Flapping Motion Research Articles

Computational analysis of inverted flag-based energy harvester in the wake of cylindrical bluff body

In the current study, the penalty immersed boundary method (PIBM) is used to numerically analyze the flapping motion of an inverted flag, placed behind a bluff body using two-dimensional viscous flow. Direct numerical simulations (DNS) are carried out by changing the Reynolds number, bending stiffness, and streamwise gap (which represents the distance from the bluff body to the fixed end of the flag) behind the inverted D-shape cylinder to find their impact on the peak-to-peak amplitude, flapping frequency of the flag. The optimal values of the stated parameters are determined and explained in how the change in geometric and flow parameters affects the flapping behavior which has an ultimate impact on energy output. The addition of a bluff body caused the high strain due to higher bending modes and curvature in the flag. It is also shown that the alternating vortical flow structures have a strong influence on the dynamical behavior of the inverted flag placed inside the wake region of an inverted D-shape cylinder. Relationships between flow velocity, streamwise gap, and the flag's bending rigidity highlight consistent trends for the enhancement of energy production. Additionally, the lateral position of an inverted flag and its effect on vorticity and energy harvesting is discussed in detail with their power spectra to find the maximum amplitude and corresponding drag force. This research would help in concluding the optimal parameters of the inverted flag for the highest energy generation behind the bluff body.

Study of X-Pattern Crank-Activated 4-Bar Fast Return Mechanism for Flapping Actuation in Robo Drones

The study of insect-inspired flapping robo drones is exciting and ongoing, but creating realistic artificial flapping robots that can effectively mimic insect flight is difficult due to the transmission mechanism's need for lightweight and minimal connecting components. The objective of this work was to create a system of constructing a flapping superstructure with the fewest feasible links. This is one of the two strokes where the fast return mechanism turns circular energy into a variable angled flapping motion (obtained through simulation results). We have simulated the displacement modifications of the forward and return stroke variation. also conducted a kinematic study of the design processes differences, finding that it is significantly faster than the advance stroke. It was also seen that one of its levers lagged behind the others when flapping because of poor boundary conditions. Modelling the suggested motor-driven flapping actuation system helps verify its structural analysis and determine if it is appropriate for use in micro air vehicle applications.

Effect of marginal variation of aspect ratio and frequency with kinematic asymmetry on flow field around flapping rigid wing in hover

Phase-locked two dimensional particle image velocimetry (PIV) measurements are used to capture flow field around rigid flat plate wings undergoing main flapping motion (hover) with water as fluid medium in quiescent condition. Experiments are conducted using asymmetric upper-lower stroke single degree of freedom main flapping motion. Two different aspect ratio (AR) 1.5 and 1.0 rectangular wings at 1.5 Hz and 2.0 Hz flapping frequency and chord based Reynolds number of the order of 104 are studied. To achieve the desired aspect ratio, wing span is varied while wing chord remains fixed. Flow features for downstroke and upstroke are comparable for all four cases investigated. This includes vortex shedding from wingtip during wing stroke, vorticity intensification caused due to vortex stretching which occurs more dominantly for AR = 1.0, occurrence of KH instability in shear layer formed due to wing sweep and added mass effect due to the flow dragged by flapping wing. Vortex filamentation and fragmentation phenomena are observed during downstroke and upstroke respectively due to faster downstroke and slower upstroke. Rossby number, which is the ratio of inertial to Coriolis force is significant for rotational flapping wing. With increase in Rossby number there is a reduction in the spanwise flow over wing which influences strength of wingtip vortex at beginning of a stroke. It is found that spanwise flow for AR = 1.5 is stronger than AR = 1.0 and consequently the strength of wingtip vortex is higher for higher aspect ratio. However, peak vorticity is higher for AR = 1.0 due to vortex stretching effect which is expected to be more dominant at lower AR due to three dimensional effects. Effect of marginal variation in wing aspect ratio, flapping frequency with kinematic asymmetry are studied using velocity field, vorticity (ωz) contours, λ2 criterion, peak vorticity variation and its spatial distribution as well as kinetic energy variation of the flow field. Kinetic energy distribution and its connection with wake capture is explored.

P271 CASEOUS CALCIFICATION OF THE MITRAL ANNULUS: ROLE OF 3D ECHOCARDIOGRAPHY

Abstract The caseous calcification of the mitral annulus (CCMA) is a rare degenerative condition of the mitral valve (0.067% prevalence in the general population) that generally affects older women with hypertension, chronic kidney disease and dyslipidemia. Usually CCMA is asymptomatic and it is associated with mild to moderate mitral regurgitation and it can cause severe mitral valve dysfunction that requires surgical treatment. CASE 1: A 84–year–old woman, with arterial hypertension, was evaluated in our clinic to perform a transthoracic echocardiogram (TTE) for a previous finding of heart murmur. TTE reveled at the level of the posterior mitral annulus a hyperechoic roundish formation with a central eco–shiny area with a maximum diameter of 20x20 mm. A tridimensional trans–esophageal echocardiography (3D TEE) allowed a better characterization of the mass showing well–defined contours, adhered to the posterior mitral annulus, systolic dislocation of the anterior mitral leaflet, with slight mitral regurgitation. Considering the morphological characteristics of the mass we concluded for a presumptive diagnosis of CMAC. We recommended regular follow–up to the patient. After 6 and 12 months the mass did not change in size and echostructure. CASE 2: An 88–year–old woman with chronic kidney disease, high blood pressure and chronic ischemic heart disease was admitted to our ward for acute heart failure. TTE showed a large an echodense mass (43 × 19 mm) involving the posterior mitral annulus, with a central echo–lucent area. A 3D TEE was performed with better mass characterization: involvement of the entire posterior mitral ring, reduced movement of the posterior mitral flap, anterior mitral flap with normal morphology and normal mobility. In consideration of the echocardiographic characteristics we concluded for the presence of CMAC. We discharged the patient with indication for a regular clinical and echocardiographic follow–up. Conclusions The 3D TTE provides adequate morphostructural information that allows in most cases to characterize the CCAM. When the transthoracic approach is difficult due to poor acoustic windows, 3D TEE can be used. Only in rare cases it is necessary to use second–level diagnostic tests such as CT and Cardiac Magnetic Resonance Imaging.

Flow measurements of jet impingement upon a semicylinder with crossflow

In this work, time-resolved particle image velocimetry (TR-PIV) measurements have been carried out to investigate the structural features of a submerged transverse round liquid turbulent jet discharged into a confined laminar crossflow. The duct Reynolds number based on crossflow velocity is fixed at Re=3000, and the impinging jet is directed to a semicylindrical concave surface located in one of the walls of a vertical square duct. The spatial development and flow dynamics are analyzed along several orthogonal planes parallel/perpendicular to the jet axis for jet Reynolds numbers based on the jet exit diameter of Rej=3000, 6000 and 9000 (jet-to-crossflow velocity ratios of r=3.27, 6.53 and 9.80), respectively. For this purpose, mean and ensemble-averaged velocity and vorticity distributions, turbulent statistics, and Reynolds shear stresses are obtained for various injection rates. Spectral analysis reveals the shedding frequencies of the wake vortices, and the pairing and breakup processes of the evolving large-scale coherent structures have been related to the measured wake Strouhal numbers. Our results indicate that due to the curvature of the target surface and the upwash of the jet impact, the size of coherent structures decreases with increase in the value of Rej. Proper orthogonal decomposition (POD) of the flow using the snapshot method is applied to extract the dominant features of the turbulent flow. It is observed that at the symmetry plane and for Rej=3000, 6000 and 9000, the energy collected by the first two dominant eddies contribute to 14.98%, 18.68%, and 17.89% of the turbulence kinetic energy, respectively. Our results show that the evolution of the time-resolved temporal coefficients of degenerate pairs of modes (1, 2) represent the flapping motion of the jet. Moreover, the amplitude of the oscillations of the flapping jet and the complexity of the flow structure increase for increasing values of Rej.

Enhancing the peak/RMS current output performance of a triboelectric nanogenerator by unidirectional charge-supplying flutter

The triboelectric nanogenerator (TENG) is an innovative technology that converts ambient mechanical energy into electricity based on electrostatic induction and triboelectrification. However, the TENG has an inherent critical problem of low peak and root mean square (RMS) output current due to its high internal impedance. Herein, we propose a unidirectional charge-supplying flutter TENG (UCSF-TENG), which exhibits highly enhanced peak/RMS current output performance. By leveraging just one rectifier diode and distinctive fluttering device design, the UCSF-TENG achieved a peak current of 5.9 A and an RMS current of 20 mA. The electrical output generation mechanism of the UCSF-TENG was systemically analyzed based on the mechanical fluttering motion analysis using a high-speed camera. In addition, the UCSF-TENG was structurally optimized via mechanical and electrical analyses for various design factors, through which it achieved an average power of 109 mW. Benefiting from such high output performance, the UCSF-TENG can successfully charge a supercapacitor of 0.22 F, power 108-W commercial lamps, and operate 12 commercial sensor arrays continuously. This work provides a promising strategy for boosting the output current performance of the TENG while maintaining integrability and portability.

Investigation of the effect of hidden vortex generator-flap integrated mechanism revealed in low velocities on wind turbine blade flow

In this study, the flap and vortex generator (VG) mechanisms which were employed separately in aircraft were used as integrated first in literature. In this mechanism, the flap motion triggered and activated the VGs when it was needed at low speeds. Thus, this flap mechanism eliminated the unnecessary drag force generation when VGs were not needed. Numerical simulations which were validated with experimental data were employed in the study. In the first step, the flow characteristics formed on the S809 airfoil with 4 different flap angles (β = 30°, 20°, 10°, 0°) were investigated without the VG. Then, those flow structures formed on the S809 airfoil with both flap and VG were examined under the same conditions. According to the results, utilizing flap and VGs together had a positive impact at low wind speeds. Moreover, due to the flap and vortex generator integrated mechanism closed up to be not unnecessary drag formation at high wind speeds, thus those structures increased further to the positive effect with the increasing wind velocity. In terms of energy output, it was shown that this novel idea provided more energy output in this study.

Twist-Coupled Flapping Mechanism for Bird-Type Flapping-Wing Air Vehicles

Abstract In flapping-wing air vehicles, the flapping mechanism is directly related to the movement of the wing making it one of the major factors in determining aerodynamic performance. In this study, a method to increase aerodynamic performance using the flapping mechanism is discussed. This paper presents a twist-coupled mechanism that can increase thrust by combining twisting motion with flapping motion. The proposed mechanism generates twisting motion by the 4-bar planar link mechanism and flapping motion by the 4-bar spatial link mechanism. The mechanism can be driven by only one actuator by connecting two crankshafts with a pair of gears and rotating them at once. Here, we define the design parameters and constraints and search for the optimal design parameters to maximize aerodynamic force. Optimization is carried out by a genetic algorithm, a global optimization algorithm, combining kinematic and aerodynamic analyses. We then search for the design parameters that maximize thrust. Based on our optimization results, the proposed mechanism has the figure-of-eight wingtip trajectory motion like the flying animals. The aerodynamic efficiency of the proposed mechanism was validated by an aerodynamic measurement test comparing a reference mechanism that can only generate flapping motion without twisting motion. For comparative validation, prototypes of the proposed mechanism and the reference mechanism were designed and fabricated. Thrust and lift were measured by the wind tunnel test. From the wind tunnel test, it is confirmed that the proposed mechanism can generate aerodynamic loads more efficiently than the reference mechanism.

A Simplified Mathematical Model of Pumped Hydrofoils

This paper presents a simplified mathematical model of a pumped hydrofoil (PH)—a surfboard elevated above water surface and connected to a tandem of hydrofoils by a strut. The PH is operated by a rider who stands on the surfboard and produces swinging up-and-down motions resulting in forward propulsion of the device. In the present paper, the description of the vertical motion of the PH is reduced to a linear oscillator excited by an oscillating mass coupled with the requirement that the weight is supported by dynamic lift of the foil(s). The inertial and damping influence of the hydrofoil(s) is accounted for by expanding unsteady lift force on the foil(s) in terms of kinematic parameters. The restoring term of the oscillator is associated with the phenomenon of automatic stabilization of shallowly submerged hydrofoils. The latter effect manifests itself in that when a hydrofoil approaches free surface, its lift decreases, and when it moves away from free surface, its lift increases. The analytical solution of the pumping foil mass-spring type forced oscillations equation allows one to calculate the flapping motion of the foil(s) and, thereafter, the period-averaged thrust generated by the PH. The resulting speed has been estimated on an assumption that the device enters its cruising mode when the thrust becomes equal to the drag, the latter comprising viscous, wave, and induced drag components. The model under discussion allows one to relate the main parameters of the system to its performance and, hopefully, provides further insight into the pumped hydrofoil phenomenon, its design methodology, and operation strategy. The review part of the paper focuses on two aspects of the problem: hydrodynamic behavior of the hydrofoil(s) in proximity to free water surface and their propulsion due to oscillations.

Kinematic Investigations of a Novel Flapping Actuation Design with Mutually Perpendicular 3 Cylindrical Joint Approach for FW-Drones

The transmission mechanism of artificial flapping-wing drones generally needs low weight and the fewest interconnecting components, making their development challenging. The four-bar Linkage mechanism for flapping actuation has generally been used till now with complex and heavy connecting designs, but our proposed novel perpendicularly organized 3-cylindrical joint mechanism is designed to be unique and lighter weight with smooth functioning performance. The proposed prototype transforms the rotary motion of the motor into a specific angle of flapping movement, where the dimensions and specifications of the design components are proportional to the obtained flapping angle. Power consumption and flapping actuation can be monitored by adjusting the motor's rotational speed to control the individual wing in this mechanism. The proposed mechanism consists of a crank with three slightly slidable cylindrical joints perpendicularly arranged to each other with a specified distance in a well-organized pattern to produce a flapping movement at the other end. In order to examine the kinematic attributes, a mathematical process approach is formulated, and kinematic simulations are performed using SIMSCAPE multibody MATLAB, PYTHON programming and COMPMECH GIM software. The proposed invention's real-time test bench prototype model is designed, tested and analyzed for flapping validation.

Dynamic Stall Investigation on a Rotating Semielastic Double-swept Rotor Blade at the Rotor Test Facility Göttingen

Experimental investigations of three-dimensional dynamic stall on a four-bladed Mach-scaled semielastic rotor with an innovative double-swept rotor blade planform are presented. The study focuses on the coupling between the aeroelastic behavior of the blade and the underlying aerodynamics. Blade bending moment and flap displacement measurements were conducted using strain gauges and optical tracking of blade tip markers. The aerodynamic behavior was characterized by means of unsteady surface pressure measurements using unsteady pressure-sensitive paint (iPSP) across the outer 65% of the blade span and fast response pressure transducers at discrete locations. Different cyclic-pitch settings were investigated at a rotation frequency of frotor = 23.6 Hz that corresponds to blade tip Mach and Reynolds numbers of Mtip = 0.282– 0.285 and Retip = 5.84-5.95 ×10 5. The findings reveal a detailed insight into the nonlinear behavior in the flap movement during downstroke. iPSP and pressure transducer data indicate that this nonlinear flap behavior is caused by a radially phase-shifted dynamic stall process at the forward and backward swept part of the blade.

A robust data-driven model for flapping aerodynamics under different hovering kinematics

Flapping wing micro air vehicles (FWMAVs) are highly maneuverable, bio-inspired drones that can assist in surveys and rescue missions. Flapping wings generate various unsteady lift enhancement mechanisms challenging the derivation of reduced models to predict instantaneous aerodynamic performance. In this work, we propose a robust data-driven, quasi-steady reduced order model (ROM) to predict the lift and drag coefficients within a flapping cycle. The model is derived for a rigid ellipsoid wing with different parameterized kinematics in hovering conditions. The proposed ROM is built via a two-stage regression. The first stage, defined as “in-cycle” (IC), computes the parameters of a regression linking the aerodynamic coefficients to the instantaneous wing state. The second stage, defined as “out-of-cycle,” links the IC weights to the flapping features that define the flapping motion. The training and test datasets were generated via high-fidelity simulations using the overset method, spanning a wide range of Reynolds numbers and flapping kinematics. The two-stage regressor combines ridge regression and Gaussian process regression to provide estimates of the model uncertainties. The proposed ROM shows accurate aerodynamic predictions for a wide range of kinematics. The model performs best for smooth kinematics that generates a stable leading edge vortex (LEV). Remarkably accurate predictions are also observed in dynamic scenarios where the LEV is partially shed, the non-circulatory forces are considerable, and the wing encounters its own wake.

Electricity Generation by Wind Using Resonance and Piezoelectric Effect

Faraday's law of Electromagnetic Induction is the working principle behind A.C.-D.C. generators, which contributes a major part of the generated electricity utilized today. However, the Photoelectric Effect used in Solar cells is also a useful source of renewable energy produced from the sun. In this research work, we have tried to generate electricity from the concept of Resonance and Piezoelectric Effect. To achieve the goal, we have used a thin strip of stretch-resistant material which naturally has the property of resisting the applied stretching force. The length of this stretch-resistant material will be set up so that the incoming airflow will make the thin strip vibrate at its resonant frequency. This will create high-amplitude mechanical vibrations on the thin strip. Now, these vibrations will be passed to the piezoelectric material. Piezoelectric materials have the property to exhibit the piezoelectric effect, which will convert the high amplitude mechanical vibrations passed by thin strips to the piezoelectric material into electrical discharge and hence, we generated electricity from wind using Piezoelectric Effect & Resonance. Due to less moving parts in our setup, it is theoretically more efficient in high wind conditions where a windmill usually fails to work. The only moving part is the thin strip which moves in a flapping motion hence, the generator is named a flapping generator. Even though the generated electricity is in a lesser amount, we can create an array of some such setups to increase the output electricity (as we do in solar energy generation) as per our requirement.

Geometric Characteristics of Flapping Foils for Enhanced Propulsive Efficiency

AbstractThe shape of a foil undergoing a combined pitching heaving motion is critical to its design in applications that demand high efficiency and thrust. This study focuses on understanding of how the shape of a foil affects its propulsive performance. We perform two-dimensional numerical simulations of fluid flows around a flapping foil for different governing parameters in the range of biological swimmers and bio-inspired underwater vehicles. By varying the foil shape using a class-shape transformation method, we investigate a broad range of foil-like shapes. In the study, we also show consistent results with previous studies that a thicker leading-edge and sharper trailing-edge makes for a more efficient foil shape undergoing a flapping motion. In addition, we explain that the performance of the foil is highly sensitive to its shape, specifically the thickness of the foil between the 18th and 50th percent along the chord of the foil. Moreover, we elucidate the flow mechanisms behind variations in performance metrics, particularly focused on constructive interference between the vortices generated at the leading-edge with the trailing-edge vortex, as well as the pressure field differences that lead to higher power consumption in less efficient foil shapes.

Generation of negative peak pressures under a separation bubble

This paper investigates the generation mechanism of negative peak pressures on a blunt plate under a separation bubble with Large Eddy Simulation (LES). Synchronized sampling of the wind pressures on and velocity fields around the plate is adopted to explore the relation between pressure fluctuations and vortex dynamics. The ordinary pressure fluctuation is found to be induced by high-frequency vortex convection. Formation of a negative peak pressure starts from the vortex head arriving at an observation point and ends up at the vortex tail leaving that location. A negative peak pressure occurs when the vortex core is right beneath/above the observation point. Spectral analysis of the wind pressures and Dynamic Modal Decomposition (DMD) for the velocity fields are combined to detect and visualize the low-frequency motion responsible for extreme pressure fluctuations. A counterpart of the low-frequency dominating component of the wind pressures is found in the velocity modal analysis, which is related to the shedding of an extreme large-scale vortical structure and demonstrates a flapping motion of the shear layer. The present study provides insights to the generation of negative peak pressures and the relation between vortex behaviors and the shear layer movement.

Stability and dynamical analysis of whirl flutter in a gimballed rotor-nacelle system with a smooth nonlinearity

AbstractWhirl flutter is an aeroelastic instability that affects aircraft with propellers/rotors. With their long and flexible rotor blades, tiltrotor aircraft are particularly susceptible. Whirl flutter is known to have destroyed aircraft and in the best case it constitutes a fatigue hazard. The complexity of whirl flutter analysis increases significantly with the addition of nonlinearities, due to the more complex dynamical behaviours that emerge as a result. Most whirl flutter stability analyses in current literature are grounded in linear theory, preventing the full discovery of the nonlinearities’ effects. Continuation and bifurcation methods (CBM) may instead be used to fully appreciate and analyse the effects of the presence of nonlinearities. Previous CBM-based work on nonlinear gimballed hub rotor-nacelle models, representing those found on tiltrotor aircraft, are capable of whirl flutter in parametric regions declared safe by linear analysis. Furthermore, it was found that they are capable of complex behaviours including limit cycle oscillations, quasi-periodic behaviour and even chaos, though the whirl flutter implications of such behaviours has not been explored. This paper investigates the impact of a smooth structural nonlinearity on the whirl flutter stability of a basic gimballed rotor-nacelle model, compared to its baseline linear stiffness version. A 9-DoF model with quasi-steady aerodynamics, a flexible wing and blades that can move both cyclically and collectively in both flapping and lead-lag motions, producing gimbal flap-like behaviour, was adopted from existing literature. A smooth stiffness nonlinearity was introduced in the blade flapping stiffness and CBM was used to find the new whirl flutter behaviours created by the presence of the nonlinearity. Time simulations, Poincaré sections and spectral analysis were then used to investigate the various behaviours found. This in turn allowed recommendations to be made concerning preferable and/or hazardous parameter combinations of use to the tiltrotor designer.

Ultrafast motion in a third generation photomolecular motor

Controlling molecular translation at the nanoscale is a key objective for development of synthetic molecular machines. Recently developed third generation photochemically driven molecular motors (3GMs), comprising pairs of overcrowded alkenes capable of cooperative unidirectional rotation offer the possibility of converting light energy into translational motion. Further development of 3GMs demands detailed understanding of their excited state dynamics. Here we use time-resolved absorption and emission to track population and coherence dynamics in a 3GM. Femtosecond stimulated Raman reveals real-time structural dynamics as the excited state evolves from a Franck-Condon bright-state through weakly-emissive dark-state to the metastable product, yielding new insight into the reaction coordinate. Solvent polarity modifies the photoconversion efficiency suggesting charge transfer character in the dark-state. The enhanced quantum yield correlates with suppression of a low-frequency flapping motion in the excited state. This detailed characterization facilitates development of 3GMs, suggesting exploitation of medium and substituent effects to modulate motor efficiency.

Experimental investigation on flow field around a flapping plate with single degree of freedom

Undesirable flapping motion of discs can cause the failure of swing check valves in nuclear passive safety systems. Time-resolved particle image velocimetry (PIV) was employed to investigate the flow characteristics around a free-to-rotate plate and the motion response, with the Reynolds numbers, based on the hydraulic diameter of the channel, from 1.32 × 104 to 3.95 × 104. Appreciable flapping motion (±3.52°) appeared at the Reynolds number of 2.6 × 104 with the frequency of 5.08 Hz. In the low-Reynolds-number case, the plate showed negligible flapping. In the high-Reynolds-number case, the deflection angle increased with reduced flapping amplitude. The torque from the fluid determined the flapping amplitude. In the low-Reynolds-number case, Karman vortices were absent. With increasing Reynolds numbers, Karman vortices developed behind the plate with larger deflection angles. Strong interaction between the wake flow from the leading and trailing edge of the plate was observed. Based on power spectrum density (PSD) analysis, the vortex shedding frequency coincided with the flapping frequency, and the amplitude was positively correlated to the strength of the vortices. Proper orthogonal decomposition (POD) modes evince that, in the case of appreciable motion, coherent structures exhibited a larger spatial scale, enhancing the magnitude of the external torque on the plate.

Flutter Control of Active Aerodynamic Flaps Mounted on Streamlined Bridge Deck Fairing Edges: An Experimental Study

Traditional aerodynamic measures with fixed geometric shapes make it difficult to relieve the wind-induced vibration issues under the continuous expansion of bridge spans. Active aerodynamic control measures would be an alternative way to improve the wind vibration performance of long-span bridges. In this study, a bridge flutter control method based on active flaps was proposed, and the main girder-active flap-suspended aeroelastic model was designed to study the control effect. A pair of active flaps was installed on both sides of the box girder near the lateral fairings, and the movement signal of the main girder was detected using internal sensors. The two flaps move relative to the deck according to the preset equations of motion. This improved the flutter stability of the system with high effectiveness compared to traditional passive aerodynamic measures. By adjusting the gain coefficient in the motion function of the flaps and the phase difference between the flaps and the deck, the changing characteristics of the critical flutter wind speed were revealed with a deeper understanding of the relationship between the phase differences and gain coefficient of the active flaps and main girder. Studies have shown that the flutter performance of the deck-flap system is significantly affected by the phase difference and gain coefficient on both sides of the aerodynamic flap. The control law of the windward flap is relatively stable, but the control effect of the leeward flap is greatly affected by the movement of the windward flap.

Synthesis of Drive Systems of Flapping and Feathering Motions for Bird-like Robot using Twist Drive Mechanism

Synthesis of Drive Systems of Flapping and Feathering Motions for Bird-like Robot using Twist Drive Mechanism