Actuating device with multiple stable positions

A mechanical actuating device for moving an aerodynamic or hydrodynamic surface includes at least one flexure member confined in an elastically deformed condition. The flexure member is movable against the force generated by its elastic deformation to move the device into one of a plurality of stable positions, in which the device, and therefore the aerodynamic or hydrodynamic surface, are held by the force generated by elastic deformation of the flexure member. Since the flexure member is always elastically deformed, it "snaps" between discrete, stable positions and is held firmly in each. In another embodiment more flexure members can be used to provide additional stable positions. In one application, the actuating device is used as a trailing edge tab for a helicopter or tiltrotor blade to reduce 1/rev vibrations. The device can be actuated manually or electrically using shape-memory alloy wires to snap the flexure members into their various stable positions.