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Fall Into the Gap: Why so much
concern about such a small gap? First, a 1/16-inch hole is huge to an
air molecule, and millions of them rush to pass through. As a result, a
gap causes air loads to appear, disappear, and reverse direction as
aileron deflection and aircraft flight angles change.
A whole book can
be written about the effects of control reversal and force/deflection
curves. It is beyond the scope of this article, but the result is that
aileron flutter is more probable with a large control-surface gap. The
airplane is back to flying rudder-only again.
Second, aileron response
diminishes. An aileron works by increasing the wing's lift on one side
while reducing its lift on its other side. It performs this miracle by
deflecting the airstream as it flows over both sides of the wing. If a
large amount of air passes through the gap, the aileron does not deflect
this air. The less air that is deflected, the slower the aircraft's roll
response is to a given aileron input.
In addition, that book on
force/deflection curves also tells us that the gap can produce a false
aileron effect that acts opposite the real control input. This increases
adverse yaw effects.
Third, the wing can experience unequal lift during
hard pullouts and maneuvers. If the gap on the left wing is larger than
the gap on the right wing, more air passes through the left side,
resulting in more lift for the right wing. This usually happens only on
hard pullouts and results in a left wing drop.
Fourth, different roll
rates, right vs. left, can result if the gap sizes are different; each
aileron's effectiveness varies by its gap size and "false aileron"
effect.
None of these results are positive. Tests with RC Precision
Aerobatics (Pattern) competition aircraft have shown that all of these
effects are present even when the gap is so small that it is nearly
invisible.
If any size gap can be problematic, eliminate it. Heat up
your model covering trim iron. Cut a 11/2-inch-wide piece of heat-shrink
plastic model covering that is the same length and color as the bottom
of the aileron and wing. Fold a sharp crease in the middle.
Deflect the
aileron as much as possible and insert the folded covering into the
bottom aileron gap. Using the trim iron, adhere the creased area. Do the
aileron side followed by the wing side. Trim the excess at the top of
the gap, and seal the top edges with a normal covering iron. Voilà! The
aileron gap is history.
Sealing all the gaps is a secret that
competitive pilots and professional builders have known for many years.
Try it on all of your sport aircraft. You may be surprised when that
sluggish roller that pulls too hard to one side with hard up-elevator
transforms into a respectable aerobatic sport machine with great
slow-speed handling.
Click on photo to view large image with caption
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