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Aviation History
1921
1921 - 0754.PDF
A rear view of the 1,000 h.p. Napier " Cub," showing the arrangement of the 16 cylinders. NOVEMBER 17, 1021 In the high compression model (5-8 to i), the normal horse-power is 450, at 2,000 r.p.m., and in the low compression model (5 to I) it is 425 at the same r.p.m. The air screw is driven by spur reduction gear at 1,320 r.p.m. The weight of the engine dry, com- plete with airscrew-boss, carburettors, induc- tion pipes, and hand-starting gear, is approximately 900 lbs., giving a weight per h.p. of about 2 lbs. The petrol consump- tion at full load comes out at -48 lb. per b.h.p. hour and the oil consumption •028 lb. The cylinders, which have a bore and a stroke of 5J ins. and 5^ ins. respectively, are single units, with sheet steel applied water jackets. The cylinders are remarkable in that they are not of the usual barrel form with open top and cylinder heads, but nave closed tops or crowns which have four holes machined in them for receiving the valve seatings. The crowns of the cylinders are machined flat on the outside to receive a monobloc aluminium casting, which unites all four cylinders, and is, practically speak- ing, a common water-cooled cylinder head carrying inlet and exhaust manifolds and valve gear. The inlet manifold, it should be noted, is in the form of a simple trough- shaped tapered aluminium casting, bolted up to the common induction passage for all four cylinders in the head block. A duplex (N.S. 2) Claudel-Hobson carburettor supplies the vertical bank and the right-hand bank, the left-hand bank being supplied by a single (N.S. 1) carburettor of the same make. are run at half-throttle, giving a b.h.p. of approximately 325. Pilots, therefore, have a great reserve of power for any eventuality which might occur. One of the principal features of the " Lion " is the arrange- ment of its twelve cylinders. These are placed in three banks of four, the central bank vertical and the outer banks at 6o° to it. In this way a particularly short and stiff crank- shaft is employed and a good balance and smoothness of running is obtained, thus adding to the reliability of the engine and reducing wear and tear. This " broad arrow " arrange- ment also makes for an exceedingly compact and neat engine, the over-all length being only 4 ft. 9 ins., the height 3 ft. and the width 3 ft. 6 ins. *• 'i ^3 11 —*._- The overhead camshafts are driven by vertical shafts through bevel gearing from the crankshaft. The main driving bevel on the crankshaft engages direct with the vertical shaft bevels of the right and left-hand groups, but the vertical shaft bevel of the central group engages with a second bevel on the left-hand shaft. The two magnetos, oil pumps and the water pump are all driven from off this end of the crankshaft through a bevel-shaft (and skew gear for the oil pumps) extending below the vertical shaft gear. The crankshaft is supported on roller bearings except at the forward end, where it is mounted in a plain bearing housed in the metal of the reduction gear drum. The pistons are cast from a special aluminium alloy, and are very short: they are fitted with four rings. The gudgeon pins are hollow, and form the final oil-conduits to the cylinder walls. S H a H H H H The Napier ''Cub1' 1,000 h.p. H 16 - c y 1 . B water- cooled engine: This view, showing the reduc- t i o.n g e ar end, gives a very good idea of the "clean' ' design of this re- markable engine. I H i S 0 B m a a a a a a a H H B B 754
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