Morphing Wing Flight Control Via Postbuckled Precompressed Piezoelectric Actuators

Abstract

The design, modeling, and testing of a morphing wing for flight control of an uninhabited aerial vehicle is detailed. The design employed a new type of piezoelectric flight control mechanism which relied on axial precompression to magnify control deflections and forces simultaneously. This postbuckled precompressed bending actuator was oriented in the plane of the 12% thick wing and mounted between the end of a tapered D-spar at the 40% chord and a trailing-edge stiffener at the 98% chord. Axial precompression was generated in the piezoelectric elements by an elastic skin which covered the outside of the wing and served as the aerodynamic surface over the aft 70% of the wing chord. A two-dimensional semi-analytical model based on the Rayleigh-Ritz method of assumed modes was used to predict the static and dynamic trailing-edge deflections as a function of the applied voltage and aerodynamic loading. It was shown that static trailing-edge deflections of 3:1 deg could be attained statically and dynamically through 34 Hz, with excellent correlation between theory and experiment. Wind tunnel and flight tests showed that the postbuckled precompressed morphing wing increased roll control authority on a 1.4 meter span uninhabited aerial vehicle while reducing weight, slop, part-count, and power consumption. Nomenclature A = extensional stiffness matrix or aspect ratio B = coupled laminate stiffness matrix b = span C L , C l = three-dimensional, section lift coefficient c = chord D = bending laminate stiffness E = total energy F a = aerodynamic force F 0 = precompression force f = frequency K = structural stiffness K = stiffness matrix k = spring stiffness L = actuator length M = applied moment vector M = mass matrix m = mass N = applied force vector n = number of shape functions P = lift force p = pressure q = amplitude T = kinetic energy t = thickness or time U = internal energy or velocity u = horizontal displacement V = potential energy or voltage w = vertical displacement = angle of attack = trailing-edge deflection = normal strain = trailing-edge end rotation = curvature = unloaded actuator strain = potential energy = density = normal stress = velocity potential = disturbed velocity potential = shape function Subscripts a = actuator b = bonding layer c = circulatory ex = external h = hinge point l = laminate m = morphing part nc = noncirculatory sp = negative spring rate t = thermal

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] …”

Inertial attitude control of a bat-like morphing-wing air vehicle

“…The possibility of having actuated wings has allowed the design of new mechanisms that improve over classical fixed/rotary-wings MAV flight performance. As a result, different morphing-wing concepts and materials have emerged together with control methodologies that allow for accurate wing-actuation [4], [5], [6], [7], [8], [9].…”