Tire parameters for landing-gear shimmy studies.

This paper discusses a tire-test machine, similar to a free-castering landing gear, which allows the determination of tire parameters necessary for accurate prediction of shimmy stability of landing gears. An adequate set of tire parameters is shown to be fei, lateral tire-spring rate; CL, lateral viscous-damping coefficient; C, coefficient of yaw; Ci, yaw time constant; and /Zi, tire torsional spring constant, ki and CL are determined from standing tire-deflection and die-away tests. The rolling tire-test machine is used to determine values for C, Ci, and fJL under simulated high-speed and low-speed taxi runs. Results for two different tires are given (18 X 5.5, 14-ply and 49 X 17, 26-ply). The importance of accurate tire data is demonstrated by showing how stability maps of a typical landing gear vary with changes in tire parameters.