Sliding Wear and Freeplay Growth due to Control Surface Limit Cycle Oscillations

Freeplay in flight control surface linkages leads to nonlinear aeroelastic behavior including limit cycle oscillations (LCO). LCO due to a constant freeplay has been extensively studied, whereas the converse phenomenon of mechanical wear and freeplay growth due to LCO is little explored. In the present work, a first-of-its-kind theoretical model for freeplay growth is developed by introducing LCO characteristics into Archard’s sliding wear model. The closed-form solution for a fixed airspeed is validated against an iterative method in prior literature and subsequently extended to the case of time-varying flight conditions. It is observed that under the action of LCO the freeplay will grow to become unbounded in finite time. The influence of the geometry and material properties of the bearings and links on freeplay growth is discussed, which can aid in actuation circuit design. The utility of the model is demonstrated by calculation of freeplay growth trends due to LCO and also by analysis of freeplay limits from the design/maintenance perspective.