Post-buckled precompressed piezoelectric flight control actuator design, development anddemonstration

Abstract

This paper describes a new class of flight control actuators using post-buckledprecompressed (PBP) piezoelectric elements. These actuators are designed to producesignificantly higher deflection and force levels than conventional piezoelectric actuatorelements. Classical laminate plate theory (CLPT) models are shown to workvery well in capturing the behavior of the free, unloaded elements. A new hightransverse deflection model which employs nonlinear structural relations is shown tosuccessfully predict the performance of the PBP actuators as they are exposed tohigher and higher levels of axial force, which induces post-buckling deflections. Aproof-of-concept empennage assembly and actuator were fabricated using theprinciples of PBP actuation. A single grid-fin flight control effector was driven by a3.5′′ (88.9 mm) long piezoceramic bimorph PBP actuator. By using the PBP configuration,deflections were controllably magnified 4.5-fold with excellent correlation between theoryand experiment. Quasi-static bench testing showed deflection levels in excess of ± 6° at rates exceeding 15 Hz. The new solid state PBP actuator was shown to reduce the partcount with respect to conventional servoactuators by an order of magnitude. Powerconsumption dropped from 24 W to 100 mW, weight was cut from 108 to 14 g, slop went from1.6° to0.02° and current draw went from 5 A to 1.4 mA. The result was that the XQ-138 subscale UAVfamily experienced nearly a 4% reduction in operating empty weight via the switch fromconventional to PBP actuators, while in every other measure gross performance wassignificantly enhanced.