Morphing wings have a large potential to improve the overall aircraft performances, in a way like natural flyers do. By adapting or optimising dynamically the shape to various flight conditions, there are yet many unexplored opportunities beyond current proof-of-concept demonstrations. This review discusses the most prominent examples of morphing concepts with applications to two and threedimensional wing models. Methods and tools commonly deployed for the design and analysis of these concepts are discussed, ranging from structural to aerodynamic analyses, and from control to optimisation aspects. Throughout the review process, it became apparent that the adoption of morphing concepts for routine use on aerial vehicles is still scarce, and some reasons holding back their integration for industrial use are given. Finally, promising concepts for future use are identified.

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

The present paper proposes a set of blending constraints expressed in lamination parameter space, applicable during the continuous optimisation of composite structures. Thicknesses and ply orientations of large composite structures are often locally optimised in response to unequal spatial load distribution. During this process, ensuring structural continuity is essential in order to achieve designs ready to be manufactured. Single step stacking sequence optimisations relying on evolutionary algorithms to enforce continuity, through the application of blending rules, are prone to the curse of dimensionality. By contrast, multi-step optimisation strategies including a continuous sub-step can optimise composite structures with reasonable computational effort. However, the discrepancies between continuous and discrete optimisation step result in performance loss during stacking sequence retrieval. By deriving and applying blending constraints during the continuous optimisation, this paper aim is to reduce the performance loss observed between optimisation levels. The first part of this paper is dedicated to the derivation of blending constraints. The proposed constraints are then successfully applied to a benchmark blending problem in the second part of this paper. Numerical results demonstrate the achievement of near-optimal easy-to-blend continuous designs in a matter of seconds.

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.

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A generic framework for morphing wing aeroelastic analysis and design is presented. The wing is discretised into an arbitrary number of wing segments. Two types of actuation mechanisms are identified: inter-rib mechanisms operating across a wing segment and intra-rib mechanisms acting between two adjacent wing segments. Virtually, any shape can be obtained by distributing four morphing modes over the entire morphing wing. Three are an intra-rib mechanism and one is an inter-rib mechanism. The intra-rib modes are wing shear, twist and extension, and the inter-rib mode is wing folding. The wing is modeled using a close coupling between a non-linear beam formulation and Weissinger aerodynamics. The framework is intended to aid quick preliminary design of morphing wings to trade-off contradictory requirements in a flight mission. The morphing wing can be optimized for discrete points in the flight mission, and for the entire flight mission. The framework can be used to predict aerodynamic performance, load distribution, aeroelastic deformations, and the required actuation forces and moments and corresponding actuation energy. Therefore, the performance gains of wing morphing can be weighed against the energy costs and weight penalties due to the presence of the actuators. The functionality of the framework is demonstrated by making use of a folding and sweeping wing test case.

In this paper, an Incremental Nonlinear Dynamic Inversion (INDI) controller is developed for the flexible aircraft gust load alleviation (GLA) problem. First, a flexible aircraft model captures both inertia and aerodynamic coupling effects between flight dynamics and structural vibration dynamics is presented. Then an INDI GLA controller is designed for this aircraft model based on sensor measurements and the Kalman filter online estimation. Besides, the fifth order Padé approximation is used to model the pure time delay in the state estimation. Furthermore, simulations of the flexible aircraft flying through various spatial turbulence and gust fields demonstrate the effectiveness of the proposed controller on rigid-body motion regulation, vertical load alleviation, wing root bending moment reduction and elastic modes suppression. Additionally, numerical perturbation tests and a Monte-Carlo study show the robustness of the proposed controller to aerodynamic model uncertainties.

This paper describes a new class of flight control actuators using post-buckled precompressed (PBP) piezoelectric elements. These actuators are designed to produce significantly higher deflection and force levels than conventional piezoelectric actuator elements. Classical laminate plate theory (CLPT) models are shown to work very well in capturing the behavior of the free, unloaded elements. A new high transverse deflection model which employs nonlinear structural relations is shown to successfully predict the performance of the PBP actuators as they are exposed to higher and higher levels of axial force, which induces post-buckling deflections. A proof-of-concept empennage assembly and actuator were fabricated using the principles of PBP actuation. A single grid-fin flight control effector was driven by a 3.5′′ (88.9 mm) long piezoceramic bimorph PBP actuator. By using the PBP configuration, deflections were controllably magnified 4.5-fold with excellent correlation between theory and 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 part count with respect to conventional servoactuators by an order of magnitude. Power consumption dropped from 24 W to 100 mW, weight was cut from 108 to 14 g, slop went from 1.6° to 0.02° and current draw went from 5 A to 1.4 mA. The result was that the XQ-138 subscale UAV family experienced nearly a 4% reduction in operating empty weight via the switch from conventional to PBP actuators, while in every other measure gross performance was significantly enhanced.