Nonlinear Unsteady Aerodynamic Modeling Through Modifications to Nonlinear Indicial Response Approach

This paper presents two nonlinear unsteady aerodynamic modeling methods of aircraft at high angles of attack, through modifications to the nonlinear indicial response approach, to get better identification results against a data set of large amplitude forced-oscillation wind tunnel test. Firstly the convolutions related to derivatives of the angular rates are remained in the model structure and the dynamic derivatives are developed to higher-order derivatives to accommodate higher degree of nonlinear characteristics. Then the nonlinear indicial model is discretized and approximated to get a nonlinear unsteady model structure using time-delayed state variables and their derivatives. The unsteadiness is represented by the time history of flight states. An alternate method is proposed by referring this model structure and the idea of Weiner model to.