On Tue, 12 Sep 2006 20:13:57 -0500, Emily
wrote:

Roger (K8RI) wrote:
On Tue, 12 Sep 2006 12:48:35 +0200, Mxsmanic
wrote:

Thomas Borchert writes:

Yes. So?
So the compass cannot always be trusted.

The *only* time a compass can almost be trusted is in straight, level,
and un-accelerated flight.

But the errors are predictable. I've seen a DG slowly wind down to
nothing and then completely fail, and I flew the plane just fine with
just the compass.

I think I may have phrased that poorly.
Let me try again? :-))

The compass tells you the truth "only" when in straight, level, and
un-accelerated flight IF outside influences are taken into account.
Those outside influences are normally predictable, but sometimes sneak
up on the unwary. In addition to magnetic variation some aircraft
develop some magnetic fields (portions of the airframe may become
magnetized) and require degaussing. Adding new equipment can sometimes
require "re-swinging" the compass. I have to be careful where I put
the Garmin GPS. It works fine on the yoke, but will swing the compass
about 60 degrees on when on the glare shield.

Around here the magnetic compass is only 6 degrees off which is close
enough. However there are areas in the lower 48 where I think you can
find close to 20 degrees. Now that is enough to notice even on a short
trip.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com