Sane, S.P.*; Dickinson, M.H.: Unsteady aerodynamic forces are important for production of force moments by flapping wings.

Insects use aerodynamic forces not only to stay in air, but also to steer and maneuver. Through changes in wing kinematics, insects can finely control the pitch, roll and yaw moments around their body and thus maneuver. In a previous study, we used a mechanical model of a fly to study the influence of wing kinematics on unsteady force generation. In this study, we extend the analysis to include moments generated during single strokes. To address how unsteady force mechanisms such as delayed stall, wake capture and wing rotation affect moments, we used an extensive data set of aerodynamic forces corresponding to different kinematic patterns, and calculated the resulting instantaneous pitch, roll and yaw moments throughout the stroke. For the kinematics that generated maximum lift, we identified sub-regions where pitch, roll or yaw are most sensitive to changes in stroke amplitude, angle of attack, flip timing, flip duration and deviation from mean stroke plane, respectively. First, for fixed flip duration and flip timing, all three moments were sensitive to variation in stroke amplitude and angle of attack within a kinematic range where lift is sufficient to support body weight. Second, for fixed stroke amplitude and angle of attack, roll moments vary little with changes in flip timing or flip duration. However, pitch and yaw moments are sensitive to changes in flip timing and duration. Third, for fixed stroke amplitude, angle of attack, flip timing and flip duration, all three moments are very sensitive to variation in the deviation from mean stroke plane. This suggests that changes in stroke deviation may be an excellent strategy for manipulation of moments around an insect’s body.