Landing gear design/maintenance analysis for nonlinear shimmy
A concise harmonic-balance-(HB) based method is demonstrated that yields the limit-cycle oscillation (LCO) response as a function of forward speed for models of any order. The linear shimmy boundary of the system is generated as a function of stiffness in the degree of freedom (DOF) containing the freeplay. Harmonic motion is assumed; and the first harmonic of the resulting restoring force is calculated. The HB method can capture unstable as well as stable LCO branches. In this case, there are two stable branches separated by an unstable one with the vertical tangency/turning points corresponding to extrema in the linear shimmy velocity boundary. Results are presented for the case of subcritical LCO due to torsional freeplay, which is common in main, as well as nose, landing gear. These are correlated to the underlying linear system behavior, and guidelines are evolved for landing gear design and maintenance.
Padmanabhan, MA; Dowell, EH
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