Elastic Wing Research Articles

Simulation Analysis of the Aerodynamic Performance of a Bionic Aircraft with Foldable Beetle Wings in Gliding Flight.

Beetles have excellent flight performance. Based on the four-plate mechanism theory, a novel bionic flapping aircraft with foldable beetle wings was designed. It can perform flapping, gliding, wing folding, and abduction/adduction movements with a self-locking function. In order to study the flight characteristics of beetles and improve their gliding performance, this paper used a two-way Fluid-Structure Interaction (FSI) numerical simulation method to focus on the gliding performance of the bionic flapping aircraft. The effects of elastic model, rigid and flexible wing, angle of attack, and velocity on the aerodynamic characteristics of the aircraft in gliding flight are analyzed. It was found that the elastic modulus of the flexible hinges has little effect on the aerodynamic performance of the aircraft. Both the rigid and the flexible wings have a maximum lift-to-drag ratio when the attack angle is 10°. The lift increased with the increase of the gliding speed, and it was found that the lift cannot support the gliding movement at low speeds. In order to achieve gliding, considering the weight and flight performance, the weight of the microair vehicle is controlled at about 3 g, and the gliding speed is guaranteed to be greater than 6.5 m/s. The results of this study are of great significance for the design of bionic flapping aircrafts.

Flutter Onset Prediction Based on Parametric Model Estimation

This paper presents a thorough evaluation of three flutter prediction techniques based on the well-understood autoregressive moving-average (ARMA) parametric model. Other than the original stability parameter that is derived from the identified autoregressive coefficients, the flutter margin and the Houbolt–Rainey (H-R) method are also presented and adjusted to provide alternative flutter predictions. From the application aspects, the empirical flutter margin, which is insensitive to the damping estimation, is first proposed. Feasibility of the empirical flutter indictor is demonstrated in this study. Taking advantage of the inherent recursive nature, the recursive least-squares algorithm with forgetting factor is suggested to perform the linear extrapolation iteratively at different flow conditions to facilitate an accurate flutter prediction. To verify the performance of the inspected methods, a linear pitch–plunge aeroelastic system and a dedicated wind-tunnel flutter test of an elastic wing are adopted to carry out the analyses for flutter statistics. While the extensive simulations are easy to implement on the aeroelastic idealization, the challenge of generating an adequate sample size based on the limited experimental data arises. To this end, the concept of surrogate data is first introduced to the flutter statistical analysis. Surrogate datasets generated via the iterative amplitude adjusted Fourier transform algorithm manage to describe the statistical behavior of the evaluated stability parameters. Both numerical and experimental results further substantiate the validity of the ARMA parametric model for aeroelastic modeling and provide alternative flutter prediction parameters with their own scope of application.

Morphological diversification has led to inter-specific variation in elastic wing deformation during flight in scarab beetles.

Insect wing shapes and the internal wing-vein arrangement are remarkably diverse. Although the wings lack intrinsic musculature to adjust shape actively, they elastically deform due to aerodynamic and inertial loads during flapping. In turn, the deformations alter the shape of the wing profile affecting the aerodynamic force. To determine how changes in wing-vein arrangement affect elastic wing deformation during free flight, we compared elastic wing deformations between free-flying rose chafers (Protaetia cuprea) and dung beetles (Scarabaeus puncticollis), complementing the comparison with wing static bending measurements. The broader relevance of the results to scarab beetle divergence was examined in a geometric morphometric (GM) analysis of wing-vein arrangement in 20 species differing in phylogeny and ecology. Despite rose chafers and dung beetles demonstrating similar flapping kinematics and wing size, the rose chafer wings undergo greater elastic deformation during flapping. GM analyses corrected for phylogenetic relatedness revealed that the two beetles represent extremes in wing morphology among the scarab subfamilies. Most of the differences occur at the distal leading edge and the proximal trailing edge of the wing, diversifying the flexibility of these regions, thereby changing the pattern of elastic wing deformation during flapping. Changes to local wing compliance seem to be associated with the diversification of scarab beetles to different food sources, perhaps as an adaptation to meet the demands of diverse flight styles.

Research on Vibration Suppression for AGARD Wing Based on State Space Model

Based on the Observer method, the unsteady aerodynamic reduced order model is established. The aerodynamic, structural and control parts are in the form of state space equations. The state feedback control law is designed by linear quadratic regulator (LQR) method, and the active flutter suppression of aeroelastic system is realized. The three-dimensional AGARD elastic wing is selected as an example. The simulation results show that the active control law designed by the model reduction technique can effectively stabilize the response of the system, and the critical speed of closed-loop flutter increases greatly.

A review on Aerodynamic performance of NACA Airfoil for various Reynolds number

Morphing and shape shifting technologies offer a wide range of applications in airplane design and are complicated to operate effectively with current existing methods. Variable camber wings is a innovative control surface technology designed as aero elastic wing shaping control device which minimizes drag throughout its flight envelope and increases performance in different flight conditions which leads to corresponding increase in airplane flight efficiency. In order to achieve these results one has to rely on different flight actuator configurations and techniques to achieve variable camber mechanism. Variable camber can be achieved span vice or chord wise on an aerofoil where a slight variation in thickness changes lift coefficient. Variable camber wing is a flexible structure that changes its shape profile at different aerodynamic load these types of wings are tested under different load conditions and Reynolds number in wind tunnel facility to have a detailed study on the performance. In this paper an attempt has been made to cover all the shape shifting and morphing wing technologies and compare the results and discuss the possibility of adaption of such technology in aerospace industry.

Elastic wing deformations mitigate flapping asymmetry during manoeuvres in rose chafers (Protaetia cuprea).

ABSTRACTTo manoeuvre in air, flying animals produce asymmetric flapping between contralateral wings. Unlike the adjustable vertebrate wings, insect wings lack intrinsic musculature, preventing active control over wing shape during flight. However, the wings elastically deform as a result of aerodynamic and inertial forces generated by the flapping motions. How these elastic deformations vary with flapping kinematics and flight performance in free-flying insects is poorly understood. Using high-speed videography, we measured how contralateral wings elastically deform during free-flight manoeuvring in rose chafer beetles (Protaetia cuprea). We found that asymmetric flapping during aerial turns was associated with contralateral differences in chord-wise wing deformations. The highest instantaneous difference in deformation occurred during stroke reversals, resulting from differences in wing rotation timing. Elastic deformation asymmetry was also evident during mid-strokes, where wing compliance increased the angle of attack of both wings, but reduced the asymmetry in the angle of attack between contralateral wings. A biomechanical model revealed that wing compliance can increase the torques generated by each wing, providing higher potential for manoeuvrability, while concomitantly contributing to flight stability by attenuating steering asymmetry. Such stability may be adaptive for insects such as flower chafers that need to perform delicate low-speed landing manoeuvres among vegetation.

Methods of determination of aerodynamic loads at flight in continuous turbulence

This paper investigates the loads which acting on the elastic high aspect ratio wing of a cargo aircraft flying in continuous turbulence. According to the requirements of CS-25, gusts that are normal to the flight path and uniform at spanwise are considered. Random gusts at continuous turbulence are described by the spectral density (PSD) of gusts suggested by Karman.The simulation of the flow around the calculated model aircraft are performed by the methods of computational aerodynamics: dipole lattice method (DLM), high order panel method (Panel), dipole lattice and constant pressure method (DLM/CPM), vortex frame method (VFM). Flow is accepted as quasi-stationary or non-stationary. The elastic mass model of the aircraft is described by beam. The discrepancies between the results of the load calculations from the continuous turbulence on the aircraft elastic wing are determined.The results show that taking into account the effects of non-stationary aerodynamics results in somewhat lower values of loads on the aircraft structure: up to 2% in the root sections of the wing and up to 5% in the end sections. The largest difference is observed using the dipole lattice method and the smallest one is in the panel method. The magnitude of the load increase from turbulence is almost the same for all the considered methods. Its main difference is observed when determining loads in horizontal flight, where the lowest values are obtained when using DLM / CPM.The main results are presented in graphical and tabular form.

Dynamic Distributed Morphing Control of an Aeroelastic Wing for a Small Drone

This paper presents a flight control approach for small unmanned aerial vehicles. The active morphing of an elastic wing was used to generate aerodynamic control forces to control both the aeroelastic deformation and the flight dynamic motion. A piezoelectric composite was chosen as the smart material that can apply direct control force and generate strain distribution on the wing. The piezoelectric actuators were designed according to the structural dynamic properties of the membrane wing. By integrating the piezoelectric forces into the finite element model, control mode shapes can be defined for each kind of morphing control input. Both the natural and the control mode shapes were used for the order reduction. Thus, the order-reduced model can demonstrate both the active morphing and the passive elastic deformation of the wing. The open-loop control response of the aeroservoelastic model shows that the passive aeroelastic deformation can be used to augment the active morphing. The flight maneuvering control response shows that the rolling moment generated by the morphing wing is enough for the lateral flight control of the small drone. The active morphing can be partly diminished by the maneuvering motion.

Aeroelastic Stability Analysis of Tailored Pretwisted Wings

In this paper, the aeroelastic stability of a tailored aircraft wing with different pretwist distributions is investigated. The structure of the wing is modeled using the geometrically exact fully intrinsic beam theory of Hodges, whereas the aerodynamic loads are simulated by an incompressible unsteady aerodynamic model. The governing nonlinear partial differential equations are discretized using a time-space scheme, and the stability of the system is sought by evaluating the eigenvalues of the linearized system. The wings have linear or quadratic pretwist distributions, and the effect of various twist angles on isotropic and tailored wings is investigated. In this study, the effect of pretwist is considered on both the aerodynamic and structural models. Moreover, the effect of wing structure taper ratio in conjunction with the pretwist is investigated. The preliminary results obtained for a wing modeled as a clamped-free beam are compared with those reported in the literature and excellent agreement is observed. It is concluded that the pretwist angle leads to mode coupling and also has a significant effect on the flutter speed of the wing. By pretwisting the wing, the flutter speed of the wing with respect to the clean wing increases until a specific twist value and then decreases. Moreover, adding the pretwist to the wing decreases the flutter frequency. Finally, results highlighting the effect of bend-twist elastic coupling and wing taper ratio in combination with the pretwist angle on the aeroelastic stability of the wing are provided.

Investigation of Dynamic Buckling of a Wing Model in Air Flow

The paper deals with studying a dynamic stability of the wing model in the ram airflow. As known, at a certain flow rate that is called critical, there is a phenomenon of self-excited non-damping flexural-torsional self-vibrations, named flutter. A two-mode elastic system wing model is under consideration, as is common in the literature in the field concerned. The paper continues and develops investigations of well-known scientists in this field, such as V.L. Biderman, S.P. Strelkov, Ya.G. Panovko, I. I. Gubanova, E.P. Grossman, J.Ts. Funen, etc. A great deal of papers dedicated to this problem and published by abovementioned and other scientists, give only the problem formulation and the derivation of equations, often in a fairly simplified form, do not offer solutions of these equations for specific numerical parameters of the wing model, and do not study how these parameters affect the flutter onset velocity.The paper details the derivation of linear differential equations of small vibrations of the wing model in the flow, determines the natural frequencies and shapes of flexural-torsional vibrations, checks their orthogonality, studies vibrations under the influence of aerodynamic force and moment, determines the critical flow velocity for a number of system parameters, and draws a conclusion about the influence of these parameters on the critical velocity. In particular, it studies how such a parameter as the distance between the center of gravity and the center of stiffness affects the critical velocity, as well as how the stiffness of the model's spring suspension, which simulates the stiffness characteristics of the wing impacts on bending and torsion. The calculation results allow us to draw conclusion concerning the methods of dealing with this phenomenon. One of the promising options may be, in addition to varying the geometric and rigid parameters of the system, the introduction of additional mass to be an analogue of the vibration damper. The paper may be of interest both for engineering students who learn the theory of mechanical vibrations, and for engineering-specialists in aero-elasticity and dynamic stability of elements in mechanical systems.

Transonic static aeroelastic and longitudinal aerodynamic characteristics of a low-aspect-ratio swept wing

Based on the CFD/CSD coupling method, the transonic static aeroelastic characteristics of the low-aspect-ratio swept wing was studied by numerical simulation. The Navier-Stokes equation was used as the fluid computational control equations. The flow field mesh deformation was performed using the Transfinite Interpolation method (TFI) method, and the data exchange on the CFD/CSD coupling interface was realized by the Constant Volume Transform (CVT) method. Based on the above method, the transonic static aeroelastic coupling calculation program was developed. The results of ONERA M6 wing static aeroelastic calculated by the coupling program were compared with wind tunnel test and reference results, and the effectiveness of the program was verified. Through numerical simulation, the influence of different angles of attack and Mach number on the static aeroelastic deformation and torsion angle of the wing are studied. Finally, by comparing the surface pressure cloud and pressure coefficient of the rigid wing and the elastic wing, the influence of static aeroelastic on the longitudinal aerodynamic characteristics and stability of the wing is mainly analyzed.

Wind-Tunnel Study of the Autoregressive Moving-Average Flutter Prediction Method

This paper presents an experimental study of flutter prediction via autoregressive moving-average (ARMA) system identification and the use of a linear stability parameter. System identification at subcritical (preflutter) conditions is based on measured structural responses to excitation by natural air turbulence. The current study investigates the application aspects of the methodology in a dedicated wind-tunnel experiment. An elastic wing was designed and manufactured using rapid prototyping and tested in a subsonic wind tunnel all the way to flutter. Structural responses were recorded by accelerometers, strain gauges, and fiber-optic sensors (measuring strains). The data were filtered, averaged, and used for system identification and flutter prediction. The study focuses on the prediction characteristics and accuracy, method applicability with various dynamic data, and signal processing techniques. It was shown that both accelerations and strains provide good data for system identification and accurate flutter prediction, even when sparse and short records are used. Averaging significantly improves the flutter onset prediction and its confidence bounds. The study results support the feasibility of using the ARMA method for flutter flight test.

Wing Elasticity Effects on Store Separation

The study explores wing elasticity effects on the store-separation process. The nominal test case is that of an unmanned aerial vehicle that carries two identical stores on two wing stations. The stores are ejected during straight and level flight at , 2500 m. Simultaneous, time-accurate analysis of the dynamic aeroelastic wing response and the store’s trajectory reveals that the most significant aeroelastic effect is a roll motion developed by the store. This roll motion is due to misalignment of the ejection force vector and the store’s center of gravity, due to the wing’s static and dynamic elastic deformations. The second part of the paper presents a parametric study of the effects of various structural and configurational parameters on the wing’s response and consequently on the store’s rolling motion. A more flexible wing, a heavier store, a larger ejection force, or a shorter ejection period all result in increased store rolling. Store ejection from an asymmetric configuration (of a single store) yielded a very similar store roll compared to the symmetric ejection. The dynamic wing response plays a major role in generating the store roll, in different conditions of friction between the store body and ejection piston. A practical observation is that the store roll is dependent on the relation between the ejection period and the low structural frequencies of the wing. This can be used to plan an optimal ejection profile.

Transonic flutter suppression for a three-dimensional elastic wing via active disturbance rejection control

The paper presents an error-based active control law for the transonic flutter suppression of a three dimensional elastic wing in a wide range of Mach numbers and dynamic pressures. The extended state observer is the key issue for the presented controller and provides the observed output signal and the observed total disturbance signal at the same time. The observed output signal obtained via the extended state observer enables one to design a feedback control law for adjusting the output errors, while the observed total disturbance signal linearizes the controlled system and guarantees the anti-interference of the proposed controller. To demonstrate the performance of the proposed controller system for transonic flutter suppression, the transonic aeroservoelastic behaviors of a three-dimensional elastic wing with both leading-edge and trailing-edge control surfaces are illustrated as the test cases. During the numerical simulations, only the tailing-edge control surface is used as the control input and the leading-edge control surface is fixed. The numerical results show that the active control law can effectively suppress the transonic flutter at a wide range of Mach numbers and dynamic pressures. Moreover, the controller system has robustness with respect to certain measurement noises and time delay.

Design And Investigation Of Flat–Upper–Surface Airfoil

Attempts to build solar High Altitude Long Endurance (HALE) airplanes are more and more frequent. In the future such airplanes may appear very useful for the economy because they may replace geostationary satellites in several applications for a fraction of cost. Unfortunately, necessary data on altitude effect on photovoltaic cells and batteries performance are not easily available. Therefore, flying testbed for their inexpensive testing is needed. Flat–upper surface airfoil was designed for application in small UAV dedicated for photovoltaic cells investigation at various altitudes. It should enable installation of rigid cells on the top of the wing without significant reduction of aerodynamic performance. It should also decrease a risk of damage of flexible cells due to the significant bending of long aspect ratio, elastic wings. This paper contains description of the design methodology, design assumptions and obtained results. Moreover experiment undertaken to evaluate the design is described as well. The wind tunnel and a semi–span model used for this experiment are presented together with obtained results. The model has exactly the same structure as envisaged structure of UAV, so flexibility of the wing is taken into account.

A simulation-based approach to modeling component interactions during design of flapping wing aerial vehicles

A new flapping wing aerial vehicle (FWAV) simulation methodology is presented that combines models of the key subsystems: (1) the actuator, (2) the battery, and (3) the wings. This approach captures component interactions that are inherently coupled in order to realize system-level designs for optimal system performance. The approach demonstrates that coupling between wing sizing, flapping motions, and loading conditions propagate into the motor–battery model to alter system-level performance properties. For the actuator subsystem model, a generalized servo motor using empirically derived coefficients to describe torque and angular velocity bandwidth in terms of voltage and current. This model is coupled with a lithium polymer battery model accounting for the nonlinear voltage drop and capacity derating effects associated with loading conditions. For aerodynamic predictions of the wing subsystem, a blade element model for predicting aerodynamic forces is coupled with an elastic wing deformation model that accounts for bending and twisting of the blade elements. System-level performance is then modeled in a design case study by coupling all of the subsystem models to account for relevant interactions, which generates a design trade space spanning a range of wing sizes, airspeeds, and flapping condition. The results from the simulation offer insight into vehicle configuration settings that provide maximum performance in terms of lift and endurance for the Robo Raven II flapping wing aerial vehicle. Experimental validation of the modeling approach shows good predictive accuracy. In addition, the presented framework offers a generalized approach for coupling interacting subsystems to improve overall predictive accuracy and identify areas where component-level improvements may offer system-level performance gains.

Cardiomyocytes-Actuated Morpho Butterfly Wings.

Morpho butterflies are famous for their wings' brilliant structural colors arising from periodic nanostructures, which show great potential value for fundamental research and practical applications. Here, a novel cellular mechanical visualizable biosensor formed by assembling engineered cardiac tissues on the Morpho butterfly wings is presented. The assembled cardiomyocytes benefit from the periodic parallel nanoridges of the wings and can recover their autonomic beating ability with guided cellular orientation and good contraction performance. As the beating processes are accompanied by the cardiomyocytes' elongation and contraction, the elastic butterfly wing substrate undergoes the same cycle of deformations, which causes corresponding synchronous shifts in their structural colors and photonic bandgaps for self-reporting of the cell mechanics. It is demonstrated that this self-reporting performance can be further improved by adding oriented carbon nanotubes in the nanoridges of the wings for the culture. In addition, taking advantage of the similar size of the cardiomyocyte and a single Morpho wing scale, the investigation of single-cell-level mechanics can be realized by detecting the optical performance of a single scale. These remarkable properties make these butterfly wings ideal platforms for biomedical research.

Flutter analysis of a viscoelastic tapered wing under bending–torsion loading

The dynamic stability of a tapered viscoelastic wing subjected to unsteady aerodynamic forces is investigated. The wing is considered as a cantilever tapered Euler–Bernoulli beam. The beam is made of a linear viscoelastic material where Kelvin–Voigt model is assumed to represent the viscoelastic behavior of the material. The governing equations of motion are derived through the extended Hamilton’s principle. The resulting partial differential equations are solved via Galerkin’s method along with the classical flutter investigation approach. The developed model is validated against the well-known Goland wing and HALE wing and good agreement is obtained. Different solution methods, namely; the k method, the p-k method, and the flutter determinant method are compared for the case of elastic wing. However, when the viscoelastic damping is introduced, the k and p-k methods become less effective. The flutter determinant method is modified and employed to carry out non-dimensional parametric study on the Goland wing. The study includes the effects of parameters such as the taper ratio, the density ratio, the viscoelastic damping of wing structure and many other parameters on the flutter speed and flutter frequency. The study reveals that a tapered wing would be more dynamically stable than a uniform wing. It is also observed that the viscoelastic damping provides wider stability region for the wing. The investigation shows that the density ratio, bending-to-torsion frequency ratio, and the radius of gyration have significant effects on the dynamic stability of the wing. Based on the obtained results, a wing with an elastic center and inertial center that are located closer to the mid-chord would be more dynamically stable.

Aerodynamic Characteristics of Elastic Wings Morphed and Vibrated in Uniform Flows and Separated Flows Around Them

In this study, experimental investigation is performed into modification to aerodynamic characteristics by distortion and vibration of planar wings with various Young’s modulus as well as flow fields around them. Motions of the wings are captured with a high-speed camera. Flows around them are evaluated with phase locked PIV technique. As a result, bending vibration of the wings is observed almost all over the angles of attack while twisting is observed around the angles giving maximum lift force. The twisting vibration causes larger aerodynamic forces and delay in the stall. It is found that amplitude of the twisting determines magnitude of variations in aerodynamic forces. Flow field measurement shows the twisting vibration generates periodic vortices shedding from the leading and trailing edges. They reduce the separation bubble on the wing, in particular, around the middle span in spite of localization of the twisting in the vicinity of the wing tip.

Analytical structural behaviour of elastic flapping wings under the actuator effect

ABSTRACTThe effect of inertial forces on the Structural Dynamics (SD) behaviour of Elastic Flapping Wings (EFWs) is investigated. In this regard, an analytical modal-based SD solution of EFW undergoing a prescribed rigid body motion is initially derived. The formulated initial-value problem is solved analytically to study the EFW structural responses, and sensitivity with respect to EFWs’ key parameters. As a case study, a rectangular wing undergoing a prescribed sinusoidal motion is simulated. The analytical solution is derived for the first time and helps towards a conceptual understanding of the overall EFW's SD behaviour and its analysis required in their designs. Specifically, the EFW transient and steady response in on-off servo condition is also attended.