Patent GB-545520-A (GB)
Title: Improvements in or relating to adjustable propellers
IPC: B64C11/34
Filed: 1940-06-08
Abstract: 545,520. Variable pitch propellers. BLANCHARD, W. J., and MACNEIL, C. S. J. June 8, 1940, No. 10060. Convention date, June 16.1939. [Class 114] In a variable-pitch propeller, each blade 20 has a hollow root portion 21 retained in rotatably adjustable position against centrifugal force in a socket 13 by means of a threaded clamping ring 22 bearing against ball bearings 23 which are secured in position by a retaining nut 24 which is adjusted by a locking member 25. Pinned fast to the hub 12 is a stationary sleeve 30 carrying packing 35 for the fluid sealing of the tubular piston rod 36 of a weighted piston head 43. Helical spline teeth 40 of small lead on the outer periphery of the sleeve 30 co-operate with similar teeth 42 on the inner periphery of a skirt 41 on the piston 43. The latter operates in a cylinder 47 having a closed outer end 48 and a flanged inner end 49 pinned at 50 to the blade root 21. The outer periphery of the skirt 41 is provided with helical spline teeth 55 of greater lead than the teeth 40, 42 to co-operate with similar teeth 56 on the inner periphery of a floating spline member 57. The outer periphery of the spline member 57 is provided with helical spline teeth 58 with a lead comparable with that of the teeth 40, 42 to co-operate with similar teeth 59 on the inner periphery of the cylinder 47. Pressure fluid may be supplied by the outer passage 73 of a regulator 70 secured to the hollow drive shaft 10, the passage 73 being selectively connected to either one of two inner concentric passages 71, 72. Fluid from passage 71 passes through a recess 77 in socket 13, the bore 76 of a nut 75, the interior of the sleeve 30, and the piston rod 36 into space 81 to move the piston 43 inwardly. Fluid from passage 72 passes through a tube 88, a passage 85 (not shown) through the space of one of the dowel pins 31, an annular space 86 located between the sleeve 30 and the cylinder 47, and containing the spline teeth which thereby become lubricated, an annular space 90, and apertures 62 in the skirt 41 into space 91 to move the piston 42 outwardly. During this outward movement the spline teeth 40, 42 rotate the skirt 41 and this tends to rotate the teeth 55, 56 and 58, 59. The teeth 58, 59 being of smaller pitch than the teeth 55, 56 offer less resistance, and the initial movement takes place between teeth 58, 59 alone. By this means the cylinder 47 rotates relatively slowly with a movement which is the sum of those caused by the teeth 40, 42 and 58, 59 over an extended distance which is within substantially the normal working range of the blade and is accurately controlled within this range. With continued outward movement of the piston 43 a nose 65 on the floating spline member 57 engages a projection 64 on the cylinder 47, further outward movement of the spline member is prevented, and the cylinder 47 is rotated more rapidly into a fully feathered position of the blade, this movement being the sum of those produced by the teeth 40, 42 and 55, 56. For reducing the pitch a reverse operation takes place, this time the spline member 57 being moved by a nose 63 on the sleeve 41. The weight of the piston assembly is so chosen as to substantially balance the centrifugal blade torque at a blade angle of about 40 degrees. The Specification as open to inspection under Sect. 91 states also that the fluid pressure may be used to move the blades in one direction only, the movement in the opposite direction being effected by overbalancing or underbalancing the weight of the piston assembly. This subject-matter does not appear in the Specification as accepted.