New Structure for an Aerodynamic Fin Control System for Tail Fin-Controlled STT Missiles

Abstract

This paper presents a new design method for an aerodynamic fin-control system for tail-fin controlled skid to turn (STT) missiles. The performance of the actuation system plays a decisive role in determining the performance of the flight control system for a highly maneuverable missile. To control the missiles by aerodynamics, control surfaces, sometimes called fins, are used. Deflection angles of these fins are the control variables of aerodynamics, but aerodynamicists prefer to use analytic variables called aileron, elevator, and rudder instead of these physical variables because these three analytic variables dominantly influence the roll, pitch, and yaw motion of the missile, respectively; and each can be considered a linear combination of four fin deflection angles. On that basis, roll, pitch, and yaw autopilots for controlling the attitudes or lateral acceleration of the missile are designed, and aileron, elevator, and rudder commands, respectively, are generated as consequence outputs of each autopilot. In the existing fin-actuation control scheme for the typical tail-fin controlled cruciform missiles, these outputs are distributed to four fin defection commands. After that, the four fins are actuated by fin controllers so that their deflections follow the commands. This paper shows that such control schemes can cause a significant deterioration in flight control system performance when fin-actuators have certain physical constraints such as slew rate, voltage, or current limit, or have an uncertainty of actuator dynamics, and proposes a new control scheme that alleviates such problems. This scheme can be widely applied to various fin-actuation control systems. But in this paper, for convenience, a tail-fin controlled cruciform missile is used as the example, and the proposed control scheme is shown to give better performance than the existing one.