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An evaluation of the commercial transport aircraft developed over the past decades evidences an increasing trend toward the use of high aspect-ratio wings. This trend is justified by the well-known effect of slender wings in reducing fuel consumption, leading to lower operational costs and a milder environmental impact. There are many studies about the effects of geometric nonlinearities on aeroelastic behavior of very flexible wings in symmetrical maneuvers. However, geometric nonlinearities may also significantly affect the aeroelastic behavior of the wing under non-symmetrical conditions, especially when ailerons are deflected. Within this context, this work presents a static fluid–structure interaction approach to evaluate the rolling characteristics of very flexible wings. First, a modified version of the very flexible Pazy Wing from Aeroelastic Prediction Workshop (AEPW-3) is proposed, now equipped with ailerons. Next, a fluid–structure interaction tool that couples a full potential aerodynamic solver with an implicit nonlinear structural solver is presented to allow simulations of wings with deflected ailerons. The presented method is applied to the modified Pazy wing considering multiple linear and nonlinear structural analyses, for different aileron deflection angles. The results show that when geometric nonlinearity effects are considered, the aileron effectiveness tends to decrease as the structural flexibility increases. On the other hand, if geometric nonlinearities are neglected, the aileron effectiveness falsely enhances as the wing flexibility rises.

Flapping wing micro aerial vehicles (FWMAVs) with flexible wings offer unique advantages across multiple scenarios due to their high energy efficiency and precision capabilities. This study explores the fluid-structure interaction (FSI) mechanisms and aerodynamic performance differences among three flexible wing motion patterns – passive twisting (PT), chordwise active twisting (CAT), and ‘Figure-8’ active twisting (FAT) – using a bidirectional FSI numerical simulation platform. A bionic wing model (aspect ratio AR = 3.86) and a Multiphysics-coupled framework were developed to evaluate the effects of dynamic wing torsion on lift and energy recovery. Results show that PT enhances aerodynamic performance by delaying flow separation and stabilising leading-edge vortices (LEVs). At 4 m/s, the average lift of flexible wings (FW) with PT is 6.31 times higher than that of rigid wings (RW). Active twisting strategies further improve efficiency: CAT increases average lift by 143% compared to PT at θmax  = 40°, while FAT achieves 14.9% energy recovery rate through wake capture and elastic potential energy release, with an elastic energy release rate 2.79 times higher than CAT. Vortex dynamics analysis reveals that active twisting optimises lift by enhancing LEV circulation and proximity to the wing surface. CAT strengthens LEV attachment near the wing root, while FAT stabilises vortices at the wingtip. This research provides insights into energy efficiency optimisation and active control strategies for FWMAVs, highlighting the benefits of flexible deformation and intelligent motion regulation in improving aerodynamic performance and energy management.

The trailing edge deformable wing is one of the main development directions of future aircraft design. The technology of active camber of wing trailing edge can significantly improve the aerodynamic performance of aircraft. In this paper, the motor drives the parabolic crankshaft and the distributed crankshaft drives the flexible skin of the trailing edge of the wing, which can realize the deflection of the trailing edge of the wing at a large angle of 0~30 degrees. At the same time, the surface of the wing is continuous and smooth. Moreover, the aerodynamic simulation results of the deformed wing show that the trailing edge deflection is beneficial to increase the lift. It can increase the maximum lift coefficient by 2 times and the maximum lift drag ratio by 18%. Adaptive flexible wing technology is applied to rocket sleds with side wings. This technology can increase the downward pressure of the side wing of the rocket block and improve the operation safety.

This paper addresses the robust output regulation and even output constraints of a flexible wing system, where an exosystem is supposed to generate the unknown time-varying output constraints, output disturbances, distributed disturbances, boundary disturbances and references. Besides the signals of displacements and velocities, high-order boundary signals are used to guarantee the exponential convergence of the tracking errors. At first, two exosystem observers are designed based on the PDE observer of the wing system in order to give the approximation of the unknown references and output constraints. Then, two observer based output feedback controls are proposed based on state feedback controls and the PDE-ODE coupled observer. For the closed-loop system, the tracking errors are proved to be convergent toward zero, and further regulated to be restrained by two unknown time-varying and positive trajectories. Numerical simulation shows the effectiveness of the proposed robust controls.

The long-range migration of monarch butterflies, extended over 4000 km, is not well understood. Monarchs experience varying density conditions during migration, ranging as high as 3000 m, where the air density is much lower than at sea level. In this study, we test the hypothesis that the aerodynamic performance of monarchs improves at reduced density conditions by considering the fluid–structure interaction of chordwise flexible wings. A well-validated, fully coupled Navier–Stokes/structural dynamics solver was used to illustrate the interplay between wing motion, aerodynamics, and structural flexibility in forward flight. The wing density and elastic modulus were measured from real monarch wings and prescribed as inputs to the aeroelastic framework. Our results show that sufficient lift is generated to offset the butterfly weight at higher altitudes, aided by the wake-capture mechanism, which is a nonlinear wing–wake interaction mechanism, commonly seen for hovering animals. The mean total power, defined as the sum of the aerodynamic and inertial power, decreased by 36% from the sea level to the condition at 3000 m. Decreasing power with altitude, while maintaining the same equilibrium lift, suggests that the butterflies generate lift more efficiently at higher altitudes.

Flight and swimming in nature can inspire the design of highly adaptive robots capable of working in complex environments. In this letter, we reviewed our work on robotic propulsion in the air and water, with a specific focus on the crucial functions of elastic components involved in the driving mechanism and flapping wings. Elasticity in the driving mechanism inspired by birds and insects can enhance both the aerodynamic efficiency of flapping wings and robustness against disturbances with appropriate design. A flapping wing surface with a stiffness distribution inspired by hummingbirds was fabricated by combining tapered spars and ribs with a thin film. The biomimetic flexible wing could generate more lift than the nontapered wing with a similar amount of power consumption. Underwater flapping-wing propulsion inspired by penguins was investigated by combining the 3-degree-of-freedom (DoF) flapping mechanism and hydrodynamic calculation, which indicates that wing bending increases the propulsion efficiency. This work demonstrates the importance of passive deformation of both wing surfaces and driving mechanisms for improving the fluid dynamic efficiency and robustness in flight and swimming, as well as providing biological insight from an engineering perspective.

Beam-like flexible structures are of interest in many fields of engineering, particularly aeronautics, where wings are frequently modelled and represented as such. Experimental modal analysis is commonly used to characterise the wing’s dynamical response. However, unlike other flexible structure applications, no benchmark problems involving high-aspect-ratio flexible wings have appeared in the open literature. To address this, this paper reports on ground vibration testing results for a flexible wing and its sub-assembly and parts. The experimental data can be used as a benchmark and are available to the aeronautical and structural dynamics community. Furthermore, non-linearities in the structure, where present, were detected. Tests were performed on the whole wing as well as parts and sub-assembly, providing four specimens. These were excited with random vibration at three different amplitudes from a shaker table. The modal properties of a very flexible high-aspect-ratio wing model, its sub-assembly and parts, were extracted, non-linear behaviour was detected and the experimental data are shared in an open repository.

Three-dimensional numerical simulations are performed to examine the effects of dynamic wing morphing of a hummingbird-inspired flexible flapping wing on its aerodynamic performance in hovering flight. The range analysis and variation analysis in the orthogonal experiment are conducted to assess the significance level of various deformations observed in the hummingbird wings on wing aerodynamic performance. It has been found that both camber and twist significantly can affect lift, and twist has an even higher significant impact on lift efficiency. Spanwise bending, whether out-of-stroke-plane or in-stroke-plane, has a negligible impact on lift and efficiency, and the in-stroke-plane bending can cause lift to decrease to an extent. Optimal parameters for determining the wing deformations are selected and tested to validate the conclusions drawn in the analysis for the results in orthogonal experiment. Through a comparison study between the optimized wings and the rigid wing, it is found that although the wing flexibility can cause the net force to decrease, the flexible wing used less energy to bring the net force closer to the vertical direction, thereby improving the lift efficiency. This study provides an aerodynamics understanding of the efficiency improvement of the hummingbird-inspired flexible flapping wing.

The increasing number of applications involving the use of UAVs has motivated the research for design considerations that increase the safety, endurance, range, and payload capability of these vehicles. In this article, the dynamics of a flexible flapping wing is investigated, focused on designing bio-inspired UAVs. A dynamic model of the Flapping-Wing UAV is proposed by using 2D beam elements defined in the absolute nodal coordinate formulation, and the flapping is imposed through constraint equations coupled to the equation of motion using Lagrange multipliers. The nodal coordinate trajectories are obtained by integrating the equation of motion using the Runge–Kutta algorithm. The imposed flapping is modulated using a proposed smooth function to reduce transient vibrations at the start of the motion. The results shows that wing flexibility yields significant differences compared to rigid-wing models, depending on the flapping frequency. Limited amplitude of oscillation is obtained when considering a non-resonant flapping strategy, whereas in resonance, the energy levels efficiently increase. The results also demonstrate the influence of different flapping strategies on the energy dissipation, which are relevant to increasing the time of flight. The proposed approach is an interesting alternative for designing flexible, bio-inspired, flapping-wing UAVs.

Over the last decades, there has been great interest in understanding the aerodynamics of flapping flight and development of flapping wing Micro Air Vehicles (FWMAVs). The camber deformation and twisting has been demonstrated quantitatively in a number of insects, but making artificial wings that mimic those features is a challenge. This paper reports the development and characterization of artificial wings that can reproduce camber and twisting deformations. By replacing the elastic material at the wing root vein, the root vein would bend upward and inward generating an angle of attack, camber, and twisting deformations while the wing was flapping due to the aerodynamic forces acting on the wing. The flapping wing apparatus was employed to study the flexible wing kinematics and aerodynamics of real scale insect wings. Multidisciplinary experiments were conducted to provide the natural frequency, the force production, three-dimensional wing kinematics, and the effects of wing flexibility experienced by the flexible wings. The results have shown that the present artificial wing was able to mimic the two important features of insect wings: twisting and camber generation. From the force measurement, it is found that the wing with the uniform deformation showed the higher lift/power generation in the flapping wing system. The present developed artificial wing suggests a new guideline for the bio-inspired wing of the FWMAV.