GB742148A - Improvements in or relating to hydraulic variable pitch propellers - Google Patents

Abstract

742,148. Variable-pitch propellers. ROTOL, Ltd. July 6, 1954 [July 6, 1953], No. 18706/53. Class 114. In a hydraulic variable-pitch propeller in which the relative movement of the ram 17 and cylinder 18 of a pitch change motor to move the propeller blades 7 towards fine pitch is normally prevented by a stop and there is provided means operable by hydraulic fluid distinct from the fluid in the hydraulic system of the pitch change motor to break down said stop so that relative movement of the ram and cylinder beyond said stop is permitted to move the blades towards fine pitch when said means is operated, relative movement of the ram and cylinder to move the blades beyond fine pitch is also normally prevented by a stop which acts either as a superfine or a super-superfine pitch stop and a valve is provided which is operable when the pressure of fluid supplied to the fine pitch side of the pitch change motor is increased above a predetermined value to divert some of said fine pitch fluid to operate means for breaking down the second said stop. The two stops comprise a single element 20 carried on a spring finger 21 and are prevented from moving inwards by a member 23 carried by a member 26 the other end of which is a piston 26a sliding in a fixed cylindrical element 40. The member 26 abuts at 36 a partly hollow rod 34 having a piston 33 sliding in a cylinder 10 attached to the hub 18 and carrying a member 30 which on one side forms a chamber 35 at the rear of the piston 33 and on the other forms a seating for springs 31, 32 urging the member 26 against the abutment 36. The fine pitch fluid duct 15 surrounds the coarse pitch fluid duct 16 which has an abutment 44 against which a hollow valve member 42 is urged by a spring 43. During normal flight the pitch change range is limited at the fine pitch end by the stops 20 which are held in inoperative position on the a diameter of member 23 on member 26, as shown. When it is required to allow the blades of a carrier-borne aircraft to move into a superfine pitch, or in the case of a land-based aircraft into a super-superfine pitch, pressure fluid is admitted to the passage 27 (which may be an automatic operation on lowering the undercarriage). The fluid flows through passages 61, 62 and 34a via ports 37 and 38 into the chamber 35 whereupon the piston 33, rod 34 and member 26 together with member 23 are displaced together through a distance X to the left, allowing the stops 20 to spring inwardly on to the b diameter of member 23. Thus the lock between the shoulder 22a on the sleeve of the ram 17 and the stop 20 is broken, and fine pitch fluid delivered through the duct 15 moves the ram 17 to the left until the shoulder 22b contacts the stop 20. The blades 7 are then in a superfine position. When it is required to move them into a super-superfine position, or in the case of a land-based aircraft into reverse pitch, the pressure of fine pitch fluid in the duct 15 is increased, e.g. automatically when the undercarriage touches down, so that the fluid passing through ports 45 acts on the land 48 to move the valve 42 to the left against the spring 43, thus allowing the high fine pitch pressure to be transmitted via ports 46, 54, 55 and passage 56 into chamber 41 where it,acts on piston 26a against springs 31, 32 to move the member 26 still further to the left an amount Y. This permits the stops 20 to spring onto the diameter c, and the ram 17 is then free to move further to the left to shift the blades into the super-superfine or reverse pitch position.