Flutter control based on ultrasonic motor for a two-dimensional airfoil section

This paper presents how to use an ultrasonic motor, which features high torque at low speed, small size and low weight, as an actuator in the flutter control of a two-dimensional airfoil section. The paper begins with the design of a two-dimensional airfoil model with the piecewise-linear torsional stiffness in pitch direction and a control surface driven by an ultrasonic motor. Then, it gives the experimental modeling of the airfoil section and the servo, composed of the control surface and the ultrasonic motor, as well as the identification of system parameters through the use of a simple approach of nonlinear least squares estimation. Afterwards, the paper presents the dynamic equation of the aeroservoelastic equation based on Theodorsen's aerodynamic load, and the numerical simulations for the sub-optimal control of flutter. Finally, the paper outlines the experimental study of the flutter control of the airfoil section in a wind tunnel test, where the critical flutter speed of controlled system could be increased by 13.4%, and the flutter was effectively suppressed when the flow speed exceeded the critical flutter speed of the uncontrolled system.