FRY, SN *; DICKINSON, MH: Kinematics and aerodynamics of free flight maneuvers in Drosophila

The impressive aerial maneuvers performed by flies pose interesting questions for neurophysiology, biomechanics and behavior. Recent research has identified several unsteady aerodynamic mechanisms that explain how hovering insects generate lift forces large enough to remain aloft. With this knowledge as a base, we set out to determine how free-flying Drosophila actively manipulate these mechanisms for flight stabilization and maneuvering. We captured free-flight sequences containing rapid turns (body saccades) using 3 high speed cameras and extracted the wing and body kinematics using custom data analysis techniques. To assess the functional significance of the observed changes in wing kinematics during the maneuver, we used these kinematic patterns to drive a dynamically scaled robotic model of Drosophila equipped with force sensors to directly measure the flight forces. The results show that during a saccade the mean stroke position of the outside wing is shifted backward. During the upstroke, the angle of attack is higher, resulting in increased drag. Due to the backward motion of the wing during the upstroke, this force points in the direction of flight and hence contributes to forward propulsion. The outside wing also rotates earlier and begins the downstoke at a low angle of attack. As a consequence, the mean flight force on this wing is larger and directed more forward. Conversely, the inside wing is shifted to a more forward position, has a low angle of attack during the upstroke, flips late and begins the downstroke with a high angle of attack, generating a smaller and more backward directed mean flight force. Our measurements are in accordance with the observed body kinematics during the maneuver and promise important insights into flight control mechanisms based on unsteady aerodynamics.