Flexible Wing Research Articles

Measurement of wing motion, deformation, and inertial forces of a biomimetic butterfly.

This paper introduces a method for measuring wing motion, deformation, and inertial forces in bio-inspired aircraft research using a camera motion capture system. The method involves placing markers on the wing surface and fitting rigid planes to determine the wing's spatial axis. This allows for describing the wing's rigid motion and obtaining deformation characteristics, such as deflection, twist angle, and gap distance of the forewing and hindwing. An image-based method is proposed for determining wing mass distribution, mass blocks, and mass points for inertial force measurement. The study addresses wing motion, deformation, and inertial force measurement in a real butterfly-like flapping wing vehicle and demonstrates the effectiveness of the approach. The results reveal that inertial forces play a negligible role in the generation of lift peaks and contribute minimal lift during the entire flapping cycle. Furthermore, a transitional phase between downstroke and upstroke is found in flexible wing motion, which has high lift production. This measurement approach offers a rapid and effective solution to experimental challenges in bio-inspired aircraft design and optimization.

Observer-Based Adaptive Control for a Coupled PDE–ODE System of a Flexible Wing

Observer-Based Adaptive Control for a Coupled PDE–ODE System of a Flexible Wing

Unsteady load alleviation on highly flexible bio-inspired wings in longitudinally oscillating freestreams

This study delves into the aerodynamic behaviour of a highly flexible NACA 0012 aerofoil, drawing inspiration from avian feathers to handle a gust. We first examined unsteady flow on a rigid wing both experimentally and numerically and then explored the implications of introducing wing flexibility purely numerically. Our findings underscore the potential of composite materials in alleviating the oscillating aerodynamic forces on a wing under a streamwise gust. This behaviour is attributed to its capacity to destabilize the laminar separation bubble, fostering a more stable turbulent boundary layer. While direct avian evidence remains limited, it is postulated that in nature, such mechanisms could mitigate undesired wing flapping, optimizing energy consumption in perturbed environments.

A Smart Wing Model: From Design to Testing in a Wind Tunnel with a Turbulence Generator

The paper concerns the technology of the design, realization, and testing of a flexible smart wing in a wind tunnel equipped with a turbulence generator. The system of smart wing, described in detail, consists mainly of: a physical model of the wing with an aileron; an electric servomotor of broadband with a connecting rod-crank mechanism for converting the rectilinear motion of the servoactuator into the aileron deflection; two transducers: an encoder for measuring the deflection of the control aileron and an accelerometer mounted on the wing to measure its bending and torsional vibrations; a procedure for determining the mathematical model of the wing by experimental identification; a turbulence generator in the wind tunnel; implemented ℋ∞ and LQG algorithms for active control of vibrations. The attenuation experimentally obtained for the aeroelastic vibrations of the wing, but also for those accentuated by the turbulence, reaches values of up to 50%.

Nonlinear fluid-solid coupling responses of flexible skin-based morphing camber wings

Two original finger-like morphing camber wings (MCWs) based on flexible woven and corrugated composite skins are elaborately designed and skillfully manufactured, and experimentally validated. It is manifested that both original finger-like MCWs could flexibly and continuously morph without buckling and wrinkling, illustrating the ideal morphing camber function. In accordance with the MCWs geometries and constitutive relationships of flexible composite skins, novel analytical model is then devised for predicting the material and geometric nonlinear mechanical behaviours of the MCWs. Good agreement has been achieved between the experiments and the predictions, demonstrating the effective usage of new analytical model of finger-like MCWs. Finally, new fluid-solid coupling FE model is generated for evaluating fluid-solid interaction on mechanical responses of the MCWs under aerodynamic pressure. It is born out that fluid-solid coupling has a significant adverse impact on mechanical behaviours of finger-like MCW, and flexible woven composite skin holds superiority over flexible corrugated composite skin in terms of out-of-plane deformation resistance and bearing-load capacity under aerodynamic pressure. New model opens an avenue to numerically evaluate fluid-solid interaction on mechanical responses of the MCWs under aerodynamic pressure.

Insect‐Inspired Drones: Adjusting the Flapping Kinetics of Insect‐Inspired Wings Improves Aerodynamic Performance

Insects flap their wings through a highly specialized musculoskeletal system that allows the wings to rotate about three degrees of freedom. Consequently, the wingtip trajectory is adjustable in 3D, and accompanied with appropriate wing feathering (wing pitch). Remarkably, the complex flapping motion is achieved by thoracic muscles acting on the wing hinge. The wings themselves do not possess muscles but adjust their shape and orientation by elastically deforming due to the loads applied on them during flapping. Previous attempts to develop insect‐inspired flapping drones have mostly focused on simplified linear flapping mechanisms, which do not utilize the interaction between the wing flexibility and flapping kinematics to its full potential. Here, the aim is to improve flapping drones’ performance by introducing mechanisms that mimic insects’ flight. The first is an elastic beam mechanism, allowing the wing root to swing during flapping, and the second is a passive wing pitch mechanism that allows the wing to rotate at stroke reversals. The two mechanisms are tested using high‐fidelity insect‐inspired 3D‐printed wings and show a sixfold improvement of aerodynamic performance compared to linear flapping kinetics of the same flexible wings. This underscores the necessity of bioinspired flapping mechanisms in future flapping drones.

Aerodynamics and stability of hawkmoth forward flight with flexible wing hinge

Aerodynamics and stability of hawkmoth forward flight with flexible wing hinge

Adaptive dynamic programming base on MMC device of a flexible high-altitude long endurance aircraft

Flexible high-altitude long endurance (HALE) aircraft face challenges such as the delay effect caused by aeroelasticity and low efficiency during high-altitude cruising. This paper addresses a new active control scheme that replaces traditional aerodynamic control surfaces with longitudinal and lateral moving masses and adopts an observer-based adaptive dynamic programming (ADP) control strategy, aiming to solve the attitude control of HALE aircraft with flexible wings. Firstly, considering the account of unsteady aerodynamics, attitude angular velocity, and moving masses, complete dynamic model is established for a flexible aircraft, in order to more accurately describe the state of the HALE aircraft. This model includes two moving masses to replace traditional ailerons and elevators. It is difficult to design attitude control strategies considering the delay effects and unknown dynamic disturbances of HALE aircraft. To this end, the actor-critic structure of the ADP approach is designed to achieve the near-optimal control strategy of the system, which eliminates the need for prior knowledge of model parameters. A fixed time disturbance observer (FTDO) is proposed to estimate the future tracking error information and unknown disturbances to improve the control performance of the attitude. Finally, the stability of the system is proved via the Lyapunov technique and a comprehensive simulation of HALE aircraft is provided. The simulation results show that the proposed control algorithm can enable the aircraft attitude angles to quickly response and maintain stability under gust wind. Compared with a single ADP control strategy, this paper's algorithm has advantages in response speed and error.

Bi-direction and flexible multi-mode morphing wing based on antagonistic SMA wire actuators

This work evaluates the viability of a cutting-edge flexible wing prototype actuated by Shape Memory Alloy (SMA) wire actuators. Such flexible wings have garnered significant interest for their potential to enhance aerodynamic efficiency by mitigating noise and delaying flow separation. SMA actuators are particularly advantageous due to their superior power-to-weight ratio and adaptive response, making them increasingly favored in morphing aircraft applications. Our methodology begins with a detailed delineation of the fishbone camber morphing wing rib structure, followed by the construction of a multi-mode morphing wing segment through 3D-printed rib assembly. Comprehensive testing of the SMA wire actuators’ actuation capacity and efficiency was conducted to establish their operational parameters. Subsequent experimental analyses focused on the bi-directional and reciprocating morphing performance of the fishbone wing rib, which incorporates SMA wires on the upper and lower sides. These experiments confirmed the segment’s multi-mode morphing abilities. Aerodynamic assessments have demonstrated that our design substantially improves the Lift-to-Drag ratio (L/D) when compared to conventional rigid wings. Finally, two phases of flight tests demonstrated the feasibility of SMA as an aircraft actuator and the validity of flexible wing structures to adjust the aircraft attitude, respectively.

Experimental investigation on aerodynamic characteristics of flexible wing MAV under horizontal gust

A flexible wing micro air vehicle and a rigid wing micro air vehicle, both with flying wing designs, were designed and developed, and the aerodynamic characteristics of the flexible micro air vehicle and the rigid micro air vehicle under steady wind and horizontal gust were studied in a wind tunnel. The difference in aerodynamic characteristics between flexible wing and rigid wing micro air vehicles was given. The research results showed that the aerodynamic characteristics of a flexible wing were better than those of a rigid wing under both steady wind and horizontal gust environments, and a flexible wing had the ability to delay stall and mitigate the impact of gust, which was beneficial to stable flight. The particle image velocimetry measurement results showed that due to the deformation of the flexible wing, the flow patterns on the rigid wing and flexible wing surfaces were different, resulting in changes in the aerodynamic characteristics of micro air vehicles.

Flow sensing on dragonfly wings.

One feature of animal wings is their embedded mechanosensory system that can support flight control. Insect wings are particularly interesting as they are highly deformable yet the actuation is limited to the wing base. It is established that strain sensors on insect wings can directly mediate reflexive control; however, little is known about airflow sensing by insect wings. What information can flow sensors capture and how can flow sensing benefit flight control? Here, we use the dragonfly (Sympetrum striolatum) as a model to explore the function of wing sensory bristles in the context of flight control. Combining our detailed anatomical reconstructions of both the sensor microstructures and wing architecture, we used computational fluid dynamics simulations to ask the following questions. (1) Are there strategic locations on wings that sample flow for estimating aerodynamically relevant parameters such as the local effective angle of attack? (2) Is the sensory bristle distribution on dragonfly wings optimal for flow sensing? (3) What is the aerodynamic effect of microstructures found near the sensory bristles on dragonfly wings? We discuss the benefits of flow sensing for flexible wings and how the evolved sensor placement affects information encoding.

Adaptive observer based controls for a flexible wing system under unknown output disturbances

This paper considers a wing system under unknown output disturbances, references, distributed disturbances and boundary disturbances. These signals have unknown frequencies, amplitudes and phases, and are then supposed to be from an exosystem with an unknown matrix. In this sense, we firstly find the wing system merely under the references and output disturbances, for which the PDE observer can be easily designed based on the measurable outputs. Then, an adaptive observer is designed for a detectable exosystem so that the references have known coefficients and approximately known states. Adaptive observer based controls are then proposed for the closed-loop system so that the convergence of tracking error and the boundedness of the states are guaranteed. Two simulation examples are compared to show the robustness of the designed controls.

A Framework for Rapidly Predicting the Dynamics of Flexible Solar Arrays in the China Space Station with a Verification Based on On-Orbit Measurement Data

The Chinese space station is a complex structure with large flexible appendages. Obtaining the on-orbit response characteristics of such a structure under different working conditions is a traditional and classic challenge in the field of dynamics. To address the on-orbit dynamics of the China Space Station, the basic equations for dynamic reduction, assembly and data recovery of linear and nonlinear substructures are derived based on the reduction and recovery theory, and a fast coupling analysis framework for flexible systems with nonlinear attachments is formed. This coupling analysis framework is adopted to quickly acquire the dynamic response of the China Space Station during in-orbit operation, thereby guiding the design. Taking SZ-15 radial docking to the Chinese Space Station as the object, the substructure of six nonlinear flexible arrays is reduced, the full flexible dynamic equation of the space station is assembled, and the response of each part of the flexible wing during the docking process is analyzed and recovered. By designing a reasonable and reliable flexible wing test scheme in-orbit, the acceleration at the root and top of the flexible wing during the docking of SZ-15 is obtained. The measured data in-orbit show that the acceleration analysis results of the typical parts of the flexible wing have a good agreement, which verifies the correctness of the fast coupling analysis framework of the flexible system. Hence, the dynamic coupling characteristics analysis of the main structure of the space station and the flexible wing based on this method can better guide the rationality of the design of the dynamic characteristics of the Chinese Space Station.

Aerodynamic Analysis of Hovering Flapping Wing Using Multi-Plane Method and Quasi-Steady Blade Element Theory

In the design of flapping-wing micro-size air vehicles capable of hovering, wings serve as the primary source of hovering power, making the analysis of aerodynamics and aerodynamic efficiency crucial. Traditional quasi-steady models treat the wings as single rigid plane, neglecting the deformable characteristics of flexible wings. This paper proposes a multi-plane method that, in conjunction with various design parameters of flexible wings in a two-dimensional plane, analyzes their deformation characteristics under the assumption of multiple planes in three-dimensional space, and describes the deformation of wings during flapping. By combining the quasi-steady aerodynamic model, aerodynamic analysis of the deformed wings can be conducted. The relationship between the slack angle, wing flapping position, and wing deformation are analyzed, along with their effects on aerodynamics and aerodynamic efficiency. Experiments validate the deformation patterns of wings during flapping and compare the simulated aerodynamic forces with measured ones. The results indicate that wing deformation can be accurately described by adjusting the parameters in the multi-plane method and that the aerodynamic analysis using this method closely approximates the average lift results. Additionally, the multi-plane method establishes a connection between wing morphology and aerodynamic forces and efficiency, providing valuable insights for aerodynamic analysis.

Folding angle and wing flexibility influence the flight performance of origami winged fruits

Folding angle and wing flexibility influence the flight performance of origami winged fruits

WITHDRAWN: Visualized neural network-based vibration control for pigeon-like flexible flapping wings

This study investigates pigeon-like flexible flapping wings, which are known for their low energy consumption, high flexibility, and lightweight design. However, such flexible flapping wing systems are prone to deformation and vibration during flight, leading to performance degradation. It is thus necessary to design a control method to effectively manage the vibration of flexible wings. This paper proposes an improved rigid finite element method (IRFE) to develop a dynamic visualization model of flexible flapping wings. Subsequently, an adaptive vibration controller was designed based on non-singular terminal sliding mode (NTSM) control and fuzzy neural network (FNN) in order to effectively solve the problems of system uncertainty and actuator failure. With the proposed control, stability of the closed loop system is achieved in the context of Lyapunov’s stability theory. At last, a joint simulation using MapleSim and MATLAB/Simulink was conducted to verify the effectiveness and robustness of the proposed controller in terms of trajectory tracking and vibration suppression.The obtained results have demonstrated great practical value of the proposed method in both military (low-altitude reconnaissance, urban operations, and accurate delivery, etc.) and civil (field research, monitoring, and relief for disasters, etc.) applications.

Coupled fluid-structure simulation of a flapping wing using free multibody dynamics software

AbstractComputer simulations offer invaluable insights into fluid-structure interaction phenomena, increasing our understanding of complex behaviors within fluid flows and enabling predictions of consequential effects. This paper explores flapping wing simulation using an original toolchain based on free software. The structural domain is modeled using multibody dynamics, interfaced with arbitrary fluid dynamics solvers through a general-purpose multiphysics coupling library. The proposed toolchain is validated against benchmark models, demonstrating its effectiveness in various applications. Our study, inspired by experimental ones, applies this coupling to investigate the hydroelastic behavior of a flexible wing. Wing motion characteristics, structural properties, and convergence criteria are analyzed through numerical simulations. While achieving appreciable agreement with experimental data on wing motion ratios, challenges in dealing with large displacements have been identified. Nonetheless, the present study provides valuable insights into fluid-structure interactions, laying the groundwork for future refinements in computational modeling techniques and advancing the understanding of bio-inspired flight mechanisms.

Rapid dynamic aeroelastic response analysis of the highly flexible wing with distributed propellers influence

Abstract A rapid nonlinear aeroelastic framework for the analysis of the highly flexible wing with distributed propellers is presented, validated and applied to investigate the propeller effects on the wing dynamic response and aeroelastic stability. In the framework, nonlinear beam elements based on the co-rotational method are applied for the large-deformation wing structure, and an efficient cylinder coordinate generation method is proposed for attached propellers at different position. By taking advantage of the relatively slow dynamics of the high-aspect-ratio wing, propeller wake is modeled as a quasi-steady skewed vortex cylinder with no updating process to reduce the high computational cost. Axial and tangential induced velocities are derived and included in the unsteady vortex lattice method. For the numerical cases explored, results indicate that large deformation causes thrust to produce wing negative torsion which limits the displacement oscillation, and slipstream mainly increases the response values. In addition, an improvement of flutter boundary is found with the increase of propeller thrust while slipstream brings a destabilising effect as a result of the increment of dynamic pressure and local lift. The great potential of distributed propellers in gust alleviation and flutter suppression of such aircraft is pointed out and the method as well as conclusions in this paper can provide further guidance.

Analysis and Design of Bat-Like Flapping-Wing Aircraft

As the only flying mammal in nature, bats have superb flight skills and aerodynamic characteristics that have been the subject of research by scholars from all over the world. In recent years, the research on bionic flapping-wing aircraft has made good progress. However, such research mostly uses birds or insects as the research objects, and there are few studies on bat-imitating flapping-wing aircraft. This paper combines the characteristics of bats’ flexible wings to model and analyze the aerodynamic theory and parameters of the flexible wings of bat-like flapping aircraft. The longitudinal dynamic and kinematic model design of bat-like flapping aircraft is based on the pitch angle of LQR. In terms of height control, the controller uses energy control methods to complete the closed-loop longitudinal channel control of the bat-like flapping aircraft. Finally, this study performed the simulation and flight experimentation of the designed bat-like flapping aircraft, demonstrating the correctness of this system.

Theoretical research on dynamic modeling of rigid–flexible coupling system with double joint folded wing

For meeting the requirements of tactical missiles seeking miniaturized launch devices for storage, transportation, and launch, a tube-launched missile wing is adopted, which folds before launch and quickly unfolds after launch. As a structure installed on the missile body to generate the required aerodynamic force for manipulating the missile, the tube-launched missile wing can effectively stabilize the missile’s flight attitude. At present, most research on the unfolding mechanism of missile folding wings is focused on one-time folding. When the wingspan is large, multiple folding is required to meet the launch requirements of modern tube-launched missiles. Therefore, this article designs a dual-joint folding wing deployment mechanism and studies the rigid–flexible coupling dynamic modeling and related technologies of folding wings based on this structure. Based on the inertial coupling between large-scale rigid body motion and structural flexible deformation, the folding wing breaks through the element convergence of the model and achieves the applicability of the structural model through zero-order approximation model analysis and other technologies. Simulation results show that the hybrid coordinate method can fully and accurately display the vibration information of flexible folding wings. At different speeds, the first-order coupling model is more advanced than the zero-order coupling model. In addition, increasing rotational speed, increasing wing thickness, and reducing wing span length can effectively increase the fundamental frequency of wing flutter. The structural design of folding wings has shown important reference significance.