Design, construction and characterization of a flightworthy piezoelectric solid state adaptive rotor

The development of a new type of flightworthy adaptive rotor system is presented. By building upon earlier adaptive rotor work, a new miniature solid state adaptive rotor (SSAR) was built using directionally attached piezoelectric (DAP) torque-plates controlling Hiller servopaddles. These servopaddles change the rotor disk tilt and thereby induce changes in forces and moments for flight control. To demonstrate the concept, a 23.5 in diameter helicopter rotor was built using DAP servopaddles at the hub. The servopaddles were constructed from PZT-5H piezoceramic actuator sheets bonded symmetrically at 45 degree . An aluminum substrate and a high temperature cure was used to provide precompression. Analytical modeling was accomplished by laminated plate theory along with strip theory aerodynamics and inertial relations. Because propeller moments are proportional to servopaddle deflections at a fixed rotational speed, it was possible to cancel them out by balancing an aeroelastic coupling between the center of mass, aerodynamic center and elastic axis. Bench testing of the SSAR showed that the rotor system could produce static servopaddle deflections in excess of plus or minus 5.8 degree with good agreement between theory and experiment. With the spinning rotor, the servopaddles demonstrated dynamic capability in excess of 2.5 rev super(-1). As the rotor speed was increased, deviations between linear theory and experiment also increased. Nonetheless, the rotor still demonstrated plus or minus 2.7 degree servopaddle deflections at full rotor speed (1600 RPM). A detailed weight statement of the conventional and SSAR systems shows that the SSAR helicopter experienced a 40% reduction in flight control system weight, which resulted in an 8% cut in total aircraft gross weight, a 26% drop in parasite drag and a drop in flight control system part count from 94 components down to five.