the control surfaces ahead of the hinge lines at their tips, or inset balanced with extension(s) of the control surface into cut-outs in their supporting fixed surface. Frise ailerons use a variant of the latter balance, with the nose of the up-going surface projecting below the wing, but not vice versa, to provide both balancing and asymmetric drag. Irving balanced ailerons have no projections but harness the aileron deflection induced change of pressure above and below the wing, sensed via the hinge gap, to assist the motion. Mass balancing Flutter occurs when the control surface is displaced from its intended deflection. Because the ailerons are on the long, narrow wings which can twist under load, they are the surface most prone to oscillate. If the centre of gravity is behind the hinge, the surface can move like a pendulum and undergo forced simple harmonic motion with increasing amplitude. Adding balancing weights which make the centre of gravity and hinge line coincident solves the problem. These weights may be in the nose of the surface, or lighter masses attached further ahead of the hinge externally. References Notes Bibliography Oscar Parkes British Battleships Watercraft components Aircraft controls