I recall reading an article by Barnaby Wainfan (my childhood hero) in Kitplanes magazine several years ago. I cannot find the article but found a reference to it on a Yahoo Bearhawk web posting.
https://groups.yahoo.com/neo/groups/...messages/14814
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14814aileron trailing edge
collinc2002 <collinc@ipa.net>
Feb 1, 2003
There seems to be some confusion as to the purpose and nature of
altering trailing edges to trim an airplane. I don't consider myself
to be an expert or anything on the subject, but I did build a RV-6A
once upon a time and still have a copy of a newsletter from Van's
covering the subject. The article is quite lengthy but very
informative (August 92' edition)
Briefly Van notes the dramatic effect that the trailing edge radius
can have on aileron control loads and the undesirable effects (even
dangers) of excessive trailing edge radii. He notes that there is a
tendency among builders to "underbend" the trailing edges and end up
with a trailing edge which bulges out somewhat. This causes a lower
hinge moment which means lighter control forces. In some cases it
causes "aileron snatch", a tendency for the ailerons to seek a
neutral (hands off) position slightly to either side of center. This
condition is impossible to trim and makes the airplane touchy to fly
because the stick must be held in the center; a condition which is
easily upset by light turbulence and/or pilot inattention.
Fortunately the condition is easily accomplished by clamping blocks,
hand seamers, or even hand pressure.
A by-product of this technique can be used for lateral (aileron)
trim. Since altering the trailing edge radius alters stick force, it
follows that altering only one aileron could affect laterl trim. The
essential info is that lateral balance can be achieved by decreasing
the trailing edge radius of the aileron on the light wing.
Van refers to an article in Dec. 91 KITPLANES magazine by Barnaby
Wainfan on "Wingtip Trailing Edges". Information in this article
helps explain why this phenomenon works. The simplest explanation is
as follows. Air flowing over any surface of the aircraft tends to
remain attached to the surface. When the surface curves, the air will
tend to stick to that surface until the curvature is too sharp and
separation occurs. This is what happens on the trailing edge radii
of the ailerons. Because the air pressure on the bottom of the
aileron is greater than on the top, the bottom air tends to follow
the trailing edge curvature more than the top air does. What
results is an upward jet of air. This upward jet of air pulls (or
pushes?) the aileron down and lifts the wing. Thus ,if we reduce the
radius of an aileron trailing edge, we will decrease the jet action,
that the aileron will move upward, and the wing will come down
(become heavier).
Hope this helps...
Collin Campbell #370
Bolivar, MO
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Hope this helps...
- Roger