Patent GB-833470-A (GB)
Title: Improvements in or relating to variable pitch airserews
Inventor: GODDEN THOMAS EDWARD
IPC: B64C11/38
Filed: 1956-12-07
Abstract: 833,470. Variable pitch airscrews. ROTOL Ltd. March 7, 1958 [Dec. 7, 1956], No. 37526/56. Class 114. In an airscrew having a pitch change motor comprising a ram 17 movable by hydraulic fluid in a cylinder 18 to adjust the pitch of the blades 12, and mechanical locking mechanism 22 to lock the ram against movement corresponding to movement of the blades in the pitch fining direction into fine pitch, the locking mechanism is normally maintained in an inoperative state at least during controlled pitch changing movements of the blades in the pitch fining direction, but changes automatically to an operative state both on such release of the fluid pressure supply to the pitch change motor that the blades would during operation of the airscrew tend to move uncontrolled in the pitch fining direction, and on attainment by the airscrew of a speed in excess of a predetermined speed. Fig. 1 shows the ram 17 at the coarse pitch end of its movement with the blades 12 feathered. To move the blades into normal pitch change range, fine pitch fluid is supplied through channel 42, annular chamber 43 and ports 44 to rearward side of ram 17 to move the ram forward thereby moving the blades in the pitch fining direction, the hydraulic fluid on the forward side of the ram exhausting through a gap 31, the clearance between the fingers 23 carrying the stops 22, ports 142 in a sleeve 83, annular chamber 41, passage 40, circumferential groove 106 in a lock valve member 100, and channel 39. The fine pitch fluid is also supplied through channels 140, 141 to groove 139 and ports 138 in a sleeve 112, thence to groove 116a in a control valve 115 and via ports 131, groove 136, and channels 130 to chamber 69 to rear of a jack piston 65, displacing the latter to the left until a flange 67 thereon displaces a ring 25 against the action of a spring 81 to bring the diameter 27 of the ring 25 radially within the inwardly projecting parts of stops 22. The ram 17 has a sleeve 32 with grooves 38, the shoulders of which click over formations 24 on the stops 22 as the ram continues to move in the pitch fining direction until the step 37 engages the stops 22, this engagement constituting the fine pitch stop. To release this latter stop (to move the blades into a super fine, or even reverse, pitch) fluid under pressure is supplied to oilway 45, from whence it is conveyed to grooves 79, ports 78 and chamber 76 where it displaces a piston 72 to the left so that a flange 71a on the rear thereof moves the ring 25 to bring its diameter 28 radially within the inwardly projecting parts of the stops 22. The step 37 forces the stops 22 on to diameter 28 and passes over the stops under the action of the fine pitch fluid acting on the rearward side of the ram. When a predetermined speed is exceeded, flyweights 124 overcome the load in springs 128 and 122 and displace valve 115 rearwardly to abut stop 114 so that the chamber 69 to the rear of the jack piston 65 communicates with a drain channel 50 via channels 130, grooves 136, ports 131, inside of sleeve 112, bore of stem 117 and chamber 49. Spring 81 is therefore able to move ring 25 and jack piston 65 rearwardly so that the stops 22 are held out in the path of the sleeve 32. Upon any kind of failure of the fine pitch fluid pressure resulting in a fall of pressure in the fine pitch fluid channel 42 and hence on the rear of valve 100, a spring 127 is able to displace valve 100 rearwardly to its closed position thus closing the channel 40 and trapping the hydraulic fluid on the forward side of the ram 17 thereby preventing the blades from moving in the pitch fining direction. The blades may however be feathered if desired by the feathering pump supplying fluid to channel 39, thence via groove 106 in valve 100, a non- return valve 111, chamber 41, ports 142 and gap 31 to the forward side of ram 17. Specification 775,780 is referred to.