Wing Camber Research Articles

Design and Application of Cross-Shaped Cellular Honeycombs for a Variable Camber Wing

Cellular honeycomb cores with overlying flexible skins have been proposed for use as deformable structures for morphing aircraft. Airfoils with a variable camber trailing edge require the camber to be changed continuously, which is pursued by the reconfiguration of both the underlying structures and the flexible skins. The honeycomb cores, which provide underlying support to the flexible skins for bearing the out-of-plane aerodynamic loads, must have low in-plane stiffness andhigh out-of-plane bearing capability. In this paper, a kind of cross-shaped honeycomb is designed and manufactured. Analytical, numerical, and experimental studies for the in-plane effective moduli of the cross-shaped honeycomb are carried out. The results demonstrate that the cross-shaped honeycomb has substantial in-plane deformability. A conceptual design of the variable camber trailing edge based on the crossshaped honeycomb is proposed and modeled using MSC.NASTRAN software. Simulation results show that the cross-shaped honeycomb can provide substantial in-plane deformation and adequate out-of-plane support, satisfying the deformability and bearing capacity requirements of the variable camber trailing edge.

Space–time computational analysis of bio-inspired flapping-wing aerodynamics of a micro aerial vehicle

We present a detailed computational analysis of bio-inspired flapping-wing aerodynamics of a micro aerial vehicle (MAV). The computational techniques used include the Deforming-Spatial-Domain/Stabilized Space---Time (DSD/SST) formulation, which serves as the core computational technique. The DSD/SST formulation is a moving-mesh technique, and in the computations reported here we use the space---time version of the residual-based variational multiscale (VMS) method, which is called "DSD/ SST-VMST." The motion and deformation of the wings are based on data extracted from the high-speed, multi-camera video recordings of a locust in a wind tunnel. A set of special space---time techniques are also used in the computations in conjunction with the DSD/SST method. The special techniques are based on using, in the space---time flow computations, NURBS basis functions for the temporal representation of the motion and deformation of the wings and for the mesh moving and remeshing. The computational analysis starts with the computation of the base case, and includes computations with increased temporal and spatial resolutions compared to the base case. In increasing the temporal resolution, we separately test increasing the temporal order, the number of temporal subdivisions, and the frequency of remeshing. In terms of the spatial resolution, we separately test increasing the wing-mesh refinement in the normal and tangential directions and changing the way node connectivities are handled at the wingtips. The computational analysis also includes using different combinations of wing configurations for the MAV and investigating the beneficial and disruptive interactions between the wings and the role of wing camber and twist.

Kinematic plasticity during flight in fruit bats: individual variability in response to loading.

All bats experience daily and seasonal fluctuation in body mass. An increase in mass requires changes in flight kinematics to produce the extra lift necessary to compensate for increased weight. How bats modify their kinematics to increase lift, however, is not well understood. In this study, we investigated the effect of a 20% increase in mass on flight kinematics for Cynopterus brachyotis, the lesser dog-faced fruit bat. We reconstructed the 3D wing kinematics and how they changed with the additional mass. Bats showed a marked change in wing kinematics in response to loading, but changes varied among individuals. Each bat adjusted a different combination of kinematic parameters to increase lift, indicating that aerodynamic force generation can be modulated in multiple ways. Two main kinematic strategies were distinguished: bats either changed the motion of the wings by primarily increasing wingbeat frequency, or changed the configuration of the wings by increasing wing area and camber. The complex, individual-dependent response to increased loading in our bats points to an underappreciated aspect of locomotor control, in which the inherent complexity of the biomechanical system allows for kinematic plasticity. The kinematic plasticity and functional redundancy observed in bat flight can have evolutionary consequences, such as an increase potential for morphological and kinematic diversification due to weakened locomotor trade-offs.

变弯度机翼准定常流动分离特性的实验研究

A test model of variable camber wing is developed as the first step of the work, which is capable of enough camber variation with acceptable mechanical stability and control accuracy. Corresponding experimental platform is established to conduct the aerodynamic load measurements and related flow visualization. Plentiful tunnel experiments depict distinction on the aerodynamic characteristics between the steady and quasi-steady flow separation behaviors. The distinction is interpreted with two types of stall mechanisms caused by the camber deformation: the leading-edge stall and the trailing-edge stall. Under the circumstance of flow separation, the morphing aircraft’s flow structure depends not only on the current boundary conditions but also relates with the previous history.

3D reconstruction and analysis of wing deformation in free-flying dragonflies

Insect wings demonstrate elaborate three-dimensional deformations and kinematics. These deformations are key to understanding many aspects of insect flight including aerodynamics, structural dynamics and control. In this paper, we propose a template-based subdivision surface reconstruction method that is capable of reconstructing the wing deformations and kinematics of free-flying insects based on the output of a high-speed camera system. The reconstruction method makes no rigid wing assumptions and allows for an arbitrary arrangement of marker points on the interior and edges of each wing. The resulting wing surfaces are projected back into image space and compared with expert segmentations to validate reconstruction accuracy. A least squares plane is then proposed as a universal reference to aid in making repeatable measurements of the reconstructed wing deformations. Using an Eastern pondhawk (Erythimus simplicicollis) dragonfly for demonstration, we quantify and visualize the wing twist and camber in both the chord-wise and span-wise directions, and discuss the implications of the results. In particular, a detailed analysis of the subtle deformation in the dragonfly's right hindwing suggests that the muscles near the wing root could be used to induce chord-wise camber in the portion of the wing nearest the specimen's body. We conclude by proposing a novel technique for modeling wing corrugation in the reconstructed flapping wings. In this method, displacement mapping is used to combine wing surface details measured from static wings with the reconstructed flapping wings, while not requiring any additional information be tracked in the high speed camera output.

The transonic dip in aeroelastic divergence speed—An explicit formula

Using continuum models we develop a closed form analytical formula for the divergence speed as a function of the Mach number and in particular its dependence on wing camber. There is a transonic dip even when the angle of attack is zero and it depends on the wing thickness ratio. For nonzero camber the angle of attack in fact plays a lesser role. The main analytical tool is the Possio integral equation which is shown to have an explicit solution. Neither CFD nor FEM is employed.

A Potential Role for Bat Tail Membranes in Flight Control

Wind tunnel tests conducted on a model based on the long-eared bat Plecotus auritus indicated that the positioning of the tail membrane (uropatagium) can significantly influence flight control. Adjusting tail position by increasing the angle of the legs ventrally relative to the body has a two-fold effect; increasing leg-induced wing camber (i.e., locally increased camber of the inner wing surface) and increasing the angle of attack of the tail membrane. We also used our model to examine the effects of flying with and without a tail membrane. For the bat model with a tail membrane increasing leg angle increased the lift, drag and pitching moment (nose-down) produced. However, removing the tail membrane significantly reduced the change in pitching moment with increasing leg angle, but it had no significant effect on the level of lift produced. The drag on the model also significantly increased with the removal of the tail membrane. The tail membrane, therefore, is potentially important for controlling the level of pitching moment produced by bats and an aid to flight control, specifically improving agility and manoeuvrability. Although the tail of bats is different from that of birds, in that it is only divided from the wings by the legs, it nonetheless, may, in addition to its prey capturing function, fulfil a similar role in aiding flight control.

A Bendable Load Stiffened Wing for Small UAVs

A bendable load stiffened wing, developed at the University of Florida, has the ability to load stiffen in the positive flight load direction while remaining compliant in the opposite direction, enabling UAV storage inside smaller packing volumes. The wing employs an under-cambered airfoil with a swept planform providing dissimilar stiffness in the flight load and the folding direction. A comparative experimental study is performed using two wing geometries; straight camber and swept camber. The load stiffening ability is tested by performing three point bend tests while monitoring the wing root airfoil shape change using a visual image correlation technique. For the wing utilizing a swept camber design, increase in the root airfoil camber with increased loading resulted in a load stiffening structure. Swept camber wing showed a higher load carrying capacity (7 g's load factor) over a straight camber wing design (2 g's load factor), still maintaining the compliant nature in the folding direction. Long term storage induced creep deformations are small in both of the wing geometries. By increasing the wing stiffness, sweepback helps in reducing spanwise residual creep strain. Wind tunnel tests at Re = 7×104 of both the straight camber and the swept camber wing show similar L/D ratios. The sweepback helps in improving the static stability of the wing. Thus the bendable load stiffened wing has a clear advantage of offering stiffness improvement and reducing storage induced creep residual strains while maintaining the aerodynamic efficiency and improving the static stability of the wing.

The effect of body size on the wing movements of pteropodid bats, with insights into thrust and lift production

In this study we compared the wing kinematics of 27 bats representing six pteropodid species ranging more than 40 times in body mass (M(b)=0.0278-1.152 kg), to determine whether wing posture and overall wing kinematics scaled as predicted according to theory. The smallest species flew in a wind tunnel and the other five species in a flight corridor. Seventeen kinematic markers on the midline and left side of the body were tracked in three dimensions. We used phylogenetically informed reduced major axis regression to test for allometry. We found that maximum wingspan (b(max)) and maximum wing area (S(max)) scaled with more positive allometry, and wing loading (Q(s)) with more negative allometry (b(max)∝M(b)(0.423); S(max)∝M(b)(0.768); Q(s)∝M(b)(0.233)) than has been reported in previous studies that were based on measurements from specimens stretched out flat on a horizontal surface. Our results suggest that larger bats open their wings more fully than small bats do in flight, and that for bats, body measurements alone cannot be used to predict the conformation of the wings in flight. Several kinematic variables, including downstroke ratio, wing stroke amplitude, stroke plane angle, wing camber and Strouhal number, did not change significantly with body size, demonstrating that many aspects of wing kinematics are similar across this range of body sizes. Whereas aerodynamic theory suggests that preferred flight speed should increase with mass, we did not observe an increase in preferred flight speed with mass. Instead, larger bats had higher lift coefficients (C(L)) than did small bats (C(L)∝M(b)(0.170)). Also, the slope of the wingbeat period (T) to body mass regression was significantly more shallow than expected under isometry (T∝M(b)(0.180)), and angle of attack (α) increased significantly with body mass [α∝log(M(b))7.738]. None of the bats in our study flew at constant speed, so we used multiple regression to isolate the changes in wing kinematics that correlated with changes in flight speed, horizontal acceleration and vertical acceleration. We uncovered several significant trends that were consistent among species. Our results demonstrate that for medium- to large-sized bats, the ways that bats modulate their wing kinematics to produce thrust and lift over the course of a wingbeat cycle are independent of body size.

Nonlinear Modeling and Aeroelastic Analysis of an Adaptive Camber Wing

stations using actuators for which actuation force magnitudes are determined iteratively using linearized influence coefficients. Flow solutions are obtained using a high-order panel method, and aeroelastic coupling is performed using the in-house code SAMOA. For morphed-wing configurations, induced drag is reduced by creating washout. By conducting static aeroelastic analysis actuation, force magnitudes are determined and favorable aerodynamic effects are identified. Results indicate that use of a nonlinear structural model is essential in capturing the stiffening behavior observed during application of spanwise variable camber.

Artificial Cambered-Wing for a Beetle-Mimicking Flapper

In this paper, we have attempted to improve the aerodynamic force generation ability of an artificial wing by implementing initial wing camber in the flexible artificial wing. This initial camber is used to create passive wing camber during flapping motion. We modified original artificial wing by removing many minor vein structures in the wing and then placed the initial camber between two major veins. Stiffness measurements for the original artificial wing and the present wing with initial camber were conducted to compare the stiffnesses of the two artificial wings, and the similarities of the two wings are discussed. A flapping test was carried out using a previously-built flapper that can flap at higher than 25 Hz flapping frequency to verify the wing camber effect. Finally, a performance comparison between uncambered- and cambered-wings was also undertaken based on observations using a high-speed camera and force measurements from wired-flight tests and swing tests. The comparison showed that the cambered-wing could produce about 10% higher thrust than the uncambered-wing.

SMA Actuated Mechanism for an Adaptive Wing

A preliminary study of an adaptive unmanned aerial vehicle (UAV) wing actuated by shape memory alloy (SMA) devices is presented. The wing consists of a sandwich box substructure, flexible ribs, and a flexible laminated skin. The adaptation capability to the changing flight conditions is obtained via airfoil shape adjustments. Torsion SMA tubes are employed for wing camber control, while levers powered by SMA wires are employed for local shape control. A new architecture is proposed: the downward or upward actuation torque is provided by counterrotating concentric tubes connected through a clutch and a positioning piezoelectric motor to the flexible ribs. These actuator tubes are heated one at a time while the other is made free by the clutch in order to obtain any wanted shape without waiting for cooling. The capability of the wing to bear the aerodynamic loads, the power required by the actuators, and their force and torque are assessed by finite-element simulations. An improved version of a recently dev...

Stiffness requirement of flexible skin for variable trailing-edge camber wing

The method for analyzing the deformation of flexible skin under the air loads was developed based on the panel method and finite element method. The deformation of flexible skin under air pressures and effects of the local deformation on the aerodynamic characteristics were discussed. Numerical results show that the flexible skin on the upper surface of trailing-edge will bubble under the air loads and the bubble has a powerful effect on the aerodynamic pressure near the surface of local deformation. Then the stiffness requirements for flexible skin of variable trailing-edge were given by using the Jacobs rule, i.e., the maximum displacement of skin is not greater than 0.1% of wing chord. Results show that the in-plane stiffness can be reduced by increasing the ratio of bending stiffness to in-plane stiffness. Although the deformation of flexible skin increases with the in-plane stiffness decreasing, it depends on the bending stiffness. When the bending stiffness exceeds critical value, the deformation of flexible skin only depends on the bending stiffness and has nothing to do with the in-plane stiffness. The conclusions can be used for the structural design of flexible skin.

Demonstration of an in situ morphing hyperelliptical cambered span wing mechanism

Research on efficient shore bird morphology inspired the hyperelliptical cambered span(HECS) wing, a crescent-shaped, aft-swept wing with vertically oriented wingtips. Thewing reduces vorticity-induced circulation loss and outperforms an elliptical baselinewhen planar. Designed initially as a rigid wing, the HECS wing makes use ofmorphing to transition from a planar to a furled configuration, similar to that of acontinuously curved winglet, in flight. A morphing wing concept mechanism ispresented, employing shape memory alloy actuators to create a discretized curvatureapproximation. The aerodynamics for continuous wing shapes is validated quasi-staticallythrough wind tunnel testing, showing enhanced planar HECS wing lift-to-dragperformance over an elliptical wing, with the furled HECS wing showing minimalenhancements beyond this point. Wind tunnel tests of the active morphing wing prove themechanism capable of overcoming realistic loading, while further testing may berequired to establish aerodynamic merits of the HECS wing morphing maneuver.

Bat-Inspired Wing Aerodynamics and Optimization

A S ENGINEERS search to make micro air vehicles more stable, maneuverable, and efficient, many are turning toward biology for inspiration. Bats adapt to their environment by morphing their wings in flight. Depending on their niche, certain species soar and glide [1], whereas others perform barrel rolls in nature [2] and can pull up to 4.5g in obstacle courses [3].Morphological changes afford bats great agility at low speeds, and they are able tomaintain stability and control at low Reynolds numbers, in which viscous effects and leading edge laminar separation bubbles cause nonlinearities in lift [4–6]. Bats achieve these feats with fingerlike jointed bone structures and flexible wing membranes. These unique traits allow them to change camber and twist in flight, unlike avian span changes. Recent studies investigate replicating flapping bat flight [7–9], whereas others focus specifically on flexible, membrane wing benefits at low Reynolds numbers for improvements in gust alleviation and delayed stall characteristics [10–12]. These wings are passive elements, and it is difficult to attach control surfaces to them for flight authority. By actively controlling and morphing flexible wings, conventional controllers can be replaced. Aircraft morphing allows single vehicles to have multiple functions, ideally with continuous lifting surfaces to alleviate drag and vibration and increase efficiency. This is the focus of Garcia et al. [13], which proposes a nonflapping wing with twist capabilities. Morphing enables tailoring of wing shapes to multiple flight regimes, from takeoff through cruise to landing [14–16]. Many mechanisms have been proposed for morphing, such as the smart joint, an active rigidity composite suited to actuating a batlike membrane wing in flight [17]. This low-profile device can be embedded at joints in the fingerlike skeletal wing structure as a bimorph actuator [18]. Whereas this work focuses on static wing configurations rather than morphing behavior, results help specify actuator requirements used for a variable camber and twist wing. In this work, two key features of bat flight are studied, uniquely evolved bat wing planforms adapted to environments, and capabilities afforded through variable camber and twist, and are applied to rigid, fixed wing designs for small man-made craft. The goal of this study is not to mimic natural bat flight, but to understand how certain aspects of bat flight apply to the engineering problem of wing design for micro air vehicles. II. Background and Motivation

Preliminary study of an adaptive wing with shape memory alloy torsion actuators

This paper presents a preliminary design study aimed to verify the feasibility of an adaptive wing for a small unmanned aircraft (UAV), which is entirely actuated by shape memory alloy devices (SMA). The capability of the wing to bear the aerodynamic loads, the power required by the actuators and their force and torque during flight are assessed by finite element simulations. The wing consists of a sandwich box sub-structure with laminated faces, flexible ribs and a flexible skin. The adaptation capability to the changing flight conditions is obtained via airfoil shape change and local shape adjustments. Counter rotating, concentric torsion SMA tubes are employed for wing camber control, while levers powered by SMA wires are employed for local shape control. The external and the internal tubes control, respectively, the downward and the upward motions. They are connected to the flexible ribs through an electro-mechanical clutch and a positioning piezoelectric motor. Actuation occurs heating a tube at a time and making free the other by the clutch. With deformation limited to 4%, to allow a complete shape recovery by SMA, the wing appears capable to smoothly deform, with small stresses. A mean rotation of 21.7° of the flexible ribs and a rotation of 40° at the tip can be obtained, which are equivalent to a rotation of 30° of an aileron or flap of a conventional wing. A variable camber variation can be obtained at cruise speed, with a variation at least of 10° from the tip to the root. Also a local shape variation can be obtained, corresponding to a 4.5% increase of the thickness of the airfoil at 55% of the chord, while at 40% of the chord the thickness is reduced by 3.9%. The torque applied by the actuator tubes, which is up to 200 N m, and the peak power of 1223 W required for actuation appear compatible for an UAV.

Membrane Micro Air Vehicles with Adaptive Aerodynamic Twist: Numerical Modeling

Micro air vehicles are typically characterized by a low aspect ratio wing operating at low Reynolds numbers (104): aerodynamics involve a three-dimensional flow field with numerous regions of separated flow. Furthermore, aerodynamic twist can be built into the wing through the use of a thin membrane skin, to adaptively increase the wing camber. This work formulates a static aeroelastic model of such a wing, by coupling a linear membrane model to a well-validated steady laminar Navier–Stokes solver. The membrane deformation causes a significant pressure redistribution which increases lift and longitudinal static stability, though a drag penalty also develops. The efficiency of a rigid wing increases with Reynolds number, but decreases for a membrane wing, as the deformation generally provides a nonoptimal airfoil shape. Membrane deformation leads to larger separation bubbles, and acts as a barrier to the tip vortex formation. At high angles of attack, the aerodynamic twist causes a direct interaction between the recirculating flow and the tip vortices, indicating potential roll instabilities.

Determinate structures for wing camber control

An investigation of truss structures for the purpose of creating a continuously variablecamber trailing edge device for an aircraft wing is presented. By creating structures thatare both statically and kinematically determinate and then substituting truss elements foractuators, it is possible to impose structural deflection without inducing member stress.A limited number of actuators with limited strain capabilities are located within thestructure in order to achieve a target deflected shape starting from an initially symmetricprofile. Two objective functions are used to achieve this: a geometric objective for whichthe target displacement is fixed and a shape objective for which the target displacement isdependent on the surface shape of the targeted aerofoil. The proposed shapeobjective function is able to offer improvements over the geometric objective byremoving some of the constraints applied to the targeted structure joint locations.Four methods for selecting the location of a set of actuators are compared, namelyexhaustive search, a genetic algorithm, stepwise forward selection (SFS) and incrementalforward selection (IFS). Both SFS and IFS are variations of regression methods for subsetselection; in each case an approach has been created to allow the imposing of upper andlower bounds on the search space. It is shown that the genetic algorithm is well suited toaddressing the problem of optimally locating a set of actuators; however, regressionmethods, particularly IFS, can provide a rapid tool suitable for addressing large selectionproblems.

THE AERODYNAMICS OF THE BRITISH LATE TRIASSIC KUEHNEOSAURIDAE

Abstract: The Kuehneosauridae (Late Triassic, Britain, USA) had remarkable adaptations, most notably their elongate mid‐dorsal ribs that were presumably covered with a skin membrane in life. These lateral ‘wings’ have always been linked with some form of gliding adaptation, but quantitative studies have been limited. Here, we provide a thorough aerodynamic analysis of both genera of British kuehneosaurids based on theory and on experiments with life‐sized models in a wind tunnel. Of the two genera, Kuehneosuchus, with elongate ‘wings’, was a glider, and Kuehneosaurus, with much shorter ‘wings’, was a parachutist. Kuehneosuchus most probably had highly cambered wings and no additional skin membranes on hands or feet, nor did it have a cruropatagium. Lappets on the hyoid apparatus, as seen in Draco, were probably present to enhance pitch control. Kuehneosuchus was capable of gliding at angles (θ) between 13 and 16 degrees, at speeds between 7 and 9 m/s, and was probably very manoeuvrable when airborne. Kuehneosaurus was capable of parachuting (θ > 45 degrees) at speeds between 10 and 12 m/s. It is unclear whether the British kuehneosaurid material represents two genera, as assumed here, two species of one genus, or sexual dimorphs of a single species, where the gliding Kuehneosuchus was the male, which used its gliding and perhaps highly coloured ‘wings’ to display to the parachuting Kuehneosaurus.

Quantifying the complexity of bat wing kinematics

Body motions (kinematics) of animals can be dimensionally complex, especially when flexible parts of the body interact with a surrounding fluid. In these systems, tracking motion completely can be difficult, and result in a large number of correlated measurements, with unclear contributions of each parameter to performance. Workers typically get around this by deciding a priori which variables are important (wing camber, stroke amplitude, etc.), and focusing only on those variables, but this constrains the ability of a study to uncover variables of influence.Here, we describe an application of proper orthogonal decomposition (POD) for assigning importances to kinematic variables, using dimensional complexity as a metric. We apply this method to bat flight kinematics, addressing three questions: (1) Does dimensional complexity of motion change with speed? (2) What body markers are optimal for capturing dimensional complexity? (3) What variables should a simplified reconstruction of bat flight include in order to maximally reconstruct actual dimensional complexity?We measured the motions of 17 kinematic markers (20 joint angles) on a bat (Cynopterus brachyotis) flying in a wind tunnel at nine speeds. Dimensional complexity did not change with flight speed, despite changes in the kinematics themselves, suggesting that the relative efficacy of a given number of dimensions for reconstructing kinematics is conserved across speeds.By looking at subsets of the full 17-marker set, we found that using more markers improved resolution of kinematic dimensional complexity, but that the benefit of adding markers diminished as the total number of markers increased. Dimensional complexity was highest when the hindlimb and several points along digits III and IV were tracked.Also, we uncovered three groups of joints that move together during flight by using POD to quantify correlations of motion. These groups describe 14/20 joint angles, and provide a framework for models of bat flight for experimental and modeling purposes.