Post-buckled precompressed elements: a new class of control actuators for morphing wingUAVs

Abstract

This paper describes how post-buckled precompressed (PBP) piezoelectric benderactuators are employed in a deformable wing structure to manipulate its camberdistribution and thereby induce roll control on a subscale UAV. By applying axialcompression to piezoelectric bimorph bender actuators, significantly higher deflectionscan be achieved than for conventional piezoelectric bender actuators. Classicallaminated plate theory is shown to capture the behavior of the unloaded elements. ANewtonian deflection model employing nonlinear structural relations is demonstrated topredict the behavior of the PBP elements accurately. A proof of concept 100 mm(3.94′′) span wing employing two outboard PBP actuator sets and a highly compliantlatex skin was fabricated. Bench tests showed that, with a wing chord of 145 mm(5.8′′) and an axialcompression of 70.7 gmf mm−1, deflection levels increased by more than a factor of 2 to15.25° peak-to-peak, with a corner frequency of 34 Hz (an order of magnitude higher thanconventional subscale servoactuators). A 1.4 m span subscale UAV was equippedwith two PBP morphing panels at the outboard stations, each measuring 230 mm(9.1′′) in span. Flight testing was carried out, showing a 38% increase in roll control authorityand 3.7 times greater control derivatives compared to conventional ailerons. The solid statePBP actuator in the morphing wing reduced the part count from 56 down to only 6,with respect to a conventional servoactuated aileron wing. Furthermore, powerwas reduced from 24 W to 100 mW, current draw was cut from 5 A to 1.4 mA,and the actuator weight increment dropped dramatically from 59 g down to 3 g.