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 100 mm (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 145 mm (5.8 ) and an axial compression of 70.7 gmf mm −1 , deflection levels increased by more than a factor of 2 to 15.25 • peak-to-peak, with a corner frequency of 34 Hz (an order of magnitude higher than conventional subscale servoactuators). A 1.4 m span subscale UAV was equipped with 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 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 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.

Solid State Adaptive Rotor Using Postbuckled Precompressed, Bending-Twist Coupled Piezoelectric Actuator Elements

“…Figure 10 shows the results from that "edge." By employing the practical experience and modeling techniques of [46][47][48][49][50][51][52], it can be seen that amplification ratios (AR) on the order of 3.5-3.8 are most generally achieved by bidirectional piezoelectric control actuation. Accordingly, the measured AR of 3.8 is seen to be an excellent achievement for the world's first torsionally amplified low-net passive stiffness piezoelectric actuator.…”

“…Rather than pushing the structure through to a bistable situation, a highly controlled axial force could be used to induce a postbuckling effect. This effect would be seen to drive actuator deflections to very high values, but not sacrifice moment generation capability [46][47][48][49][50][51][52][53][54]. These PBP structures outperformed any other piezoelectrically driven actuators by factors of 3 and 4.…”

“…The analytical models called upon were established in [46][47][48][49][50][51][52] to determine the amount of axial forces required to fundamentally null the net passive stiffness of the pizoelectric actuator element. The overall PBP assembly design was laid out to provide several overarching properties:…”

Adaptive Fight Control Actuators and Mechanisms for Missiles, Munitions and Uninhabited Aerial Vehicles (UAVs)

“…46 This discovery was shown to dramatically improve flight control actuator performance and has been integrated into a number of flight control systems. [47][48][49][50][51][52][53] …”

Design space of embeddable variable stiffness bi-stable elements for morphing applications

“…Most of the underlying mechanisms rely on coupling several physical domains, rendering the approaches active or semi-active. Alternatively, stiffness adaptation capacity can originate in the structurally elastic phenomena of buckling [7][8][9][10][11][12][13][14][15][16][17] and multi-stability [18][19][20][21][22][23][24][25].…”