Experimental Studies on Freeplay Induced Limit Cycle Oscillations and Their Major Drivers

A new experimental wind tunnel test-bed has been developed for the study of limit cycle oscillations induced by control surface freeplay. A thorough examination of several factors affecting the limit cycle is presented—starting from a reference configuration, the effect of changes in inertia and stiffness, a time-varying gap size, gravitational loading, and aerodynamic preload due to an angle of attack. Both time-marching simulations and describing functions analytical methods have been used to understand the experimental measurements and study the capability of the methods to capture the physical behavior. Good agreement was found in all cases, and physical insights are gained from the mathematical models. Limitations of the analytical tools are also addressed, focusing on the important difference between the self-excited dynamics of the nonlinear system and its forced response to external excitation.