Meeting Abstract
Flying fruit flies must control all six degrees of body motion via subtle changes in wing kinematics. Several studies indicate that changes in wing pitch, which largely determine the angle of attack, are particularly important for controlling body yaw. In addition, prior research suggests that flies might regulate wing pitch via a passive mechanism in which they only adjust the torsional stiffness about the long axis of the wing. During each stroke, the wing then rotates under inertial and aerodynamic torque to adopt the correct angle of attack. However, this model does not preclude the possibility that flies also actively rotate their wings through the action of the wing hinge and steering muscles. The goal of our study was to develop a general model of wing rotation to gain insight into the relative contributions of active and passive mechanisms. Using realistic morphometric and kinematic values from the literature, we derived an equation of motion for the pitch axis of the wing. We solved for the time history of wing pitch and compared it to the actual pattern generated by a fly, using kinematics collected from free flight sequences. We performed a sensitivity analysis on various parameters and found that the solution depends quite strongly on the location of the center of pressure, the mass distribution of the wing, and the level of smoothing applied to the positional data. For data from free flight, in which the mid-stroke angle of attack is relatively constant at ~45°, we found that the center of pressure is quite close to the axis of rotation and the aerodynamic torque is smaller than inertial torque. Based on the relationship between the required torque and the wing pitch angle, our results suggest that flies must exert some active control over wing pitch to achieve their remarkable aerial agility.
