Skid to turn control of the APKWS missile using trajectory linearization technique

This paper presents the design and simulation results of an autopilot for the US Army´s APKWS missile. The concept is to add on a guidance section to the existing Hydra 70 unguided rocket airframe. The guidance section is to be mounted onto existing hardware using a deroll bearing which permits the motor to roll freely while the guidance section is roll stabilized. The Hydra 70 has unusual dynamic and aerodynamic characteristics, which include a very large intentional induced roll moment which is heavily influenced by down wash effects on the rear spin inducing fins from large aerodynamic angles and the displacement of the control canards. Moreover, angle of attack tracking with control canards makes the problem nonminimum phase. The autopilot consists of a nonlinear inverse subsection which places the missile on the nominal commanded trajectory, and a linear time varying trajectory regulating controller. The regulating controller is formulated using a new parallel differential eigenvalue stability concept. An advantage of the proposed design method is that the controller gains are computed symbolically such that a full flight envelope autopilot can be designed without resorting to pointwise gain scheduling. Simulation results are shown to demonstrate the effectiveness of the trajectory linearization control technique