Flight of the fruit fly

There comes a time in each of our lives where we grab a thick section of the morning paper, roll it up and set off to do battle with one of nature's most accomplished aviators—the fly. If, however, instead of swatting we could magnify our view and experience the world in slow motion we would be privy to a world-class ballet full of graceful figure-eight wing strokes, effortless pirouettes, and astonishing acrobatics. After watching such a magnificent display, who among us could destroy this virtuoso? How do flies produce acrobatic maneuvers with such precision? What control mechanisms do they need to maneuver? More abstractly, what problem are they solving as they fly? In this article and the associated video presentation of my invited lecture from the ${71}^{\mathrm{st}}$ Annual Meeting of the American Physical Society's Division of Fluid Dynamics, I describe the challenges associated with answering these questions, our attempts to investigate them, and, through various demonstrations depicted in the video, qualitatively illustrate the mechanisms used by these insects to achieve these astonishing behaviors.

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Figure 1

We successfully modeled Drosophila's flight stabilization reflex as a PI controller. PI controller models describe Drosophila flight stabilization along yaw (a), (b), roll (c), (d), and pitch (e), (f) body angles. (a), (c), (e) Representative perturbation and correction maneuvers, with image data and corresponding 3D reconstructions. (b), (d), (f) Controlled wing kinematic quantity vs time (data points), with curve fits corresponding to predictions of a PI controller model. In each case, the body angular velocity and total angular displacement about a particular degree of freedom (yaw, roll, or pitch) is summed with appropriate coefficients to determine the PI controller prediction for the relevant wing-stroke parameter: difference in angle of attack for the left and right wing for yaw; difference in wing-stroke amplitude for roll; difference in the front stroke angle for pitch. In F, we plot the body pitch velocity representing the proportional term (P term: solid gray line), the total angular displacement representing the integral term (I term: dashed black line), and their appropriately weighted sum that corresponds to the PI controller prediction (PI Ctrl: solid blue line). Adapted from Refs. [9, 11, 12].