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Aviation History
1947
1947 - 1082.PDF
PRATT & WHITNEY WASP MAJ CAM RINGS TORQUEMETER AIRSCREW REDUCTION GEAR EXHAUST VALVE are not staggered in the same way as on the usual two-row engine, but the four cylinders of each of the seven fore - and - aft banks are arranged helically around the crankcase. permits the maximum quantity of cooling air to reach the barrels while creating the lowest cooling drag due to changes in direction #f flow, and it also makes for accessibility of sparking plugs, ignition harness, etc. Composition An exploded view of the engine would, from front to rear, reveal the main structural units to be: reduction gear, magneto section, five crankcase divisions (power section), supercharger, accessory drive casing and car- burettor. The reduction gear is of the sun-and-planet type. The airscrew shaft is carried in a plain lead- bronze bearing at the rear end, and at the front end a roller bearing and a deep-groove ball bearing absorb the radial and thrust loads. In the nose of the casing is the fully feathering, reversing, constant-speed unit. Provision is made for a torquemeter, the components of which are integral with the reduction gearing. The fixed or sun gear is located in its case by means of external helical splines on its periphery which engage TAPPETS with corresponding splines on the inside diameter of the casing. The direction of the splines is such that the driving torque transmitted through the pinions of the reduction gear train tends to force the fixed gear rear- wards. This pressure is counteracted through the medium of pistons housed within the fixed gear and operated by oil pressure. When the rearward thrust due to torque is balanced, oil pressure behind the piston .is transmitted through a diaphragm to a closed column of oil connected with the torquemeter pressure gauge in the cockpit, and the shaft horse-power under flight condi- tions may thus be determined. A cast magnesium case supports the seven interchange- able Scintilla magnetos and their drives. Each mag- neto provides dual ignition for the four cylinders behind it through short, screened leads which, with the mag- netos, are pressure ventilated. The five sections of the crankcase proper, all of which are substantially similar, are aluminium alloy forgings split at the centre line of each row of cylinders and held together with through bolts.
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