Feedback mechanism and controller design for longitudinal control of propulsion-controlled aircraft

Using engine thrust for flight control, also known as Propulsion-Controlled Aircraft (PCA), is a possible emergency control method after total failure of normal flight control system. However, the mechanism differences between PCA manipulation and conventional control surface, as well as the slow response of engines thrust, bring PCA control new characteristics and problems. This paper studies the longitudinal control problem of PCA. Firstly, the feedback effects of different parameters on longitudinal control were studied using the root locus method, revealing the PCA longitudinal feedback control mechanism, and clarifying the key control parameters. Furthermore, the basic assumption of PCA research is extended from traditional "trimmed state" to a more general "non-trimmed state". A transition state control method for pitch trajectory based on vertical speed is proposed for the case of unbalanced jamming and unknown position of elevators. Then, a dynamic pressure based pitch control method is developed for trajectory control in equilibrium state. The results show that, the proposed transition control method can effectively suppress trajectory oscillations caused by unbalanced elevator jamming, enabling the aircraft to quickly stabilize in a new trim state, and can accommodate the maximum trim range of elevator jamming. The proposed steady-state control method has good control effect, and good robustness against wind interference and center of gravity changes, which can enable the aircraft to land safely in PCA mode.