Methodology for in-flight tracking of helicopter rotor blades using shape memory alloy actuators

This paper describes the concept, design, fabrication and testing of a shape memory alloy (SMA) wire actuated tab for in-flight tracking of helicopter rotors. To achieve fine adjustment of tab angle, it is equipped with a locking mechanism and a position feedback controller. The primary components of the actuator are the SMA wires, a fiberglass clamp and a fiberglass hinge tube. The clamp and the hinge tube allow for two separate sets of SMA wires to be utilized. One set of the wires is heat activated while the other remains at ambient conditions. The actuator was mounted in an NACA 0012 blade section chord. Bench-top and open-jet wind tunnel tests conducted on a wing section with 2-wire and 4-wire actuators mounted inside the profile and at a maximum angle of attack of 15 deg and velocity of 120 ft/sec (Mach.11) are described. It is shown that a 2-wire actuator, with an initial plastic deformation of 4.2% is sufficient to deflect the tab down by 31 deg at a wind speed of 120 ft/sec. In bench-top tests, a position feedback controller demonstrated the ability to track a desired tab position in about 10 seconds. The locking mechanism showed the ability to lock the tab in a desired position during power-off condition.