Development of an SMA Actuator for In-flight Rotor Blade Tracking

A new and improved solution to the helicopter blade-tracking problem has been investigated. A discrete, blade-installed actuator utilizing shape memory alloy (SMA) torsion tubes has been developed to enable in-flight rotor tracking. SMA torsion tubes from three materials were tested and one was selected for its cyclic stability. Improved tube fabrication, heating, end attachment methods, and locking schemes were developed. The final prototype actuator employed two biaxial SMA tubes for actuation/bias, an SMA-activated lock for power off operation, and integrated microprocessor control electronics. Tests under static and dynamic loading showed that actuation requirements, except for bandwidth, were met. Increased bandwidth may be obtained by improved control algorithms or cooling. The developed SMA actuator enables an in-flight, real-time adjustment of a blade-tracking tab. Projected payoffs are reduced maintenance cost as well as reduced helicopter vibrations and improved performance.