Experimental Studies on Dynamic Freeplay Nonlinearity

In the present manuscript, some novel results obtained in the context of an ongoing research at POLIMI are presented. The work focuses on the effect of multiple freeplay nonlinearities on the aeroelastic behaviour of a full-configuration aeroelastic wind tunnel aircraft model. The demonstrator is equipped with an active flutter suppression system, allowing the study of the interactions between the LCO created by the nonlinearities and the control system. In the first phase of the project, the horizontal tail plane was redesigned and used to extensively study a single nonlinearity, both with static and dynamic gap. It was found that LCO could be observed regardless of the gap size, including regulatory agencies’ limits. Also, the mechanism triggering LCO was studied, which is strongly related to the turbulence level. The effect of different rates of change of the gap size are discussed. Presentation of results for the horizontal tail are followed by results for the new version of the vertical tail plane. Preliminary numerical results are presented, showing a similar behaviour of the rudder LCO relative to the elevator LCO of the horizontal planes. In the next stage of the project, planned for the end of 2022, the entire aircraft model will be tested with all the nonlinearities active simultaneously.