Post-buckled precompressed elements: A new class of control actuators for morphing wing UAVs

Abstract

This paper describes how post-buckled precompressed (PBP) piezoelectric bender actuators are employed in a deformable wing structure to manipulate its camber distribution and thereby induce roll control on a subscale UAV. By applying axial compression to piezoelectric bimorph bender actuators, significantly higher deflections can be achieved than for conventional piezoelectric bender actuators. Classical laminated plate theory is shown to capture the behavior of the unloaded elements. A Newtonian deflection model employing nonlinear structural relations is demonstrated to predict the behavior of the PBP elements accurately. A proof of concept 100mm (3.94 ′′) span wing employing two outboard PBP actuator sets and a highly compliant latex skin was fabricated. Bench tests showed that, with a wing chord of 145mm (5.8′′) and an axial compression of 70.7gmfmm-1, deflection levels increased by more than a factor of 2 to 15.25° peak-to-peak, with a corner frequency of 34Hz (an order of magnitude higher than conventional subscale servoactuators). A 1.4m span subscale UAV was equipped with two PBP morphing panels at the outboard stations, each measuring 230mm (9.1′′) in span. Flight testing was carried out, showing a 38% increase in roll control authority and 3.7 times greater control derivatives compared to conventional ailerons. The solid state PBP actuator in the morphing wing reduced the part count from 56 down to only 6, with respect to a conventional servoactuated aileron wing. Furthermore, power was reduced from 24W to 100mW, current draw was cut from 5A to 1.4mA, and the actuator weight increment dropped dramatically from 59g down to 3g. © IOP Publishing Ltd.