Reducing shimmy oscillation of a dual-wheel nose landing gear based on torsional nonlinear energy sink

Shimmy is described as a self-induced oscillation for the landing gear which is a threat to the handing quality and safety of aircraft taxiing on the ground. This paper proposes a novel torsional nonlinear energy sink (NES) serving as a passive vibration suppression device to mitigate shimmy oscillation of a dual-wheel nose landing gear (DW-NLG). The mechanical characteristic of the NES based on the cam-roller mechanism is studied, and a ten-dimensional nonlinear dynamical model of the DW-NLG coupled with NES is established which considers the coupling of torsional, lateral and longitudinal motions as well as nonlinear tire model. A bifurcation analysis is carried out and the stable area as well as limit cycle oscillation (LCO) amplitude for DW-NLG coupled with and without NES are obtained, together with time history, phase portrait and frequency spectra to show its shimmy performance. In addition, the effect of NES and DW-NLG structural parameters on the shimmy performance is discussed at length, the stable parameter domain and shimmy occurred area are investigated and presented according to two-parameter Hopf bifurcation analysis. The results indicate that the torsional dominated shimmy area shrinks effectively and the lateral dominated shimmy area decreases slightly, the maximum LCO amplitude and shimmy occurred speed range reduce, which ultimately expands the stable area and improves the DW-NLG shimmy performance effectively, the considering of strut longitudinal motion is able to further enhance the DW-NLG torsional shimmy stability. Meantime, the shimmy suppression performance of the NES can be improved with larger inertia, while the effects of damping and stiffness are limited. The bifurcation analysis of DW-NLG structural parameters indicates that the wheel separation distance, tire vertical stiffness, strut torsional stiffness and torsional damping, caster length and rake angle have an important effect on the shimmy performance, while the effect of wheel rotational inertia is limited. Thus, the application of proposed torsional NES results in effective benefits on shimmy suppression of the DW-NLG, which is able to provide new idea and guidance for landing gear engineering design.