Patent GB-499514-A (GB)
Title: Variable pitch propeller
IPC: B64C11/42
Filed: 1937-08-31
Abstract: 499,514. Screw propellers. MATTEUCCI, R. Aug. 31, 1937, No. 23833. Convention date, Aug. 31, 1936. [Class 114] A variable-pitch propeller with a pitch changing mechanism comprising a piston actuated by fluid pressure in opposition to a spring is provided with a fluid control unit with which are associated stop members limiting the upper and lower pitch settings for normal flying conditions and further means associated with the control for establishing at least one predetermined intermediate setting. In addition, an auxiliary fluid may be used for the purpose of setting the blades to negative pitch for braking or to infinite pitch for feathering. The control may be linked with the throttle control of the engine. The stop members may comprise mechanical units subject to centrifugal force which become inoperative when the engine is stopped. Each propeller blade 8 is mounted over a spigot 9 on the propeller boss and has an outer ring 11 to which is secured a weight 12, the moment of the centrifugal force of which is adapted to balance the moments of the torque and centrifugal force upon the blade. The sleeve 11 is also connected to a slider member 14 upon a piston-rod 15, the rod being connected to a piston 16 having an annular extension 16<1> adapted to move into a space at the end of the cylinder 1 formed between the cylinder and a flanged sleeve 24, this being for the purpose of cushioning the piston at this end of its stroke. A spring 23 is provided for moving the piston in one direction and to the other side fluid is supplied through ports in a sliding valve extension 25 which moves within a ported sleeve 34, the ports of which are coupled by pipe lines 35, 36 through a control distributer 37 with a supply pump 45. An extension of the valve chest 50 is connected by a pipe 38 with a chamber 40 having therein valves 67, 68, of which valve 68 controls the flow of fluid back to the chamber 4 and to the pump. Upon the piston-rod 15 is a carrier 15<1> adapted to bear against a buffer spring 22 at the outer end of the cylinder. The cover 17 of the cylinder has an internal annular member 21 and an annular cavity 21<1> with which engage pawl members 18 that are pivotally carried at 19 by the slider 14 and are under spring restraint 20. These members 18 constitute the mechanical stop for limiting the movement of the piston. The pump delivery pipe 46 has a byepass 48 with relief valve 47, and a side tube 49 leads from 46 to the chamber 40 through valve 67. The tube 49 is connected to the control 37 by a tube 52. A tube 59 leads past a valve 55 to a discharge tube 54 which is run back to the casing 4 or oil reservoir therein. A further auxiliary system using compressed air is provided. A supply tank 60 is coupled to a chamber 61 with valves 64, 65 in lines 72, 66. The line 66 passes to the valve 67 of chamber 43, and has a branch to a cylinder 69 containing a piston 70 which controls the valve 55. A further branch 75 is connected by a flexible tube 142 with a unit 77 coupled to the engine controls 100. The line 72 delivers to a cylinder 73, a piston thereon controlling the valve 68. The tubes 72, 75 are connected to valves 81 discharging to atmosphere which are coupled to the control rod 98 for manual actuation of the engine controls 100. The rod 98 is connected to a notched bar 94, the notches co-operating through a ball with notches in a quadrant 92 rigidly secured to the rocking lever 86 which controls the valves 64, 65 and which is movable by the lever 88. When the ball is opposite a notch in the bar 94 the quadrant 92 may be moved by the lever 88 ; in other positions the quadrant and bar are locked together except when the ball is in the notch in the quadrant. The hand-controlled elements are preferably connected to points on the joystick 101 of the aircraft, valve 51 being connected by cable 103 to a lever 106, the rocking lever 86 by cable 107 to a lever 110, and device 77 by cable 112 to a lever 113. The lever 110 is interconnected through a pawl 114 with a piston in a cylinder receiving compressed air when the wheel brakes are actuated. The parts as shown in Fig. 1 correspond to highpitch position of the blades and mean and low pitch positions are obtained with appropriate positioning of the distributer 37. To obtain a negative pitch, the auxiliary system is employed to initiate the act. By movement of the handle 88 valve 65 is opened which causes valve 67 to open and admit pressure to overcome the spring and force the main piston 16 to its extreme left, meanwhile the pressure on control piston 70 closes the valve 55 and the oil pump works up to a pressure corresponding to the rated pressure of safety valve 47, which value is higher than the air pressure, and oil then passes in to the cylinder 1 to maintain the piston 16. Simultaneously, air under pressure passes along tube 75 to the engine control device 77. If the engine ceases to function, the blades are first slowed by being given a negative pitch, and when the propeller stops, the " braking " function is released and the pawls 18 enter the recess 21<1> to hold the propeller in the infinite pitch or feathered position. The device 77 includes a cylinder 125 connected at 126, Fig. 16, with the levers 127. Inside is a piston 130 acting against a spring 129 and having a hollow rod 131 which communicates through the flexible tube with tube 75. The piston also has a solid rod 135 which is connected to the fuel control levers 100 and also by the cross-piece 136 and rods 137 with a collar 138. The latter is connected by rods with pistons 140 in cylinders open to the flexible tube 142. When air passes through the tubes 75, 142, the rods move to the right and the levers 100 are moved, since cylinder 125 is held by levers 127. The degree of movement depends upon the abutment of the collar 138 with a rotatable sleeve 143 or with pins 144 thereon, rotational setting of the sleeve being effected by cable 112. The timing of the slider valve 25 and sleeve 31 may be adjustable on assembly as by providing the sleeve with a number of ports which can be put into operable position by angular setting of the sleeve. In a modification, two groups of stop pawls 18 are provided, each group having different lengths, and there is connected to one group a lever for cutting them out of action, which lever is operated by the auxiliary system. In one construction, the central parts are all hollow or annular so that there is a clear opening along the axis for firing a projectile. As an alternative the piston is a compound one with two springs the two parts moving as one except for obtaining, infinite pitch when there results a lessening in length by the two parts telescoping under the influence of a pressure fluid.