Freeplay-Induced Limit-Cycle Oscillations in a T-Tail: Numerical vs Experimental Validation

To investigate the effect of control-surface freeplay, an aeroelastic wind-tunnel model of a T-tail with freeplay in the control chain was developed. The T-tail rig presents a conventional vertical fin represented only by its main structural component: the main spar. No aerodynamic sectors have been used to reproduce the aerodynamic contribution of a horizontal tail. This was chosen because of the limited size of the wind-tunnel chamber. Two numerical models were developed. The first one describes the dynamics of the tail by a state-space system with nonlinearity represented as a lumped element in the actuator feedback loop, and the second is described by the high-order harmonic balance approach, where the response of the nonlinear system is approximated with a periodic signal. The two approaches are then validated against experimental measurements collected during wind-tunnel testing. The results of this validation process as well the numerical and experimental approaches adopted are reported in this paper.