Abstract: A simple but realistic method for identifying nonlinear stiffness and damping of a widely used aircraft air-oil shock strut has been developed in this paper In the method a power series expansion is used to model the nonlinear dynamic properties of the strut,and after intro- ducing new variables,the nonlinear identification problem can be reduced to a linear one with unknown linear parameters.An unbiased, efficient and consistent estimator for the vector of the linear parameters is obtained-under conditions of minimizing the sum of squares residuals which are assumed to be stationary and uncorrelated with the observed data. The order and the most ef- fective independent variables in the model are determined by the criterion of residual series corre- lation information entropy and the procedure of the best subset regression respectively Experi- ment demonstrates that the results are quite satisfactory and the method developed is realistic,which can be used to study the dynamic properties of the strut in full detail.

Key words: lamding gear, shock absorbers, nonlinear systems, parameter identification