Online parameter estimation issues for the NASA IFCS F-15 fault tolerant systems

This paper focuses on specific issues relative to real-time online estimation of aircraft aerodynamic parameters at nominal and post-actuator failure flight conditions. A specific parameter identification (PID) method, based on Fourier transform, has been applied to an approximated mathematical model of the NASA IFCS F-15 aircraft. In this effort different options relative to the application of this PID method are evaluated and compared. Particularly, the direct evaluation of stability and control derivatives versus the estimation of the coefficients of the state space system matrices evaluation is considered. Furthermore, the options of considering individual control surfaces (left and right) versus total surfaces as inputs to the PID process are discussed. Finally, since the PID method relies on the use of derivative terms, the option of using time domain derivatives versus frequency domain derivatives is also evaluated. Results are presented in terms of the accuracy and reliability of the estimates of selected stability and control derivatives.