 2002 Feb 5, 17:40 -0600
At 07:37 AM 2/5/02, John LeRoy wrote: >... > >>> [bw] Instead, bigger airplanes used a flux gate sensor ... > >> Actually on modern "big" airplanes like the747-400 I used to drive the > >> navigation system has no magnetic compass at all! > > > > > >> John LeRoy > >> M/V Traveller > > > there is a whisky compass, but its not part of the navigation system. >... >It is highly unlikely that the aircraft will lose both GPS systems and all >three FMCs. > >John LeRoy Wandering probably too far afield now... but the electronic flight instrument system (EFIS) aboard the 747-400 displays several compass roses on the tubes, and INS does not inherently produce magnetic orientation unless it senses the motion of an inertial axis 'fixed in space' wrt to a fixed body in the Earth frame - [much as Sperry's gyrocompass did ] and applies the variation appropriate to some supposed lat/lon to derive the mag heading. I seem to recall that's how an INS system initializes, but I haven't reviewed that system recently - I expect this is the 'compassless' attribute John has in mind. Pity that INSs are very very dear (and drift with time unless resynced with other inputs!) Brian Whatcott Altus OK Eureka!
