Interaction between wear processes and limit cycle oscillations of a control surface with free-play non-linearity

This paper provides a detailed study of a non-linear aeroelastic phenomenon first addressed by Safi et al., i.e. coupling a model for wear in mechanical linkages to the aeroelastic response of a non-linear wing—aileron or stabilizer—elevator system. The aeroelastic behaviour of these systems with free-play structural non-linearity in the control surface restoring moment is examined. The underlying dynamics and deterioration of the system due to ageing are investigated. Extensive numerical simulations are performed using Wagner' function to evaluate the aerodynamic forces. The resulting equations are integrated numerically to give time histories of the airfoil—aileron motion. Regions of limit cycle oscillations (LCOs) and chaotic vibration are identified well below the linear flutter speed. Finally qualitative and quantitative wear analyses are presented to provide relationships to predict the depth of wear in the mechanical connections experiencing LCOs. The problem is shown to be coupled with an accelerating wear rate as the free play develops.