Longitudinal Hinfinity Stability Augmentation System for a Thrust-Vectored Unmanned Aircraft

The development of discrete longitudinal H infinity stability augmentation system to improve the handling qualities of a radio-controlled unmanned aircraft is presented. The aircraft features thrust-vector control by deflection of a cold jet to expand the operating envelope. Output sensitivity and a control sensitivity minimization problem are considered to suppress low-frequency gust disturbance and high-frequency noise disturbance and to ensure proper control allocation between the elevator and the thrust flap. Gain scheduling is avoided by designing a single controller at the operating point most sensitive to perturbations in actuators and the aerodynamic model. To this end, a systematic method to choose the design operating point is presented. The closed-loop system is comprehensively tested for robust stability using mu analysis and for robust performance over the entire cruise envelope. Disturbance and sensor noise rejection capabilities are assessed for realistic gust and sensor noise using nonlinear simulation and hardware in loop simulation. The entire design procedure, is performed in discrete time