Pitch Perfect: How Fruit Flies Control their Body Pitch Angle

TL;DR

This study investigates how fruit flies actively control their body pitch angle during flight, revealing a fast, linear proportional-integral control mechanism that stabilizes their orientation after perturbations.

Contribution

It provides the first direct experimental evidence that fruit flies use a PI controller to stabilize their pitch angle during flight, combining high-speed video and simulations.

Findings

Flies correct pitch deflections of up to 40 degrees in about 29 ms.

Corrective responses are initiated within 10 ms after perturbation.

Flies can recover from pitch perturbations exceeding 150 degrees.

Abstract

Flapping insect flight is a complex and beautiful phenomenon that relies on fast, active control mechanisms to counter aerodynamic instability. To directly investigate how freely-flying D. melanogaster control their body pitch angle against such instability, we perturb them using impulsive mechanical torques and film their corrective maneuvers with high-speed video. Combining experimental observations and numerical simulation, we find that flies correct for pitch deflections of up to 40 degrees in 29 +/- 8 ms by bilaterally modulating their wings' front-most stroke angle in a manner well-described by a linear proportional-integral (PI) controller. Flies initiate this corrective process after only 10 +/- 2 ms, indicating that pitch stabilization involves a fast reflex response. Remarkably, flies can also correct for very large-amplitude pitch perturbations--greater than 150 degrees--providing a regime in which to probe the limits of the linear-response framework. Together with previous studies regarding yaw and roll control, our results on pitch show that flies' stabilization of each of these body angles is consistent with PI control.