Aerodynamic characteristics in hoverfly voluntary takeoff under different initial body orientations

Voluntary takeoff in non-jumping insects requires aerodynamic support, effective force reorientation, and economical force production, yet how initial body orientation and wing deformation affect takeoff aerodynamics remains insufficiently understood. In this study, voluntary takeoff of hoverflies ( Syrphus, Syrphidae ) is investigated by combining takeoff experiments with computational fluid dynamics simulations. Three initial body orientations, including horizontal, head-up, and head-down orientations, are examined to analyze the takeoff kinematics and aerodynamics. The results show that wing-generated aerodynamic force provides the main contribution to body weight support, while the estimated leg force acts as an auxiliary contribution during initial liftoff. Lift remains the dominant component of the wing-generated aerodynamic force acting on the body, whereas the reversal of drag direction between the downstroke and upstroke contributes to the horizontal and vertical allocation of the resultant aerodynamic force under the corresponding body orientation. Although the simplified rigid wing generates higher aerodynamic forces, it also requires a larger flapping aerodynamic moment and a higher aerodynamic power consumption. By contrast, the deformable wing reduces power expenditure more strongly than it reduces aerodynamic output, resulting in higher aerodynamic efficiency. These findings improve the understanding of non-jumping insect takeoff and provide insight into the design of micro air vehicles requiring efficient and maneuverable takeoff.