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Aviation History
1932
1932 - 0625.PDF
FLIGHT, JUNE 24, 1932 here is the Napier engineers' interpretation of what such an engine should be. While the demand for cleaner design, and the meeting of that demand, results in increased performance, there is also a growing desire for more power. This is not neces sarily wanted for greater performance, but may be utilised for carrying a slightly greater load. For example, 120 h.p. or so has been found to suffice for a machine carrying three people. If a four-seater is to have sufficient power reserve, some 150 h.p. is needed, unless, of course, the aircraft in question is of quite exceptional aerodynamic efficiency. The Napier firm decided that on all these scores, and also because of the extra smoothness of run ning which the straight six-cylinder arrangement gives, their new type should have six cylinders. The new Napier E.97 engine is, then, a straight-six air- cooled inverted engine, the weight of which is 410 lb. and the normal power 150 b.h.p., which gives a specific weight, at normal power, of 2.73 lb./h.p. At full power the specific weight becomes 2.41 lb./h.p. Ultra lightness has not been sought in the design of the engine, but rather a very robust unit capable of running for very prolonged periods without needing overhauling. The first experi mental engine was, as recorded in FLIGHT several weeks ago, installed in a " Spartan " aeroplane, and in that machine this engine has now done 150 hours without giving any serious trouble and without needing more than the usual occasional attention. A photograph of the " Spartan " "light plane powered with the Napier E.97 engine was published in our issue of April 29, 1932, and showed how neatly the new engine can be built into an aircraft. The crankcase of the E.97 engine is a light metal alloy " box " with rounded sides and top, and shows in ternally six large webs, which carry the plain bearings for the six-throw crankshaft, the seventh bearing being situ ated in the end of the. crankcase. At the forward end of the crankcase is a combined journal and thrust ball bearing which takes the thrust of the airscrew. The cylinders, which have steel barrels screwed into the aluminium alloy heads, are bolted to the bottom of the crankcase by eight studs each, and have two " overhead " valves in each cylinder, operated by an " overhead " cam shaft which is housed in a completely enclosed casing. The camshaft is driven by vertical shaft at the rear end of the engine. The absence of push rods at the sides of the engine results in a very neat external appearance, and, as our photographs will show, the only excrescences on the engine are the Claudel-Hobson carburettors on the left- hand side. As these are placed low, it is a very easy matter for the aircraft designer, in most types at any rate, to provide for direct gravity feed from the petrol tank. The pistons, which are of the full skirted type, are of light aluminium alloy, and each is fitted with two com pression rings and two scraper rings. Hollow gudgeon pins of large diameter are used. All connecting rods are of H section, and machined from j11111111 111111111111111111111ii 11 ii 111111111111ii11111 40 tl •'' 111' 11' i 11 1111 ri 7ft 170 1700 ,5* 1900 2000' 2100 CRANKSHAFT SPEED R P.M. 2200 2300 THE NAPIER E.97 ENGINE : Power and Consumption Curves. solid steel forgings. The big ends are lined with white metal. The crankshaft is machined from a solid steel forging, and is of standard six-throw type, as shown in one of our photographs. It runs in plain bearings, except for the thrust bearing at the forward end. This is of the deep- groove ball-bearing type. Lubrication is by pressure pump to the main bearings and big ends, the pump being driven off the vertical drive shaft. At the forward end of the engine an oil tube joins rtMcmsJFL SOME DETAIL COMPONENTS OF THE E.97 : On the left a cylinder, piston, connecting rod and gudgeon pin ; on the right the crankcase and crankshaft. (FLIGHT Fhotos.) 577
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