Novel, bi-directional, variable camber airfoil via macro-fiber composite actuators

A novel, bi-directional variable camber airfoil design employing a type of piezoceramic composite actuator known as Macro-Fiber Composite (MFC) is presented. From a broader perspective, the study aims to understand the behavior of solid-state aerodynamic force generation in high dynamic pressure airflow. The novel airfoil employs two active surfaces and a single four-bar (box) mechanism as the internal structure. The airfoil produces deflection in both directions from a flat camber line. The paper focuses on actuation modeling and response characterization under aerodynamic loads. A parametric study of aerodynamic response is employed to optimize kinematic parameters of the airfoil. The concept is fabricated implementing eight MFC 8557-P1 type actuators in a bimorph configuration to construct the active surfaces. The box mechanism generates deflection and camber change as predicted. Wind tunnel experiments are conducted on a 12.6% maximum thickness, 127 mm chord airfoil. Aerodynamic and structural performance results are presented for a flow rate of 15 m/s and Reynolds Number of 127,000. Non-linear effects due to aerodynamic and piezoceramic hysteresis are identified and discussed. A lift coefficient change of 1.67 is observed purely due to voltage actuation. A maximum L/D ratio of 26.7 is recorded through voltage excitation. Results are compared to conventional, fixed-camber airfoils evaluated by other researchers.