Dynamic Response of Landing Gear Taxiing on Uneven Runways

An analytical landing gear model of simulating actual aircraft taxiing behavior by the power spectral density method is formulated. The dynamic model deals with not only shock-absorber non-linear damping and air-spring stiffness, but also tire non-linear damping and stiffness. The validity of this model is demonstrated with a comparison of frequency-domain and time-domain analytical results of dynamic response for two aircrafts, Boeing 707 and Boeing 737-94. The equivalent linearization technique in probabilistic method is introduced to treat landing gear non-linear parameters such as shock-absorber air-spring force, hydraulic damping and Coulomb friction, and tire stiffness. It is concluded that the air-spring stiffness and damping of shock-absorber have a great effect on root-mean-square of sprung-mass overload. The decrease of air-spring stiffness and increase of shock-absorber damping cause on obvious reduction in vibration level. An approach for determining the lower limit of air-spring stiffness and the upper limit of shock-absorber damping is presented, which is useful to assess and improve dynamic properties of aircraft as well as landing gears. For instance, it may give 43% and 60% reduction in root-mean-square sprung-mass overload(i.e., aircraft gravity overload) respectively for Boeing 707 and Boeing 737-94 aircraft by selecting the presented air-spring stiffness and shock-absorber damping.