Darryl - to a point you are correct. If the linkage system were infinitely large then it would also be infinitely heavy and there would of course be no flutter. You could not drive the control surface either, which is a problem, and the aeroplane would be a tad heavy for takeoff, which is a bigger problem!!!

By making the control linkage system heavy you are reducing the resonant frequency of the system. If it is heavy enough then resonance will not occur at any speed above the stall, ie. after takeoff. This is not a proper solution. You would need massive servos to get the desired control response, and there are still no guarrantees that resonance will not occur at some harmonic (multiple of the fundamental resonant frequency).

The proper solution is to make the linkages light and stiff. There are no resonant modes below the fundamental, so if the fundamental occurs above the airplane's maximum speed then it can be assumed that no resonance will occur below this speed.

Keep in mind that the system under consideration here is EVERYTHING that moves with the control surface. You MUST keep the moments of inertia low, the masses low, the stiffnesses high, and ZERO free play.

For ailerons, before you mass balance then try the following;

1. Short, light, stiff pushrods (titanium - aluminium is lighter but it WILL fail by fatigue eventually).
2. Ball race rod-ends.
3. Lightweight servo arms.
4. Light weight horns on the ailerons (and use aluminium screws - from MicroFasteners).
5. Split the ailerons if they are large ie. 4 instead of 2 and use smaller servos.
6. DO NOT join ailerons together, especially left to right. This is very bad and can result in a particularly destructive resonant mode (destructive = spectacular, show stopper!!!). Ailerons should be driven by independent servos.

Ailerons need to be stiff in torsion because they are driven from a single point. Torsional flex modes contribute to the elasticity of the entire control system and therefore flutter. Using two links to the surface may help but is offset by the increased live mass of the two linkages. A better solution is to just increase the torsional stiffness. You could build the entire aileron on a lightweight, thinwall carbon fibre tube. This would provide for very high torsional stiffness. The structure behind the tube is just a passenger so make it very light indeed. The LE of the aileron would then be circular, which is what we want anyway for a good wing seal.

Horn placement should be to prevent additive torsional vibration modes, ie. not in the centre and not at 1/3, or 1/4, or any other low value integral fraction, but keeping each section as short as possible. Just off centre, say 5/11 would be a good place. Keep in mind that driving the ailerons from adjacent servos increases the moment of inertia of the wing and so reduces the crispness of the aileron response. Driving the torque tube from the wing root may be a viable option.

PS. For readers unfamiliar with the term Moment of Inertia.

For linear motion - the MASS of an object is that property of an object which resists linear acceleration (linear motion).
For rotary motion - the MOI of an object is that property of an object which resists angular acceleration (rotary motion).

Linear: Force = Mass x Accelration
Rotary: Torque = MOI x angular acceleration

High MOI = Weights concentrated at tips
Low MOI = Weight concentrated near centre of rotation

I hope this clarifies a few points. If anyone is helped by this discussion then it is worth the trouble.
Cheers all.