On few-parameter generic families of vector fields on the two-dimensional sphere

1,256,123. Fluid-pressure servomotor systems. BELL AEROSPACE CORP. March 10, 1969 [April 11, 1968], No.12415/69. Heading G3P. A redundant channel control system for a motor 11 consists of two-stage servo-valves 30, 40, 50 having separate supplies P 1 -P 3 and returns R 1 -R 3 and serving to supply respective fluid-pressure signals 16, 17, 56 to switch 15 whose operation is controlled by a unit 20 having three comparators each of which compares one of three monitor signals 34, 44, 54 and the associated return pressure R 1 -R 3 with one other of the signals and its return pressure. The comparator of Fig. 3, for example has pistons 101, 101 1 responsive respectively to the signals in lines 34, 35, and 44, 45. Signals 34, 44 indicate the positions of the second stage spools of valves 30, 40 whereas signals 35, 45 indicate the return pressures. When the algebraic sum of signals 34, 35, 44, 45 overcomes the bias of spring 107 or 107 1 , the pistons 101, 101 1 move to position spool 121. Upon failure of a servo-valve, the comparators act to remove the faulty servo-valve from the control loop. The output of the switch 15 controls the motor 11. Each servo-valve can have a first-stage flapper positioned by a torque-motor and the spool positions are monitored by auxiliary flappers. In a modified comparator, only one spring is used.