AN ELECTRICALLY OPERATED HYDRAULIC CONTROL VALVE 



■35 



iioiilinearities, the fin position is controlled in strict accordance with the 

 summation of the input signals applied to the amplifier. 



The first design of the servo circuits was made by using the slopes and 

 magnitudes of typical and extreme points of operation as obtained 

 from Figs. 11 and 12. The design of the servo equalization networks 

 was obtained by successive refinements made during actual tests of the 

 complete servo systems. These tests were performed with the aid of 

 rather elaborate simulators that subjected the systems to the condi- 

 tions of actual flight. 



The characteristics of the valve and the amplifier which drives it, as 

 applied to a servomechanism, can best be illustrated by plotting gain and 

 phase shift versus fretjuency in an open loop. Fig. 19 is such a graph. 

 This information was gathered by applying an input signal to the servo 

 amplifier from an oscillator. The valve was driven by the amplifier in 

 the usual manner. The valve controlled the flow of oil to a piston which 

 operated a load that was equivalent to a typical aerodynamic load as 

 seen by the control surface. The voltage from the fin-position potenti- 

 ometer was compared to the amplifier input. Fig. 19 shows the phase and 

 amplitude comparison of these two voltages. A small amount of feedback 

 was used to prevent the piston from drifting to one end of the cylinder. 



40 



36 



32 



28 



-" 24 



m 



u 



S 20 



? 16 

 < 



o 



12 



-180 



-170 



-160 



ai 



LLI 



a. 



-150 O 



LU 



Q 



Z 

 -140 - 



-130 '^ 

 LD 

 If) 

 < 



-120 ? 



-110 



-100 



0.6 0.8 1.0 2 3 4 5 6 8 10 



FREQUENCY IN CYCLES PER SECOND 



20 



30 



- 90 



Fig. 19 — Frequencj- characteristics of J -7 valve. 



