Numerical investigation of model reference adaptive control for hypersonic aircraft

To address the attitude control of hypersonic aircraft, an approach of direct model reference adaptive control (MRAC) is followed. The basis for MRAC is that a system of which only the outputs are known has to track a reference model that can be a simple approximation of the actual system. By combining the output error, the model state, and the model control parameters into a reference signal, proportional and integral gains can be computed that are adapted to the value of the reference signal. To apply MRAC it is necessary that the controlled nonlinear system is almost strictly passive. The design of the combined longitudinal/lateral MRAC system is centred around a linearized reference model of the winged cone configuration at a Mach 5.6 fight condition. The results of some fundamental response tests are discussed, as well as altitude and cross-range transitions. It appears that MRAC seems to be a promising concept when applied to hypersonic space planes. Although it is too early to say that the current configuration of the controller is robust with respect to design uncertainties and environmental perturbations, there are still many improvements possible that will enhance performance. One drawback, however, is the large number of design parameters that can be tuned to influence the performance.