In article ,
says...
"Casey Wilson" wrote in message
...
What is the mechanics for causing the turning error in the first place?

In a magnetic compass, you've got a needle that is aligning itself with the
lines of Earth's magnetic field. In particular, the lines go between the
north and south poles, and the needle tries to line up parallel to them.
However, the magnetic field is not parallel to the surface of the Earth. It
curves down toward the poles, and the curvature is greater the farther north
you go.

If you're heading is due north or due south, the needle is aligned with the
airplane's longitudinal axis and you get an accurate reading. When you
bank, because the magnetic field is curved, the compass needle actually
deflects downward a bit to line up with the magnetic field, which causes it
to rotate on its pivot.

If you are headed due north, the needle's downward pointing results in a
heading indication opposite of the turn you're about to commence. Headed
due south, the same downward pointing is reversed relative to the airframe,
and results in a heading indication in the same direction of the turn you're
about to commence.

The effect becomes more pronounced the farther north you go, since the
magnetic field is more curved as you get closer to the pole.

Of course, everything is reversed in the southern hemisphere.

This effect is, of course, completely different from other types of compass
error, such as that caused by acceleration.

Bad example methinks - acceleration error is exactly the
same...
The effect is the same (the needle does not deflect
'normally'). The cause is the same (magnetic dip).

--
Duncan