Search

A physical model for a micro air vehicle with Flapping Rotary Wings (FRW) is investigated by measuring the wing kinematics in trim conditions and computing the corresponding aerodynamic force using computational fluid dynamics. In order to capture the motion image and reconstruct the positions and orientations of the wing, the photogrammetric method is adopted and a method for automated recognition of the marked points is developed. The characteristics of the realistic wing kinematics are presented. The results show that the non-dimensional rotating speed is a linear function of non-dimensional flapping frequency regardless of the initial angles of attack. Moreover, the effects of wing kinematics on aerodynamic force production and the underlying mechanism are analyzed. The results show that the wing passive pitching caused by elastic deformation can significantly enhance lift production. The Strouhal number of the FRW is much higher than that of general flapping wings, indicating the stronger unsteadiness of flows in FRW.

Recent discoveries in the fields of flapping wing aerodynamics and fluid–structure interaction have demonstrated that flexible wings can generate more lift than rigid wings. However, the implications of wing flexibility on the flight dynamics of flapping wing flyers is still an open research question. The main difficulty is that the free flight of flapping flyers with flexible wings is a result of the dynamic balance between unsteady aerodynamics, fluid–structure interaction, and flight dynamics. This study presents a fully coupled three-way flight simulator that solves the two-dimensional Navier–Stokes equations, tightly coupled to the Euler–Bernoulli beam equations of the wing and the nonlinear multi-body equations of motion for the dynamics at the fruit fly scale. A novel trim algorithm is used to determine the hover equilibrium in the longitudinal plane. The control inputs, i.e. the flapping amplitude, stroke plane angle, and flapping offset angle as well as the initial conditions are determined that effectively eliminate average body accelerations to less than 3% of gravitational acceleration. The resulting hover equilibrium control parameters flapping amplitude, stroke plane angle and the total power required agree well with the biological observation of fruit flies. Body oscillations in hovering free flight affect the flexible response of the wing compared to prescribed body motion without oscillation. The affected wing motion reduces the lift coefficient by up to 8.7% for the stiffest wing, necessitating slightly different control inputs to achieve trim. Finally, the power required to achieve hover equilibrium is 32%–94% lower for flexible wings than for rigid wings that are actively rotated to match the same passive pitch schedule.

The wing shape and kinematics of flapping wing nano air vehicles play a crucial role in the effectiveness of the system. Optimizing these design parameters allows for greater endurance during flight due to a reduction in the needed aerodynamic power. In this study, seven insects' wings are considered in order to investigate which wing shape requires less amount of aerodynamic power for forward flight missions. A strip theory model is employed and verified for two types of birds, namely, Jack Daw, and Mew Gull. Then, this aerodynamic theory is utilized to model and optimize the kinematics of the seven wings with a particular investigation on the impacts of the dynamic twist on the performance of bio-inspired nano air vehicles. Each wing is divided into strips that are individually analyzed and integrated over the full wingspan to determine the needed aerodynamic power and propulsive efficiency. The use of this modified strip theory is beneficial because it includes the unsteady aerodynamic effects and the possible change in the wings' dimensions. A parametric study is then carried out to determine the optimum wing shape and associated dynamic twist of the flapping wing nano air vehicle when considering two scenarios. In the first scenario, the wingspan for all considered seven wing shapes is considered the same. As for the second scenario, the seven wing shapes are considered with same wing surface. The results show that for same wingspan and wing surface, the bio-inspired honeybee and bumblebee wing shapes have the optimum performances, respectively. The performed analysis gives guidelines on the optimum design of flapping wing nano air vehicles for forward flight applications.

Purpose This paper aims to describe the concept of morphing tailless aircraft with discontinuous skin and its preliminary kinematic solution. Project assumptions, next steps and expected results are briefly presented. Design/methodology/approach Multidisciplinary numerical optimization will be used to determine control allocation for wing segments rotation. Wing demonstrator will be fabricated and tested in wind tunnel. Results will be used in construction of flying model and design of its control system. Flight data of morphing demonstrator and reference aircraft will result in comparative analysis of both technologies. Findings Proposed design combines advantages of wing morphing without complications of wing’s structure elastic deformation. Better performance, stability and maneuverability is expected due to wing’s construction which is entirely composed of unconnected wing segments. Independent control of each segment allows for free modeling of spanwise lift force distribution. Originality/value Nonlinear multipoint distribution of wing twist as the only mechanism for control and flight performance optimization has never been studied or constructed. Planned wind tunnel investigation of such complex aerodynamic structure has not been previously published and will be an original contribution to the development of aviation and in particular to the aerodynamics of wing with discontinuous skin.

This paper proposes a family of high-pressure capturing wing configurations that aim to improve the aerodynamic performance of hypersonic vehicles with large volumes. The predominant visual feature...

This paper examines the application of formation flight to micro air vehicles with regard to possible power savings. Results of an experimental investigation on echelon formations using low-aspect-ratio (AR=2) flat plate rectangular wings at low Reynolds number (Re=35,000) are presented. One-, two-, and three-wing configurations are tested in a low-speed wind tunnel. To quantify the power savings by lift enhancement and drag reduction, the aerodynamic loads acting on each wing are measured using specific balances while the trailing wings of the formation are being traversed laterally and vertically in fine steps. In addition, the flowfields of the wing wakes are measured using particle image velocimetry. The force and flowfield measurements show that the optimal positions for lift enhancement appear at slightly spanwise overlapping between the leading and trailing wings.

Experiments were conducted on a flexible, finite-span cyber–physical wing model in the wind tunnel to study the structural kinematics for a wing undergoing stall flutter. The wing model was designed to be weak in torsion and stiff in bending to exhibit stall flutter oscillations. The physical deformation of the wing surface was mapped at 38%, 58%, 78%, and 98% span using a stereo vision motion tracking system. From these measurements, the wing motion is decomposed and shown to consist of a principally torsional (pitching) oscillation consistent with the first mode for a cantilevered beam in free vibration. A two equation empirical model of the wing motion was then developed and compared to the measured stall flutter motion.

In aircraft wing design, engineers aim to provide the best possible aerodynamic performance under cruise flight conditions in terms of lift-to-drag ratio. Conventional control surfaces such as flaps, ailerons, variable wing sweep and spoilers are used to trim the aircraft for other flight conditions. The appearance of the morphing wing concept launched a new challenge in the area of overall wing and aircraft performance improvement during different flight segments by locally altering the flow over the aircraft’s wings. This paper describes the development and application of a control system for an actuation mechanism integrated in a new morphing wing structure. The controlled actuation system includes four similar miniature electromechanical actuators disposed in two parallel actuation lines. The experimental model of the morphing wing is based on a full-scale portion of an aircraft wing, which is equipped with an aileron. The upper surface of the wing is a flexible one, being closed to the wing tip; the flexible skin is made of light composite materials. The four actuators are controlled in unison to change the flexible upper surface to improve the flow quality on the upper surface by delaying or advancing the transition point from laminar to turbulent regime. The actuators transform the torque into vertical forces. Their bases are fixed on the wing ribs and their top link arms are attached to supporting plates fixed onto the flexible skin with screws. The actuators push or pull the flexible skin using the necessary torque until the desired vertical displacement of each actuator is achieved. The four vertical displacements of the actuators, correlated with the new shape of the wing, are provided by a database obtained through a preliminary aerodynamic optimization for specific flight conditions. The control system is designed to control the positions of the actuators in real time in order to obtain and to maintain the desired shape of the wing for a specified flight condition. The feasibility and effectiveness of the developed control system by use of a proportional fuzzy feed-forward methodology are demonstrated experimentally through bench and wind tunnel tests of the morphing wing model. Proportional fuzzy feed-forward architecture control validation by wind tunnel tests of a morphing wing.

Inspired by the high performance of rotary and insect flapping wings capable of vertical take-off and landing and hovering (VTOLH), a novel flapping wing rotor (FWR) has been developed by combining the above two types of wing motions. The FWR offers an alternative configuration for micro air vehicles (MAV) of such high flight performance. Unlike the well-studied aerodynamics of rotary and insect-like flapping wing with prescribed wing motion, the aerodynamic lift and efficiency of the FWR associated with optimal kinematics of motion has not been studied in a systematic manner before. This investigation is therefore focused on the FWR optimal kinematic motion in terms of aerodynamic lift and efficiency. Aerodynamic analysis is conducted for a FWR model of aspect ratio 3.6 and wing span 200 mm in a range of kinematic parameters. The analysis is based on a quasi-steady aerodynamic model with empirical coefficients and validated by CFD results at Re ∼ 3500 . For comparison purpose, the analysis includes rotary and insect-like flapping wings in hovering status with the FWR at an equilibrium rotation speed when the thrust equals to drag. The results show that the rotary wing has the greatest power efficiency but the smallest lift coefficient. Whereas the FWR can produce the greatest aerodynamic lift with power efficiency between rotary and insect-like flapping wings. The results provide a quantified guidance for design option of the three types of high performance MAVs together with the optimal kinematics of motion according to flight performance requirement.

Flapping rotary wing, rotating wing, and flapping wing are feasible wing layouts applicable to micro-air-vehicles capable of hovering flight. A numerical study in this paper presents which wing layout can be more efficient in terms of aerodynamic power for the given kinematic and geometric parameters with or without the constraint of vertical force. In the cases under typical conditions, rotating wing layout is the most efficient one when a small vertical force is needed. However, if a much larger vertical force is required, flapping rotary wing is the only wing layout that fulfills the requirements of the two aspects due to its coupling effect. At relatively high Reynolds number (Re>2000), flapping amplitude (>70°), and aspect ratio (=6), comparative relationships from the cases under typical conditions among three wing layouts in terms of vertical force and aerodynamic power efficiency are kept unchanged. Nevertheless, at relatively low Re(

In this paper, a novel decambering technique has been implemented using a vortex lattice method to study the effects of wing twist on the induced drag of individual lifting surfaces in configuration flight including post-stall angles of attack. The effect of both geometric and aerodynamic twist is studied. In the present work, 2D data of NACA0012 airfoil from XFoil at R e = 1 × 10 6 is used to predict 3D post-stall data using geometric twist for a single wing and compared with literature. The effect of aerodynamic twist is implemented by using different airfoils along wing–span and the resulting wing C L –α and C d i –α are compared with experiment. Study of wings of different aspect ratios with & without aerodynamic twist on both leading and trailing wings helps to understand the effect of twist on the lift and induced drag when they are varied on both wings simultaneously and individually.

In this brief, the control problem for flexible wings of a robotic aircraft is addressed by using boundary control schemes. Inspired by birds and bats, the wing with flexibility and articulation is modeled as a distributed parameter system described by hybrid partial differential equations and ordinary differential equations. Boundary control for both wing twist and bending is proposed on the original coupled dynamics, and bounded stability is proved by introducing a proper Lyapunov function. The effectiveness of the proposed control is verified by simulations.

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.

This work presents a wing deformation analysis of a twin-sting-mounted commercial aircraft model. Twin-sting arrangements minimize flow disturbances around the model fuselage and tail; on the other hand, they cause important changes in the flow field around the wing and also increase aerodynamic interference at the wing and aeroelastic effects on the wing. In some cases, these effects can alter the normal downwash developed behind the wing, modifying the flow pattern at the tail. Consequently, when tail aerodynamics is a major concern, this kind of support interference should be carefully evaluated. The methodology developed in this work employs an unstructured FEM-based flow solver for computing aerodynamic loads. These loads are then transferred to a finite element structural model in order to assess the geometrical deformation of the wing caused by torsional moment exerted by supporting mechanism. The analysis described involves three different twin-sting support configurations taking into account angle of attack variations and Mach numbers spanning from subsonic of high transonic ranges.

Experimental study on the unsteady aerodynamics analysis and power consumption of a folding wing is accomplished using a wind tunnel testing. A...

An aerodynamic model for tandem flapping wings is proposed. The model attempts to represent insects such as the dragonfly. Two advances are presented: the aerodynamic model with tandem wings flapping simultaneously, and the wing stroke optimization. The aerodynamic model accounts for the inflow effects of the front wing (fore-wing) on the rear wing (hind-wing).The stroke is optimized at two right conditions (acceleration and level right) by using a heuristic optimization procedure (particle swarming). The vector of the design variables consists of 28 independent parameters (14 per wing), each with a constrained range derived from the maximum available power, the right muscle ratio and kinematics of real insects. The cost function is the propulsive efficiency coupled with constraints for right stability. Prediction of the level rightefficiency is in agreement with the right muscle efficiency. The maximum acceleration is found to be dependent on the size of the right muscle. Finally, a study of the wing shape is presented for both level and accelerating right conditions.

The objective of this work is to assess the potential and limitations of current practice in computational fluid dynamic modeling in predicting vortical flowfields over a generic 53-degree swept diamond wing with rounded leading edges. This wing was designed under STO AVT Task Group 183 and has a constant NACA 64A-006 airfoil section with a leading edge radius of 0.264 percent chord. CFD simulations were run for different angles of attack at a Mach number of 0.15 and a Reynolds number of 2.7 × 10 6 based on the mean aerodynamic chord to match experiments. The wind tunnel experiments of the diamond wing were carried out in the Institute of Aerodynamics and Fluid Mechanics of the Technische Universitat Munchen, Germany and include aerodynamic lift, drag, and pitch moment measurements as well as span-wise pressure distributions at different chord-wise locations. This data set is used to validate the CFD results. The results presented demonstrate that the CFD compare well with the experiments at small angles of attack; the pitch moments predicted by the SARC turbulence model provide a better match to experimental results than the SA model at moderate angles of attack; and at high angles of attack, CFD predictions are not as good. The flow visualization results show that a leading-edge vortex is formed above the upper surface of the wing at an angle of attack of about eight degrees. This vortex becomes larger and stronger when the angle of attack is increased. With increasing angle of attack, the vortex formation point moves upstream and the vortex core moves inboard towards the wing center. Finally, the computational results show that the flow over the diamond wing is relatively steady throughout the range of angles of attack.

This paper presents a new non-linear formulation of the classical Vortex Lattice Method (VLM) approach for calculating the aerodynamic properties of lifting surfaces. The method accounts for the effects of viscosity, and due to its low computational cost, it represents a very good tool to perform rapid and accurate wing design and optimization procedures. The mathematical model is constructed by using two-dimensional viscous analyses of the wing span-wise sections, according to strip theory, and then coupling the strip viscous forces with the forces generated by the vortex rings distributed on the wing camber surface, calculated with a fully three-dimensional vortex lifting law. The numerical results obtained with the proposed method are validated with experimental data and show good agreement in predicting both the lift and pitching moment, as well as in predicting the wing drag. The method is applied to modifying the wing of an Unmanned Aerial System to increase its aerodynamic efficiency and to calculate the drag reductions obtained by an upper surface morphing technique for an adaptable regional aircraft wing.

Wing kinematics in forward-flying fruit-flies was measured using high-speed cameras and flows of the flapping wing were calculated numerically. The large lift and thrust coefficients produced by the wing were explained. The wing flaps along a forward-tilting stroke plane. In the starting portion of a half-stroke (an upstroke or downstroke), the wing pitches down to a small pitch angle; during the mid portion (the wing has built up its speed), it first fast pitches up to a large pitch angle and then maintains the pitch angle; in the ending portion, the wing pitches up further. A large aerodynamic force (normal to the wing surface) is produced during the mid portion of a half-stroke. The large force is produced by the fast-pitching-up rotation and delayed-stall mechanisms. As a result of the orientation of wing, the thrust that propels the insect is produced by the upstroke and the major part of the vertical force that supports the weight is produced by the downstroke. In producing the thrust the upstroke leaves a “vortex ring” that is almost vertical, and in producing the vertical force the downstroke leaves a “vortex ring” that is almost horizontal.

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).

Vortex formation has numerous influences on the aerodynamic characteristics of fixed-wing micro air vehicle wings. Despite the mature understanding of vortices on fixed-wing and flapping micro air vehicle wings, the behavior of vortices over the morphing micro air vehicle wing has not been fully explored. Thus, the current work is conducted to investigate the influence of vortex structure over a series of twist-morphing micro air vehicle wings. Twist morphing micro air vehicle and baseline wings are simulated through fluid–structure interaction analysis. The validation results for each wing exhibited good correlation in the overall lift coefficient distribution trend. The vortex formation results show that vortex formations are significantly altered throughout angle of attack changes. For a given angle of attack cases below the stall angle, each morphing wing exhibited higher intensities of tip vortex structure formations and leading edge vortex–tip vortex interactions compared to the baseline wings. Stronger leading edge vortex–tip vortex interactions improved the low-pressure region over the morphing wing surface and further induce better lift performance. In fact, the morphing wing with higher morphing force induces better lift performance.

A micro air vehicle with a bird-mimetic up-down and twisting wing drive system was developed in this study. The Flapping-wing Micro Air Vehicle (FMAV), with a 50 cm wingspan and a double-crank drive system, performed successful flights of up to 23 min. The performance and capabilities of the FMAV were enhanced by adapting a number of unique features, such as a bird-mimetic wing shape with a span-wise camber and an up-down and twisting wing drive mechanism with double-crank linkages. This lift-enhancing design by mimicking the flapping mechanism of a bird’s wing enabled the 210 g FMAV to fly autonomously in an outdoor field under wind speeds of less than 5 m·s−1. Autonomous flight was enabled by installing a flight control computer with a micro-electro-mechanical gyroscope and accelerometers, along with a micro video camera and an ultralight wireless communication system inside the fuselage. A comprehensive wind tunnel test shows that the FMAV with a high-camber wing and double-crank mechanism generates more lift and less net thrust than the FMAV with a flat wing and single-crank mechanism, which confirms the improved performance of the developed FMAV, as well as the superior slow flying or hovering capabilities of the FMAV with a high-camber wing and double-crank wing drive system.

A practical mathematical model with low computational time and good accuracy is applied to investigate the aerodynamic characteristics and static height stability of the compound wing-in-ground effect (WIG). The compound WIG consists of a main wing with low aspect ratio and an endplate, and an outer wing with high aspect ratio. To validate the present mathematical model, a numerical simulation is performed so that numerical results had a good agreement with the experimental data. The analysis shows that the main wing is useful in the extreme ground effect zone and the outer wing enhances performance of the compound WIG in the weak ground effect zone. In order to satisfy the static height stability of the compound WIG it is evaluated by Irodov's criterion. Influence of junction position of outer wing on the main wing is investigated on the static height stability of compound WIG. A comparison of Irodov's criterion shows that static height stability improves with moving the outer wing position backward into the trailing edge of the main wing and this led to a decrease in the tail area. The proposed mathematical model could be appropriate for aerodynamic optimization of WIG crafts with the compound wing.

This paper investigates the influence of forward-swept wing (FSW) positions on the aerodynamic characteristics of aircraft under supersonic condition (Ma = 1.5). The numerical method based on Reynolds-averaged Navier–Stokes (RANS) equations, Spalart–Allmaras (S–A) turbulence model and implicit algorithm is utilized to simulate the flow field of the aircraft. The aerodynamic parameters and flow field structures of the horizontal tail and the whole aircraft are presented. The results demonstrate that the spanwise flow of FSW flows from the wingtip to the wing root, generating an upper wing surface vortex and a trailing edge vortex nearby the wing root. The vortexes generated by FSW have a strong downwash effect on the tail. The lower the vertical position of FSW, the stronger the downwash effect on tail. Therefore, the effective angle of attack of tail becomes smaller. In addition, the lift coefficient, drag coefficient and lift–drag ratio of tail decrease, and the center of pressure of tail moves backward gradually. For the whole aircraft, the lower the vertical position of FSW, the smaller lift, drag and center of pressure coefficients of aircraft. The closer the FSW moves towards tail, the bigger pitching moment and center of pressure coefficients of the whole aircraft, but the lift and drag characteristics of the horizontal tail and the whole aircraft are basically unchanged. The results have potential application for the design of new concept aircraft.

This work presents a step toward bridging the gap between flight dynamics simulation of ram-air parachutes and high-fidelity computational fluid dynamics. Today's parachute design codes mainly rely on the empirical or semi-empirical methods generated from wind tunnel experiments and drop tests. The outcome of this study will hopefully help to reduce the cost of experiments and drop testing in the design of future canopies and to better understand the aerodynamic characteristics of these geometries. In this work, the parachute geometries were modeled as rigid rectangular wings with an aspect ratio of two and zero anhedral angle. The wings have seven opening cells and the trailing edge is deflected or not deflected. To validate computational methods, the aerodynamic predictions of similar wings, but with closed and round inlets, are compared with experimental data available from the Subsonic Wind Tunnel at United States Air Force Academy. Total lift and drag force coefficients were measured at a Reynolds number of 1.4 million. The results show that computational predictions of fine (closed-inlet) grids match the experimental data very well up to the stall angle. Both experiments and simulations show that closed wings have sharp stalling characteristics. The aerodynamics of closed wings up to stall can be approximated by linear functions and their derivatives. The closed wings show a negative static stability with respect to changes in the angle of attack. The open wings, on other hand, have positive static stability in the longitudinal and lateral directions. The open wings exhibit highly nonlinear unsteady aerodynamic characteristics; they also stall earlier and have higher drag values than the closed wings. The aerodynamic derivatives of open and closed wings were estimated using a linear regression method and training data simulated in small-amplitude oscillations in pitch, yaw, and roll directions. While the open wings have large oscillations in aerodynamic coefficients over the yawing and rolling hysteresis loops, lateral aerodynamic derivatives of the open and closed wings are similar. Finally, the results show that model predictions are reasonably accurate for use in flight-dynamics simulations.

This study investigates the aerodynamic tradeoffs of a box-wing aircraft configuration using high-fidelity aerodynamic optimization. A total of five optimization studies are conducted, where each study extends the previous one by progressively adding a combination of design variables and constraints. Examples of design variables include wing twist and sectional shape; examples of constraints include trim and stability requirements. In all cases, the objective is to minimize inviscid drag at a prescribed lift and a Mach number of 0.78. Aerodynamic functionals are evaluated based on the discrete solution of the Euler equations, which are tightly coupled with an adjoint methodology incorporating a gradient-based optimizer. For each study, an equivalent conventional tube-and-wing baseline is similarly optimized in order to enable direct comparisons. It is found that the transonic box-wing aircraft considered here, for which the height-to-span ratio is about 0.2, produces up to 43% less induced drag than its c...

Hovering ability is one of the most desired features in Flapping-Wing Micro Air Vehicles (FW-MAVs). This paper presents a hybrid design of flapping wing and fixed wing, which combines two flapping wings and two fixed wings to take advantage of the double wing clap-and-fling effect for high thrust production, and utilizes the fixed wings as the stabilizing surfaces for inherently stable hovering flight. Force measurement shows that the effect of wing clap-and-fling significantly enhances the cycle-averaged vertical thrust up to 44.82% at 12.4 Hz. The effect of ventral wing clap-and-fling due to presence of fixed wings produces about 11% increase of thrust-to-power ratio, and the insect-inspired FW-MAV can produce enough cycle-averaged vertical thrust of 14.76 g for lift-off at 10 Hz, and 24 g at maximum frequency of 12.4 Hz. Power measurement indicates that the power consumed for aerodynamic forces and wing inertia, and power loss due to gearbox friction and mechanism inertia was about 80% and 20% of the total input power, respectively. The proposed insect-inspired FW-MAV could endure three-minute flight, and demonstrate a good flight performance in terms of vertical take-off, hovering, and control with an onboard 3.7 V-70 mAh LiPo battery and control system.

Atmospheric conditions at high-altitudes challenges aircraft wing design. High altitude operations require high-performance solutions in air vehicle aerodynamics such as wing configuration, drag reduction, high value of lift coefficient. High-altitude aircraft developed at the moment have significant size due to those requirements. Overall goal is to overcome the storage and transportation limitations of high altitude aircraft and implement portability options. Therefore a portable high altitude aircraft wing was developed. It is necessary for the UAV to have a high value of aerodynamic quality Kmax, for maximum achievable altitude. High value of aerodynamic quality requires large wing aspect ratio λ, which is determined by the wing area and wing length. Two computational 3D model of UAV wing were made and analyzed for lift distribution over the span. To eliminate possible errors, flow calculation around the wings are executed by various aerodynamic computational methods which are panel-vortex method and finite element method. For wing profile R-III-A-15 airfoil was selected. Both wing have identical geometry parameters except the tip of second wing has an angle of -5°. Result of analyzes shows that lift distribution over the span is not optimal. Therefore further optimizations were made. Three different wing geometry designed for improving the first version of the portable high UAV wing. These are straight wing, combined wing with straight center section and trapezoid console, straight wing with elliptical tip. Those wings were compared for value of Сумах and Kмах and lift distribution over the span. Results clearly demonstrate advantages of straight wing with elliptical tip section, which allows for a continual flow of finite wings to a much greater extent than other reviewed options, which makes it possible to ensure effective control by the roll at supercritical flight conditions such as stall and tail spin. However, other important characteristics, especially Сумах and K мах have not significantly reduced compared.

This paper presents a numerical investigation of the effects of chordwise flexibility on flapping wings at low Reynolds number. The numerical simulations are performed with a partitioned fluid–structure interaction algorithm using artificial compressibility stabilization. The choice of the structural dimensionless parameters is based on scaling arguments and is compared against parameters used by other authors. The different regimes, namely inertia-driven and pressure-driven wing deformations, are presented along with their effects on the topology of the flow and on the performance of a heaving and pitching flapping wing in propulsion regime. It is found that pressure-driven deformations can significantly increase the thrust efficiency if a suitable amount of flexibility is used. Significant thrust increases are also observed in zero pitching amplitude cases. The effects of the second and third deformation modes on the performances of pressure-driven deformation cases are discussed. On the other hand, inertia-driven deformations generally deteriorate aerodynamic performances of flapping wings unless the behavior of the wing deformation is modified by the presence of sustainable superharmonics in a way that produces slight improvements. It is also shown that wing flexibility can act as an efficient passive pitching mechanism that allows fair thrust and better efficiency to be achieved when compared to a rigid pitching–heaving wing.

Computational model is developed to analyze aerodynamic loads and flow characteristics for an automobile, when the rear wing is placed above the trunk of the vehicle. The focus is on effects of the rear wing height that is investigated in four different positions. The relative wind incidence angle of the rear wing is equal in all configurations. Hence, the discrepancies in the results are only due to an influence of the rear wing position. Computations are performed by using the Reynolds-averaged-Navier-Stokes equations along with the standard k-ε turbulence model and standard wall functions assuming the steady viscous fluid flow. While the lift force is positive (upforce) for the automobile without the rear wing, negative lift force (downforce) is obtained for all configurations with the rear wing in place. At the same time, the rear wing increases the automobile drag that is not favorable with respect to the automobile fuel consumption. However, this drawback is not that significant, as the rear wing considerably benefits the automobile traction and stability. An optimal automobile downforce-to-drag ratio is obtained for the rear wing placed at 39 % of the height between the upper surface of the automobile trunk and the automobile roof. Two characteristic large vortices develop in the automobile wake in configuration without the rear wing. They vanish with the rear wing placed close to the trunk, while they gradually restore with an increase in the wing mounting height.

Computational fluid dynamics (CFD) analyses are conducted to evaluate the gliding performance of a three-dimensional (3-D) corrugated wing while considering variations in the corrugation pattern across the wing span. Comparisons with the smoothly profiled counterpart assess the overall effect of wing corrugation on the gliding performance of the 3-D dragonfly wing, with primary focus on the effect of three-dimensionality as compared to the 2-D model. Earlier simulations of both 2-D and 3-D gliding corrugated wings showed oscillations on lift and drag, while in nature, such force fluctuation would be undesirable and unrealistic. In contrast, no non-realistic fluctuations are present in this simulation. The feature included here, which has been neglected in the earlier studies, namely the variation of leading edge orientation along the wing span, is the crucial detail for preventing such non-realistic oscillations. Furthermore, strong spanwise flow occurs in the 3-D corrugated wing used in this study, which earlier models have been incapable to capture.

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.

As flying wing aircraft has no tail and adopts blended-wing-body design, most of flying wing aircrafts are directional unstable. Pitching moment couples seriously with rolling and yawing moment when control surfaces are deflected, bringing insecurity to landing stage. Numerical simulation method and semi-empirical equation estimate method were combined to obtain a high aspect ratio flying wing aircraft’s aerodynamic coefficients. Modeling and simulation of landing stage were established by MATLAB/Simulink. The control coupling effect on lift and drag characteristics and anti-crosswind landing capability was studied. The calculation results show that when the high aspect ratio flying wing aircraft was falling into the deceleration phase, appropriate to increase the opening angle of split drag rudder can reduce the trimming pitching moment deflection of pitch flap, thereby reduce the loss of lift caused by the deflection of pitch flaps. Flying wing aircraft can be rounded out successfully by using the pitch flap gently and steady. Both side-slip method and crabbed method can be applied to the landing of high aspect ratio flying wing aircraft in crosswind, the flying wing aircraft’s anti-crosswind landing capability was weakened by the control coupling effect of split drag rudder and elevon. Sideslip method was recommended in the crosswind landing of flying wing aircraft after calculation and analysis.

To lessen the deterioration of fixed-wing aerodynamic performance associated with chord Reynolds numbers below 100,000, flexible membrane wing designs have been studied and proposed as an alternative for micro air vehicle use. The beneficial effects of a flexible membrane can include higher lift, steeper lift-curve slope, delayed stall, gentle stall characteristics, and greater efficiency. These benefits have been attributed to both the time-averaged and dynamic deformation of the membrane. This work discusses the geometric and prestrain effects on a batten-reinforced, free trailing-edge membrane wing in low-Reynolds-number (50,000) flow. The global aerodynamic forces on the wings with varying wing aspect ratio, cell aspect ratio, and prestrain level were measured. The results show that the aerodynamic advantages of the flexible membrane are retained for the low-aspect-ratio wings. The optimal membrane cell aspect ratio is found to be approximately 1. The comparison of the aerodynamic forces between the low-aspect-ratio membrane wings and the corresponding three-dimensional-printed wings with the time-averaged deformation indicates the importance of membrane dynamic motion for the derived aerodynamic benefits.

The aviation industry is dominated by the domain of heavier-than-air, fixed-wing, subsonic flight, and central to any design in this domain is the wing itself. One of the earliest debates in aviation still centres around the usefulness of the wing volume. On the one hand it is held that the wing, as an inevitable necessity, should provide the volume also for the payload. On the other, it is argued that more efficient wings do not even have sufficient volume for the entire wing structure. This work proposes precise definitions of theWing Densityand theInflation Factor, two parameters that can quantitatively reflect the economic and technological trends in aviation. The wing volume of a hypotheticalIdeal Wingis derived from theOperational Parametersof any givenFlight Objectiveand compared to the volume requirement of that flight objective. We conclude that the dominant aircraft configuration of the future is likely to remain within the same family of the current dominant configuration, in conflict with some older predictions.

In this paper it is presented the design optimization of the rear wing of a sports car. The wing profile was parameterized with three variables, the angle of attack was the fourth variable and the objective function was to minimize the lift over drag ratio. Three virtual models were considered: a model without rear wing, a model with a rear wing with initial profile and position and a model with optimized rear wing. For these three models the drag and lift coefficients were calculated for comparison along with drag and lift forces.

The design space for morphing wings is incredibly broad and allows for a wide range of improvements versus fixed wing aircrafts such that each type of morphing can be useful for different purposes. This work introduces a novel concept for a twist morphing wing segment where only a segment of the wing is actuated which causes a rotation of the tip of the wing while the base segment fixed. The morphing segment consists of a smart soft composite structure made from PDMS and PLA which is actuated by multiple embedded SMA wires. This structure was implemented in a UAV-sized wing and was tested both in still-air conditions and in an open-type wind tunnel to determine the actual impact of this mode of actuation. Results show that this concept can improve the aerodynamic properties of the wing, particularly at low angles of attack.

We investigated the effect of wing kinematics modulation, which was achieved by adjusting the location of trailing-edge constraint at the wing-root, i.e., by adjusting the wing-root offset, on the generation of aerodynamic forces in a hovering insect-mimicking Flapping-Wing Micro Air Vehicle (FW-MAV) by numerical and experimental studies. Three-dimensional wing kinematics measured using three synchronized high-speed cameras revealed a clear difference in the wing rotation angle of a wing section for different wing-root offsets. The extrapolated wing kinematics were in good agreement with the measured ones for various wing-root offsets. The Unsteady Blade Element Theory (UBET) was used to estimate the forces generated by the flapping wings and validated by comparison with results of measurements performed using a load cell. Although the thrust produced by a flapping wing with a wing-root offset of 0.20 was about 4% less, its force-to-input-power ratio was about 30% and 10% higher than those with the offsets of 0.10 and 0.15 , respectively. This result could be explained by analyzing the effective Angle of Attack (AoA) and the force components computed by the UBET. Thus, a flapping wing with a wing-root offset of 0.20 ; can be regarded as an optimal twist configuration for the development of the FW-MAV.

Flapping wings for small aerial vehicles have revolutionary potential for maneuverability and endurance. Ornithopters fail to achieve the performance of their biological equivalents, despite extensive research on how animals fly. Flapping wings produce peak forces due to the stroke reversal of the wing. This research demonstrates in-flight measurements of an ornithopter through the use of image processing, specifically measuring instantaneous forces. Results show that the oscillation about the flight path is significant, being about 20% of the mean velocity and up to 10 g׳s. Results match forces with deformations of the wing to contrast the timing and wing shape of the upstroke and the downstroke. Holding the vehicle fixed (e.g. wind tunnel testing or simulations) structural resonance is affected along with peak forces, also affecting lift. Non-contact, in-flight measurements are proposed as the best method for matching the flight conditions of flapping wing vehicles.

In this paper, an approach is described to implement autonomous (waypoint tracking) flight in a testbed airframe, which uses wing twist for roll control. These flights were performed using an existing commercial autopilot. Aileron effectiveness was identified as a parameter that could be modified to maintain roll control during autonomous flight. A modeling process was then developed to calculate the aileron effectiveness for a wing shaping demonstrator aircraft utilizing numerically determined aerodynamic properties. Simulations and flight tests with the testbed aircraft were performed that demonstrated suitability of the approach for autonomous flight. In-flight aileron doublets were used to validate the aileron effectiveness predicted by the numerical model, which matched within 7%.

In this paper, the effect of aerodynamic damping produced by store rear horizontal fins on the aeroelastic instability of a wing with a large underwing store is investigated in an incompressible flow. The wing is modeled by using the classical Euler–Bernoulli beam theory while the unsteady strip aerodynamic theory based on the Wagner function is used to simulate the aerodynamic field. The underwing store is modeled as a concentrated mass attached to the wing by a rigid pylon and has rear horizontal fins. The numerical results of the developed generic and simple model are compared with available results, and an excellent agreement is observed. It is found that the aerodynamic damping of the store produced by its rear fin can compensate the flutter boundary of the wing-store configuration and therefore for more accurate analysis, in addition to the store weight and location, the effect of store fin must also be considered.

This paper proposes novel wing planforms that reduce induced drag by exploiting the slipstream in aircraft driven by propellers in tractor configuration. The novel planforms are determined by optimization through an extended lifting-line theory that accounts for slipstream effects and an optimizer that includes the option of using an appropriate number of Bezier polynomial weights as control parameters describing wing planform. The optimization package written for the purpose (PROWING) minimizes a user-selected cost function, subject to a wide class of geometric and mechanical constraints on such variables as root chord, tip chord, span, wing area, bounds on wing twist and chord, airfoil profiles, root bending moment, etc. A general feature of the optimal wing planforms so generated is that the chords are shorter within the slipstream and longer on either side of it. For a wing of aspect ratio 12 and prescribed wing area, PROWING predicts that an optimal planform can reduce induced drag by about 9.15%, wi...

Experiments were performed on flexible and rigid rectangular aspect ratio 2 wings undergoing pure rotational motion. Chordwise wing flexibility was modeled by a 1 degree-of-freedom linkage of rigid panels, free to pivot about the midchord. For each wing, unsteady force measurements were acquired for three-quarter-span Reynolds numbers of 10,000, 15,000, and 25,000 and leading-edge angles of attack from 0 to 70 deg. Dye flow visualization was used to establish flow structure similarity over the Reynolds number range. Thin-airfoil theory for finite, low-aspect-ratio wings was compared to the experimental lift measurements. Results show that the lift generated by the flexible wing rotating in a quiescent flow increased with instantaneous geometric angle of attack and wing camber, even at angles of incidence above static stall. Passive deformation of the posterior wing section played an important role in lift generation during wake encounters by increasing the camber of the wing and geometric angle of attack,...

In this work improvements on the geometry of a high aspect ratio aircraft wing are studied, in order to reduce the wing in-flight deformation, without changing the drag of the aircraft and without increasing the structural weight. For this, from a reference rectangular wing, one new wing with elliptical planform has been defined; and comparative analyses of loads and structural deformation have been made for the wings considered: the original rectangular wing and the new corresponding elliptical wing. The aerodynamic analysis is based on the lifting line approach. A computer routine is made by the authors based on this approach, to obtain both induced drag values and the load distribution of the two wings, the original one and the corresponding elliptical. Based on the loads, spars for the two wings have been defined, and in order to evaluate the vertical displacements in flight, a finite element routine have been used. The main result of this study is the comparison of the deformation of wings considered, subjected to the same load factor, and for the same aircraft mass. The results obtained are encouraging for further developments using the present methodology.

The application of active circulation control gives rise to a substantial increase in lift compared to conventional wings. Initial studies of the aeroelastic behaviour of a circulation-controlled wing have shown additional instabilities due to the active circulation control. Besides the heave flutter phenomenon, further investigation also reveals a destabilising effect of the aerodynamic derivatives related to pitch, which is peculiar to circulation-controlled wings. The goal of the present paper is to investigate these phenomena in detail.

This study numerically investigates the aerodynamic effects of deformation on three-dimensional low aspect ratio wings engaged in hover kinematics. The immersed-boundary finite-volume method is used to solve the Navier–Stokes equations. Deformations are actively prescribed and are represented as deflections about axes that transect the rectangular planform. Two distinct deformation modes associated with tip and root deflection are explored, in addition to a rigid wing counterpart. Variation of the phase between deflection and flapping enables mimicry of a range of wing behavior observed in nature. It is found the introduction of root or tip deflection can increase efficiency by as much as 19.5% or 19.0% respectively. The development of vortical structures about the wing is investigated. It is shown that while the rotational axis of the leading-edge vortex is insensitive to deformation, the shape and orientation of cores of the vortex is modified.

Previous studies on chordwise flexibility of flexible wings generally relied on simplified two-dimensional (2D) models. In the present study, we constructed a simplified three-dimensional (3D) model and identified the role of the chordwise flexibility in full flapping motion. This paper includes two parts, the first part discusses the aerodynamic effects of the chordwise flexibility in a typical hovering-flight case; the second part introduces a parametric study of four key parameters. The primary findings are as follows. Flexibility generally degrades the lift performance of the flexible wings. However, in two special cases, i.e. when stroke amplitude is low or pitch rotation is delayed, the flexible wings outperform their rigid counterparts in lift generation. Moreover, flexibility reduces the power consumption of the flexible wings. A wing with small flexibility generally achieves a marginally higher flapping efficiency than its rigid counterpart. Furthermore, reducing stroke amplitude can effectively improve the lift performance of the very flexible wings. Aerodynamic performances of the flexible wings are not as sensitive as the rigid wing to phase difference and mid-stroke angle of attack. The effects of Re are the same for the flexible and rigid wings.