Numerical and Experimental Investigations on Freeplay-Based LCO Phenomena on a T-Tail Model

Limit cycle oscillations (LCO) are of great interest for aeronautic engineers. They may strongly affect performance and life of aeroservoelastic systems. For quite some time, studies have focused on increasing the understanding of the physics behind the freeplay-induced LCOs, striving to find general rules, particularly, if possible, for certification purposes. However, few studies reproduced experimentally the gap sizes required by regulatory agencies, and no experimental studies tackled dynamically time-varying nonlinearities. In the present work, a new experimental capability is presented. The final goal is to capture by tests the behavior of realistic systems, with fully flexible control surfaces, efficient variation of freeplay magnitude, and the time-varying evolution of freeplay. The new experimental model created also makes it possible to change the nominal stiffness at the hinge and the control surface inertia, effectively allowing the study of the sensitivity to parametric uncertainty. Several experimental campaigns will be carried out using this new experimental test article and capabilities, providing valuable data that can also be used by other researchers or practitioners to verify their numerical methods. In the context of this first manuscript, some numerical methods have also been introduced and explored. Initial experimental results have been generated. The results are of great interest, as they show a peculiar limit cycle behavior that cannot fully be modeled using a describing function approach. This exemplifies the necessity to always complement frequency domain LCO simulations with time marching simulations. Further, it was experimentally shown that even when current certification freeplay limits are met LCO can develop. However, with careful design the effect of LCO on the main structure of an aeroservoelastic system can be minimized, as it will also be shown.