Studying the Effect of Freeplay on Nose Landing Gear Shimmy Using a Fully Nonlinear Model

Shimmy is a common instability of landing gear systems which has been known for a long time. Yet, it is often studied using simplified dynamic models in which the chief system nonlinearities are neglected. Particularly, the influence of worn components and loose joints manifesting itself as a freeplay nonlinearity has been only touched upon in few works. The present paper utilizes a fully nonlinear landing gear dynamic model to obtain nonlinear stability boundaries and to study the onset, severity, frequency jumps, and mode shifts of the system as a result of the torque link freeplay. Using stability maps in the parameter space and time histories of the oscillations the degrading effect of excessive clearance and wear in the torque links is demonstrated, which in turn offers insights for designing shimmy-free landing gears.