Flutter
Caused by flex in the structure
cures:
Reduce flex in the structure. Flutter is when the wing and the aileron vibrate out of phase with each other.
a. Sheeted wing is stiffer than an open structure.
b. Dual aileron servos with straight pushrods are stiffer than a single servo with torque rods
c. A tight hinge gap is stiffer because thee is less exposed hinge to flex. Otherwise, gap decreases response because of air leakage but has no effect on flutter.
d. A sealed hinge gap is just mechanically reinforced by the sealing strip. If sealing your hinge gap stops flutter, the hinges were installed sloppily in the first place.
e. linkages should be attaced as far out on the control horn as possible. For the same torque, there is less force in the pushrods/clevises
f. Larger-stiffer control horns help
g. Built-up sheeted control surfaces have a much higher natural frequency than solid surfaces. Also they are stronger because the grain direction always is aligned with the local forces instead of being unidirectional as in solid wood.
h. Sharp trailing edges allow less force to be transmitted to the control surfce by the alternating vortex sheets as they depart the control surface. When ONE sharp trailing edge is impractical, two sharp trailing edges can be used (Squared trailing edge). Rounded trailing edges are worst by this theory, both in terms of flutter and control response.
i. The control surface should be slightly thicker than the aerodynamic surface to which it is atached. This provides energy to reattach the flow that has to separate to jump the hinge bevel. Also improves control response at small deflections that would otherwise be submerged in the separation bubble.
j. Mass balancing is effective. Mass balancing is also awkward. If a model airplane needs mass balancing, nine times out of six it's because the other elements of the system are still not adequately stiff.
k. Aftermarket heavy-duty servo horns are stiffer
l. E-Z connectors are asking for trouble. Use clevises.
m. Reinforce the area of the control surface where the control horn attaches. If solid balsa, at least pierce the area and soak it with thin ca. Even better is a hardwood insert. This gives a firm support for the control horn.
n. Any bend in the pushrod must be eliminated. This includes z-bends.
o. Install a hinge no farther than 3" apart.
p.Hinges should be within 1" of the ends of the control surface.
q. Install the control horn through a hinge. This transmits the forces directly to the structure without springing the control surface.
r. Monokote or oracover are stiffer than low-temperature films. Tight covering adds a lot to the stiffness of a structure.
s. Mount the control horn in the middle third of the control surface-not at the end. This reduces twist in the control surface.
t. Ball-links put an off-center load on the control horn. Avoid ball links unless there is some weird geometry that makes them necessary. Then use the stiffest control horn that you can find.
U. Mount the servo in a reinforced mount that cannot easily deflect.

If you do all this and you STILL have flutter, send me pictures.