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Aviation History
1943
1943 - 0391.PDF
FEBRUARY IITH, 1943 FLIGHT WRIGHT DOUBLE-ROW CYCLONE alloy casting. This section holds the thrust bearing and houses the airscrew speed reduction gears, which give either 16: 9 or 3: 2 reduction ratios. To provide outlets for the 14 pipes to the cylinder intake ports the supercharger front housing has been enlarged. In addition to acting as the front wall of the diffuser cham- ber, this section is provided with seven mounting bosses designed for use with rubber mounting blocks or the Wright Dynamic Suspension mounting. The accessory drive section forms a mounting for the diffuser plate, holds the impellor and impellor drive shafts, and houses the self-turning Cuno oil filter, two gun syn- chroniser drives, fuel pump and two tachometer drives. The down-draught carburettor is mounted on this section, which also forms the induction passages to the impellor. The rear cover plate for mounting of the other accessories is a magnesium alloy casting similar in most respects to that used for the single-row Cyclone. On this plate are pads for the two magnetos, generator, starter, oil pump and spare accessory drive. It also forms the support for the shafts and gears of these drives. To realise the inherent advantages of single-piece master connecting rods, the crankshaft is designed in three pieces to permit the use of such rods. The three pieces are clamped together with the centre section, consisting of the two crankpins at 180 deg. from each other, with a journal for the centre main roller bearings. The entire shaft is hollow throughout to provide passage for the central oil supply, each crankpin being drilled for two oil outlets to the bearing. This makes an oil cleaning centrifuge of the crankpin chamber. A flat machined on each crankpin carries the oil out along the bearing surface. The rear of the crankshaft has an internally splined extension for inser- tion of the accessory drive and starter shaft. Counterweights of the crankshaft incorporate the Wright Dynamic Damper, eliminating the effects of torsional vibration on the engine and airscrew. Reduction Gearing - The 50-spline (S.A.E.) airscrew shaft is machined from,an alloy steel forging and is hollow throughout its length. It is supported by two steel-backed copper-lead bushingsrunning on the front of the crankshaft, on which is mounted the thrust bearing. The rear of the shaft is forged into asix-legged spider, each leg supporting one of the pinions used in the airscrew speed reduction system. The shaft isdrilled to provide lubrication channels to these pinion bear- ings. The planetary reduction gear is essentially the sameas used on previous Cyclones. Machined from alloy steel forgings, the one-piece masterrods differ in appearance from single-row rods mainly in that each accommodates only six articulated rods insteadof eight. The shank is an H section, the flanges of which are a continuation of the flanges at the channel at thecrankpin end. The steel-backed copper-lead crankpin bear- ings are a shrink fit into the bore of the master rod. Theshells are dowelled into place, with six oil holes in each bearing supplying oil from this bearing out through the rodto the knuckle pins. The articulated rods are I sections, also machined from alloy steel forgings. The split bronzeknuckle and piston pin bushings are pressed into the rods and the ends spun over. Knuckle pins are nitralloy steel, with their nitrided sur-faces given a micro-finish. The pins are a press fit into the master rod, and are secured by a flange at one endand locking plates at the other. Tile pistons are full trunk type aluminium alloy forgings,the heads strengthened and cooled internally by ribbing. Five ring grooves are used, four above the gudgeon pinand one in the skirt.. A single compression ring fits in each of the three grooves nearest the top of the piston, with twovented oil control rings in the fourth groove and an oil scraper ring in the bottom groove. The oil ring groovesare drilled to permit drainage into the piston interior. The Wright Cyclone Model C14A. The large carburettor :S anon-icing Chandler-Groves, and ignition is by two Scintilla magnetos. Two valve-operating cams are fitted, each of which issupported on journals mounted on the front and rear of the main crankcase. Each cam is an alloy steel forginghaving two sets of cam lobes which are given a micro-finish. The cams are driven through intermediate gears from twogears, one integral with the airscrew reduction drive gear, and the other attached to the rear end of the crankshaft.Both cams rotate at one-sixth crankshaft speed in a counter- crankshaft direction. The cams actuate the valves by apush-rod and rocker-arm system, which incorporates drilled pasages to provide fully internal automatic valve gearlubrication. A solid intake valve and a hollow exhaust valve partially filled with sodium follow the usual Cyclonepractice. A single supercharger impellor is used, driven by inter-mediate gears from the accessory drive shaft. The con- ventional intermediate gears may be replaced b)' the Wrighttwo-speed supercharger drive, giving the same "sea-level performances and greatly increased power output at highaltitudes. The supercharger drive ratio is 7.00:1, 7.40:1, or 7.14:1 and 10.00:1, depending on the model.. Curvedintake pipes lead out radially from the diffuser chamber to the cylinders. Lubrication System The lubrication system is of the full-pressure type to allsurfaces except the cylinder walls and piston pins. These are lubricated by oil sprayed from the main crankpin bear-:ings. A single housing on the rear of the engine contains both the pressure and scavenge pumps. All engine oildrains to a sump at the bottom of the engine, directly behind the lower front cylinder, whence it is removedby the scavenge pump and returned to the external oil supply. Non-icing carbuiation is provided by a large Chandler-Groves type carburettor, similar in design to those used on the G-100 Series Cyclones. Ignition is supplied by twoScintilla magnetos through Breeze shielded ignition cables. Drives for all accessories and flight instruments are virtu-ally identical with those of previous Cyclones. It may be seen from the above description that thedouble-row Cyclone 14 cannot be considered a new engine except when taken as a whole. Behind its component partsis the experience of the single-row Cyclone, a background which explains its immediate acceptance. Recent ordersby the U.S. Army Air Corps have brought the engine to the forefront as a dominant American military type, a posi-tion long held by its single-row predecessor.
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