The mechanics and control in flapping flight

Bo Cheng, Purdue University

Abstract

Flying animals with flapping wings exhibit extraordinary ability to control their flight, they demonstrate rich repertoire of agile maneuvers but remain surprisingly stable during hover. This thesis worked towards an integrative understanding of such biological flight system based on multidisciplinary and collaborative efforts from engineers and biologists. I first studied the open-loop flight dynamics by investigating the effect of body movements on the changes in flight forces/torques, deriving analytical models for the flight dynamics at hover. Based on these models, the flight was found to be passively unstable in both longitudinal and lateral dynamics, as consistent with previous simulation studies. The body yaw rotation was then found to create substantial damping (flapping counter torque, FCT) during rapid turning maneuvers (saccades) in flapping fliers ranging in size from fruit flies to large birds. Our FCT model predicts that isometrically scaled animals experience similar damping on a per-wingbeat time scale, resulting in similar turning dynamics in wingbeat time regardless of body size. It was also found that in fruit flies, the damping due to FCT can account for a large part of the deceleration during saccades, but active yaw torque from asymmetric wing motion is required to terminate body rotation. Finally, I studied the active control strategy used by hawkmoth in exquisitely controlled pitch maneuvers. The realistic wing motions during the maneuver were recreated in a dynamically scaled wing model to experimentally determine the flight force/torque. The control strategies were then identified by comparing open-loop dynamics to the observed closed-loop dynamics, where it showed that feedback control based on pitch angle and angular velocity is essential to stabilize the flight.

Degree

Ph.D.

Advisors

Deng, Purdue University.

Subject Area

Mechanical engineering|Biomechanics

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