The application of a modified stepwise regression (MSR) method to the estimation of aircraft stability and control derivatives

A programme of research has now been completed in the College of Aeronautics (CoA) at Cranfield University to investigate the use of a Modified Stepwise Regression (MSR) procedure. The technique was applied to data obtained from a small BAe Hawk aircraft model flown in a dynamic wind tunnel facility in order to try to estimate the aerodynamic stability and control derivatives of the model. A variety of preliminary experiments were performed to enable the static stability of the Hawk model to be evaluated and estimates for a limited number of aerodynamic derivatives were obtained. The initial experiments also allowed data acquisition and processing systems to be developed. Experience of flying and controlling the model in the wind tunnel was gained. The MSR technique was implemented in the form of a FORTRAN 77 software program. Computer simulations of both the full scale Hawk aircraft and scaled wind tunnel model were written. MSR was found to produce perfect derivative estimates when using noise-free data produced by the aircraft simulations. Various mathematical models were produced to represent the reduced order small perturbation equations of motion for the Hawk in the wind tunnel. Different methods for re-constructing the perturbation variables were implemented. Although the MSR procedure did not perform optimally with experimental data, some insight into both the MSR method and the practical difficulties associated with using a small dynamic rig has been gained.