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Large-scale flapping-wing flying robotic birds have huge application potential in outdoor tasks, such as military reconnaissance, environment exploring, disaster rescue and so on. In this paper, a multiple modes flight control method and system are proposed for a large-scale robotic bird which has 2.3 m wingspan and 650 g mass. Different from small flapping wing aerial vehicle, the mass of its wings cannot be neglected and the flapping frequency are much lower. Therefore, the influence of transient aerodynamics instead of only mean value are considered in attitude estimation and controller design. Moreover, flight attitude and trajectory are highly coupled, and the robot has only three actuators----one for wings flapping and two for tail adjustment, it is very difficult to simultaneously control the attitude and position. Hence, a fuzzy control strategy is addressed to determine the command of each actuator by considering the priority of attitude stabilization, trajectory tracking and the flight safety. Then, the on-board controller is designed based on FreeRTOS. It not only satisfies the strict restrictions on mass, size, power and space but also meets the autonomous, semi-autonomous and manual flight control requirements. Finally, the developed control system was integrated to the robotic prototype, HIT-phoenix. Flight experiments under different environment conditions such as sunny and windy weather were completed to verify the control method and system.

Solar drones have garnered considerably research attention in recent years due to their continuous cruising capability, and the feasibility of design schemes is sensitive to the weight of structure. Sandwich box beam composed of carbon fiber and polymethacrylimide (PMI) foam is conducive to realize the lightweight of structure. In this study, a two-stage optimization design methodology for sandwich box beam is proposed. This methodology is primarily based on a low-order analytical method for evaluating stress/deflection and the linear buckling analysis method combined with experimental correction factor for predicting the buckling eigenvalues. Subsequently, a case study was conducted using an 18-m wingspan solar drone, where the results of mechanical test verified the optimization results. For validating the use of sandwich box beam in solar drones of other scales, additional analysis was conducted based on three aspects: (A) effects of stiffness and stability constraints on the design of sandwich box beam; (B) crucial role of the weight of foam inter layer and application scope of sandwich box beam; (C) best method to improve the buckling eigenvalue of sandwich box beam. Overall, the methodology and general rules presented in this paper can support the design of light wing beam for solar drones.

The role of leading-edge vortex (LEV) in lift generation for revolving wings is not well-understood. We aim to discern the effect of LEVs and TEVs on revolving flat and twisted wings through a detailed analysis of planar flow in the wing sections. We present a simple quasi-two-dimensional model to estimate the lift distribution over the wingspan by coupling the potential flow and lifting line theory (modified to incorporate the effect of wing rotation) and incorporating the presence of vortices. This semi-analytical model estimates a fairly accurate sectional force trend for low-moderate AoA at each wing section and subsequently the net lift force developed on the wing. Three-dimensional numerical simulations verify the developed theory. The present results underscore the role of LEVs and TEVs in the mechanism of lift generation. Furthermore, the proposed theoretical model serves as a non-intrusive method to estimate the lift distribution over the wingspan from a three-dimensional velocity field.

This work presents the Topology Optimisation of the Morphing Variable Span of Tapered Wing (MVSTW) using a finite element method. This topology optimisation aims to assess the feasibility of internal wing components such as ribs, spars and other structural components. This innovative approach is proposed for the telescopic mechanism of the MVSTW, which includes the sliding of the telescopically extended wing into the fixed wing segment. The optimisation is performed using the tools within ANSYS Mechanical, which allows the solving of topology optimisation problems. This study aims to minimise overall structural compliance and maximise stiffness to enhance structural performance, and thus to meet the structural integrity requirements of the MVSTW. The study evaluates the maximum displacements, stress and strain parameters of the optimised variable span morphing wing in comparison with those of the original wing. The optimised wing analyses are conducted on four wingspan extensions, that is, 0%, 25%, 50% and 75%, of the original wingspan, and for different flight speeds to include all flight phases (17, 34, 51 and 68m/s, respectively). Topology optimisation is carried out on the solid wing built with aluminium alloy 2024-T3 to distribute the wing components within the fixed and moving segments. The results show that the fixed and moving wing segments must be designed with two spar configurations, and seven ribs with their support elements in the high-strain area. The fixed and moving wing segments’ structural weight values were reduced to 16.3 and 10.3kg from 112 to 45kg, respectively. The optimised MVSTW was tested using different mechanical parameters such as strains, displacements and von Misses stresses. The results obtained from the optimised variable span morphing wing show the optimal mechanical behaviour and the structural wing integrity needed to achieve the multi-flight missions.

The reduction of aircraft noise over the past decades has generated a growing awareness that the characteristics of a signal can be equally or more important to annoyance than the sound pressure le...

An 80-mg double piezo-actuated insect-inspired flapping-wing robot is presented in this Letter. With the design of the two piezoelectric actuators placed back to back, each wing of this robot is independently driven and controlled, giving this robot the ability to achieve asymmetric flapping of the two wings to generate torques for steering. The piezoelectric actuators are designed with electrical insulation and structural reinforcement to improve the reliability under high-voltage and high-frequency drive mode. Fibre directions of each component of the robot are reasonably designed to enhance strength and stiffness. The average lift generated by the robot is measured by a customised lift measurement system found to be proportional to the square of the input voltage amplitude. The three steering torques generated by the robot are measured separately by a customised lift measurement system. Each steering torque can only be linearly modulated by its specific control variable of the input voltages. With a total weight of 80 mg and a wingspan of 3.5 cm, this robot can generate sufficient lift to take off and independently modulate all three steering torques with good decoupling, which is vital for the further controlled flight.

Installing winglets can notably improve the aerodynamic performance of solar aircraft. This paper proposes a multi-constraints optimization method of winglets for solar aircraft, aiming to enhance the corresponding uninterrupted cruising capability. An optimization objective function is formed and is separately studied in aerodynamic and structural terms. Qualitative analysis shows that the winglet design parameters are restricted by four special constraints (geometry, aerodynamics, energy and stability) of solar aircraft. The optimization process is constructed on the basis of a multi-island genetic algorithm, and carried out for a 15 m wingspan solar aircraft. Although the designed winglet is not as good as the traditional winglet in terms of drag and structural weight, the designed winglet provides a better 24 h cruising capability. The sensitivity between the objective function and the design parameters is investigated, and the winglet effects vary with respect to the wing aspect ratio (AR = 10, 15, 19.6). The effect of the constraints is analysed quantitatively, and some basic laws are obtained. Moreover, the feasible design region and the possible optimal design parameters of winglets for different wing configurations are explored. The calculation results show that when the aspect ratio exceeds a certain value, the winglets will not benefit the aircraft.

This work focuses on a novel pseudomeasurement-aided estimation scheme for angle of attack (AOA) in a mini unmanned aerial vehicle with a 1.61 m wingspan. A scale-reduced model of the same is used ...

This paper analyzes the effects of propeller flow on the linear coupled longitudinal and lateral dynamics of a 150 mm wingspan fixed wing micro air vehicle (MAV). The effects propeller flow on the lift, drag, pitching moment and side force is obtained through wind tunnel tests. The aerodynamic forces and moments are modeled as a function of angle of attack, sideslip angle, control surface deflection and propeller rotation per minute. The nonlinear six degrees of freedom model is linearized about straight and constant altitude flight conditions for different trim airspeed to obtain linear coupled longitudinal and lateral state space model. The eigenvalues and eigenvectors of linear coupled longitudinal and lateral state space model are compared with and without propeller flow effects. The variation in the natural frequencies and damping ratios of short period mode, phugoid mode and Dutch roll mode are analyzed for various trim airspeed. An increase in the natural frequency is observed for phugoid mode and Dutch roll mode with propeller effects. The stability of the spiral mode is enhanced by the propeller flow and also the response of the roll subsidence mode is faster with propeller effects. Detailed analysis of eigenvalues and eigenvectors shows the importance of incorporating propeller flow in analyzing the dynamics of the MAV.

The present paper deals with the take-off performance analysis of PrandtlPlane aircraft. The PrandtlPlane is a Box-Wing configuration based on Prandtl’s “Best Wing System” concept, which minimizes the induced drag once wingspan and lift are given. The take-off dynamics is simulated implementing the non-linear equations of motion in a numerical tool, which adopts a Vortex Lattice Method solver to evaluate the aerodynamics characteristics taking also ground effects into account. The take-off analysis is performed for both a PrandtlPlane and a reference monoplane, with the aim of comparing the performance of the two different architectures. The preliminary results show the potential advantages of the PrandtlPlane, such as runway length reduction and improved passenger comfort.

Drone is an aircraft, which is specially designed without the aid of pilots. Drones are used in many areas such as surveillance, military and agricultural applications. The conventionally used drone aircrafts have been analyzed and some drawbacks have been found out in taking off as it requires long take off distance. This work aims to design an effective magnus wing rotor for a drone aircraft and to implement the same in the surveillance industry and in reconnaissance so as to make sure that the current indifference in applying the magnus wing rotor is eliminated by the effective functioning of the UMV Rotor. This refurbished design will increase the reliability of the magnus wing UMVs and it will equalize the commercial value with the other type of drone vehicles. The lift force generated by the fixed aircraft and the quadcopter is very less when compared to the magnus wing UMVs with the similar wingspan and fuselage geometry. The wingspan is greatly reduced by the magnus wing application and it can carry greater payload with tremendous lift force generation. The main objective of the proposed work is to redesign the rotor with the axially fixed spiral spokes which theoretically increases the vortex strength of the UMVs thereby increasing the lift of the cylinder as per the analytical calculation and the analysis of the particular drone design. The magnus wing rotor has a drawback as it suffers an abrupt lifting failure when there is any power cut off. The span discs attached at the ends will reduce the jeopardy by acting like a flywheel as a temporary energy storage mechanism and thereby giving an option for the application in the relevant industries.

To realize safe mobile sensing in spaces around people, a flapping-wing robot with a weight of 1.15 g, wingspan of 115 mm, and three paired actuators is designed and fabricated in this study. The paired-wing actuators enable the suppression of wing–body and wing–wing coupling vibrations, as well as enhance the lift force. A model-based design of a stable flight controller was considered, where the lift force was assumed to work at an acting point on spatio-temporal average. Furthermore, an adaptive control law was employed for parameters that could not be measured. The effectiveness of the proposed controller was demonstrated through flight experiments.

The aerodynamics of the glider with supersonic airfoil have been optimized numerically by combining the multi-island genetic algorithm (MIGA) with the simulated annealing (SA) methods. The corresponding results show that the improved hybrid MIGA-SA method can effectively solve the glider optimal design issues such as nonlinear, discontinuous, and multi-dimensional multimodal function etc. The glider optimal aerodynamic geometry can be quickly obtained by using of the hybrid MIGA-SA method under the conditions of huge design space and low calculating resource requirements. The optimized results have also indicated that the aerodynamic characteristics for the double curved airfoil are always superior to the hexagonal airfoil. The total length of wing span located closer to the constraint value can greatly increase the wing area, decrease wing load and benefit in gliding. The final optimal geometry can greatly extend the flight distance for the glider. These results could provide the reference data for designing the gliders with supersonic airfoil in aerodynamic geometry, control system as well as the structural optimal.

Heavier-than-air flight at any scale is energetically expensive. This is greatly exacerbated at small scales and has so far presented an insurmountable obstacle for untethered flight in insect-sized (mass less than 500 milligrams and wingspan less than 5 centimetres) robots. These vehicles1–4 thus need to fly tethered to an offboard power supply and signal generator owing to the challenges associated with integrating onboard electronics within a limited payload capacity. Here we address these challenges to demonstrate sustained untethered flight of an insect-sized flapping-wing microscale aerial vehicle. The 90-milligram vehicle uses four wings driven by two alumina-reinforced piezoelectric actuators to increase aerodynamic efficiency (by up to 29 per cent relative to similar two-wing vehicles5) and achieve a peak lift-to-weight ratio of 4.1 to 1, demonstrating greater thrust per muscle mass than typical biological counterparts6. The integrated system of the vehicle together with the electronics required for untethered flight (a photovoltaic array and a signal generator) weighs 259 milligrams, with an additional payload capacity allowing for additional onboard devices. Consuming only 110–120 milliwatts of power, the system matches the thrust efficiency of similarly sized insects such as bees7. This insect-scale aerial vehicle is the lightest thus far to achieve sustained untethered flight (as opposed to impulsive jumping8 or liftoff9). Sustained flight of an insect-sized flapping-wing aerial vehicle weighing just 259 milligrams that does not need to fly tethered to an off-board power supply is demonstrated.

Conventional flap and slat high-lift surfaces actuation systems in a commercial aircraft consist of actuators mechanically connected via a transmission system across the wingspan, driven from a centralised power drive unit comprising of a hydraulic, electric, or hybrid hydraulic/electric motor arrangement. The permanent coupling to the shafts makes the entire flap system move in unison, as do the slats. This paper will investigate and discuss different potential system architecture, and present the benefits associated with such architecture. It will also present the advantage that can be linked to a full electric flap configuration.

The application of the Kutta–Joukowski (KJ) theorem to estimating the lift of a flying animal based on wake velocity fields often leads to significant underprediction of the lift, which is known as the wake momentum paradox. This work attempts to answer the puzzling question on whether the KJ theorem is legitimate in its use for complex viscous unsteady wakes generated by flapping wings. The limitations in applying the KJ theorem to flapping wings are quantitatively examined through numerical simulations of viscous incompressible flows over three flapping wing models. The three flapping wing models studied in this work are a flapping wing with a fixed wingspan, a flapping wing with a dynamically changing wingspan and a dihedral flapping wing. The KJ theorem fails to give a satisfactory prediction of the time-averaged lift unless an effective span length is correctly computed. We propose a wake-sectional Kutta–Joukowski (WS-KJ) model to predict the time-averaged lift, where the effective span length is computed based on the time-averaged distance between the streamwise vorticity centroids in the right and left half sides of the Trefftz plane. The WS-KJ model incorporates the spatial evolutionary effects of the complex vortex structures in the wake and significantly improves the prediction of the time-averaged lift. The physical foundation for such improvement is explored. In addition, the time-dependent amplitude and phase changes of the unsteady lift are discussed as the fluid acceleration effect.

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.

For the 5MW offshore wind turbine blade, the control and discrete equations of the fluid domain and structural domain were established respectively, and the calculation formulas of blade loads and damping coefficient were given. Furthermore, the blade entity modeling was completed by using UG and ANSYS Workbench. Based on it, the numerical calculation of blade vibration characteristics under different wind and rotating speeds was carried out, and the reliability verification was conducted by the wind tunnel test. The results of calculation indicate that the numerical results of the first principal stresses at the blade surface along the span-wise direction are consistent with the results of wind tunnel test, which verifies the reliability of the theory and numerical models. Both the influences of the bidirectional fluid-structure interaction (BFSI) and the rotation effect on the characteristics of blade vibration should be underlined. The increase of wind or rotating speed results in the nonlinear increase of the maximum span-wise displacement of the blade and of the Mises-stresses. Under different wind or rotating speed, the blade’s maximum displacement occurs at its tip, its maximum Mises-stresses appear at the relative wingspan of 0.55, and the contribution of rotating speed and average wind speed to the displacement or Mises-stress along the span-wise direction is similar.

The conceptual design and optimization of a tilt-rotor Micro Air Vehicle (MAV) for a well-defined mission are performed. The objective of this design cycle is to decrease the design time in order to efficiently create a functional tilt-rotor drone. A flight mission is firstly defined for a tilt-rotor MAV performing hovering and cruise flight scenarios. Secondly, a complex wing shape is chosen and modeled in order to determine the final shape. The initial shape is scaled in order to acquire an arbitrary wingspan of one meter. For the specific area and wingspan, the aspect ratio of the designed wing shape is found to be equal to 2.32. Thirdly, a constraint analysis of the MAV is performed by using an energy balance analysis for six different flight scenarios. This analysis yields the required power loading and wing loading. Fourthly, the weight of the vehicle is estimated using both statistical and computational methods. After estimating the total weight and the wing loading of the MAV, the surface of the wing is determined, yielding a final wingspan of 0.76 m. Subsequently, considering the total weight of the designed MAV, the needed lift coefficient is determined. Fifthly, using the lift coefficient in conjunction with XLFR5, a batch of airfoils is selected and analyzed to evaluate the aerodynamic coefficients of the wing with each airfoil. This analysis ultimately leads to the optimum airfoil being selected. Finally, design of the fuselage and tail, internal components selection, and servo-mechanisms design are carried out prior to a stability analysis. All these proposed steps are needed to design efficient and functional tilt-rotor MAVs. Keywords: Aerodynamic analysis, Sizing, Tilt-rotor MAV, VTOL, Stability

The intermittent gliding flight method takes advantage of the updraft is adopted to increase the flight endurance time of a type of multifunctional morphing unmanned aerial vehicle (UAV). This type of UAV is able to be folded before launch, launch from a cylindrical launch tube, and adjust the wing span and sweep angle during flight. It has the advantages of convenient storage and transportation and can use the energy of the updraft. In order to effectively utilize the updraft, the mathematical model of updraft is established, and an updraft judging method is proposed. In order to complete the intermittent gliding flight, the flight progress is divided into two stages and a segmentation control law is proposed. During the intermittent gliding stage switching, the wing sweep angle and wing span length are varied to accommodate requirements of different stages. H∞ robust control design method for gain scheduling based on linear parameter varying model is used to ensure the stability of the morphing UAV during the wings change. The mathematical simulation verifies the effectiveness of the morphing control algorithm. After that, a semi-physical simulation verification involving a mathematical UAV model with a physical wing changing mechanism, a physical embedded flight control module, the real flight attitude, and the virtual route are implemented. It has been verified that the morphing UAV can remain stable throughout the entire cycle of the intermittent gliding. Moreover, the intermittent gliding flight with updraft can reduce the fuel consumption of the morphing UAV and increase its flight endurance time.

A wind turbine blade design inspired by a tree seed called Triplaris Americana is presented. The blade was designed by means of an analysis of the seed’s curvature and airfoil along its wingspan ; the result is as a non-conventional horizontal axis wind turbine composed of three blades. A computational fluid dynamic simulation was performed in order to estimate the operational loads . The blade’s structure was designed by means of composite structural design, resulting in six zones with different laminates of carbon fiber . The balance of the aerodynamic and inertial loads was achieved in order to guarantee a minimum change in blade’s geometry to prevent a performance reduction. Finally, a manufacturing simulation by means of vacuum assisted resin infusion was performed. Four injections strategies were proposed with three of them considered successful based on a complete mold filling and the time limit imposed by the polymerization time of the resin.

Having an exciting array of applications, the scope of unmanned aerial vehicle (UAV) application could be far wider one if its flight endurance can be prolonged. Solar-powered UAV, promising notable prolongation in flight endurance, is drawing increasing attention in the industries’ recent research and development. This work arose from a Bachelor’s degree capstone project at Hong Kong Polytechnic University. The project aims to modify a 2-metre wingspan remote-controlled (RC) UAV available in the consumer market to be powered by a combination of solar and battery-stored power. The major objective is to greatly increase the flight endurance of the UAV by the power generated from the solar panels. The power system is first designed by selecting the suitable system architecture and then by selecting suitable components related to solar power. The flight control system is configured to conduct flight tests and validate the power system performance. Under fair experimental conditions with desirable weather conditions, the solar power system on the aircraft results in 22.5% savings in the use of battery-stored capacity. The decrease rate of battery voltage during the stable level flight of the solar-powered UAV built is also much slower than the same configuration without a solar-power system.

An investigation was conducted to evaluate the effectiveness of a passive gust alleviation device (PGAD) installed in a flying-wing aircraft of 62.3 m wing span at large swept back angle. It was performed by numerical analysis and validated by wind-tunnel test of a 1:25 reduced scale physical model of dynamic similarity to the full-scale aircraft. The 1-cosine gust model with a range of gust parameters specified in the airworthiness regulation CS-23 was taken in the gust response analysis that led to 7 ∼ 9 % gust alleviation results by employing the PGAD. The gust response dominated by the first three modes of the aircraft was most critical in the frequency close to the first bending mode of the wing. The wind-tunnel test model was designed and manufactured based on dynamic scaling law, and proved to be of excellent dynamic similarity by the deviation of less than 5.5% between the first three modes of the physical model measured by vibration test and the full-scale aircraft model. The wind tunnel test results show that the gust response of the model in the specified range was reduced by 8.3 ∼ 14.3 % according to the measured wing tip deflection associated with the PGAD oscillation amplitude at 4.0 ∘ ∼ 15.5 ∘ . The present study shows that the numerical analysis of gust response and alleviation of a full-scale aircraft installed with PGAD can be validated by wind tunnel test of a scaled physical model with dynamic similarity.

International audience; The classical aeroelastic scaling theory used to design scaled models is based on the assumption that complete flow similarity exists between the full aircraft and the scaled model. When this condition is satisfied, the scaling problem of the model can be treated as a structural design problem only, where the scaled aerodynamic shape is preserved. If, on the other hand, this hypothesis no longer holds if the scaled model is constrained to fly at low speed and low altitude, for example and both the aerodynamic shape and the flexibility of the structure are exactly scaled, then the static response exhibits significant discrepancies in the aerodynamic loads and structural displacement. To design a flying demonstrator with scaled static response when flow similarity cannot be fulfilled, we present a multidisciplinary optimization-based method that allows some freedom in the design of the wing shape (while keeping the scaled wingspan) to update the wing geometry and structural properties to ensure equivalent scaled loads and overall wing displacement. To illustrate this method, we apply it to a 1:5 version of the uCRM wing at subsonic flight condition. While the errors in air loads using the classical theory are around 16%, the presented method achieves errors lower than 1%, with a good agreement for the wingtip displacement.

Leading-edge-vortex (LEV) formation often characterizes the unsteady flows past airfoils and wings. Recent research showed that initiation of LEV formation on airfoils in two-dimensional flow is closely tied to the criticality of the so-called leading-edge suction parameter (LESP). To characterize the LEV initiation on wings in three-dimensional flow, a large set of pitching wings was studied using Reynolds-averaged Navier–Stokes computations (computational fluid dynamics, CFD). The CFD results showed that the pitch angle and spanwise location for LEV initiation varied widely between the different wings. The same cases were also analysed using an unsteady vortex-lattice method (UVLM), which assumes attached flow. Low-order prediction of LEV initiation is assumed to occur at the pitch angle when the UVLM-calculated LESP at any point on the wing span first becomes equal to the pre-determined critical LESP for the airfoil. For all the cases, the predicted pitch angles and spanwise locations for LEV initiation from the low-order method agreed excellently with the corresponding CFD predictions. These observations show that LEV initiation on finite wings is governed by criticality of leading-edge suction, enabling the prediction of LEV initiation on an unsteady finite wing using attached-flow wing theory and the critical LESP values for the airfoil sections.

The introduction of disruptive innovations in the transport aviation sector is becoming increasingly necessary. This is because there are many very demanding challenges that the transport aviation system will have to face in the years ahead. In particular, the reduction in pollutant emissions from air transport, and its impact on climate change, clearly must be addressed, moreover, sustainable solutions must be found to meet the constantly increasing demand for air traffic, and to reduce the problem of airport saturation at the same time. These three objectives seem to be in strong contrast with each other, in this paper, the introduction of a disruptive airframe configuration, called PrandtlPlane and based on a box-wing lifting system, is proposed as a solution to face these three challenges. This configuration is a more aerodynamically efficient alternative candidate to conventional aircraft, introducing benefits in terms of fuel consumption and providing the possibility to increase the payload without enlarging the overall aircraft wingspan. The development and analysis of this configuration, applied to a short-to-medium range transport aircraft, is carried out through a multi-fidelity physics-based approach. In particular, following an extensive design activity, the aerodynamic performance in different operating conditions is investigated in detail, the structural behaviour of the lifting system is assessed, and the operating missions of the aircraft are simulated. The same analysis methodologies are used to evaluate the performance of a benchmark aircraft with conventional architecture, with the aim of making direct comparisons with the box-wing aircraft and quantifying the performance differences between the two configurations. Namely, the CeRAS CSR-01, an open-access virtual representation of an A320-like aircraft, is selected as the conventional benchmark. Following such a comparative approach, the paper provides an assessment of the potential benefits of box-wing aircraft in terms of fuel consumption reduction and increase in payload capability. In particular, an increase in payload capability of 66% and a reduction in block fuel per pax km up to 22% is achieved for the PrandtlPlane with respect to the conventional benchmark, while maintaining the same maximum wingspan.

Made available in DSpace on 2021-06-25T10:27:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 The slat represents an important airframe noise source as it extends over almost the entire aircraft wingspan. Most studies of slat noise consider idealized geometries. However, for practical applications, several elements are installed on its cove, such as bulb seals to avoid direct contact with the main wing surface. Previous investigations of an unswept and untapered MD30P30N airfoil reported that the flow dynamics and the corresponding acoustic noise are very sensitive to the presence and location of the bulb seal. For certain locations a second recirculation bubble is created inside the slat cove and the acoustic narrowband peaks are intensified. The present paper shows that the two-bubble topology promotes the recirculation of turbulence within the slat cove. Spectral proper orthogonal decomposition analysis based on the radiated pressure intensity is used to identify the flow structures responsible for sound generation. Even though the recirculating turbulence is mostly incoherent, it interacts with the coherent Kelvin-Helmholtz vortices in the initial part of the mixing layer. Then, vortex merging and straining lead to the formation of complex vortex clusters. Our results show that the origin and evolution of these clusters are consistent with Rossiter's mechanism responsible for the narrowband peaks. The enhanced recirculation accelerates the cluster evolution leading to wider clusters and lower-frequency Rossiter modes. Department of Aeronautical Engineering University of São Paulo, Av. Trabalhador São Carlense, 400 UNESP-São Paulo State University, Av. Profa. Isette Correa Fontão 505 Aeronautics Institute of Technology, Praça Marechal Eduardo Gomes 50 ETSIAE-UPM (School of Aeronautics) Universidad Politécnica de Madrid, Plaza del Cardenal Cisneros 3 UNESP-São Paulo State University, Av. Profa. Isette Correa Fontão 505

In this paper, a trajectory optimization strategy for the hypersonic morphing aircraft is proposed, and the AMPI method is used to generate the online trajectory with initial state errors. Firstly, the aerodynamic model and propulsion model of the hypersonic morphing aircraft were established considering the wingspan and the scramjet. Secondly, the optimization strategy was proposed via Gauss pseudospectral method considering the control variables including angle of attack (AOA) and wingspan. The optimized trajectory met the final constraints and path constraints with the objective to minimize the time of the ascent phase. Then, the AMPI method was used to generate online trajectory without solving OCP or NLP on the base of trajectory database calculated by the optimization strategy. The simulation results indicate high accuracy of AMPI method and the final errors corresponding to different initial errors were acceptable. The mean value of the CPU time of the method was about 0.1 second, which shows real-time capability.

The development of unmanned aerial vehicles (UAVs) has undergone extensive development in recent years, responsible for reducing operational and manufacturing costs and also preserving the pilot in missions that present risks. The pursuit of greater flight autonomy in fixed wing UAVs is aimed at the aircraft development, which can generate the highest possible lift with the lowest weight and drag. In this context the flying wing is considered the ideal aircraft, but it has instability during flight due to the absence of warping. With the use of a computerized system for corrections, a 1.20m wingspan UAV with flexible characteristics is proposed and developed in this work, considering all its stages: aerodynamic analysis, construction and configuration, remotely controlled tests, and autonomous mission with image acquisition. As a result of its operation, we could perform both remote controlled and autonomous flights acquiring images, which demonstrates the effectiveness of the project and used embedded systems.

Quantitative measurements obtained from medical images guide clinicians in several use cases but manually obtaining such measurements are both laborious and subject to inter-observer variations. We develop a hybrid deep reinforced regression framework to robustly measure the Cardio-Thoracic ratio (CTR) from Chest X-ray (CXR) images, thereby directly identifying the presence of Cardiomegaly. The proposed hybrid framework initially employs a CNN based Regressor on pre-processed images to obtain approximate critical points. As the actual critical points are based on human expert’s experience and subject to labeling uncertainties, a deep reinforcement learning (deep RL) approach is specifically designed to fine-tune estimated regression points from the CNN Regressor. The final regressed points are then used to measure CTR. Wingspan and ChestX-ray8 datasets are used for validating the proposed framework. The proposed framework shows generalization ability on ChestX-ray8 and outperforms the state-of-the-art results on Wingspan.

In the present study, a bionic flapping mechanism of a spatial six-bar configuration was designed to transform a single rotation of a motor into a three degrees of freedom “flapping–twist–swing” cooperative motion of a flapping wing. The kinematics model of the flapping mechanism movement was constructed. The flapping trajectory of the wing based on the kinematics model was to mimic the motion of a pigeon wing in landing flight. To reduce the manufacturing complexity, the flapping mechanism was simplified with only two degrees of freedom (flapping and twist) retained. Finally, a prototype model with a 0.9 m wing span was built and tested. A comparison among the experimental data, theoretical calculation results, and ADAMS simulation results revealed that the difference in the flapping and the twist amplitude between experimental observations and theoretical calculation results was 12.5% and 2.3%, respectively. This was owing to the elastic deformation of the bar and the mechanism simplification. The comparison results also indicated that the maximum difference in the inertial force was 5.9% in up-stroke and 6.7% in down-stroke, respectively. The experimental results showed that the inertial force of the model with the wing patagium was approximately 2.2 N, and the maximum positive and negative lift was 2.1 N and −1.5 N, respectively. It is hoped that this study can provide guidance for the design of bionic flapping wing mechanisms of a flapping wing aircraft for short landing flight.

This study designed a vertical take-off and landing tailsitter unmanned aerial vehicle (UAV) with a long endurance time. Nine parameters of the tailsitter UAV were investigated. Using a 2k full factorial test, 512 experiments on the nine parameters were conducted at their maximum and minimum values. The time coefficient and air resistance were calculated using the computational fluid dynamics (CFD) method under different parameter combinations. The analysis of variance determined that the specific factors influencing the time coefficient and air resistance were the root chord, wingtip chord, wingspan, and sweep angle. By carrying out a central composite design (CCD) test, 25 sample points of the four particular factors were constructed. The time coefficient and air resistance were simulated under different structural parameter combinations using the CFD method. CFD simulation was verified by carrying out a wind tunnel test, and the results revealed that the aerodynamic coefficient error was less than 5%, while the air resistance error was less than 6%. The response surface methodology (RSM) for the time coefficient and air resistance was established using a genetic aggregation method. A multi-objective genetic algorithm (MOGA) was used to optimize the parameters with regard to the maximum time coefficient and minimum air resistance. The optimal structural parameters were wing root chord length at 315 mm, wingtip chord length at 182 mm, wingspan length at 1198 mm, and sweep angle at 16&deg, Compared with the original layout and size, the time coefficient of the new design of the tailsitter UAV improved by 19.5%, while the air resistance reduced by 34.78%. The results obtained by this study are significant for the design of tailsitter UAVs.

With the increasing interest in wireless communications from solar-powered aircraft-based high altitude platforms (HAPs), it is imperative to assess the feasibility of their deployment in different locations with the constraints on energy consumption and payload weight under consideration. This paper considers the energy management of solar-powered aircraft-based HAPs for wireless communications service provisioning in equatorial regions and regions further up the northern hemisphere. The total solar energy harvested and consumed on the shortest day of the year is analyzed, and it is explained how this determines the feasibility of long endurance, semi-permanent missions. This takes into account the different aircraft-based HAPs and the energy storage systems currently available, and how these can be deployed for wireless communications. We show that the solar-powered HAPs are energy and weight limited, and this depends largely on the platform&rsquo, s wingspan available for the deployment of solar collectors. Our analysis show that services can be provided for a duration of 15&ndash, 24 h/day using current platforms, with wingspans ranging between 25&ndash, 35 m, depending on the configuration and coverage radius. Furthermore, we show that doubling an aircraft&rsquo, s wingspan can increase its payload capacity by a factor of 6, which in turn enhances its feasibility for wireless communications.

Morphing aircraft are the flight vehicles that can reconfigure their shape during the flight in order to achieve superior flight performance. However, this promising technology poses cross-disciplinary challenges that encourage widespread design possibilities. This research aims to investigate the flight dynamic characteristics of various morphed wing configurations that can be incorporated in small-scale UAVs. The objective of this study was to analyze the effects of in-flight wing sweep and wingspan morphing on aerodynamic and flight stability characteristics. Longitudinal, lateral, and directional characteristics were evaluated using linearized equations of motion. An open-source code based on Vortex Lattice Method (VLM) assuming quasi-steady flow was used for this purpose. Trim points were identified for a range of angles of attack in prestall regime. The aerodynamic coefficients and flight stability derivatives were compared for the aforementioned morphing schemes with a fixed-wing counterpart. The results indicated that wingspan morphing is better than wing sweep morphing to harness better aerodynamic advantages with favorable flight stability characteristics. However, extension in wingspan beyond certain limits jeopardizes the advantages. Dynamically, wingspan and sweep morphing schemes behave in an exactly opposite way for longitudinal modes, whereas lateral-directional dynamics act in the same fashion for both morphing schemes. The current study provided a baseline to explore the advanced flight dynamic aspects of employed wing morphing schemes.

Prandtl introduced the best wing system or Box Wing a century ago and showed its exceptional lift-induced drag performance with respect to wing systems having the same wingspan and lift (Prandtl, L., “Induced Drag of Multiplanes,” NACA TN-182, 1924.). In this work, and for the first time, their superior induced drag properties are verified in compressible and transonic regimes. The aerodynamic forces are obtained by analyzing computational fluid dynamics data, and the drag is subdivided in induced, viscous, and wave contributions. This decomposition is provided by a recently introduced aerodynamic force breakdown technique based on the vortex-force theory and allows an unambiguous definition of the lift-induced drag. The methodology is applicable to incompressible, compressible, and transonic flows. This paper will address whether the Best Wing system provides interesting induced drag performance also in transonic viscous flow.

RarePlanes is a unique open-source machine learning dataset that incorporates both real and synthetically generated satellite imagery. The RarePlanes dataset specifically focuses on the value of synthetic data to aid computer vision algorithms in their ability to automatically detect aircraft and their attributes in satellite imagery. Although other synthetic/real combination datasets exist, RarePlanes is the largest openly-available very-high resolution dataset built to test the value of synthetic data from an overhead perspective. Previous research has shown that synthetic data can reduce the amount of real training data needed and potentially improve performance for many tasks in the computer vision domain. The real portion of the dataset consists of 253 Maxar WorldView-3 satellite scenes spanning 112 locations and 2,142 km^2 with 14,700 hand-annotated aircraft. The accompanying synthetic dataset is generated via AI.Reverie's simulation platform and features 50,000 synthetic satellite images simulating a total area of 9331.2 km^2 with ~630,000 aircraft annotations. Both the real and synthetically generated aircraft feature 10 fine grain attributes including: aircraft length, wingspan, wing-shape, wing-position, wingspan class, propulsion, number of engines, number of vertical-stabilizers, presence of canards, and aircraft role. Finally, we conduct extensive experiments to evaluate the real and synthetic datasets and compare performances. By doing so, we show the value of synthetic data for the task of detecting and classifying aircraft from an overhead perspective., Comment: To appear in WACV 2021 - 11 pages

In a famous report about the induced drag of multiplanes, L. Prandtl conceived the Best Wing System: the lifting system having the minimum induced drag among all the other ones, for assigned wingspan and lift. The resulting shape was a box-wing, asymptotically equivalent to a multiplane having infinite wings. At the end of the report, he gave the performance of this optimal lifting system (in terms of dimensionless induced drag and vertical gap) through a curve, without presenting the method he used. Nowadays, modern computational aerodynamics show an excellent agreement between the numerical results and Prandtl’s prevision. The first part of the paper aims at clarifying which method Prandtl used for the Best Wing System only. In the second part of the paper, starting from Prandtl’s different approach for the biplane and triplane problem, we propose a simple model for the evaluation of the induced drag of multiplanes, using notions an aerodynamicist of 1920s likely had. We show that the limit multiplane having infinitely many wings, under the ansatz of elliptic lift distribution on the outermost wings and constant lift distribution on the innermost ones, matches the Best Wing System curve. This leads to a simple but interesting interpretation of the actual results.

Tailless airplanes with swept wings rely on variations of the spanwise lift distribution to provide controllability in roll, pitch and yaw. Conventionally, this is achieved utilizing multiple control surfaces, such as elevons, on the wing trailing edge. As every flight condition requires different control moments (e.g. to provide pitching moment equilibrium), these surfaces are practically permanently displaced. Due to their nature, causing discontinuities, corners and gaps, they bear aerodynamic penalties, mostly in terms of shape drag. Shape adaptation, by means of chordwise morphing, has the potential of varying the lift of a wing section by deforming its profile in a way that minimizes the resulting drag. Furthermore, as the shape can be varied differently along the wingspan, the lift distribution can be tailored to each specific flight condition. For this reason, tailless aircraft appear as a prime choice to apply morphing techniques, as the attainable benefits are potentially significant. In this work, we present a methodology to determine the optimal planform, profile shape, and morphing structure for a tailless aircraft. The employed morphing concept is based on a distributed compliance structure, actuated by Macro Fiber Composite (MFC) piezoelectric elements. The multidisciplinary optimization is performed considering the static and dynamic aeroelastic behavior of the resulting structure. The goal is the maximization of the aerodynamic efficiency while guaranteeing the controllability of the plane, by means of morphing, in a set of flight conditions.

The pitching moments of a fighter model at an incidence of 32° without and with nine airbrakes are simulated by solving the unsteady Reynolds-averaged Navier–Stokes equations. The maximum reduction (60.22%) of the total pitching moment is obtained by the airbrake with deflection angle of 60° and length of 0.115 times the wing span. Furthermore, the unsteady flowfields are predicted by the improved delayed detached-eddy-simulation model. The breakdowns of the forebody and strake vortices are advanced, and the flow is blocked by the airbrake, jointly leading to a reduction of the pitching moment. Surprisingly, the pressure fluctuations on the oblique vertical tail are also attenuated due to the existence of the airbrake. A maximum reduction of overall sound pressure level by 11.8 dB is found near the leading-edge on the outer surface of the vertical tail due to the use of the 60T1 airbrake. The bursting vortices from the forebody and strake move towards the symmetry plane owing to the low-pressure region after the airbrake, weakening the unsteady interactions between the bursting vortices and oblique vertical tail.

In this letter, we present the design and the performance of a prototype bioinspired flapping-wing micro aerial vehicle with piezoelectric direct-driven actuation. This type of actuation is superior in terms of structural simplicity because it does not include any transmission mechanism. Instead, a unimorph piezoelectric actuator directly drives the wing. We designed and fabricated a two-wing prototype with a wingspan of 114 mm and successfully demonstrated takeoff using an external power source under a one-degree-of-freedom constraint. The total mass of the prototype was 598 mg, and the maximum measured lift force was 6.52 mN (665 mgf) at a driving voltage of 100 V. We achieved tethered flight using the proposed direct-driven piezoelectric actuator considering the constraint.

In highly flexible aircraft, the large structural slenderness associated to their high-aspect-ratio wings, while bringing challenges to the design, analysis, and control of such aircraft, can be pro-actively exploited for improving their flight performance, resulting in mission-adaptive morphing configurations. This paper studies the optimum wing bending and torsion deformation of highly flexible aircraft, with distributed control loads along the wing span to achieve the optimum wing geometry. With the goal of improving flight performance across the entire flight regime, a modal based wing shaping optimization is carried out, subject to the requirement of trim and control cost limitation. While a single objective of the minimum drag can be used to find the optimum wing geometry, this paper further considers a trade-off between flight efficiency and structural integrity. In this trade-off study, a multi-objective optimization is formulated and performed, targeting for both minimizing the drag to improve flight efficiency and reducing the gust-induced wing bending moment to enhance the structural integrity. Finally, this paper explores the minimum control cost for different targets of combined flight efficiency and structural integrity. This paper provides not only an efficient way to search for the desired wing planform geometry at a given flight condition but also insights of the required control effort that is necessary to maintain the wing geometry.

An optimized and comprehensive method is proposed in order to design an efficient micro unmanned air vehicle with morphing and growing capabilities. In the sizing process, to select the optimum wing shape, three different shapes are compared based on an aerodynamic analysis, and a tapered wing is selected for the compressed mode. Then, since the wingspan, wing area, wing loading, and other parameters are changing as function of time, a transition analysis is carried-out during the sizing process. By using the calculated surface area and considered aspect ratio for compression and expansion modes, the wingspan is determined as function of time. Considering the estimated weight, the required lift coefficient is calculated and then two types of airfoils are selected. Finally, after completing the optimal geometric design, aerodynamic analyses are carried out to investigate the performance of the growing drone. The proposed strategy for designing efficient micro unmanned air vehicles for a well-defined mission can be utilized and extended to design other growing micro unmanned systems depending on the mission.

Aiming at large-scale offshore wind turbine blades, governing equations in fluid domain and motion equations in structural domain with geometric nonlinearity were built by the aid of ALE method. A three dimensional model under fluid-structure interaction (FSI) was established by using UG software and Geometry module, and numerical calculation for FSI vibration characteristics of wind turbine blades under the effects of wind shear and fluctuating wind was carried out based on ANSYS Workbench. The results indicate that the contribution of the combined action to displacement and Mises stress chiefly derives from the wind shear effect, which not only causes a comparatively larger increase for the maximum displacement and Mises stress, but also becomes bigger and bigger with the increase of average wind speed, and the fluctuating wind effect is insignificant. The maximum value of Mises stress in the blade section appears at the relative wingspan of 0.55, the maximum Mises stress varying with relative span length decreases progressively from the middle to both sides of the blade, and the contribution of wind shear effect alone, the combined action or wind speed increment to stress also shows the same change rule. Furthermore, in the maximum stress section along wingspan, Mises stress along the direction of blade thickness or chord length respectively presents two distribution laws, and reaches the maximum on the blade surface.

Active high-lift aircraft need exceptional aerodynamic control performance to operate at low airspeed. In this study a new concept for the improvement of controllability is investigated, incorporating the special capabilities of a blown Coanda flap system. The blowing system along the flaps is divided into twelve independently controllable segments. This provides the opportunity to influence the lift distribution along the wingspan by individual blowing performance settings for each segment without changing the flap deflection. This offers the chance to control the airplane in the final approach phase with fully deflected flaps by using only the blowing system and to dedicate specific control tasks to particular segments. A model for the blowing system influence on the local wing aerodynamics is implemented in an existing nonlinear full aircraft flight mechanics model. The system capabilities in terms of roll control and the climb performance are investigated by criteria evaluation and dynamic simulation assessment. The ability to fly turn/altitude change maneuvers by utilizing the active high-lift system is proven and a corresponding control concept is presented. It also includes the compensation of different blowing failure cases, which leads to acceptable but still improvable aircraft reactions.

Wing shape and kinematics of flapping wing nano air vehicles are two important factors in their design process. These factors require an optimal design in terms of decreasing the needed aerodynamic power. Since, insects are regarded as the best natural flier in hovering flight, seven of their wings are considered in order to determine the best wing shape for hovering applications. Because of the difference in the original bio-inspired shape of these wings, two scenarios are studied, namely, considering the same wingspan and same wing surface. Using the quasi-steady approximation to model the aerodynamic loads and a basic gradient approach to optimize the kinematics of the wing, the optimum Euler angles, required aerodynamic power, and hence the best wing shape for each scenario are analytically determined. The results show that the wing shape and surface strongly impact the aerodynamic characteristics and performances of the chosen wing shapes. It is demonstrated that the twisted parasite wing shape is a good candidate to minimize the required aerodynamic power during hovering. The strategy used in this analysis can be used to evaluate the performance of any realistic wing shape design and could provide a guideline for selecting the best wing shape and kinematics for flapping wing nano air vehicles with hovering capabilities.

Following the emergence of small flight-capable flapping-wing micro air vehicles, efforts toward autonomous outdoor operations of these small robots outside controlled laboratory conditions have been made. For the robots to overcome wind disturbances, it necessitates better insights into the interaction between the aerodynamics of flapping wings in the presence of winds and the robot's actuation system. In this paper, we consider the effects of constant frontal wind on a direct-drive flapping wing robot with passively rotating hinges and a compliant transmission. A simplified quasi-steady model that encapsulates the effects of frontal wind on aerodynamic forces is proposed. The model facilitates the calculation of periodic aerodynamic forces from nominal flapping kinematics. When combined with the dynamics of the actuation system, we are able to predict the lift force generated by the robot from the driving signals, without direct measurements of the flapping kinematics or the angle of attack. The proposed framework was experimentally verified on a flapping-wing robot prototype with a single wingspan of 76 mm. The results reveal up to 40% increases in lift when the robot was subject to 2.5 m/s horizontal winds. An analysis of the frequency response of the system is also provided to explain the resonance principles of the robot in the presence of frontal winds.

The development of a fixed-wing nano air vehicle that fits inside a cube of 75 mm is described in this paper. A novel aircraft configuration that satisfies the static and dynamic stability and the mission performance requirements is developed. A performance index is formulated to identify a suitable airfoil as there does not exist a single airfoil that achieves the mission required specifications. Eppler-61 is identified as the suitable airfoil since the value of its performance index is maximum among other airfoils selected for the analysis. The static stability of the nano air vehicle is analyzed using the aerodynamic characteristics obtained from the wind tunnel tests. The outcomes of this analysis indicate that the vehicle is statically stable. The analysis also indicates significant aerodynamic cross-coupling between longitudinal and lateral aerodynamic coefficients. The dynamic stability analysis indicates that the nano air vehicle is dynamically stable. Furthermore, the dynamic stability of the vehicle is validated by flight test results. Published version

For researching on the rules of icing distribution on rotating blade of horizontal axis wind turbine, a Quasi-3-D method is proposed to research on icing on rotating blades of horizontal axis wind turbine by numerical simulation. A 2-D and 3-D method of evaluating the irregular shape of ice has been established. The model of rotating blade from a 1.5 MW horizontal axis wind turbine is used to simulate the process and shape of icing on blade. The simulation is carried out under the conditions with four important parameters including ambient temperature, liquid water content, medium volume drop diameter, and icing time. The results reveal that icing mainly happens on 50% ~ 70% of the blade surface along wingspan from tip to root of blade. There are two kinds of icing shapes including horn shape icing and streamline shape icing. The study can provide theoretical basis and numerical reference to development of anti and deicing strategy for wind turbine blades.

Wake vortex encounters (WVE) can pose significant hazard for en-route aircraft. We studied the sensitivity of wake vortex (WV) circulation and decay to aircraft mass, altitude, velocity, density, time of catastrophic wake demise event, eddy dissipation rate, wing span, span-wise load factor, and WV core radius. Then, a tool was developed to compute circulations of WV generat-ed/encountered by aircraft en-route, while disregarding unrealistic operational conditions. A comprehensive study is presented for most aircraft in the Base of Aircraft Data version 4.1 for different masses, altitudes, speeds, and separation values between generator and follower air-craft. The maximum WV circulation corresponds to A380-861 as generator: 864 and 840 m2/s at horizontal separation of 3 and 5 NM, respectively. In cruise environment, these WV may de-scend 1000 ft in 2.6 min and 2000 ft in 6.2 min, while retaining 74% and 49% of their initial strength, respectively. The maximum circulation of WV encountered by aircraft at horizontal separation of 3 NM from an A380-861 is 593, 726, and 745 m2/s, at FL200, FL300, and FL395, re-spectively. At 5 NM, the circulations decrease down to 578, 708, and 726 m2/s. Our results allow reducing WVE simulations only to critical scenarios, and thus perform more efficient test pro-grams for computing aircraft upsets en-route. This research was funded by SESAR Joint Undertaking (SJU), grant number 699247, as part of the European Union’s Horizon 2020 (H2020) research and innovation program: R-WAKE project

Insects are excellent fliers because of their ability to generate precise wing kinematics and deform their wings for the sufficient production of unsteady aerodynamic forces. Most of the previous studies on the effects of wing kinematics on the aerodynamics have been limited to the use of rigid wings, and leaves the contribution of wing flexibility unknown. Here, an experiment was conducted to investigate the effect of varied sweep duration and timing of rotation on the unsteady aerodynamic characteristics of hovering flexible and rigid wings at Re of 104. This study found that the forces generated by the flexible wing showed a conspicuous phase delay, which was more sensitive to the change in sweep duration than the timing of rotation. The transient negative lift associated with rigid wings undergoing delayed and advanced wing rotations totally disappeared in the flexible case. A digital particle image velocimetry (DPIV) measurement at the middle of stroke revealed a slight difference in the vortical structures surrounding the two wings in terms of proximity to the shed trailing-edge vortices (TEVs). Also, the linearly twisted nature of the flexible wing caused the coherent leading-edge vortex (LEV) to be stabilized throughout the wingspan. This increased the radial limit of the delayed stall from 3.6c in the rigid wing to 4.8c in the flexible wing. In general, the flexible wing with symmetric and delayed wing rotations generated the higher efficiency. The corresponding net force vectors were tilted in an almost vertical direction in comparison to the rigid wing. This is an indication that natural fliers adopt specific wing kinematics in addition to their wing deformation for the upward titling of their net force vector, which will significantly enhance their aerodynamic performance.