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The existing approach in aircraft wing design optimizes the structure for strength and buckling design criteria followed by a flutter stability check, which leads to design that may not be optimal. This study proposes the flutter stability as an integral of weight optimization by a two-step procedure. Step 1 comprises series of flutter and static analyses of finite element (FE) models with different weapon configurations and aerodynamic loads, which give limiting values of wing tip deflection and wing twist as flutter constraints. Step 2 focuses on weight optimization of the laminate for strength and stiffness design parameters along with the flutter constraints. The algorithm minimizes structural weight by ply drop, which is based on evaluation of the fitness value of laminates generated by a stochastic operator. The ply drop design algorithm is applied to optimize the FE model of a fourth-generation fighter aircraft wing box with three representative aerodynamic loads and three weapon configurations. The application evolved optimal laminate with seamless and symmetric plies, which has 35% lesser weight compared with the initial model having quasi-isotropic laminates for given strength and flutter stability design requirement. The application of genetic algorithm (GA) to get an initial laminate instead of quasi-isotropic laminates further improved the design by 2.5% weight reduction.

In gliding flight, birds morph their wings and tails to control their flight trajectory and speed. Using high-resolution videogrammetry, we reconstructed accurate and detailed three-dimensional geometries of gliding flights for three raptors (barn owl,Tyto alba; tawny owl,Strix aluco, and goshawk,Accipiter gentilis). Wing shapes were highly repeatable and shoulder actuation was a key component of reconfiguring the overall planform and controlling angle of attack. The three birds shared common spanwise patterns of wing twist, an inverse relationship between twist and peak camber, and held their wings depressed below their shoulder in an anhedral configuration. With increased speed, all three birds tended to reduce camber throughout the wing, and their wings bent in a saddle-shape pattern. A number of morphing features suggest that the coordinated movements of the wing and tail support efficient flight, and that the tail may act to modulate wing camber through indirect aeroelastic control.

Geometric and/or aerodynamic wing twist can be used to produce a lift distribution that results in a rolling moment. A decomposed Fourier-series solution to Prandtl’s lifting-line theory is used to develop analytic spanwise antisymmetric twist distributions for roll control that minimize induced drag on wings of arbitrary planform in pure rolling motion. Roll initiation, steady rolling rate, and the transition between the two are each considered. It is shown that if these antisymmetric twist distributions are used, the induced drag is proportional to the square of the rolling moment, and the induced drag during a steady rolling rate is equal to that on the wing at the same lift coefficient with no rolling rate or antisymmetric twist distribution. Results also show that if these antisymmetric twist distributions are used on straight, tapered wings without symmetric twist, any rolling maneuver for which the rolling rate and rolling moment have the same sign will always produce a yawing moment in the opposite direction. Computational results are also included, which were obtained using a gradient-based optimization algorithm in combination with a modern numerical lifting-line algorithm to find the optimum twist solutions. The resulting twist, induced drag, and yawing moment solutions compare favorably with the analytic solutions developed in the text. The solutions presented here can be used to inform the design of morphing aircraft.

Flapping wing micro-air vehicles are biologically inspired by nature flyers, specifically insects and birds. Specifically, insect wings generally consist of veins and membrane components. In this study, a structural analysis considering the vein/membrane components of an insect-like flapping wing is presented. Co-rotational (CR) finite elements are adopted in order to consider the complex wing configuration including both vein and membrane. The CR beam elements with warping degrees of freedom are employed for veins and CR shell elements for the wing membrane. The present structural analysis is verified against the analytical results obtained by an existing software, and it is validated by comparison to existing results from the literature. A fluid–structure interaction analysis is then performed. In the procedure, an aerodynamic analysis based on three-dimensional preconditioned Navier–Stokes equations is employed. Finally, a comparative study with respect to the structural characteristics is conducted. As a result, an efficiency of the present structural analysis is confirmed by comparing with the existing software. It is found that the present FSI results are in good agreement with the existing experimental and numerical results. Moreover, the passive wing twist may have a significant influence on the hover performance.

This paper analyzes the effect of spanwise distribution of twist angle on the forces generated by flapping wings as well as the power requirements. We consider four sample profiles of the twist angle as a function of spanwise location, and compute the forces and power requirements under non-accelerating level flight conditions. We investigate three different wing geometries, with varying wingspan and aspect ratios. It has been found that for planforms with moderate to high wingspans, a quadratic profile performs better than the constant and linear ones; whereas for planforms with smaller wingspans, a linear profile performs better than the rest. The analysis presented in this paper can be used to identify the most suitable wing twist profile as a function of the flight parameters and can be used as the basis for wing morphing.

The transonic buffet on an ONERA-M4 model was experimentally investigated using an unsteady pressure-sensitive paint (PSP) in the present study. Wind tunnel tests were conducted in a blowdown-type transonic wind tunnel at a Mach number of 0.84 and a chord Reynolds number of $$2.0 \times 10^6$$ . The angle of attack was varied in between $$-3.0^{\circ }$$ and $$4.0^{\circ }$$ . The left wing was painted with a polymer/ceramic PSP with low surface roughness, and the right wing was painted with a temperature-sensitive paint. The measured PSP data were processed to calculate time-series pressure coefficients, root-mean-squares pressure-coefficient fluctuations, power spectral density, coherence, and phase shift. The behavior of the unsteady pressure field was different from that observed for the NASA Common Research Model (CRM) in a previous study. The dominant frequency of the shock oscillation shifted from the low-Strouhal-number component ( $$St < 0.05$$ ) to the bump Strouhal number ( $$St = 0.11$$ for the center frequency) with increasing angle of attack. The separation processes with an increasing angle of attack were also found to be different for the two models. The separation starts from the mid-span region in the CRM, while the separation starts from the wingtip in the ONERA-M4 model. The characteristic pressure fluctuations known as “buffet cells” were not observed for the ONERA-M4 model. These differences are considered to be caused by the difference in model geometries, such as the wing twist and the airfoil cross-sectional profile.

Light jet aircraft capable of carrying 6–10 passengers over short and medium ranges find great demand in the present and future civil aviation market. Light jets often cruise at high subsonic Mach numbers enabling greater range. Consequently, the drawback associated with high Mach number flight is that it leads to the deterioration of the aircraft’s aerodynamic characteristics. Aerodynamic optimization of a typical transonic wing was performed to reduce the wing cruise drag coefficient at a fixed Mach number and lift coefficient. A surrogate-based 2D optimization of wing sections was performed. Objective function values were obtained by solving Reynolds-averaged Navier–Stokes equations. The optimal baseline wing was constructed using the optimal airfoil sections obtained from the 2D optimization. Subsequently, parametric studies were conducted using vortex lattice method to arrive at an optimal wing by varying the wing twist distribution. The optimal airfoils showed 2% and 4% reduction in drag coefficient compared to the corresponding baseline airfoils. The optimal wing showed about 4% reduction in drag coefficient compared to the baseline wing.

This paper presents the analysis of an active winglet concept applied to a long-range aircraft. The winglet is actuated along the longitudinal axis to control its cant angle. Due to aeroelastic effects, the wing twist changes and therefore impacts aircraft performance. As a consequence, this technology offers the opportunity to optimize aircraft performance throughout the flight. This ability will be evaluated using high-fidelity coupled aerodynamic and structural computations. The consideration of the wing flexibility and the impact of the winglet on the wing shape contributes to more accurate aerodynamic predictions. First, the winglet geometry is optimized for the cruise condition using surrogate models. The designed winglet reduces the drag with a limited impact on loads while ensuring the capability to change the wing tip twist through the control of the cant angle. Then, a mission analysis is performed to assess the benefits of the technology on a variety of flight conditions.

Shape Memory Alloy (SMA) actuation is often cited as significantly lighter weight and more compact than conventional actuation methods such as electromechanical (EM) or hydraulic motors. Yet there few studies directly comparing and demonstrating a SMA actuation design to a conventional design for a specific application. In this paper a complete system level design, build, and test using both SMA and EM actuation are described. Adaptive spars for a medium sized UAV wing twist application are demonstrated and a detailed comparison of size, weight, power, and performance clearly demonstrates the advantages of SMA actuation.

Detailed investigations of interference effects between over-the-wing mounted nacelles (OWN) and airframe were accomplished with the aid of high-fidelity CFD tools on two aircraft configurations. The configurations differ in a variation of the wing planform from a backward (REF3) to a forward swept layout (REF4). The impact of the OWN was investigated by using an automated process chain varying engine position, wing twist distribution, and airfoil section geometry to achieve an aerodynamically efficient aircraft design in the presence of the OWN. Ensuing from the surrogate-based optimization, the data set was used to evaluate the interference between OWN and wing.

The evaluation of the variation in aerodynamic load on a wing under the effect of elastic deformations requires solving the problem of wing deformation when wings are subjected to distributed aerodynamic load. This paper presents the calculation of coupling the aeroelastic system for 3D wings. The aerodynamic problem was solved by the doublet–source method for 3D wings, with wing thickness considered. The problem of elastic deformation was solved by the finite element method for hollow 3D wings, with beams arranged inside. Results concerning aerodynamic load on the wing were considered input parameters for the calculation concerning the problem of wing deformation, and those about the deformed wing geometry were deemed input parameters for the calculation regarding the problem of wing aerodynamics for the second calculation. The calculations concerning these problems were repeated until the wing twist angle converged. Analyses and comparisons were performed on the distributions of aerodynamic loads on the rigid and deformed wings to examine the change of the aerodynamic load depending on the structure (aerodynamic loads being functions of the external geometry of the wing, the incidence angle, and the velocity at infinity are solutions of the pure aerodynamic problem). Results regarding wing twists and stress distributions for hollow wings with and without beams inside were presented to assess the cause of changes in aerodynamic load and wing static durability. Aeroelastic calculations were formulated with different velocities at infinity to indicate the need for a suitable structural solution when the aerodynamic load is expected to reach a high value.

This paper builds an aerodynamic optimization design system by coupling the free form deformation parameterization technique, the dynamic mesh technique based on inverse distance weighting interpolation method and particle swarm optimization algorithm, Kriging surrogate model, with the computational fluid dynamics solver based on Reynolds-averaged Navier–Stokes equations. And it carries out aerodynamic optimization designs with a supersonic transport aircraft configuration. The wing shape is parameterized by defining 60 design variables and the wing twist is by four design variables. Meanwhile, the wing thickness constraints are considered. Afterwards, a single-point optimization design aiming at minimum of the supersonic cruise drag is conducted, and in order to consider the transonic cruise condition, a multipoint aerodynamic optimization design aiming at minimum of a weighted drag for the supersonic cruise drag and transonic cruise drag is performed. The analyses of optimization results illustrate the specific drag reduction, the characteristics of pressure distributions for both the supersonic cruise condition and transonic cruise condition, and how the shock wave region and strength have improved on the supersonic cruise condition. The optimization design this paper presents realizing the drag reduction is quite practical and effective, which is instructive in supersonic aircraft design.

Blended Wing Body is a revolutionary concept offering phenomenal performance advantages over conventional aircraft. There are various aerodynamic features that are added to the wing in order to adjust the lift distribution and wing twist is one of them. This paper presents a progressive study to examine the effects of twist angles on the aerodynamic characteristics of a Blended Wing Body (BWB) aircraft. CFD analysis is carried out on seven BWB models having wing twists ranging from +3° to -3°. Each model is analyzed at four different Mach numbers. The coefficient of drag (Cd) and coefficient of lift (Cl) is determined and plotted against the twist angle to obtain a trend. The Cl/Cd ratio is also calculated to observe the overall aerodynamic performance of the BWB.

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.

Wind tunnel experiments are conducted at a Reynolds number of Re = 56,000, measuring rigid flat-plates and flexible membrane wings from free-flight into ground-effect conditions. Load cell measurements, digital image correlation and particle image velocimetry are applied in high-speed to resolve time-synchronised lift, drag and pitch oscillations simultaneously with membrane and flow dynamics. Proper orthogonal decomposition is applied on flow oscillations to determine their spatiotemporal evolution. Loads, membrane motions and flow dynamics are correlated to each other to investigate their underlying coupling physics. A membrane wing’s ability of static cambering and dynamic membrane oscillations are found to be beneficial when the wing is in ground-effect, where the descent in height forces premature leading-edge vortex-shedding and drag increase. The dynamic motions of membrane wings help to exploit vortex-shedding dynamics from the leading-edge that ensures time-averaged reattached flow over the wing upper surface, resulting in further lift enhancement. Membrane wings show lag-free fluid-membrane coupling at peak-lift conditions. In post-stall conditions, the membrane is found to lag the flow dynamics, signalling the end of direct fluid-structure coupling.

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.

Effect of the reinforced leading or trailing edge on the aerodynamic performance of a two-dimensional (2D) perimeter-reinforced (PR) membrane wing at Re =2500 is investigated numerically, using a novel model of membrane wing and a fluid-structure interaction solution procedure based on the characteristic-based split (CBS) finite element method. For the PR membrane wing, it is found that the time-averaged lift will not be affected much when 20% of the membrane is reinforced at the leading edge. However, the same length of reinforcement at the trailing edge will deteriorate greatly the time-averaged aerodynamic performance. At lower angles of attack, the reinforced leading edge could trigger the shedding of the leading-edge vortices, which will increase the time-averaged lift but also make the response of the membrane much more irregular and uncontrollable. In addition, secondary vortex structures are observed at higher angles of attack when more than 60% area of the membrane wing is reinforced at the leading or trailing edge. The secondary vortices, which will push the shed leading-edge vortices away from the wing surface, are found to be the key reason for the significant drop of the lift. This paper could reveal more details of the vortex structures and structural responses of the PR membrane wing in laminar flow regime and provide a new membrane wing model for the micro air vehicles.

形態: カラー図版あり, Physical characteristics: Original contains color illustrations, 資料番号: PA1820025000

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.