Wing/body kinematics measurement and force and moment analyses of the takeoff flight of fruitflies

In the paper, we present a detailed analysis of the takeoff mechanics of fruitflies which perform voluntary takeoff flights. Wing and body kinematics of the insects during takeoff were measured using Based on the measured data, high-speed video techniques. inertia force acting on the insect was computed and aerodynamic force and moment of the wings were calculated by the method of computational fluid dynamics. Subtracting the aerodynamic force and the weight from the inertia force gave the leg force. The following has been shown. In its voluntary takeoff, a fruitfly jumps during the first wingbeat and becomes airborne at the end of the first wingbeat. When it is in the air, the fly has a relatively large ＂initial＂ pitch-up rotational velocity （more than 5 000~/s） resulting from the jumping, but in about 5 wingbeats, the pitch-up rotation is stopped and the fly goes into a quasi-hovering flight. The fly mainly uses the force of jumping legs to lift itself into the air （the force from the flapping wings during the jumping is only about 5%-10% of the leg force）. The main role played by the flapping wings in the takeoff is to produce a pitch-down moment to nullify the large ＂initial＂ pitch-up rotational velocity （otherwise, the fly would have kept pitching-up and quickly fallen down）.

Shock/shock interactions between bodies and wings

This paper examines the Shock/Shock Interactions（SSI）between the body and wing of aircraft in supersonic flows.The body is simplified to a flat wedge and the wing is assumed to be a sharp wing.The theoretical spatial dimension reduction method,which transforms the 3D problem into a 2D one,is used to analyze the SSI between the body and wing.The temperature and pressure behind the Mach stem induced by the wing and body are obtained,and the wave configurations in the corner are determined.Numerical validations are conducted by solving the inviscid Euler equations in 3D with a Non-oscillatory and Non-free-parameters Dissipative（NND）finite difference scheme.Good agreements between the theoretical and numerical results are obtained.Additionally,the effects of the wedge angle and sweep angle on wave configurations and flow field are considered numerically and theoretically.The influences of wedge angle are significant,whereas the effects of sweep angle on wave configurations are negligible.This paper provides useful information for the design and thermal protection of aircraft in supersonic and hypersonic flows.

The Unique Strategies of Flight Initiation Adopted by Butterflies on Vertical Surfaces

As the basis of flight behavior,the initiation process of insect flight is accompanied by a transition from crawling mode to flight mode,and is clearly important and complex.Insects take flight from a vertical surface,which is more difficult than takeoff from a horizontal plane,but greatly expands the space of activity and provides us with an excellent bionic model.In this study,the entire process of a butterfly alighting from a vertical surface was captured by a high-speed camera system,and the movements of its body and wings were accurately measured for the first time.After analyzing the movement of the center of mass,it was found that before initiation,the acceleration perpendicular to the wall was much greater than the acceleration parallel to the wall,reflecting the positive effects of the legs during the initiation process.However,the angular velocity of the body showed that this process was unstable,and was further destabilized as the flight speed increased.Comparing the angles between the body and the vertical direction before and after leaving the wall,a significant change in body posture was found,evidencing the action of aerodynamic forces on the body.The movement of the wings was further analyzed to obtain the laws of the three Euler angles,thus revealing the locomotory mechanism of the butterfly taking off from the vertical surface.