Patent GB-724284-A (GB)
Title: Improvements in or relating to variable pitch propellers
IPC: B64C11/42
Filed: 1952-10-09
Abstract: 724,284. Variable-pitch propellers. UNITED AIRCRAFT CORPORATION. Oct. 9, 1952 [March 6, 1952], No. 25308/52. Class 114. Pitch-changing mechanism for a propeller having variablepitch blades and movable pitch-changing control mechanism for the blades is characterized by lock means interconnecting the mechanism and the propeller hub for preventing pitch-changing movement in a low-pitch direction only, pressure means holding the lock means in unlocked position and means for disabling the holding means comprising a speed-sensitive device operatively connected to the holding means. An annular lock element 76, Fig. 1, is fixed to a blade inter-connecting gear 26 and rotating cam-portion 28 of the pitch-changing mechanism while a second lock element 80 is splined indirectly to the hub 10. Adjacent faces of the elements 76, 80 have ratchet teeth 84, Fig. 3, which permit relative movement towards high pitch but prevent it towards low pitch. Co-operating cam elements 86, 88 disengage the elements 76, 80 in certain ranges such as feathering and reversing. Disengagement is also effected by introduction of high pressure fluid through lines 70, 72 to a chamber 74 in the hub 10 between the elements, whereupon the element 76 is forced to the right against springs 78. The hydraulic circuit controlling the pitch-change and pitch-lock mechanisms is shown in Fig. 4. Fluid is pumped at high pressure from a sump 104 through a manifold 116 to a line 118 whence it passes round a valve member 122 to a line 42 on movement of the member 122 upwards from the position of Fig. 4 by a governor 126 as the result of increased engine speed. From line 42 the fluid impinges on the right of piston 32 (on the left in Fig. 1) to bring about rotation of cam 28 and gear 26 in the sense to increase propeller pitch. A land 176 is provided on the valve member 122 so that when the latter has moved upward a predetermined amount, such position corresponding to a continuing predetermined overspeed condition, the pitch lock line 70 will be disconnected from its source of pressure, line'170, and connected via line 180 to an atmospheric sump 100. Chamber 74 now being at atmospheric pressure the pitch lock engages, thus preventing change to lower pitch but permitting any automatic movement to higher pitch. When, on a reduction in speed, valve member 122 is moved down by the governor, fluid from line 42 drains via valve 161 and lower chamber 160 of a pitch lock valve 130 to sump 104. The chamber 160 is also supplied with fluid from the manifold 116 via a by-pass valve 150, the resulting pressure raising the valve member 162 to the position shown against the combined pressures of the sump 104 and a spring 164. By the downward movement of member 122 land 176 shuts off communication between the chamber 74 and the atmospheric sump 100 and permits the pressure in chamber 160 to be communicated to chamber 74 by lines 170 and 70, the pitch lock thus being held open to permit change to lower pitch. At the same time the member 122 has placed line 118 in communication with line 128 so that pressure fluid flows around valve member 162 to space 204, forcing piston 134 to the right and passing along groove 144 and line 44 to the region on the left (Fig. 4) of the piston 32, moving it to effect a reduction in pitch. Piston 134 now interrupts communication between 44 and sump 104. A manually-operated solenoid valve 220 may be provided for disconnecting line 70 and port 172 (and thus chamber 74) from the pressure line 170 and connecting it to the sump 100 to permit the pitch lock to engage. The cam 28 and related parts, Fig. 1, are described in Specifications 505,077 and 514,725. The purpose of a sleeve 38 over which piston 32 slides, is described in Specification 700,394.