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From: rah@netcom.com (Richard Hyde)
Subject: Re: compass errors
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Date: Sun, 25 Oct 1998 00:36:04 GMT
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seb@popstudios.com wrote:

: I am curious to find out the scientific explanations for all magnetic compass
: errors on acceleration, deceleration and turns on E and W heading.

ANDS: Accelerate North, Decelerate South
When on an East or West heading, accelerating causes the compass to indicate
a more Northerly heading, decelerating causes the compass to indicate
a Southerly heading.

Thought experiment:  Take a 10 ft. 2x4 and place a 2Kg weight on one
end.  Now hold it in the middle and start to run with it.  What happens?

The end with the weight swings backwards.  Towards you.

While running at a constant speed, straighten out your 2x4 so it
again extends to either side of you.  Now begin to slow down.
What happens?

The end with the weight swings forwards. Away from you.

Why?  because the weighted end has more inertia and tends to resist
moving.

Another thought experiment for those of us in the Northern hemisphere:

Picture the globe in your mind.  Put a dot on it where you are and another
dot where the North magnetic pole exists.  Draw a line between the two
points.  Where does it go?

Well, it goes North, obviously, but more importantly it also goes DOWN.

The compass points directly through the earth towards the location
where the North magnetic pole appears on the surface.  i.e. it points
North and also dips towards the ground. (For the purists, yes, I know
it's actually trying to parallel the field lines, but this is close
enough)

To compensate for this dip, a small weight is added to the Southern
end of the compass needle.

Now, imagine you are flying on an Easterly heading.

The North end of the compass is to your right, the South end (with the
weight) is to your left.

Accelerate.  What happens to the weighted end?

It swings towards you - just like the weighted end of the 2x4.

As the weight moves towards you, it moves the compass dial as well. In this
case, clockwise, as seen from above.

You will appear to be turning towards the North.

Once you resume unaccelerated flight, the compass can return to it's
normal position.

You should be able to derive the rest of the ANDS behavior from this.

Cheers,

Rick

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|   Richard Hyde  |  RaH@netcom.com  |  This space intentionally left blank  |  
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