Fatigue load evaluations of aircraft landing gear based on dynamic analysis in frequency domain

An analytical landing gear model of simulating actual aircraft taxing: behavior by the power spectral density method is formulated The dynamic model deals with not only shock-absorber non-linear damping and non-linear air-spring stiffness, but also tire non-linear dumping and stiffness. The validity of this model is demonstrated with a comparison of frequency-domain and rime-domain analytical results of dynamic response for the aircraft Boeing 707 The equivalent linearization technique in probabilistic method is introduced to treat landing gear nonlinear parameters such as shock-absorber air-spring force, hydraulic damping and Coulomb friction, and lire stiffness. The Rayleigh distribution function and the Gaussian distribution function proposed hv Kowalewski and Sjostrom are introduced to describe the distributions of load amplitudes and mean toads. Fatigue damage calculation and life prediction are discussed on the basis of the distributions of mean loan's and load amplitudes. An engineering case is studied for a Boeing 707 landing gear. It is concluded that the landing gear under the assumptions in this paper is with enough fatigue strength and the decrease of air-spring stiffness and increase of damping of shock-absorber may lower the fatigue damage.