Bending Mode Stabilization in Tactical Missiles using Disturbance Observer vs Phase Stabilization Approach

In tactical missiles, three-loop autopilot has been the corner stone in Flight Control System (FCS) design from its inception till date. This linearized approach to autopilot design are constrained by variations in aerodynamic parameters, cross coupling in pitch-yaw-roll channels and flexibility modes. In this work, a de novo approach to flexibility mode filtering has been presented wherein the missiles structural oscillations are considered as an external disturbance in the pitch rate output channel and its rejection in the same channel using a Q-filter design commonly known as a disturbance observer. This work, compares bending modes (flexibility modes) stabilization using phase stabilization technique with the previously enunciated novel approach. Further, different approaches for phase stabilization are discussed and results are analyzed. The estimation of flexibility mode oscillations and rejection of same has been analyzed using various Q-filter designs and then the results compared with the phase stabilization methods.