On a Bistable Flap for an Airfoil

This paper presents the design and wind tunnel testing results of a full scale helicopter rotor blade section with an electromechanically actuated bistable trailing edge flap. The bistability of the flap derives from the use of bistable composite material. In one state the flap follows the profile of the standard rotor blade section. In its second stable state the flap deflects the trailing edge downwards by ten degrees. The flap system is designed to change between these two positions when the helicopter moves between hover and forward flight conditions. The bistability of the flap system means that the electromechanical actuator is only required to do work to transit between these two stable states, not to maintain the states. Tests were conducted in the University of Bristol’s large low speed wind tunnel. These open loop tests consisted of measurements of lift, drag, and pitching moment when the flap is in both stable states. Some preliminary transitory analysis was also conducted.