The pitching-down flapping is a new type of bionic flapping,which was invented by the author based on previous studies on the aerodynamic mechanisms of fruit fly(pitching-up)flapping.The motivation of this invention i...The pitching-down flapping is a new type of bionic flapping,which was invented by the author based on previous studies on the aerodynamic mechanisms of fruit fly(pitching-up)flapping.The motivation of this invention is to improve the aerodynamic characteristics of flapping Micro Air Vehicles(MAVs).In this paper the pitching-down flapping is briefly introduced.The major works include:(1)Computing the power requirements of pitching-down flapping in three modes(advanced,symmetrical, delayed),which were compared with those of pitching-up flapping;(2)Investigating the effects of translational acceleration time,Δτ_t,and rotational time,Δτ_r,at the end of a stroke,and the angle of attack,α,in the middle of a stroke on the aerodynamic characteristics in symmetrical mode;(3)Investigating the effect of camber on pitching-down flapping.From the above works, conclusions can be drawn that:(1)Compared with the pitching-up flapping,the pitching-down flapping can greatly reduce the time-averaged power requirements;(2)The increase in Δτt and the decrease in Δτ_r can increase both the lift and drag coefficients, but the time-averaged ratio of lift to drag changes a little.And α has significant effect on the aerodynamic characteristics of the pitching-down flapping;(3)The positive camber can effectively increase the lift coefficient and the ratio of lift to drag.展开更多
As a kind of actuation mechanism for power-by-wire(PBW) actuation systems of more/all electrical aircraft, an electro-hydrostatic actuator(EHA) is a highly integrated local hydraulic actuation system. It is a volume c...As a kind of actuation mechanism for power-by-wire(PBW) actuation systems of more/all electrical aircraft, an electro-hydrostatic actuator(EHA) is a highly integrated local hydraulic actuation system. It is a volume control system consisting of a motor, a pump, an actuator, etc.,which has features of high efficiency and reliability. However, the poor dynamic characteristic is one of the main factors restricting its wide application in aircraft. In this paper, the reason for the poor dynamic characteristic of an EHA is revealed from the perspectives of the natural frequency characteristic and the power requirement, respectively. In other words, the insufficiency of the motor output power at a high frequency is the main factor causing the poor dynamic characteristic of the system, and methods which include increasing the maximum output torque of the motor, reducing the rotational inertia of the motor-pump group, and adopting a double-motorpump group configuration are proposed in this paper, by which the dynamic characteristic of the system can be improved. The feasibility of those methods are verified by simulations. Finally, the dynamic characteristic is tested on an EHA prototype, and results show that saturation of the output torque of the motor is the main factor restricting the dynamic characteristic of the EHA system.展开更多
As a very basic flight mode, ascending flight is obviously of great importance to all kinds of manmade and natural fliers. Yet, for the most commonly seen fliers - insects, researches on this flight mode are rare. In ...As a very basic flight mode, ascending flight is obviously of great importance to all kinds of manmade and natural fliers. Yet, for the most commonly seen fliers - insects, researches on this flight mode are rare. In this paper, we combined both experimental measurements and numerical simulations to investigate the kinematical characteristics, aerodynamic performance and power requirement of ascending flight in fruit flies （Drosophila virilis）. The flies ascend at an advance ratio of about 0.12. The most significant characteristic of ascending flight is larger stroke amplitude compared to hovering, while the other kinematics is very similar. From an aerodynamics point of view, this increased stroke amplitude is needed to overcome the negative effects of＂downwash flow＂, caused by the upward motion of the fly. Same as hovering, the ascending fruit flies utilize delayed stall and fast pitching-up mechanisms to generate the majority of the lift required for balancing the weight and body drag. By using a larger stroke-amplitude to overcome the negative effects of＂downwash flow＂, larger energy cost （about 20%） than that of equivalent hovering is required.展开更多
文摘The pitching-down flapping is a new type of bionic flapping,which was invented by the author based on previous studies on the aerodynamic mechanisms of fruit fly(pitching-up)flapping.The motivation of this invention is to improve the aerodynamic characteristics of flapping Micro Air Vehicles(MAVs).In this paper the pitching-down flapping is briefly introduced.The major works include:(1)Computing the power requirements of pitching-down flapping in three modes(advanced,symmetrical, delayed),which were compared with those of pitching-up flapping;(2)Investigating the effects of translational acceleration time,Δτ_t,and rotational time,Δτ_r,at the end of a stroke,and the angle of attack,α,in the middle of a stroke on the aerodynamic characteristics in symmetrical mode;(3)Investigating the effect of camber on pitching-down flapping.From the above works, conclusions can be drawn that:(1)Compared with the pitching-up flapping,the pitching-down flapping can greatly reduce the time-averaged power requirements;(2)The increase in Δτt and the decrease in Δτ_r can increase both the lift and drag coefficients, but the time-averaged ratio of lift to drag changes a little.And α has significant effect on the aerodynamic characteristics of the pitching-down flapping;(3)The positive camber can effectively increase the lift coefficient and the ratio of lift to drag.
基金the National Natural Science Foundation of China(No.51475020)the National Key Basic Research Program of China(No.2014CB046400)
文摘As a kind of actuation mechanism for power-by-wire(PBW) actuation systems of more/all electrical aircraft, an electro-hydrostatic actuator(EHA) is a highly integrated local hydraulic actuation system. It is a volume control system consisting of a motor, a pump, an actuator, etc.,which has features of high efficiency and reliability. However, the poor dynamic characteristic is one of the main factors restricting its wide application in aircraft. In this paper, the reason for the poor dynamic characteristic of an EHA is revealed from the perspectives of the natural frequency characteristic and the power requirement, respectively. In other words, the insufficiency of the motor output power at a high frequency is the main factor causing the poor dynamic characteristic of the system, and methods which include increasing the maximum output torque of the motor, reducing the rotational inertia of the motor-pump group, and adopting a double-motorpump group configuration are proposed in this paper, by which the dynamic characteristic of the system can be improved. The feasibility of those methods are verified by simulations. Finally, the dynamic characteristic is tested on an EHA prototype, and results show that saturation of the output torque of the motor is the main factor restricting the dynamic characteristic of the EHA system.
基金This work was supported by a grant from the National Natural Science Foundation of China （11232002）.The author Yanpeng Liu also would like to acknowledge the supports from China Scholarship Council （CSC, 201306025020） and BMCE （YETP 1083）.
文摘As a very basic flight mode, ascending flight is obviously of great importance to all kinds of manmade and natural fliers. Yet, for the most commonly seen fliers - insects, researches on this flight mode are rare. In this paper, we combined both experimental measurements and numerical simulations to investigate the kinematical characteristics, aerodynamic performance and power requirement of ascending flight in fruit flies （Drosophila virilis）. The flies ascend at an advance ratio of about 0.12. The most significant characteristic of ascending flight is larger stroke amplitude compared to hovering, while the other kinematics is very similar. From an aerodynamics point of view, this increased stroke amplitude is needed to overcome the negative effects of＂downwash flow＂, caused by the upward motion of the fly. Same as hovering, the ascending fruit flies utilize delayed stall and fast pitching-up mechanisms to generate the majority of the lift required for balancing the weight and body drag. By using a larger stroke-amplitude to overcome the negative effects of＂downwash flow＂, larger energy cost （about 20%） than that of equivalent hovering is required.
