Three loop Lateral Missile Autopilot Design in Pitch Plane using State Feedback & Reduced Order Observer (DGO)

–A flight path rate demand modified three-loop lateral missile autopilot design methodology for a class of guided missile, based on state feedback, output feedback, reduced order Das & Ghosal observer (DGO) is proposed. The open loop undamped model of three-loop autopilot has been stabilized by using pole placement and state feedback. The non-minimum phase feature of rear controlled missile airframes is analyzed. The overall response of the three-loop autopilot has been significantly improved over the classical two-loop design. It has been established through this paper that the initial negative peak occurring in the time response due to the non-minimum phase zeros, the reduction of which posed a major challenge so far in autopilot design, is reduced to some extent as compared to that of two-loop design. Steady state value of flight path rate has also improved over the classical two-loop design. Body rate demand is met exactly due to integrator applied in the forward path thus making the steady state body rate error zero. Reduced order Das & Ghosal observer is implemented successfully in this design to estimate two states elevator deflection and its rate while the other two states are measured by accelerometer & rate gyro. It has also been established that addition of an observer (an auxiliary dynamic system) to the system does not impair the system stability; it only appends its own poles (Eigen values) with the original system poles. Finally a numerical example has been considered and the simulated results are discussed in details. Keywords––Three Loop Pitch Missile Autopilot, Angle of attack, Flight path rate demand loop, Rate Gyro, Accelerometers, Aerodynamic control, Luenberger Observer, Das & Ghosal Observer, Generalized Matrix Inverse, LQR, and Ackermann.