AX ELECTRICALLY OPERATED HYDRAULIC CONTROL VALVE 713 



The roll system's reference is an "Amount Gyro," which is a free-free 

 gyro oriented on the ground prior to missile launch. The brush of a four- 

 tap potentiometer (Item 2 in Fig. 1) is corniected to the outer gimbal and 

 provides a dc signal whose sign and magnitude indicate the roll position 

 with respect to the stable e(iuilii)rium point. This signal is the principal 

 input to the servo amplifier that drives the valve. 



A roll-position error exists in the situation illustrated in Fig. 1. The 

 valve is driven in the direction to cause the oil flow to rotate the ailerons, 

 which in turn will roll the missile toward the null position. As the missile 

 rolls, the winding of the roll-amount potentiometer rotates with it. The 

 brush stays fixed in space with the gyro gimbal. 



The aerodynamic coupling between the aileron position and the mis- 

 sile's roll position is a complex and variable term in the feedback loop 

 of the servo. The nature of the aerodynamic coupling is such that an 

 other\\ase simple servo problem becomes considerably more compli- 

 cated. During a normal flight the aerodynamic stiffness, and hence the 

 gain in the feedback loop, varies over a 50:1 range. A first order correc- 

 tion for this change is accomplished by a variable gain local loop around 

 the valve, cylinder and amplifier. A potentiometer (Item 3 in Fig. 1) is 

 geared to the fin in such a way that a dc signal is produced, which is 

 proportional to fin position. The gain of this local loop is varied by 

 supplying the potentiometer with voltages that are directly propor- 

 tional to the measured aerodynamic stiffness. In this way the amount 

 of the deflection of the aileron is made inversely proportional to the 

 aerodynamic stiffness. This effect results in an approximately constant 

 torcjue about the roll axis of the missile for a given signal. The local loop 

 around the fin position also reduces the effect of any non-linear charac- 

 teristics of the valve. 



A third input to the servo amplifier is provided by a potentiometer 

 that is driven by a spring-restrained gyroscope mounted so that the 

 sensitive axis is aligned with the missile's roll axis. The dc signal pro- 

 duced is proportional to the roll rate. This signal provides some anticipa- 

 tion to the roll position loop. It performs the function of a tachometer in 

 a conventional servo. It also insures that the roll rate is limited to a 

 value that can be handled by the position loop. If very high roll rates 

 were allowed to exist, the roll amount gyro would produce a signal 

 changing in sign at such a rate that the ailerons would be unable to 

 keep up or reduce the rate. 



The roll servo insures that the missile's orientation is aligned with the 

 free-free gyro. This enables the yaw and pitch servos to steer about 

 their assigned axes in a consistent manner. The two steering servos are 



