Robust roll autopilot design to reduce couplings of a tactical missile

The purpose of this work is to decrease coupling effects of a tactical missile by designing a robust autopilot for its roll channel. In tactical STT missiles due to control strategy, in order to execute acceleration commands, roll angular velocity should be kept close to zero. Generally, in the design of autopilot for many of tactical missiles the inter influences of channels is neglected. However, three channels of the missile impact each other in different ways including kinematic, inertia and aerodynamic couplings. Aerodynamic coupling is a dominant in roll channel dynamics appearing as induced and control cross coupling roll moments. In this paper first the coupling terms are modeled considering literature. Next, the system is linearized as input–output using models of induced and control cross coupling roll moments. Also, for increasing robustness of the autopilot against modeling errors, uncertainties, and external disturbances, an uncertainty and disturbance estimation (UDE) controller is used. To evaluate the performance of the designed controller, the results were compared with three controlling methods namely a PD controller based on simple dynamics model, a PD controller based on modified dynamics model and a robust controller based on the extended state observer (ESO). Flight simulation results revealed that if the approximate relationship of induced and control cross coupling roll moments are appropriately modeled, UDE control performance outperforms other methods and couplings between pitch and yaw channels are significantly decreased.