Desired trajectory and guidance force generators for an aircraft

Abstract

An aircraft guidance and control system for a desired trajectory consists of four main parts: the desired trajectory generator, the guidance force generator, the commanded signals generator, and the automatic flight controller. This paper deals primarily with the trajectory generator and the guidance force generator. Cubic spline functions are used to generate the desired trajectory which passes through the given intercept points, because it generates the trajectory with minimum curvature. If time is used as the independent variable for the cubic spline functions, the airspeed cannot be set to a desired value. Therefore, flight distance is chosen as the independent variable. This enables us to set the airspeed to the desired constant value. The guidance force generator is then designed. The guidance force depends significantly on the magnitude of the guidance error correction gains. Since the constant gains cannot always guide the aircraft on the desired path, fuzzy logic is used to adjust the gains. The simulation results show that cubic spline functions generate the very smooth desired trajectory and fuzzy logic is a useful method to adjust the guidance error correction gains. Thus, the aircraft can be guided on the desired path with small position error even if the path is severely curved. (Author)