680,482. Synchronized claw clutches; epicyclic gear. UNITED AIRCRAFT CORPORATION. May 11, 1950 [May 21, 1949], No. 11767 / 50. Classes 80 (i) and 80 (ii). [Also in Groups XXVI, XXIX and XXXIII] A toothed clutch 50, 54, between each of a number of parallel engine-shafts 5, 6, of multiple power-plant and freely mounted pinions 11 driving a common wheel 16 on the single-parallel shaft 18, Fig. 2, of a contrarotating aircraft propeller, has a fluid-coupling 60, 96, Fig. 3, which is filled only for synchronising the toothed clutch, and a positive balk 140, 106 for preventing asynchronous engagement. The axially-fixed driven clutch-member 54 forms 'part of the impeller 60 of the fluidcoupling, which is splined to the driven pinion 11, whilst the axially movable clutch-member 50 slides on the input shaft 5 on splines 102, which also carry a ring 98 having external teeth 104 engaging with limited circumferential clearance in axial slots 106 in an extension balk-sleeve of the freely-mounted turbine 96 of the fluid-coupling. With the fluid-coupling filled, as described below, for synchronizing, and transmitting torque with slip, the said torque causes the ring 98 to turn in opposition to centralising springs 146, Fig. 4, until its teeth 104 are at one end of the slots 106, taking with it the sliding clutch-member 50, rightward engaging movement of which is then prevented by butting engagement of balk-teeth 140 on the clutchmember 50 against the ends of the slots 106. Under synchronous conditions, absence of torque on the fluid-coupling causes the springs 146 to centralise the ring-teeth 104 in the slots 106 which latter then permit entry (without circumferential clearance) of the balk-teeth 140, to free the clutch-member 50 for engagement. Control is hydraulic and procedure for clutch engagement, either for driving the running gear-wheel 16 from an engine shaft 5, or for driving the shaft 5 from the running wheel 16 for starting an engine, is to turn a rotary valve 110, Fig. 3, the initial movement of which supplies pressure-oil through a duct 116 to fill the fluid-coupling, which then transmits full-load torque with slip which diminishes (but does not vanish) as synchronism approaches. This torque moves the slots 106 to balk position, as above described, so that when, during further movement of the control-valve 110 through half its extreme range, oil pressure is directed to the left faces of a group of clutch-actuating pistons 68, the latter move the clutch-member 50 axially to the balk position, and then compress clutchloading springs 78. With the engine shaft 5 driving, when the fluid-coupling attains minimum slip, the operator decelerates the engineshaft 5, the consequent initial overrun producing synchronism as the torque on the fluid-coupling vanishes, whereupon the springs 146 release the balk-slots 106 to permit full engagement of the positive clutch-member 50 with the driven teeth 54, under axial spring-load. The controlvalve 110 is then turned to the limit of its stroke, cutting off the supply to the fluid-coupling, which drains through holes 130, the clutchpistons 68 remaining. under pressure. For clutch-disengagement, the valve 110 is turned fully back to its original position to supply pressure-oil to the right faces of the pistons 68 which disengage the clutch through the springs 78 when torque-load is taken off the clutch teeth 50, 54 by the operator decelerating the engineshaft 5. To prevent overheating of the fluid coupling a valve 158, carried on a stem 156 of high thermal expansion coefficient, opens automatically to relieve the coupling above a predetermined temperature. The contra-rotating propeller drive comprises an input sun 24, Fig. 2, fast on the propeller shaft 18; planets 26 on a carrier 28 fast to an outer sleeve 35 carrying one propeller; a ring- gear 32 fast on an inner sleeve 36 carrying the other; and a reaction ring 42 meshing smaller planet-steps 38, to ensure fixed-proportioned opposite rotation of the propellers. Only one of the engines need have a starter, the others being started from it through their clutches.