Gust responses in flying insects: Insights into their kinematic response and recovery strategies

Although large aircraft can fly in all sorts of turbulent wind conditions, smaller crafts such as micro air vehicles (MAVs) are more susceptible to ambient fluctuations in wind speed and, therefore, more difficult to control. MAVs are inspired by insects that can stabilize themselves rapidly when perturbed by natural gusts, yet there are few studies that directly address the gust responses of either flying insects or small crafts. Here, we investigated the flight of freely flying black soldier flies subjected to a discrete head-on aerodynamic gust in the form of a repeatable vortex ring generated under controlled laboratory conditions. We recorded their flight motion using two high-speed cameras and analyzed body and wing kinematics in 14 trials. Our aim was to characterize various flight parameters that insects control when they encounter these abrupt gusts. Under these conditions, the body roll angles of insects typically undergo a large change in about 2 wing beats (WB) (~20 ms). The insect recovers from these perturbations in about 9 WB. This roll is countered by the insect with highly asymmetric wing stroke amplitudes, presumably to generate the necessary counter torques. They are also accompanied by changes in pitch-down attitude and flight deceleration. From these readings, we can gain insights into how the flapping insects become unstable and how they recover their stability through passive and active mechanisms.