Flapping Wing Research Articles

Energy Harvesting Characteristics of a Flapping Wing with the Oscillating Aspirators in Uniform Flows and Shear Flows

Energy Harvesting Characteristics of a Flapping Wing with the Oscillating Aspirators in Uniform Flows and Shear Flows

A Cyborg Insect Reveals a Function of a Muscle in Free Flight

While engineers put lots of effort, resources, and time in building insect scale micro aerial vehicles (MAVs) that fly like insects, insects themselves are the real masters of flight. What if we would use living insect as platform for MAV instead? Here, we reported a flight control via electrical stimulation of a flight muscle of an insect-computer hybrid robot, which is the interface of a mountable wireless backpack controller and a living beetle. The beetle uses indirect flight muscles to drive wing flapping and three major direct flight muscles (basalar, subalar, and third axilliary (3Ax) muscles) to control the kinematics of the wings for flight maneuver. While turning control was already achieved by stimulating basalar and 3Ax muscles, electrical stimulation of subalar muscles resulted in braking and elevation control in flight. We also demonstrated around 20 degrees of contralateral yaw and roll by stimulating individual subalar muscle. Stimulating both subalar muscles lead to an increase of 20 degrees in pitch and decelerate the flight by 1.5 m/s2 as well as an induce in elevation of 2 m/s2.

The effect of elastic couplings and material uncertainties on the flutter of composite high aspect ratio wings

In this paper, the stochastic aeroelastic stability analysis of a composite high aspect ratio wing with various elastic couplings is investigated. The wing consists of a rectangular spar-box made from composite materials. Due to its high aspect ratio, the wing structure is modelled using the exact beam formulation, and the aerodynamic loads acting on the wing are simulated using an unsteady lifting line theory. A composite spar-box cross section is considered, and the effect of various effective parameters on the aeroelastic stability of the wing is studied. First, a baseline composite wing is designed and the effect of three different elastic couplings on the stability of the wing is determined. These three elastic couplings that affect the aeroelastic design of the composite wing are the out-of-plane (flap)-twist, the in-plane (lag)-twist and the extension-twist. Furthermore, the effect of uniformly distributed load on the aeroelastic stability of the wing is assessed for various layups. Finally, the effect of material uncertainties on the aeroelastic stability of the composite wing with various couplings is studied. It is observed that the type of elastic coupling has a significant effect on the sensitivity of the flutter speed and frequency of the composite wing due to the randomness of the material properties. In particular, the aeroelastic behaviour of the wing with lag-twist coupling is more sensitive to the material uncertainties than other two layups.

Comparative Analysis of the Characteristics of the Vortex Wake behind a Flapping Wing Performing Oscillations of Different Types

Comparative Analysis of the Characteristics of the Vortex Wake behind a Flapping Wing Performing Oscillations of Different Types

On three-dimensional printing of 17-4 precipitation-hardenable stainless steel with direct metal laser sintering in aircraft structural applications

The martensitic 17-4 precipitation-hardenable stainless steel is one of the commercially established materials for structural engineering applications in aircrafts due to its superior mechanical and corrosion resistance properties. The mechanical processing of this alloy through a conventional manufacturing route is critical from the dimensional accuracy (Δ d) viewpoint for development of innovative structural components such as: slat tracks, wing flap tracks, etc. In past two decades, a number of studies have been reported on challenges being faced while conventional processing of 17-4 precipitation-hardenable stainless steel for maintaining uniform thickness of aircraft structural components. However, hitherto little has been reported on direct metal laser sintering of 17-4 precipitation-hardenable stainless steel for development of innovative functional prototypes with uniform surface hardness (HV), Δ d, and surface roughness ( Ra) in aircraft structural engineering. This paper reports the effect of direct metal laser sintering process parameters on HV, Δ d, and Ra for structural components. The results of study suggest that optimized settings of direct metal laser sintering from multifactor optimization viewpoint are laser power 100 W, scanning speed 1400 mm/s, and layer thickness 0.02 mm. The results have been supported with scanning electron microscopy analysis (for metallurgical changes such as porosity (%), HV, grain size, etc.) and international tolerance grades for ensuring assembly fitment.

Aerodynamic analysis of hummingbird-like hovering flight

Flapping wing micro aerial vehicles are studied as the substitute for fixed and rotary wing micro aerial vehicles because of the advantages such as agility, maneuverability, and employability in confined environments. Hummingbird’s sustainable hovering capability inspires many researchers to develop micro aerial vehicles with similar dynamics. In this research, a wing of a ruby-throated hummingbird is modeled as an insect wing using membrane and stiffeners. The effect of flexibility on the aerodynamic performance of a wing in hovering flight has been studied numerically by using a fluid–structure interaction scheme at a Reynolds number of 3000. Different wings have been developed by using different positions and thicknesses of the stiffeners. The chordwise and spanwise flexural stiffnesses of all the wings modeled in this work are comparable to insects of similar span and chord length. When the position of the stiffener is varied, the best-performing wing has an average lift coefficient of 0.51. Subsequently, the average lift coefficient is increased to 0.56 when the appropriate thickness of the stiffeners is chosen. The best flexible wing outperforms its rigid counterpart and produces lift and power economy comparable to a real hummingbird’s wing. That is, the average lift coefficient and power economy of 0.56 and 0.88 for the best flexible wing as compared to 0.61 and 1.07 for the hummingbird’s wing. It can be concluded that a simple manufacturable flexible wing design based on appropriate positioning and thickness of stiffeners can serve as a potential candidate for bio-inspired flapping-wing micro aerial vehicles.

Modeling and flapping vibration suppression of a novel tailless flapping wing micro air vehicle

This paper establishes and analyzes a high-fidelity nonlinear time-periodic dynamic model and the corresponding state observer for flapping vibration suppression of a novel tailless Flapping Wing Micro Air Vehicle (FWMAV), named NPU-Tinybird. Firstly, a complete modeling of NPU-Tinybird is determined, including the aerodynamic model based on the quasi-steady method, the kinematic and dynamic model about the mechanism of flapping and attitude control, combined with the single rigid body dynamic model. Based on this, a linearized longitudinal pitch dynamic cycle-averaged model is obtained and analyzed through the methods of neural network fitting and system identification, preparing for the design of flapping vibration suppression observer. Flapping vibration is an inherent property of the tailless FWMAV, which arises from the influence of time-periodic aerodynamic forces and moments. It can be captured by attitude and position sensors on the plane, which impairs the flight performance and efficiency of flight controller and actuators. To deal with this problem, a novel state observer for flapping vibration suppression is designed. A robust optimal controller based on the linear quadratic theory is also designed to stabilize the closed-loop system. Simulation results are given to verify the performance of the observer, including the closed loop responses combined with robust optimal controller, the comparison of different parameters of observer and the comparison with several classic methods, such as Kalman filter, H-infinity filter and low-pass filter, which prove that the novel observer owns a fairly good suppression effect on flapping vibration and benefits for the improvement of flight performance and control efficiency.

Soap Film Visualization of a 10 cm-Span Flapping Wing

Flapping wing micro-air-vehicles (FWMAVs) animate the small-space dexterous flight, hovering, and energy-saving characteristics of birds and insects, and are believed to have enlightenment for the development of bionic flight in the future. When designing FWMAVs, detailed unsteady aerodynamic information is required. Besides the computational fluid mechanics (CFD) technology study, the flow visualization is also needed to assist this research. This article innovatively used soap film visualization with high-speed photography to record two kinds of the 2D flow fields laterally and longitudinally, respectively, generated by a flapping wing of 10 cm span. Different from the qualitative comparison of soap film imaging with the conventional smoke tracing method, the subsequent processing of the soap film images was demonstrated. This work explains how to quantify the soap film imaging into lift and thrust forces, and the corresponding results are compared with the wind tunnel force measurement data preliminarily.

Behavioural assessment of three chicken genotypes under free-range, semi-intensive, and intensive housing systems

The present study evaluated the effects of housing systems (free-range, semi-intensive, and intensive) on the behaviour of chickens over 10 weeks period (7-16 weeks of age. A total of 360 birds were selected and subjected to different housing systems. A Randomized Complete Block Design (RCBD) considered the following: 3 genotypes (RNN, BNN, and NN) × 2 sexes (30 cockerels and 30 pullets = 60 / genotype) × 3 housing systems (free-range, semi-intensive, and intensive) = 18 experimental units with 20 birds per unit = 360 birds. Regarding behavioural response, male birds under the intensive system were more aggressive and showed more sitting and standing behaviour followed by semi-intensive and free-range systems. Jumping, running, walking and wing flapping behaviours were higher in semi-intensive birds followed by free-range and intensive systems. Regarding females, RNN and BNN chicken revealed higher running behaviour than NN. In terms of housing systems, birds reared in the intensive system were more aggressive and showed an increased frequency of sitting and standing behaviours followed by semi-intensive and free-range systems. Birds under the free-range system spent most of their time in feeding and wing flapping followed by semi-intensive and intensive housing systems. Jumping, running, and walking was more pronounced in the semi-intensive system followed by a free-range and intensive system. It was concluded that RNN and BNN chickens expressed more natural behaviours under semi-intensive and free-range systems than NN chickens; hence, crossbred chickens could be reared under such types of environments to achieve their maximum genetic potential.

Bioinspired Feathered Flapping Wing UAV Design for Operation in Gusty Environment

The flight of unmanned aerial vehicles (UAVs) has numerous associated challenges. Small size is the major reason of their sensitivity towards turbulence restraining them from stable flight. Turbulence alleviation strategies of birds have been explored in recent past in detail to sort out this issue. Besides using primary and secondary feathers, birds also utilize covert feathers deflection to mitigate turbulence. Motivated from covert feathers of birds, this paper presents biologically inspired gust mitigation system (GMS) for a flapping wing UAV (FUAV). GMS consists of electromechanical (EM) covert feathers that sense the incoming gust and mitigate it through deflection of these feathers. A multibody model of gust-mitigating FUAV is developed appending models of the subsystems including rigid body, propulsion system, flapping mechanism, and GMS-installed wings using bond graph modeling approach. FUAV without GMS and FUAV with the proposed GMS integrated in it are simulated in the presence of vertical gust, and results’ comparison proves the efficacy of the proposed design. Furthermore, agreement between experimental results and present results validates the accuracy of the proposed design and developed model.

Development of a quasi-linear parameter varying model for a tiltrotor aircraft

The research presented in this paper focuses on the development of a quasi-Linear Parameter Varying (qLPV) model for the XV-15 tiltrotor aircraft. The specific category of qLPV modeling technique, known as the model stitching technique, is employed to model the time-varying dynamics of XV-15 tiltrotor aircraft over the entire flight envelope. In this modeling approach, discrete linear state-space models are interpolated through lookup tables as function of scheduling parameters with the implementation of nonlinear equations of motion. The XV-15 qLPV model is configured with four scheduling parameters: altitude, nacelle incidence angle, wing flap angle and velocity. Additionally, a computational complexity analysis is presented. In particular, computational sensitivity of qLPV models configured with lookup tables to number of states and number of scheduling parameters is demonstrated. This is done to show the feasibility of real-time implementation of qLPV models with increasing fidelity (number of states) and expanding dynamic flight envelope (number of scheduling parameters).

Aeroelastic analysis and flutter control of wings and panels: A review

AbstractFlutter is a self‐excited vibration under the interaction of the inertial force, aerodynamic force, and elastic force of the structure. After the flutter occurs, the aircraft structures will exhibit limit cycle oscillation, which will cause catastrophic accidents or fatigue damage to the structures. Therefore, it is of great theoretical and practical significance to study the aeroelastic characteristics and flutter control for improving the aeroelastic stability of aircraft structures. This paper reviews the recent advances in aeroelastic analysis and flutter control of wings and panel structures. The mechanism of aeroelastic flutter of wings and panels is presented. The research methods of aeroelastic flutter for different structures developed in recent years are briefly summarized. Various control strategies including the linear and nonlinear control algorithms as well as the active flutter control results of wings and panels are presented. Finally, the paper ends with conclusions, which highlight challenges of the development in aeroelastic analysis and flutter control, and provide a brief outlook on the future investigations. This study aims to present a comprehensive understanding of aeroelastic analysis and flutter control. It can also provide guidance on the design of new wings and panel structures for improving their aeroelastic stability.

Wing Flutter Suppression under the Influence of Fuel Sloshing in External Tank

The control of aeroelastic response of a wing section with influence of the fuel sloshing in external tank is examined through analytical studies. Based on the simplified mass-spring-damper equivalent mechanical model of the liquid sloshing and the dynamic modeling method of the wing/store system, the aeroelastic model of the two-dimensional wing/external tank/fuel sloshing system is established in this paper. The aeroelastic instability of the system is studied, and a flutter suppression controller is designed based on linear active disturbance rejection control (LADRC). The stability analysis shows that the tracking error and the estimation error of the linear state observer (ESO) are convergent. It is shown through simulation results that wing flutter suppression under the interference of fuel sloshing and external tank vibrating can be achieved by using two control surfaces.

Lift and Drag Performance Based on Varying Flapping Wing Camber at Low Reynolds Number of Micro Air Vehicles (MAVs)


 
 
 Flapping-Wing Micro Air Vehicles (FW-MAVs) are small hand-held flying vehicles that can maneuver in constrained space owing to their lightweight, low aspect ratio and the ability to fly in a low Reynolds number environment. In this study, the aerodynamic characteristics such as time-averaged lift (CL avg) and time-averaged drag (CD avg) of camber wings with different five wind tunnel test models with 6, 9, 12, and 15 per cent camber were developed and the results were compared with a flat wing to assess the effects of camber wing on the aerodynamic performance for flapping flight applications. The experiments were performed in an open chamber with non-return airflow with a test section of (0.3 x 0.3) m and capable of speeds from 0.5 to 30 m/s. The (CL avg) and (CD avg) as functions of the angle of attack at 100, associated with flapping frequency at 9 Hz and low Re = 3600 of the flapping motions concerning the incoming flows are measured by using a strain gauge balance and KYOWA PCD- 300A sensor interface data acquisition system. It is found that camber would bring significant aerodynamic benefits in a higher lift in comparison to the flat wing and increase with increasing camber instead of drag shows contrary a decreasing of performance with increase drag when the camber raised.
 
 

Coupled Aeroelastic Study of a Flexible Micro Air Vehicle-Scale Flapping Wing in Hovering Flight

Instantaneous force and structural deformation experiments were performed on a flexible, structurally characterized, low-aspect-ratio representative flapping wing. A six-component force balance was used to measure aerodynamic-force time history over a flap cycle. A VICON motion capture setup tracked the wing deformations while flapping. Measured aerodynamic forces and wing deformations were compared against coupled computational fluid dynamics/computational structural dynamics (CFD/CSD) aeroelastic analysis results. The CFD solver is an unsteady Reynolds-averaged Navier–Stokes solver. The CSD solver is a general-purpose multibody dynamics solver capable of modeling geometrically nonlinear beam and shell elements. The CFD/CSD results were able to capture the overall trend in aerodynamic forces and wing deformations. Although predicted and measured variations in lift were similar, the drag-force magnitudes tended to be underpredicted by the coupled aeroelastic solver. The coupled CFD/CSD solver was used to evaluate the influence of wing flexibility on wing performance. Results showed that, in particular instances, decreasing wing stiffness increased the time-averaged aerodynamic lift and lift-to-power ratio. Decreased wing stiffness led to reduced leading-edge vortex circulation strength. This suggests that the increased wing performance is mainly due to a redirection of the resultant force vector allowed by the increased wing compliance.

Lift Disturbance Cancellation with Rapid-Flap Actuation

Mitigation of vertical aerodynamic disturbances by means of a simple mechanical flap is investigated experimentally. A wall-to-wall NACA 0006 wing is bisected about the midchord for a 50%-chord flap length. Experiments are performed in a water tunnel at a chord-based Reynolds number of . The wing is driven in a sinusoidal vertical plunge motion as a spatially uniform, temporally varying surrogate to a vertical disturbance. Concurrently, the flap is actively deflected in a survey of kinematic parameters designed to suppress the influence of a plunge-induced disturbance. Plunge rates explored amount to disturbances incurred over a temporal range from one convective time to eight convective times. Two methodologies are employed to guide selection of flap deflection phase and amplitude necessary to preserve the baseline zero-lift state () of the undisturbed wing. In the first method, Theodorsen’s model is applied to arrive at an analytical solution to flap kinematics for a given prescribed plunge history. The theoretical derivation makes the standard assumptions of attached flow, planar wake, and no leading-edge vortical formations. Direct force measurements reveal reduction in lift transients by flap actuation of up to 87%, verifying the applicability of Theodorsen’s classical model. Further improvement is sought in a second method where empirical state-space modeling is formulated for lift cancellation. In this approach two separate lift models for wing plunge and flap deflection are constructed independently, and their superposition is employed to approximate the total lift in combined plunge and deflection motions. It is shown that although the empirical state-space approach performs similar to the inviscid theory of Theodorsen’s model, the empirical model proves more effective in suppressing the formation of the leading-edge vortex induced by plunge.

Efficiency-Optimal Rigidity Configuration of Passive Torsional Flapping Wings

In this work, a simple analytical tool for the efficient, optimal design of passive torsional flapping wings, which is usually done with the complex fluid–structure interaction method, is proposed. For thin-skin-wrapped spar–rib wing structures, the propulsion efficiency was modeled based on the momentum theorem, and the wing passive torsion was modeled based on the thin-wall-tube torsional vibration theorem. A forward efficiency-optimal design method for passive torsional flapping wings was thereby developed. The proposed method was validated through numerical simulation and a wind-tunnel experiment for a 0.85-m-span flapping-wing model with multiple wing torsional rigidity configurations. The group with the torsional rigidity optimized by the presented method displayed the best efficiency performance. The proposed method has potential applications for the concept design and performance evaluation of flapping-wing aircraft.

Size effects of vane-type rectangular vortex generators installed on high-lift swept-back wing flap on lift force and flow fields

Size effects of vane-type rectangular vortex generators installed on high-lift swept-back wing flap on lift force and flow fields

Natural loss of function of ephrin-B3 shapes spinal flight circuitry in birds.

Flight in birds evolved through patterning of the wings from forelimbs and transition from alternating gait to synchronous flapping. In mammals, the spinal midline guidance molecule ephrin-B3 instructs the wiring that enables limb alternation, and its deletion leads to synchronous hopping gait. Here, we show that the ephrin-B3 protein in birds lacks several motifs present in other vertebrates, diminishing its affinity for the EphA4 receptor. The avian ephrin-B3 gene lacks an enhancer that drives midline expression and is missing in galliforms. The morphology and wiring at brachial levels of the chicken embryonic spinal cord resemble those of ephrin-B3 null mice. Dorsal midline decussation, evident in the mutant mouse, is apparent at the chick brachial level and is prevented by expression of exogenous ephrin-B3 at the roof plate. Our findings support a role for loss of ephrin-B3 function in shaping the avian brachial spinal cord circuitry and facilitating synchronous wing flapping.

Design and analysis of an innovative flapping wing micro aerial vehicle with a figure eight wingtip trajectory

Abstract. A multi-mode flapping wing micro air vehicle (FWMAV) that uses a figure eight wingtip motion trajectory with wing flapping, rotation, and swing motion is presented in this paper. The flapping wing vehicle achieves three active degrees of freedom (DOF) wing movements only with one driving micromotor which has a good balance in the mechanism design (that is inspired by natural fliers) and total weight. Owing to these characteristics being integrated into the simple mechanism design, the aerodynamic force is improved. The aerodynamic performance of the thrust force is improved by 64.3 % compared to one that could only flap up and down with one active DOF under the condition of routine flapping frequency.