Stability analysis of tactical missile autopilots based on vector margin

A novel stability computation approach for tactical missile autopilots is detailed. The limitations of traditional stability margins are exhibited. Then the vector margin is introduced and compared with sensitivity function to show their essential relationship. The longitudinal three-loop autopilot for tactical missiles is presented and used as the baseline for all the available linear autopilots. Ten linear autopilot topologies using all the measurable feedback components are given with the identical closed-loop characteristic equation and time-domain step response. However, the stability of the ten autopilots differs when considering the actuator dynamics, which limits their application. Then vector margin method is adopted to compute and evaluate the stability of all available autopilots. The analysis and computation results show that the vector margin method could better evaluate autopilot stability.