Modeling and robust coupled control of air-breathing hypersonic vehicle considering propulsion and aeroelastic effects

Considering intricate coupling between engine and flight dynamics and complex interaction between flexible and rigid modes, a longitudinal dynamic model for a flexible air-breathing hypersonic vehicle is developed. Unlike conventional aircraft, air-breathing hypersonic vehicles require the propulsion system to be highly integrated into the airframe. Furthermore, full-scale hypersonic vehicles tend to have very lightweight and flexible structures with low natural frequencies. Therefore, the bending modes are important and affect the amount of airflow entering into the engine, thus influencing the performance of the propulsion system. The equations of motion for the flexible vehicle are derived by using Lagrange's equations and capture effect between the pitch and normal accelerations of the vehicle and the structural dynamics. And then, the uncertainties of the longitudinal model are analyzed and a robust coupled controller based on LQR is designed by using implicit model-following method with respect to variations in the vehicle dynamics resulted from fuel consumption. Finally, the simulation results show that the method introduced in this paper is feasible.