Effect of Torsional Damping on Aircraft Nose Landing-Gear Shimmy

Abstract

The bifurcation analysis method is applied in dealing with shimmy oscillations of the aircraft nose landing gear. Algorithms and details of the procedure in bifurcation analysis are described. Torsional damping of the antiswing damper is studied based on the model consisting of torsional and lateral bending modes of the landing gear. It is concluded that more linear torsional damping means more stability from torsional shimmy, although excessive damping will result in lateral shimmy at the starting speed and low vertical force. The torsional shimmy occurs prior in the area of low speed and midvertical force without sufficient linear damping. And there exists a so-called ideal damping varying with forward speed, with which no shimmy happens in the global scope below a critical vertical force. Squared torsional damping has little influence on the area of shimmy unless Bautin bifurcation appears in the dynamics system, and it is effective in controlling the amplitude of shimmy oscillations. The torsional clearance increases the unstable area of torsional shimmy obviously, but the value of the clearance does not affect the shimmy area.