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Aerodynamic ground effect in flapping-wing insect flight is of importance tocomparative morphologies and of interest to the micro-air-vehicle (MAV)community. Recent studies, however, show apparently contradictory results ofeither some significant extra lift or power savings, or zero ground effect.Here we present a numerical study of fruitfly sized insect takeoff with aspecific focus on the significance of leg thrust and wing kinematics.Flapping-wing takeoff is studied using numerical modelling and high performancecomputing. The aerodynamic forces are calculated using a three-dimensionalNavier--Stokes solver based on a pseudo-spectral method with volumepenalization. It is coupled with a flight dynamics solver that accounts for thebody weight, inertia and the leg thrust, while only having two degrees offreedom: the vertical and the longitudinal horizontal displacement. The naturalvoluntary takeoff of a fruitfly is considered as reference. The parameters ofthe model are then varied to explore possible effects of interaction betweenthe flapping-wing model and the ground plane. These modified takeoffs includecases with decreased leg thrust parameter, and/or with periodic wingkinematics, constant body pitch angle. The results show that the ground effectduring natural voluntary takeoff is negligible. In the modified takeoffs, whenthe rate of climb is slow, the difference in the aerodynamic forces due to theinteraction with the ground is up to 6%. Surprisingly, depending on thekinematics, the difference is either positive or negative, in contrast to theintuition based on the helicopter theory, which suggests positive excess lift.This effect is attributed to unsteady wing-wake interactions. A similar effectis found during hovering.

Aerodynamic ground effect in fruitfly sized insect takeoff