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A servoflap that uses a piezoelectric bender to deflect a trailing edge flap for use on a helicopter rotor blade was designed, built, and tested. This servoflap design is an improvement over a design developed previously at MIT. The design utilizes a new flexure mechanism to connect the piezoelectric bender to the control surface. The efficiency of the bender was improved by tapering its thickness with length. Also, the authority of the actuator was increased by implementing a nonlinear circuit to control the applied electric field, allowing a greater range of actuator voltages. Experiments were carried out on a bench test article to determine the frequency response of the actuator, as well as hinge moment and displacement capabilities. Flap detections of 11.5 deg or more were demonstrated while operating under no load conditions at frequencies up to 100 Hz. The data indicate that if properly scaled, the actuator will produce flap deflections greater than 5 deg at the 90% span location on a full- scale helicopter. In addition, the first mode of the actuator was at 7/rev frequency of the target model rotor. Proper inertial scaling of this actuator could raise this modal frequency to greater than 10/rev on an operational helicopter, which is adequate for most rotor control purposes. A linear state space model of the actuator was derived. Comparisons of this model with the experimental data highlighted a number of mild nonlinearities in the actuator's response. However, the agreement between the experiment and analysis indicate that the model is a valid tool for predicting actuator performance.
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