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Purpose – The purpose of this study is to develop an active controller of both leading-edge (LE) and trailing-edge (TE) control surfaces for an unmanned air vehicle (UAV) with a composite morphing wing. Design/methodology/approach – Instead of conventional hinged control surfaces, both LE and TE seamless control surfaces were integrated with the wing. Based on the longitudinal state space equation, the root locus plot of the morphing wing aircraft, with a stability augmented system, was constructed. Using the pole placement, the feedback gain matrix for an active control was obtained. Findings – The aerodynamic benefits of a morphing wing section are compared with a wing of a rigid control surface. However, the 3D morphing wing with a large sweptback angle produces a washout negative aeroelastic effect, which causes a significant reduction of the control effectiveness. The results show that the stability augmentation system can significantly improve the longitudinal controllability of an aircraft with a morphing wing. Practical implications – This study is necessary to analyse the effect of a morphing wing on an UAV and perform a comparison with the rigid model. Originality/value – The control surfaces assignment plan for trim, pitch and roll control was obtained. An active control algorism for the morphing wing was created to satisfy the required stability and control effectiveness by operating the LE and TE control surfaces according to flight conditions. The aeroelastic effect of control derivatives on the morphing aircraft was considered. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate energy harvesting from the unfavorable gust response of a piezoelectric wing. An aeroelectroelastic model is built for the evaluation and improvement of the harvesting performance. The structural model is built based on the Euler–Bernoulli beam theory. The unsteady aerodynamics, combined with 1-cosine gust load, are obtained from Jones׳ approximation of the Wagner function. The state-space equation of the aeroelectroelastic model is derived and solved numerically. The energy conversion efficiency and output density are defined to evaluate the harvesting performance. The effects of the sizes and location of the piezoelectric transducers, the load resistance in the external circuit, and the locations of the elastic axis and gravity center axis of the wing are studied, respectively. The results show that, under a given width of the transducers in chordwise direction, there are one thickness of the transducers corresponding to highest conversion efficiency and one smaller optimal value for the output density. The conversion efficiency has an approximate linear relationship with the width. As the transducers are placed at the wing root, a maximum conversion efficiency is reached under a certain length in the spanwise direction, whereas a smaller length helps reaching a larger output density. One optimal resistance is found to maximize the conversion efficiency. The rearward shift of either the elastic axis or gravity center axis improves the energy output while reducing the conversion efficiency. [ABSTRACT FROM AUTHOR]

An investigation was made into the nonlinear aeroelastic behavior of a composite wing with morphing trailing edge actuated by curved beams. Based on the design concept, an experimental wing model was built and a finite element model was created using MSC Patran/Nastran software. Impact test of the experimental model was carried out and the test data were used to validate the finite element models. In order to investigate the effect of freeplay nonlinearity between discs attached to the curved beams and wing skins, a nonlinear aeroelastic equation in modal coordinate was created. Generalized structural mass, damping, and stiffness matrixes were printed with DMAP language in Nastran. Doublet lattice method and Roger’s approximation were used to calculate unsteady aerodynamic influence coefficients matrix. In the analysis, the effect of morphing stiffness on critical flutter speed was studied. In addition, Hopf bifurcation and limit cycle oscillation were detected for the aeroelastic system with freeplay. The results show that the freeplay nonlinearity may reduce convergence speed and accelerate divergence of aeroelastic responses. [ABSTRACT FROM PUBLISHER]

A morphing flap integrated with an actuation mechanism was designed and investigated. Based on structure parameters from static experiments, a finite element model of the flap was created within MSC Patran software. Normal modal analysis and linear flutter analysis were carried out firstly. V-g and V-f curves were obtained to determine the critical flutter speeds with and without the actuation mechanism. Structural mass, damping, stiffness, and aerodynamic matrixes were printed with DMAP language to form an aeroelastic equation in modal coordinate. The freeplay nonlinearity between disks attached to the curved beams and wing skins was considered in the aeroelastic analysis. An unsteady aerodynamic influence coefficients matrix was calculated by Roger's approximation. The nonlinear aeroelastic equation in modal coordinate was solved by an iterative program written with MATLAB software. Based on the reduced-order aeroelastic model, the effect of freeplay on aeroelastic responses was investigated. Numerical results show that the freeplay nonlinearity may reduce critical flutter speed, leading to supercritical Hopf bifurcation. [ABSTRACT FROM AUTHOR]

Abstract: Aeroelastic two-dimensional wing section with both trailing-edge (TE) and leading-edge (LE) was investigated in this paper through numerical simulation in time domain. Structural stiffness and damping in pitch degree of freedom were represented by nonlinear polynomials. Open-loop limit cycle oscillation (LCO) characters of two examples were studied, and flutter boundaries with initial conditions were obtained. Parametric uncertainties in both pitch stiffness and damping were considered in the design of adaptive control laws to depress LCOs. Firstly an adaptive controller based on partial feedback linearization was derived for the wing section with a single TE control surface. Secondly a structured model reference adaptive control law was designed for the aeroelastic system with both TE and LE control surfaces. The results show that the designed control laws are effective for flutter suppression, and that considering damping uncertainty has positive effect on flutter control. It may reduce convergent time or increase flutter speed. [Copyright &y& Elsevier]

In this paper, a piezoaeroelastic energy harvester based on an airfoil with double plunge degrees of freedom is proposed to additionally take advantage of the vibrational energy of the airfoil pitch motion. The analytical model of the proposed harvester is built, and an equivalent model using the well-explored pitch–plunge configuration is presented. The nonlinear aerodynamics is calculated based on the dynamic stall model. The dynamic response, average power output, energy harvesting efficiency, and cut-in speed (flutter speed) of the proposed harvester are numerically studied. It is demonstrated that the harvester with double-plunge configuration outperforms its equivalent pitch–plunge counterpart in terms of both the power output and energy harvesting efficiency beyond the flutter boundary. In addition, case studies are performed to reduce the cut-in speed and to enhance the energy harvesting efficiency of the proposed harvester, including the airfoil mass characteristics, the configuration, mass, damping, and stiffness characteristics of the two plunge supporting devices, and the load resistances in the external circuits. It is shown that the cut-in speed is greatly reduced by increasing the airfoil mass while tuning the mass eccentricity. The mass of the first (windward) supporting device should be a bit smaller than that of the second one for an applicable cut-in speed and a high-energy harvesting efficiency. Besides, the decrease of airfoil mass moment of inertia or the damping of the supporting devices is shown to be beneficial for the energy harvesting performance. In addition, the optimal location of the first supporting device is found to be at the airfoil leading edge. Decreasing the distance between the two supporting devices reduces the cut-in speed. The load resistances affect the cut-in speed slightly, and optimal values are found to maximize the energy harvesting efficiency. [ABSTRACT FROM AUTHOR]

Abstract: Nonlinearities in aircraft mechanisms are inevitable, especially in the control system. It is necessary to investigate the effects of them on the dynamic response and control performance of aeroelastic system. In this paper, based on the state-dependent Riccati equation method, a state feedback suboptimal control law is derived for aeroelastic response and flutter suppression of a three degree-of-freedom typical airfoil section. With the control law designed, nonlinear effects of freeplay in the control surface and time delay between the control input and actuator are investigated by numerical approach. A cubic nonlinearity in pitch degree is adopted to prevent the aeroelastic responses from divergence when the flow velocity exceeds the critical flutter speed. For the system with a freeplay, the responses of both open- and closed-loop systems are determined with Runge–Kutta algorithm in conjunction with Henon’s method. This method is used to locate the switching points accurately and efficiently as the system moves from one subdomain into another. The simulation results show that the freeplay leads to a forward phase response and a slight increase of flutter speed of the closed-loop system. The effect of freeplay on the aeroelastic response decreases as the flow velocity increases. The time delay between the control input and actuator may impair control performance and cause high-frequency motion and quasi-periodic vibration. [ABSTRACT FROM AUTHOR]