As part of the Smart Structures for Rotorcraft Consortium project, blade mounted servo-flap actuators are being developed in the Active Materials and Structures Laboratory. These actuators are being designed for use as part of a closed loop vibration, noise and/or performance control system. One possible design for such an actuator is a piezoelectric bimorph bender. The bender is mounted to the rotor blade spar and extends back to a trailing edge flap. Current research in the lab is involved with developing and implementing a high efficiency discrete actuator for such rotor control purposes.
Previous research was centered on developing a piezoelectric multimorph bender. A bench-test model of such an actuator was built and tested in the Active Materials and Structures Lab.
Experimental measurements on this actuator have shown that it can deliver flap deflections greater than 5 deg for a 20% of chord flap located at the 90% span location of an operational helicopter. Furthermore, the first resonant frequency of this actuator is at 90 Hz, which is equivalent to the 7/rev scaled rotor frequency. Proper inertial design of the flap can increase this first modal frequency to as high as 10/rev, which is more than adequate for helicopter rotor control. In addition to having a high bandwidth, the frequency response of this actuator is also relatively constant over this bandwidth, as is demonstrated in the films showing actuator deflections at 0.5, 10, and 61 Hz.
Recent research into interdigitated electrode piezoelectric fiber composites indicates that a bender composed of such composites can yield a greater energy density than that of the Hall and Prechtl bender discussed above. To test this hypothesis, a bender using IDEPFCs was constructed as part of an undergraduate senior project at MIT by Corinne Ilvedson and Malinda Lutz under the direction of Professor Steven R. Hall. A photo of this actuator is shown below as well as a movie of its experimental performance.