Effect Of Wing Flexibility Research Articles

Design of morphing wing for aerodynamic performance considering the wing flexibility effects

This paper provides an insight into ongoing research aimed at designing a morphing wing with the ability to continuously adapt its aerodynamic shape. The wing is targeted at a general purpose unmanned aerial vehicle. The morphing wing concept outlined in the paper is based on continuous camber changes of the wing leading and trailing edges, allowing optimal performance in different flight regimes. The aeroelastic tailoring method is used to design the load carrying structure of the wing in order to define the optimal stiffness and strength of the structure, which are considered as fixed in subsequent design steps. The research proposes a novel modular design approach that combines aerodynamic shape optimisation and aeroelastic considerations for designing morphing wing surfaces.

Wing flexibility effect on aerodynamic performance of different flapping wing planforms

Uniform downwash of a revolving or flapping wing is a key indicator of aerodynamic efficiency. Although the slack-angle of flexible wings can significantly alter the downwash due to the inherent aerodynamic twist, its effect on the downwash distribution for a change in planform remains unknown. In this study, the effect of wing flexibility (slack-angle β) on the unsteady aerodynamic characteristics is investigated using three wing planforms. The study reveals that ββ > 5° can suppress the wing planform effect, leading to the generation of the same amount of lift at mid-stroke. To emphasize on the role of wing flexibility, further comparisons are made with rigid cases for each change in planform. A change in planform for the rigid cases significantly affects the position of the tip vortices (TiVs). But, the TiV positions of the flexible wings remained unchanged, helping to generate a wider downwash area to enhance the lift in contrast to that of the rigid-wing counterparts. The study found that the flexible and rigid wings can generate two distinct downwash patterns, which are respectively near uniform and tip-oriented, during the flapping motion. The ability of the flexible wings to sustain the wider near uniform downwash irrespective of the selected planform is paramount for enhanced aerodynamic performance.

The spatial-temporal effects of wing flexibility on aerodynamic performance of the flapping wing

In this paper, three-dimensional fluid–structure interaction simulation of flapping of a flexible wing is carried out. The aerodynamic effect of the flexible wing can be explained by analyzing the spatial and temporal effects of wing flexibility on aerodynamic performance. It is concluded that the flexible wing can increase the average lift and the aerodynamic efficiency. The spatial influence of flexible deformation mainly comes from the contribution of camber. In the mid-downstroke, wing flexibility results in significant camber near the wingtip, which is conducive to the attachment of the leading-edge vortex to the wing surface, thus enhancing the ability of the wingtip to generate lift. The temporal influence of flexible deformation mainly comes from the contribution of twist and bend. The fast pitching-down rotation due to the wing twist in the early downstroke is conducive to the accumulation of vorticity. The spanwise bend of the flexible wing due to the aerodynamic force and inertia can increase the flapping amplitude, which accounts for the lift increase. The above spatial-temporal effects make the flexible wing have better performance in generating lift and aerodynamic efficiency. The results are beneficial to systematically understand the aerodynamic effects of insect wing deformation and can provide guidance for the wing design of micro aerial vehicles.

Flight Dynamics Simulation Modeling of a Large Flexible Tiltrotor Aircraft

A high-order tiltrotor mathematical model is developed and validated against flight-test data for the XV-15 and simulations of a large civil tiltrotor (LCTR) concept. Rigid body and inflow states, as well as flexible wing and blade states are used in the analysis. Wing flexibility is important when modeling large aircraft where structural modes effect the frequency range of interest for flight control, generally 1–20 rad/s. Details of the formulation of the mathematical model are given, including derivation of structural, aerodynamic, and inertial loads. A novel "quasi-multibody" approach, based on numerical kinematics but without equations of constraints, allows the modeling of complex, flexible aircraft configurations in an easy to set up, and computationally very efficient manner. Assessments of the effects of wing flexibility are given. Flexibility effects are also evaluated by looking at the nature of the couplings between rigid body modes and wing structural modes.

Effect of wing flexibility on the aerodynamic performance of a robotic dragonfly

Effect of wing flexibility on the aerodynamic performance of a robotic dragonfly

Effect of Wing Flexibility on the Lift Force Generated by a 2D Model Insect Wing Flapping in Hover Mode

In this study, we numerically examine the effect of wing flexibility on the lift force generated by a modeled flapping wing that simulates an insect flight in hover mode. The flow field around the flapping wing is assumed to be two-dimensional (2D), and the flow equations are formulated with the notion of “immersed boundary” for easy handling of the moving-boundary problem. In the 2D framework, the wing chord is treated as an elastic filament. To account for the large deformation in the wing, the motion of the filament is modeled using a geometrically nonlinear equation for bending beams. Both sets of equations are then solved according to the fluid–structure interaction concept using appropriate numerical schemes. Time variation of lift force on the wing is calculated for different values of wing flexural rigidity. Effects of elastic deformation of the wing and interactions between the bending wing and vortical flow structure are discussed. Flexural rigidity that gives the highest average lift force on the wing is sought. This study affirms that the flexibility of wing and the vortex-pair capture phenomenon are crucial to the lift force generation in the flapping-wing mechanics.

Effects of wing flexibility on aerodynamic performance of an aircraft model

The low-speed wind tunnel experiment is carried out on a simplified aircraft model to explore the influence of wing flexibility on the aircraft aerodynamic performance. The investigation involves the measurements of force, membrane deformation and velocity field at Reynolds number of 5.4 × 104–1.1 × 105. In the lift curves, two peaks are observed. The first peak, corresponding to the stall, is sensitive to the wing flexibility much more than the second peak, which nearly keeps constant. For the optimal case, in comparison with the rigid wing model, the delayed stall of nearly 5° is achieved, and the relative lift increment is about 90%. It is revealed that the lift enhanced region corresponds to the larger deformation and stronger vibration, which leads to stronger flow mixing near the flexible wing surface. Thereby, the leading-edge separation is suppressed, and the aerodynamic performance is improved significantly. Furthermore, the effects of sweep angle and Reynolds number on the aerodynamic characteristics of flexible wing are also presented.

Influence of wing flexibility on the aerodynamic performance of a tethered flapping bumblebee

The flight of insects has enlightened the flying dream of human beings for centuries. Wing flexibility is often used by insects to increase their flight efficiencies. However, the mechanism of the increased efficiencies still remains mysterious. Prof. Kai Schneider's group studies the aerodynamics of a tethered flapping bumblebee using a mass-spring fluid-structure interaction numerical solver. It indicates that a higher flight efficiency or a larger lift-to-power ratio can be achieved by flapping insects with optimal mechanical properties of the flexible wings. The novel understanding of insects’ body structure and flying behavior will benefit the design of micro-air vehicles (MAVs). The sophisticated structures of flapping insect wings make it challenging to study the role of wing flexibility in insect flight. In this study, a mass-spring system is used to model wing structural dynamics as a thin, flexible membrane supported by a network of veins. The vein mechanical properties can be estimated based on their diameters and the Young's modulus of cuticle. In order to analyze the effect of wing flexibility, the Young's modulus is varied to make a comparison between two different wing models that we refer to as flexible and highly flexible. The wing models are coupled with a pseudo-spectral code solving the incompressible Navier–Stokes equations, allowing us to investigate the influence of wing deformation on the aerodynamic efficiency of a tethered flapping bumblebee. Compared to the bumblebee model with rigid wings, the one with flexible wings flies more efficiently, characterized by a larger lift-to-power ratio.

Identification of In-Flight Wingtip Folding Effects on the Roll Characteristics of a Flexible Aircraft

Wingtip folding is a means by which an aircraft’s wingspan can be extended, allowing designers to take advantage of the associated reduction in induced drag. This type of device can provide other benefits if used in flight, such as flight control and load alleviation. In this paper, the authors present a method to develop reduced order flight dynamic models for in-flight wingtip folding, which are suitable for implementation in real-time pilot-in-the-loop simulations. Aspects such as the impact of wingtip size and folding angle on aircraft roll dynamics are investigated along with failure scenarios using a time domain aeroservoelastic framework and an established system identification method. The process discussed in this paper helps remove the need for direct connection of complex physics based models to engineering flight simulators and the need for tedious programming of large look-up-tables in simulators. Instead, it has been shown that a generic polynomial model for roll aeroderivatives can be used in small roll perturbation conditions to simulate the roll characteristics of an aerodynamic derivative based large transport aircraft equipped with varying fold hinge lines and tip deflections. Moreover, the effects of wing flexibility are also considered.

Design and Evaluation of a Model-Based Controller for Flapping-Wing Micro Air Vehicles

Because of the highly integrated nature of their dynamics, flapping-wing micro air vehicles exhibit significant coupling, including interactions between aeroelastic wing behavior, actuator dynamics, and control systems. An existing model-based controller is demonstrated to exhibit reduced tracking performance and even closed-loop instability when exposed to these effects, due to differences between the models used for control design and control evaluation. Motivated by this analysis, a controller is developed that provides improved robustness despite model uncertainty by decoupling the normal form of the vehicle dynamics, which accounts for coupling of the forces and moments acting on the vehicle and enables enhanced tuning capabilities. Closed-loop stability is achieved when the control system is evaluated on a richer model that includes the effect of wing flexibility and limited actuator capabilities, despite a reduction in control effectiveness. Using the same control design methodology, a minimally actuated configuration is achieved by removing wing bias manipulation from the control parameters. It is shown that the controller is still able to stabilize the resulting system, although with a reduction in robustness against unmodeled dynamics, which is expected due to the increased dependence of the control effort on the remaining control parameters.

Wing flexibility effects on the flight performance of an insect-like flapping-wing micro-air vehicle

This study explores the effects of wing flexibility on several characteristics of flight, in this case the trim conditions, power requirements and dynamic stability of an insect-like flapping-wing micro-air vehicle (FWMAV) based on the hawkmoth Manduca sexta. The wing structure is analyzed by the finite-element method. A potential-based aerodynamic model which encompasses the unsteady panel method and the extended unsteady vortex-lattice method is employed to compute the aerodynamic forces. The motions of the FWMAV are obtained using a flexible multibody dynamics program coupled with the potential-based aerodynamic model. The results of this study show that the trim conditions of insect-like flexible and rigid FWMAVs may differ significantly from each other. When the flight speed is less than 3.0 m/s, using flexible wings is favorable, as they help the FWMAV reduce the power requirement and stabilize the lateral dynamics. However, at 3.0 m/s, these advantages are almost unnoticeable, while at 4.0 m/s, the flexible insect-like FWMAV requires even more mechanical power than its rigid counterpart.

Effects of flexibility and aspect ratio on the aerodynamic performance of flapping wings

In the current study, we experimentally investigated the flexibility effects on the aerodynamic performance of flapping wings and the correlation with aspect ratio at angle of attack α = 45°. The Reynolds number based on the chord length and the wing tip velocity is maintained at Re = 5.3 × 103. Our result for compliant wings with an aspect ratio of 4 shows that wing flexibility can offer improved aerodynamic performance compared to that of a rigid wing. Flexible wings are found to offer higher lift-to-drag ratios; in particular, there is significant reduction in drag with little compromise in lift. The mechanism of the flexibility effects on the aerodynamic performance is addressed by quantifying the aerodynamic lift and drag forces, the transverse displacement on the wings and the flow field around the wings. The regime of the effective stiffness that offers improved aerodynamic performance is quantified in a range of about 0.5–10 and it matches the stiffness of insect wings with similar aspect ratios. Furthermore, we find that the aspect ratio of the wing is the predominant parameter determining the flexibility effects of compliant wings. Compliant wings with an aspect ratio of two do not demonstrate improved performance compared to their rigid counterparts throughout the entire stiffness regime investigated. The correlation between wing flexibility effects and the aspect ratio is supported by the stiffness of real insect wings.

Modeling and parametric study of a flexible flapping-wing MAV using the bond graph approach

The focus of the present paper is the parametric dynamic study of a flexible bird-like flapping-wing micro-air vehicle (FMAV). A model of a flapping-wing MAV, containing main body, flapping mechanism, flexible wings, and propulsion system consisting of battery, DC motor, and gear box using the bond graph method is presented and then the governing equations of motion from the conceptual model is derived. Moreover, the simulation is carried out in the simulation software 20-sim. The sensitivity analysis of the flapping-wing performance to various mechanical and electrical parameters is done. In this regard, it is conducted to investigate the effect of wing flexibility, relocation of the force point of action, motor initial inertia, torsional spring stiffness, phase difference between 2 wings motion, and also the effect of changing flapping frequency on some important issues containing wing deflection, applied force and flapping angle. It is shown that the proposed bond graph model not only provides an efficient virtual dynamic framework to resolve the complexity of modeling the flexible flapping-wing MAVs but also can simplify and accelerate the process of sensitivity analysis of such complex systems.

The effect of wing flexibility on sound generation of flapping wings

In this study, the unsteady flow and acoustic characteristics of a three-dimensional (3D) flapping wing model of a Tibicen linnei cicada in forward-flight are numerically investigated. A single cicada wing is modelled as a membrane with a prescribed motion reconstructed from high-speed videos of a live insect. The numerical solution takes a hydrodynamic/acoustic splitting approach: the flow field is solved with an incompressible Navier–Stokes flow solver based on an immersed boundary method, and the acoustic field is solved with linearized perturbed compressible equations. The 3D simulation allows for the examination of both the directivity and frequency compositions of the flapping wing sound in a full space. Along with the flexible wing model, a rigid wing model that is extracted from real motion is also simulated to investigate the effects of wing flexibility.The simulation results show that the flapping sound is directional; the dominant frequency varies around the wing. The first and second frequency harmonics show different radiation patterns in the rigid and flexible wing cases, which are demonstrated to be highly associated with wing kinematics and loadings. Furthermore, the rotation and deformation in the flexible wing is found to help lower the sound strength in all directions.

Bio-Inspired Flexible Flapping Wings with Elastic Deformation

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.

Effects of wing flexibility on bumblebee propulsion

This study provides a comprehensive analysis of the effects of flexibility on bumblebee propulsion. The unusual stiffness distribution of bumblebee wings caused by the absence of veins on their outer one-third region is analyzed for the first time, with two flexible-wing models and one rigid-wing model tested in two-way Fluid-Structure Interactions (FSI) simulations. The two flexible-wing models are the uniform stiffness model in which the whole area (100%) of the wing is flexible and the reduced tip-stiffness model in which the tip region (30% of the total wing area) is more flexible than the rest of the wing. The rigid wing has been found to have the highest power economy (ratio of lift to input power), with the uniform- and reduced tip-stiffness wings being 7% and 15% less economical, respectively. The rigid wing produces drag, while both flexible-wing models produce thrust with a difference of approximately 3%. In forward flight, the positive thrust clearly highlights the importance of flexibility for the aerodynamic performance and propulsion of a bumblebee which will be unable to fly forward if its wings are modeled as rigid bodies.

Effects of wing flexibility on sound characteristics of a four-wing flapping wing micro air vehicle

The objective of this study was to understand the sound generation of flapping wings. In particular, the structural properties of the wings were varied to assess the effects of wing flexibility on the sound generation of flapping wings. A four-wing, hummingbird-inspired flapping wing micro air vehicle (FMAV) was considered. The half wing span was approximately six centimeters and the flapping frequency was approximately 25 Hz. The sound produced by the FMAV was measured using a 1/2 inches diameter microphone in an acoustic chamber under the quiescent flow condition. Time-averaged aerodynamic forces were measured by the force and torque sensor Nano17 (ATI Industrial Automation). Results revealed the characteristics of flapping-wing sound in terms of directivity, frequency response, and attenuation. Moreover, the degree of wing deformation led to a variation in the frequency response corresponding to the maximum sound pressure level as well as time-averaged aerodynamic force, even when the flapping frequenc...

Effect of wing flexibility on flight dynamics stability of flapping wing MAVs in forward flight

The paper presents a qualitative study of the effect of the wing flexibility on the flight stability of flapping wing micro air vehicles in forward flight. The longitudinal dynamic flight stability is compared between rigid wing flapping wing micro air vehicles and flexible-wing flapping wing micro air vehicles. The aerodynamics derivatives are computed respectively using the method of computational fluid dynamics and fluid–structure interaction method, and the techniques of eigenvalue and eigenvector analysis are applied to solve the equations of motion. It is shown that the flexibility can change the stability properties of the flapping micro air vehicles from unstable to stable. Besides, the position of mass center of flapping micro air vehicles is also a key factor to the flight stability, which provides a new insight to design a stable flapping wing micro air vehicle.

Aerodynamic force and vortex structures of flapping flexible hawkmoth-like wings

Aerodynamic characteristics were determined and flow visualizations were carried out in order to interpret the effects of wing flexibility for hawkmoth-like wings on aerodynamic force generation. The flexibility varied according to wing thickness: Case 1 used a 3-mm thick rigid wing, while Cases 2, 3, and 4 used 0.8-, 0.5-, and 0.35-mm thick flexible wings, respectively. The wings were constrained to a sinusoidal flapping motion in a water tank, and digital particle image velocimetry captured three sections of each wing model by fixing the position of the laser, shooting at 30%, 50%, and 70% of the rigid wing length. The flexible wings had phase delays in the stroke motion, which had influence on vortex generation, particularly the leading-edge vortex (LEV). As the wing became flexible, the vorticity of the LEV and the corresponded lift decreased. However, Case 2 had greater aerodynamic force than other cases due to the behavior of the new LEV after the wing reversal. In particular, the new LEV around the wingtip was delayed in its dispersal due to part of the LEV generated during the previous stroke. The encounter between the new LEV and the LEV residue induced the flow over the leading-edge, preventing the new LEV dispersal. Along with the higher stroke velocity after a specific time, the delayed LEV dispersal helped the flexible wing have higher lift. Cases 3 and 4, on the other hand, showed large wing deformations during flapping, which caused the vortex structures around the flapping wing to become relatively unstable. Accordingly, they had much less aerodynamic force than the previous cases. These results help to explain how flexible wings obtain more or less aerodynamic force, and they also suggest the importance of setting a specific range of flexibility to enable greater aerodynamic force for insect-inspired flapping micro aerial vehicles (MAVs).

Modeling and analysis of insect-like flexible wings at low Reynolds number

Much of the aerodynamic research conducted on insects to date has assumed that their wings are predominantly flat and rigid. In this paper, we investigate the effects of wing flexibility on the aerodynamic performance of a simple wing modeled after that of the Fruitfly, at the Reynolds number of 150. Analyses were first carried out to understand how distribution of stiffness property influences its deformation/deflection under simple static, inertial and inertial-cum-aerodynamic loadings. A class of leading-edge reinforced (LER) wings with stiffness that is sharply reduced towards the wing tip and trailing edge was found to exhibit deformations that resemble well those observed for insect wings in flight. The LER-type wings are shown to be aerodynamically superior to rigid wing and wings of uniform stiffness in terms of their improved cycle-mean lift-to-drag and lift-to-power ratios. The positive roles played by wing deformation in the aerodynamics and the beneficial energetics of elastic wing storage are discussed.