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In order to investigate the aerodynamic interference characteristics of tandem rotor, this paper simulates the hovering flow field of single rotor and tandem rotor based on the dynamic structure overset grid method and unsteady Navier-Stokes equations in computational fluid dynamics (CFD). In the study of hover state of single rotor with twist, the trajectory of the blade vortex and the change pattern are briefly analyzed. Subsequently, the flow field disturbance of tandem rotor, the vortex structure, the pull coefficient and the downwash flow are investigated. The results show that there is obvious blade vortex interference in the overlapping area of the tandem rotor, where the downwash flow reduces the effective angle of attack of the blade and thus has a significantly effect on the pull coefficient. The rotor is less disturbed when it is far from the overlapping area, and the tension coefficient does not change significantly. After integrating the pull coefficient of the upper and lower rotors in one cycle, it was found that the loss of pull coefficient of the two rotors reached 5.7% and 10.7% respectively, which proved that the aerodynamic interference between the tandem rotor in hovering condition had an important effect on the aerodynamic performance of the vehicle.

We measured the wing kinematics of fruitflies in both vertically-ascending and hovering flights and studied the aerodynamic forces and power in the two flight modes. The average ascending velocity is 0.45 m s-1; the stroke plane angle and the stroke frequency are the same as that in hovering flight, whilst the stroke amplitude is increased by 12% and the wing angle of attack in the latter half of a down- and upstroke both increased by 10%. Flow analysis shows that during ascending, the flies experience a downward inflow which reduces the effective angle of attack considerably. This problem is overcome by the increases in the stroke amplitude and the angle of attack, which result in a larger wing drag. As a result, the power at ascending is increased by 36% over that at hovering. Two very interesting observations were made. (1) Using the same power, level-forward flight can be about four times as fast as ascending flight. (2) Power for ascending flight is the same as that for carrying a load about 27% of the insect's weight at hovering.

In this paper, we analyzed the body and wing kinematics and mechanics in fruit flies' landings on a vertical pole. By high-speed video techniques and CFD method, we exhibited the detailed process of landing as follows. A fruit fly first decelerates and enters a near-hover state approximately 25 mm away from the vertical pole, then starts approaching the pole in acceleration till one of its front-legs touches the pole (touchdown). Just before touchdown, the fly's acceleration is around 6 ms-2; at touchdown, it experiences an almost instant deceleration of several g (gravitational acceleration), approximately all of which results from the leg force. After touchdown, the fly's acceleration fluctuates about zero, and the acceleration is also mainly due to the leg force; meanwhile the aerodynamic force decreases to zero and the fly's weight is gradually shifted to legs. In this period, the fly's legs act as a compression spring, and the fly can be regarded as a legs-body oscillator. In conclusion, during landing, the fly keeps accelerating towards the target and 'impinges' on the target on its legs, and the leg force, not aerodynamic force, is used to stop the insect's motion.

Here, we present a detailed analysis of the wing and body kinematics in drone-flies in free flight over a range of speeds from hovering to about 8.5 m s(-1). The kinematics was measured by high-speed video techniques. As the speed increased, the body angle decreased and the stroke plane angle increased; the wingbeat frequency changed little; the stroke amplitude first decreased and then increased; the ratio of the downstroke duration to the upstroke duration increased; the mean positional angle increased at lower speeds but changed little at speeds above 3 m s(-1). At a speed above about 1.5 m s(-1), wing rotation at supination was delayed and that at pronation was advanced, and consequently the wing rotations were mostly performed in the upstroke. In the downstroke, the relative velocity of the wing increased and the effective angle of attack decreased with speed; in the upstroke, they both decreased with speed at lower speeds, and at higher speeds, the relative velocity became larger but the effective angle of attack became very small. As speed increased, the increasing inclination of the stroke plane ensured that the effective angle of attack in the upstroke would not become negative, and that the wing was in suitable orientations for vertical-force and thrust production.

Controls required for small-speed lateral flight of a model insect were studied using techniques based on the linear theories of stability and control (the stability and control derivatives were computed by the method of computational fluid dynamics). The main results are as follows. (1) Two steady-state lateral motions can exist: one is a horizontal side translation with the body rolling to the same side of the translation by a small angle, and the other is a constant-rate yaw rotation (rotation about the vertical axis). (2) The side translation requires an anti-symmetrical change in the stroke amplitudes of the contralateral wings, and/or an anti-symmetrical change in the angles of attack of the contralateral wings, with the down- and upstroke angles of attack of a wing having equal change. The constant-rate yaw rotation requires an anti-symmetrical change in the angles of attack of the contralateral wings, with the down- and upstroke angles of attack of a wing having differential change. (3) For the control of the horizontal side translation, control input required for the steady-state motion has an opposite sign to that needed for initiating the motion. For example, to have a steady-state left side-translation, the insect needs to increase the stroke amplitude of the left wing and decrease that of the right wing to maintain the steady-state flight, but it needs an opposite change in stroke amplitude (decreasing the stroke amplitude of the left wing and increasing that of the right wing) to enter the flight.