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

A numerical study on the aerodynamic performance of a two-dimensional flapping wing in asymmetric stroke in hovering and forward flight is carried out. The effect of the asymmetry of the stroke on aerodynamic forces and flow structures of the wing is analyzed. It is found that for hovering flight appropriate asymmetric stroke can enhance the aerodynamic performance of the wing at low Reynolds number, but it may not be functioning at moderate and high Reynolds numbers. For forward flight the asymmetric stroke does not increase the lifting efficiency and propulsive efficiency of the wing simultaneously. However, it influences the time history of the aerodynamic force significantly, which may enhance the flight maneuverability of the wing. The present results provide physical insight into the understanding of aerodynamics and flow structures of insect flight with asymmetric stroke.

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