Design of Dual Media Electro Hydraulic Servo Actuator for Missile Application

Abstract

Every Missile requires some guidance or steering to ensure that the required flight trajectory is achieved. Missiles are equipped with either Aerodynamic control system or Thrust vector control system to provide the required steering forces. Electro Hydraulic Servo Actuation Systems are widely used for this purpose. In aerodynamic control system missile fins are turned using electro hydraulic servo actuators that rotate the fin to a new deflection angle. The actuators exert the forces in various directions, and generate the moments about the aerodynamic center of the missile, and thus rotate the missile in pitch, yaw and roll.So far, electro hydraulic servo actuators have been developed for operating with mineral oil based distributed hydraulic power supply system. The size and weight per unit ton of stall force is significant in such actuation systems. Dual Media Electro Hydraulic Servo Actuators, using Hydraulic Fluid and Aviation Turbine Fuel as working medium can be used with great advantage in supersonic cruise missiles. It would eliminate the need for separate actuation system thereby saving on size and weight which is of paramount importance in any missile application. However this would require modeling, design and development of actuator components, seals and electro hydraulic servo valves, for using with jet fuel as working medium. This paper focuses on the design methodology of Dual Media Electro Hydraulic Servo Actuator employed for Aero Dynamic Control (ADC) of a supersonic cruise missile. The actuator is of linear, double acting type designed for working with mineral oil based hydraulic fluid as well as aviation turbine fuel. This paper brings out design aspects which includes design of actuator components for meeting the stall load requirement, selection of electro hydraulic servo valve for meeting the rated speed and dynamic performance requirements and selection of seals to suit the requirements of dual media, working pressure and storage conditions. Actuator components were developed by using special processes like Plasma Ion Nitriding, Cryogenic treatment and Hard Anodizing for obtaining the desired properties and finish.