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Date: Mon, 12 Jul 1999 13:12:46 -0400
From: John Cooper <snopercod@CITCOM.NET>
Subject: Severe Pitch Moment with Flap Extension
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Naf--

Use a water level to measure the angle of incidence of your horizontal stab.

First, hold a small _aluminum_ level in the vertical position and rub it
gently along the leading edge of your horizontal stab. The aluminum will
leave a "pot mark" along the leading edge. If you don't have an aluminum
level, use carbon paper or be creative. This is your level reference for
the front.

Remove an elevator and stretch a piece of duct tape over from the top of
the stab's trailing edge - across the gap to the underside. Use an accurate
ruler to mark the half-way point between the top and bottom at the trailing
edge.

Using a water level, compare the elevation of the pot mark line on the
leading edge to the centerline mark on the trailing edge. Now get out your
trig tables and figure the angle <G>.

The best water level consists of a pot of some kind of pot or vessel at
least 12" in diameter with one end of a tygon tube weighted down in the
bottom. Siphon some water out the free end of the tygon so that it is full
of water with no air bubbles. Set the pot on some kind of a rigid stand and
adjust water level in the pot to bring the meniscus on the measuring end of
the tube up to the centerline of the leading edge.

The idea here is that the surface area of the pot is much greater than the
surface area of the measuring end of the tube so that if you spill a little
water out of the end of the tube it really won't effect the accuracy very
much.

If you hold a light behind the end of the tube, you can sight right over
the meniscus as it pokes its little head out of the end of the tubing and
achieve a _very_ accurate reading.

Caution: If you are doing this outside, make sure that the tygon is either
all in the sun or all in the shade. Differential temperature can effect the
readings.

Note: If absolute level is not a concern, then just fill the pot to
overflowing. That way you can top it off whenever you lose some water out
the end of the tubing. For big jobs, a garden hose works just fine, too.
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