The Aerodynamic Effects on Self-Excited Resonant Wingbeats in Insects

Flapping insects may employ one of two actuation strategies to drive their wings and maintain steady flight: synchronous actuation where each wingbeat is caused by periodic muscle contractions triggered by a neural signal, and asynchronous actuation where multiple wingbeats self excite due to an antagonistic pair of muscles which excite each other repeatedly due to stretch activated forces. In synchronous insects, the neural frequency sets the wingbeat frequency regardless of aerodynamic loading. In asynchronous insects, previous work has shown that changes in wing inertia can affect emergent kinematics but it is unclear if oncoming airflow affects this self-excited oscillator regime. We simulated this asynchronous regime in an insect-scale, robophysical model. We expected the kinematics of the tethered pitching wing to vary with wind speed due to additional forces acting on the wing and the resulting change in pitching dynamics. However, the wingbeat frequency stayed constant despite being an emergent property indicating that aerodynamic effects do not introduce another timescale to the system. Hence, despite having different underlying mechanisms these two actuation strategies can yield the same wingbeat frequencies. Their responses to perturbations may still differ as we note a small decrease in wingbeat amplitude then oscillation decay in the self-excited oscillator when experiencing strong external forces while the synchronous regime's set amplitude remains relatively unchanged.