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In this work, we use a three-dimensional computational fluid dynamics (CFD) simulation to comprehend how the two wing arrangement variables, i.e., inner/outer wing proportion and mid-stroke dihedral, affect the lift characteristic of a bat-inspired span foldable flapping wing. The employed flapping mechanism is based on previous work. In this study, the structure parameters of the flapping mechanism remain unchanged across all simulations. Based on the CFD results, the tendency and work point regarding maximum lift generation can be found by changing both of the variables. As a result, when modifying the inner/outer wing proportion without changing the total wing shape and area, the maximum time-averaged lift appears in the case of the inner wing occupying half of the semi-span. In addition, when changing the dihedral, the maximum time-averaged lift was obtained when the inner wing dihedral was equal to zero. To discuss the lift variation of the foldable flapping wing, pressure distribution and vorticity of the flow field at certain time points were provided corresponding to the instantaneous lift curves. The conclusions of this research are able to help understand the wing arrangement of birds and bats issued from natural selection, and also support the future design of flapping wing micro-aerial-vehicles. [ABSTRACT FROM AUTHOR]

X-shaped flapping wings have excellent maneuverability and flight capabilities under low-Reynolds-number conditions. An appropriate tail can extend the range of a vehicle and improve its stability. This study takes two typical configurations, the inverted T-tail and the inverted V-tail, as the research object. Considering the wings' flexible deformation in the flapping process, the computational fluid dynamics method was used to calculate the vehicles' aerodynamic characteristics, taking into account the aerodynamic interaction effect of the wings and tail. The results show that the wake of flapping wings can significantly reduce the forward flight performance of the tails. The maximum L/D ratio of the two tails decreased by about 38%, and the static stability was also dramatically reduced in the forward flight. The inverted V-tail has better performance in fast forward flight, while the inverted T-tail had better control characteristics at low speeds. The relationship between the tail layouts and aerodynamic performance is also discussed. When the inverted V-tail is in the optimal position, the longitudinal control moment can be doubled in the hovering state. This research provides a reference for the design and arrangement of flapping wings with tails, which is beneficial to the performance improvement of vehicles. [ABSTRACT FROM AUTHOR]

Flapping flight mechanisms offers a power-efficient and highly manoeuvrable basis for the development of micro air vehicles. The aerodynamic knowledge and prediction tools of the flapping wing are quite important for the design of micro air vehicles. In this paper, the unsteady aerodynamics of a flapping wing is investigated by numerical simulations and the generation of reduced-order model based on the Volterra theory for predicting the unsteady aerodynamic of a flapping wing is described. The three dimensional aerodynamic calculation is performed by solving the unsteady Reynolds-averaged Navier-Stokes equations and the user-defined functions were employed to simulate the flapping motion. The training maneuver is a flapping motion with a linearly increasing flapping frequency. Based on the Volterra theory and numerical simulation results, a reduced-order model is generated to predict the unsteady aerodynamics of a flapping wing. The system identification method is employed to generate the Volterra theory reduced-order model. The results show that the Volterra theory reduced-order model agrees well with the training data and the Volterra theory reduced-order model works well to predict the unsteady aerodynamics of a flapping wing. [ABSTRACT FROM AUTHOR]

Tandem flapping-wing micro aerial vehicles, which are inspired by dragonflies, are unique in that they have two pairs of wings, and this could increase their maneuverability during flight. In this study, a series of tandem flapping-wing arrangements were designed in polar coordinates, and the polar distance and polar angles of the hindwing were used as design variables. Such a consideration of variations in both the horizontal and vertical positions of the hindwing in the design of tandem-wing arrangements has the potential to elucidate new interaction mechanisms, leading to improvements in the aerodynamic characteristics of tandem flapping-wings. Two-dimensional numerical analyses of these arrangements were conducted. The results of these analyses showed that, compared with a single flapping wing, tandem wings can increase the lift coefficient by 78.1% with an appropriate arrangement, but decrease the lift coefficient by 51.6% with an inappropriate arrangement. The vorticity distributions for typical wing arrangements were examined to establish the effect of the design variables on the aerodynamic characteristics of the tandem wings in forward flight. Two types of wing–wake interaction mechanisms were revealed based on this analysis. Both of these interactions can significantly reduce the negative force during the upstroke, resulting in an increase in the time-averaged lift. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, investigation was made into the design, theoretical study, numerical modelling and experiment of a novel flapping wing rotor for micro aerial vehicles (MAV). Attention was firstly focused on the design of a simple, reliable and lightweight configuration of the flapping wing structure and the rotor. The design is to meet the challenging demand for high mechanical and power efficiency and vertical take-off and landing (VTOL) capability. To demonstrate the feasibility and effectiveness of the innovative design, a piezoelectric actuated flapping wing rotor model was manufactured and tested. Effort was also made to evaluate the design and analyze the dynamic behavior of the model by using finite element (FE) method. The unsteady aerodynamic force was modeled by theoretical method and CFD numerical simulation. To validate the theoretical and numerical analysis, experiment of the test model was carried out. In the experiment, the total force produced by the flapping wing rotor including the aerodynamic and inertia forces has been measured through a data process approach. The comparison shows a very good agreement between the experimental and analysis results. Improvement of the design can be made by using the methods. [Copyright &y& Elsevier]

This paper provided a design of bat-inspired tailless flapping wing unmanned aerial vehicle (UAV) based on the biological data of the large flying fox. The wing span of the UAV is 1.68 m and the total mass is 289 g. Aerodynamic characteristics at design cruise speed were analyzed based on the computational fluid dynamics (CFD) method. Selected variables within the analysis are angle of attack and flapping frequency. Prototype of the UAV has been manufactured follows the design parameters. The flapping mechanism employed a 2-DOFs revolute-spherical-spherical-revolute (RSSR) system to reflect the flapping attitude of bats. An outdoor test flight was then processed with the manufactured prototype. Onboard flight data recorder (FDR) was equipped to conserve the flight data such as flight speed, pitching angle and the three-dimensional position of the flight. It is shown by the data obtained from the FDR that the bat-inspired UAV is able to achieve the stable cruise with circular route at flight speed 6.8 m/s with the average angle of attack 4.1 degrees and flapping frequency 3.7 Hz. Test flight shows that the UAV is able to provide a 5 minutes free outdoor cruise with the equipped Li-Po battery. Research proves that the tailless configuration flapping wing UAV is able to sustain a stable flight, which provides a new design possibility for future researches. [ABSTRACT FROM AUTHOR]

Bionic aircrafts have become a hot topic in the research on unmanned aerial vehicles (UAVs). By mimicking the flight mechanics and wing morphology of living organisms, bionic aircraft not only improve aerodynamic performance, stealth, and convenience but also enable single aircraft to complete multiple specific tasks. To further improve the practical performance of bionic aircraft, a fixed-flapping hybrid morphing wing aerial vehicle (F-FWAV) is designed, and the aerodynamic and flight mechanics are studied. First, kinematic simulations are conducted on the designed F-FWAV, and the kinematic characteristics of the flapping wing are analyzed. Then, flight tests are conducted on the aircraft model, and time-domain and frequency-domain analyses were performed on the data of the pitch angle and roll angle during level flight, high angle of attack (AOA) maneuvering and landing, indicating that the pitch and roll angles of the F-FWAV are coupled. CFD numerical simulations are used to obtain the cruise points of the F-FWAV under different AOAs, frequencies, and freestream velocities. The results of the mutual interference between the fixed wing and flapping wing sections show that the flapping wing section provides more than 50 % of the lift of the entire flight process, and the downward flapping movement of the flapping wing section increases the edge vortex of the fixed wing section, thereby increasing the lift of the fixed wing section. [ABSTRACT FROM AUTHOR]