781,368. Variable pitch propellers. GENERAL MOTORS CORPORATION. Jan. 24, 1956 [Feb. 3, 1955], No. 2275/56. Class 114. In a control system for a variable pitch propeller having blades mounted for rotation about their longitudinal axes and subject during propeller rotation to external twisting moment forces tending to rotate the blades to a predetermined pitch position, a control valve is operable to supply fluid, from a source under variable high pressure, to a motor which adjusts the blade pitch in opposition to the external forces and is also operable to supply fluid from a constant low pressure source to the motor to assist the external forces to adjust the blade pitch. A master gear 26, Fig. 1, formed with a cam slot 209 controlling a follow up movement, coordinates the pitch change of all the blades when the piston 15 is displaced by fluid pressure to vary the pitch through a helical spline mechanism. Fluid under high pressure, which enters a chamber 16 below the piston 15 to increase the pitch, traverses a pitch lock valve 27 from a passage 28 fed by pressure compensating valves 54<SP>1</SP>, 54 which permit free flow towards the chamber 16 and a restricted flow in the opposite direction. A passage 225 feeds these valves and is itself controlled by a solenoid-actuated valve 44, the solenoids being excited by an electronic speed governor, such as that described in Specification 765,771 [Group XXIX], operating wherever the speed deviates from that set by a hand lever 206. A passage 42 in which is a minimum pressure valve 41 connects the solenoid valve 44 with the high pressure side 36 of pumps 30, 31, 32 driven by the propeller. The actual pressure is controlled by a valve assembly 43 similar to that described in Specification 725,181 which also sets forth the pitch lock pilot valve 38. During normal operation the pitch is controlled by a governor valve assembly 45, and with the exception of the solenoid valve 44, the valves are subject to centrifugal force as the propeller rotates. Increased pitch is effected by the high pressure fluid working at about 3600 lbs. per square inch ; decreasing results from the natural tendency of the blade aided by low pressure fluid at about 400 lbs. per square inch, provided by pressure reducing valve 39 for actuating the valves. A low pressure passage 49 leads from the valve 39 to a passage 66, Fig. 3, in the governor valve assembly 45 and communicating with an annular chamber 126 open to an annular groove in a sleeve 132 having a closed end 133. In Fig. 3 the valve assembly 45 is viewed from the opposite side to that of Fig. 1. The sleeve 132 slides in a stationary ported sleeve 121 and over a fixed piston 141, the arrangement providing a chamber 145 below and a smaller chamber 144 within the sleeve 132. In the governor controlled range, an increase in centrifugal force consequent upon increased speed lifts a plunger 87 in the governor valve assembly 45 and opens the chamber 145 to exhaust permitting fluid at low pressure in the smaller chamber 144 to move the sleeve 132 downwardly to connect the high pressure passages 42 and 225 independently of the solenoid valve 44 and restrictor valve 54. The plunger 87 moves in a follow-up sleeve 68 connected at its upper end to a lever 86 of which the other end is pivoted to the sleeve 132 so that the downward movement of the sleeve 132 lifts the follow-up sleeve 68 cutting off the supply to the chamber 144. On reverse movement of the plunger 87, it increases the pressure in the chamber 145 and opens the chamber 16 to exhaust through the compensating valve 54. Fluid at a very low pressure then effect the decrease in pitch. The rise of the plunger 87 lifts one end of a lever 96 pivoted to it, against the action of a spring 102, the lever turning about a pivot 97. A stationary control ring 171, Fig. 4, surrounding the propeller hub has an offset annular tang 170, engaging a shoe 165 supported by a carriage 98 which is thus reciprocated to produce a mechanical jitter in the lever 96 as its pivot 97 rolls on the carriage 98. The lever 96 reacts on the plunger 87 causing variable release of the pressure in the chamber 145. In addition, a pivoted arm 152 rolls on a fixed cam surface 155 as the propeller rotates and reciprocates a piston valve 148 to produce fluctuating pressure in the chamber 145. If the propeller overruns the engine, a solenoid 174 moves the ring 171 until a roller 172 on the carriage 98 engages an incline 173 on the lever 96 to rock it clockwise, Fig. 4, and lift the plunger 87 and permit high pressure fluid to feather the blades automatical. ly. Feathering may be effected manually by setting the lever 206 at F. This switches on an electric feathering pump 254 and moves a stationary control ring 204 surrounding the hub to displace to the left, Fig. 1, a carriage 188 linked to one end 186 of a floating lever 184 ; the other end 185 of the lever is linked by a rod 205 to the cam slot 209 in the master gear 26. The end 185 being held by the rod and cam, the centre pivot 183 of the lever moves to the left engaging the underside of the lever 96 to lift the plunger 87 and increase the pitch. With the control lever 206 set in the negative pitch position N, a rotary valve 50 opens a path for the low pressure fluid to a chamber 109 above the upper abutment of the spring 102 to increase the tension of the spring and its resistance to the centrifugal force tending to raise the plunger 87, the lever 96 being held against the roller 180. Specification 724,855 also is referred to.