Through simulations based on quasi-steady aerodynamic model and dynamically scaled robotic wing experiments, I systematically investigated the effect of body rotation on aerodynamic force and torque production in flapping wing fliers. The passive damping during different types of body rotation is explored. I started the analysis with the yaw rotation of the stroke plane, which is characterized by rapid turning maneuvers (saccades) in free flying insect and birds. Both simulation and robotic wing experiment showed that body rotation causes a substantial aerodynamic counter torque, termed flapping counter-torque (FCT), which acts in the opposite direction of turning. I further showed that the stroke averaged FCT is linearly dependent on the flapping frequency and rotational velocity. Force measurements on the dynamically scaled robotic wing undergoing realistic saccade kinematics of fruit fly Drosophila indicated that although passive aerodynamic damping due to FCT can account for a large part of the deceleration during saccade, active yaw torque from asymmetric wing motion is required to terminate body rotation. Furthermore, a mathematical model based on a quasi-steady analysis successfully predicted the deceleration dynamics of seven phylogenetically and morphologically dissimilar flying animals spanning six orders of magnitude in body mass, indicating FCT is a unifying principle in the flapping flight dynamics across a wide range of flying animals.

Similarly, I continued to investigate the FCT mechanisms during roll and pitch rotations. Both robotic wing experiments and mathematical models indicated FCT also exist in these two types of rotation. Collectively, I showed that the stroke averaged FCT is linearly dependent on the rotational velocity and the flapping frequency despite the type of rotation. For roll and yaw rotations, my model provided close estimations of the stroke-averaged values of FCT measured in robotic experiments. However, for pitch rotation, the model tended to greatly underestimate the FCT, which might due to the neglected unsteady aerodynamic mechanisms, especially the wake capture.