GB791620A - Improvements in or relating to fluid pressure operated actuators for flying control surfaces and the like - Google Patents

Abstract

791,620. Hydraulic jacks; fluid-pressure servomotor-control systems. BRITISH MESSIER, Ltd. Sept. 30, 1955 [Oct. 7, 1954], No. 28952/54. Classes 69 (2) and 135. [Also in Group XXVIII] An hydraulic jack for controlling an allmoving aircraft tailplane has screw means associated with the jack piston which are braked in order to lock the piston in any assumed position relative to its cylinder, and is provided with means for progressively decreasing the braking on application of pressure to the jack. A jack piston 18 is secured to the airframe and a jack cylinder 15 is provided in a casing 11 pivotally connected to the tailplane 13. A rotatable rod 27 having a screw connection with the piston is formed with a head 30 forming one part of a friction clutch, the other part 31 of which is non-rotatable and is urged into engagement with the head 30 by a spring 38, being disengaged by fluid pressure acting on the annular face of a piston 37 disposed in a clutch control cylinder 36. On manually moving a distributing valve 44 to either side of the neutral position shown, liquid is supplied from an inlet 67 to one side or the other of the jack piston 18, and also, through a duct 65 to the clutch control cylinder 36 to act on the piston 37. A bleed passage 39 passes from the left-hand chamber of the cylinder 36, through the piston to the right-hand chamber which is connected to exhaust through a fixed restriction 81. The left-hand chamber is also connected through a fixed restriction 85 to a port 82 of a clutch control valve 70, and thence around a reduced part of the valve to an exhaust duct 78. As pressure builds up on either side of the jack piston 18 it acts through a duct 76 or 77 on an extension 74 or a land 72 of the valve 70 and moves it to the right against the pressure of a spring 71. Port 82 is thus gradually closed and pressure builds up in the clutch control cylinder 36 to disengage the clutch. The housing of valve 44 is provided in the moving casing 11 thus producing a follow-up action for re-centring the valve.