The effects of translational, figure-eight and double-figure-eight flapping trajectories on the dragonfly aerodynamics were numerically studied by solving the Navier-Stokes equations. There is a common characteristic regarding the lift/drag force coefficients that the downstroke flapping provides the lift forces while the upstroke flapping creates the thrust forces for different flapping trajectories. The maximum lift force coefficient exceeds five for the translational trajectory. It is greater than six for the figure-eight and double-figure-eight flapping trajecto- ries, which is sufficiently larger than unity under the steady state flight condition. The ellipse and dou- ble-figure-eight flapping trajectories yield the de- crease of the lift force, while the figure-eight flapping trajectory yields higher lift force as well as the thrust force than the translational flapping one. During the insect flight, the wing flapping status should be changed instantaneously to satisfy various require- ments. Study of the flapping trajectories on the insect aerodynamics is helpful for the design of the Mi- cro-air-vehicles (MAVs).
