17.8 Friday, Jan. 4 Stroke features involved in the stabilization of longitudinal forward flight in flies ELZINGA, M. J.*; DICKINSON, M. H.; California Institute of Technology; University of Washington; University of Washington firstname.lastname@example.org
The ability to regulate forward speed is an essential capability for flying animals. Here, we use a dynamically scaled robot to gain insight into how flapping insects adjust stroke features to regulate and stabilize level forward flight. The results suggest that few changes to hovering kinematics are actually required to meet lift and thrust requirements, and the primary driver of equilibrium velocity is the aerodynamic pitch moment. This finding is consistent with prior hypotheses and observations regarding the relationship between body pitch and flight speed in fruit flies. We considered three different deformations of hovering wing kinematics, which were inspired by previous experimental studies and that result in the generation of a pitch moment: a shift in the mean stroke position, upstroke to downstroke differences in wing rotation angle, and upstroke to downstroke differences in stroke deviation. The results suggest that a shift in the mean stroke position is a likely candidate for trimming the pitch moment at all speeds, whereas shifts in the wing rotation angle are required only at high speeds. The results also show that the dynamics may be stabilized with the addition of a pitch damper, but the magnitude of required damping increases with flight speed. We posit that differences in stroke deviation between the upstroke and downstroke play a critical role in this stabilization. Fast mechanosensory feedback of the pitch rate enables active damping which becomes inherently gain scheduled with flight speed when pitch torque is generated by differences in deviation. This provides an elegant solution for flight stabilization across a wide range of flight speeds.