Active and passive stabilization of body pitch in insect flight

TLDR

Flying insects have evolved sophisticated sensory‑motor systems that keep them upright against intrinsic flight instabilities. The authors aim to predict pitch‑instability growth rates and to determine how active control and passive drag can stabilize flight. They develop a theoretical model of pitch instability from flapping‑wing aerodynamics and test it by magnetically perturbing fruit flies to observe rapid active control. Experiments show fruit flies use fast active control, and even when sensors are disabled, high‑drag fibers enable passive stability, confirming the model and extending it to other hovering animals and robots.

Abstract

Flying insects have evolved sophisticated sensory-motor systems, and here we argue that such systems are used to keep upright against intrinsic flight instabilities. We describe a theory that predicts the instability growth rate in body pitch from flapping-wing aerodynamics and reveals two ways of achieving balanced flight: active control with sufficiently rapid reactions and passive stabilization with high body drag. By glueing magnets to fruit flies and perturbing their flight using magnetic impulses, we show that these insects employ active control that is indeed fast relative to the instability. Moreover, we find that fruit flies with their control sensors disabled can keep upright if high-drag fibres are also attached to their bodies, an observation consistent with our prediction for the passive stability condition. Finally, we extend this framework to unify the control strategies used by hovering animals and also furnish criteria for achieving pitch stability in flapping-wing robots.