Patent GB-607321-A (GB)
Title: Improvements in or relating to means for actuating poweroperated control surfaces and the like
IPC: B64C13/24
Filed: 1946-01-24
Abstract: 607,321. Fluid-pressure servomotors. FAIREY AVIATION CO., Ltd., and CHURN, C. R. Jan. 24, 1946, No. 2392. [Class 135] A hydraulic servomotor for actuating the control surfaces of boats and aircraft has a reaction piston within the usual jack piston and the pilot's control is connected directly with the servo - control valve and through a lost-motion connection with the reaction piston, fluid pressure admitted to the jack acting in the opposite direction against the reaction piston to produce a sense of "feel " at the pilot's control. Fig. 1 shows a piston 12 with hollow stems 13, 14, movable in a cylinder 10 anchored to the aircraft. The cylinder chambers 20, 21 communicate with the hollow stems through passages 16, 17 opening into chambers 18, 19 formed between the inside of the stems and a reaction piston 22 slidable in the piston 12. The stem 14 is connected to the control surface by a rod 15. The reaction piston 22 has three lands 22a, 26, 25, the space between the two latter forming a gallery 28 connected to the chamber 19 by a passage 29 and ports 30, 31. The stem 13 carries a servo-control valve 32 by which ports 36, 37 and hence the two cylinder chambers 20, 21 and the reaction piston chambers 18, 19 are placed selectively in communication with a hydraulic pressure inlet 35 or an exhaust port 35a. The valve piston 33 is connected by a link 39 with the pilot's control rod 38. The link 39 is formed in part as a sleeve sliding on a stem 42 of the reaction piston and having a pin-and-slot connection 40, 41 therewith. On operation of the piston 33 by the pilot's rod 38, pressure is admitted to one of the chambers 20, 21 and simultaneously to one of the chambers 18, 19 where it acts in the opposite direction on the reaction piston which takes up the lost motion at the slot 40 and exerts on the pilot's control a reaction proportioned to the force on the piston 12, the proportion depending upon the relative areas of the piston faces. In a modification (Fig. 2, not shown), the movement of the land 22a is limited by the piston 12 and by an internal flange in the stem 14 so that if the hydraulic pressure fails the pilot's control first takes up the lost motion at the slot 40 and then that between the reaction piston and the piston 12 so as to operate the control surface directly. The lost motion between the slot 40 and the pin 41 can be dispensed with by rotating the stem 42 so that the pin 41 engages a recess 40a, Fig. 1. In another modification (Fig. 3, not shown), the reaction piston has only one land and is slidable in a chamber in the free end of the stem 13. The two parts into which the chamber is divided by the land or piston are selectively connected to pressure and exhaust as also through flexible pipes, are the cylinder chambers 20, 21. Rings on the stem of the reaction piston inside and outside its operating chamber limit its movement relative to the main piston and permit of direct manual operation if the hydraulic pressure fails. Fig. 4 shows an arrangement in which the power cylinder 10 of the servomotor already described is normally locked in an anchorage 56, but is released therefrom to permit of its axial movement and hence of direct manual operation of the control surface if the hydraulic pressure fails. The anchorage 56 has a chamber 57 containing an annular spring-pressed locking piston 58, Fig. 6, normally exposed to the hydraulic pressure through a passage 60. The piston 58 has ramps 69, Fig. 7, adapted to depress outwardly springing jaws 68 on a collet 67 into an annular groove 61 in the power cylinder. When the jaws 68 are released, and the cylinder 10 is moved axially, a roller 66 is forced out of the groove 61 and a piston valve 62 cuts off the passage 60 from the hydraulic pressure supply 46.