What is: Flutter is a rapid vibration of any control surface, which can destroy it very quickly.

What causes flutter: The turbulences and the pressure pulses of the stream of air flowing around the control surface, create forces that push that surface to rotate around the hinges' line, in an harmonic oscillation or vibration. That vibration may grow until reaching resonance conditions, when the frequencies of the disturbing oscillation and the control surface match. The conditions that make flutter appear more easily are: high air speed, loose linkages and big control surfaces.

How to prevent it: Tapeing the hinge line is always good, because it eliminates turbulences created by air leaks between the high and low pressure sides of the wing. However, the only known effective cure for flutter is to move the center of gravity or mass of the control surface to the hinges' line. No mass moving, no reinforced oscillation or resonance is possible. To achieve that in models and real airplanes, balancing weights are installed on the control surface in front of the hinge' line, so the assembly just balances at that line.

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