On Wed, 3 Nov 2004 17:19:09 -0500 Chris Metzler <[EMAIL PROTECTED]> wrote: > > I'll check my algebra again,

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Checked; I can't find a mistake. As a third check, I ran it through Maple and got the same result. It appears to have the correct limiting behavior for both pitch --> 0 and roll --> 0 independently. And the problem seems straightforward to me. The compass needle is constrained to move on the horizontal plane in the aircraft's reference frame; the question is simply what's the (perpendicular) projection of the magnetic field vector onto that plane, and what direction does that point? You can move the plane by from level flight towards the north pole by yaw, then pitch, then roll; or you can do the opposite transformations on the magnetic field vector itself (same order, but opposite value of angles), and get the same relative orientation of the field vector to the aircraft. So I think this is analytically correct. What's the weird behavior? For what part of parameter space? -c -- Chris Metzler [EMAIL PROTECTED] (remove "snip-me." to email) "As a child I understood how to give; I have forgotten this grace since I have become civilized." - Chief Luther Standing Bear

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