SANE, Sanjay P.; DICKINSON, Michael H.: The isolation and modeling of wake capture during insect flight

During flight, insects control the aerodynamic forces on their wings through subtle alterations in their wing kinematics. These alterations allow the insects to generate the requisite moments for control of pitch, roll or yaw while maintaining sufficient lift to stay aloft. Until recently, it was not possible to easily translate the knowledge of wing kinematics into the resultant aerodynamic forces. In a previous study, we used a dynamically scaled model of Drosophila to show that in addition to the delayed stall mechanism, unsteady forces are generated by added mass inertia, wing rotation, and the interception of the wake from a previous stroke (wake capture). The purpose of this study was to specifically isolate and model the forces due to wake capture. From the difference between the measured forces and the forces predicted by a model that included both translation and rotation, we could selectively isolate the forces due to wake capture for a variety of different kinematic patterns. Wake capture is manifest as a narrow force peak immediately following stroke reversal. We have modeled wake capture as a force enhancement due to a transient increase in fluid velocity dependent on the kinematics of the previous stroke. When combined in a comprehensive quasi-steady model that included added mass inertia, translational force and rotational force, the predicted time course of aerodynamic forces shows good agreement with measured force traces. This model may find use in providing quick estimates for flight energetics, as well as building efficient control algorithms for micro-mechanical flapping insects.