torsional aileron flutter

A flutter caused by the wing twisting under loads imposed on it by the movement of the ailerons. The diagram gives the sequence for a half-cycle. In Figure A, the aileron is displaced slightly downward, exerting an increased lifting force on the aileron hinge. In Figure B, the wing twists about the torsional axis; the trailing edge rises, taking the aileron up with it. The center of gravity of the aileron is behind the hinge line; its inertia tends to make it lag behind, increasing the aileron lift, and so increasing the twisting motion. Figure C indicates that the torsional reaction of the wing has arrested the twisting motion, but the air loads on the aileron cause it to overshoot the neutral position, placing a down load on the trailing edge of the wing. Figure D shows that the energy stored in the twisted wing, along with the aerodynamic load of the aileron, causes the wing to twist in the opposite direction. Torsional aileron flutter can be prevented either by mass balancing the ailerons so that their center of gravity is on, or slightly ahead of, the hinge line, or by making the controls irreversible. All aircraft, except those that have power controls with no normal reversion, have their controls mass balanced.