Experiments on control of limit-cycle oscillations in a typical section

The experimental application of active control to reduce or eliminate limit -cycle oscillations in a typical section airfoil is presented. The test rig consists of a three-degree-of-freedom typical section which has free play in the flap restoring stiffness. Such a free play was intended to mimic tha t associated with control surface mechanism backlash in a real system. Cont rol is effected by means of an actuator acting on the nap. A linear quadrat ic Gaussian optimization scheme is used to design a compensator that will a ccomplish three goals: 1) reduce or eliminate limit-cycle oscillations, 2) increase the Butter boundary, and 3) be robust to variations in the now vel ocity, Although the typical section is a nonlinear dynamic system, the cont rol system design was based on the linear typical section with no free play . The results presented indicate that each of these goals was accomplished. More specifically, limit-cycle oscillations were eliminated, the flutter v elocity was increased by 17%. and the control system was stable over a wide range of Row conditions.