I do not believe that sealing a hinge, on it's own, has is great (or direct) cure for flutter, although some secondary effects do apply.

What it does, is this. First, sealing the gap does reduce "loss". This does increase the effectiveness of the surface. This means that the surface needs slightly less movement to achieve the same desired control effect. In consiquence, slightly greater leverage can be given (meaning low hole in the servo horn and high hole in the surface horn) can be used. This does help increase the speed required to flutter, due to the "advantage" of the servo.

Secondly, sealing the surface can add a bit of stiffness, due to the material "crammed" into the gap, this makes movement less drastic, and helps reduce the "odds" that flutter will occour.

Airspeed causes flutter. If a pilot (or designer) claims that a plane WILL NOT FLUTTER, then that person has not experimented with enough airspeed. There is no such thing as an airplane that WILL NOT FLUTTER. There is no such thing as a "mod" that eliminates the chance of flutter, only one that changes the speed at which an airplane WILL FLUTTER. Yes, some "mods" actually lower flutter speed, meaning an increase in chance of flutter.

The only proven method of directly ruducing the chance of flutter is to reduce airspeed. The only proven method to increase the speed required for flutter is to add a mass balance. Otherwise, we only can better the stiffness of the control system. High Torque servos and short (stiff) push rods do help.

I seal all surfaces on all aerobatic planes. No discussion, and no reason to not do so. I do not, however, consider it to be a replacement for discretion for throttle stick placement.

Once again, all aircraft will flutter!