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Aviation History
1935
1935 - 0434.PDF
218 FLIGHT. FEBRUARY 28, l935 A NEW SMALL ENGINE The Cirrus "Minor" a 3,605 c.c. Four-in-line, Developing 70-80 b.h.p. THERE is undoubtedly a demand for small engines of about 70-80 h.p., particularly for the small two- or four-seater twin-engined machine, and it is only natural that firms specialising in four-in-line air-cooled engines should turn their attention to this market. Readers will remember that last year the Cirrus-Hermes Engineering Company left Croydon and was to a considerable extent re-formed, under the chairmanship of Mr. Robert Blackburn; large, modern and spacious works were erected at Brough, adjoining those of the Blackburn Aeroplane and Motor Company. Some little time before the move to Brough, Mr. C. S. Napier, younger son of the well-known aero engine designer of that name, joined the company as technical director, and one of the first things he did was to produce, in collabora tion with Mr. A. H. Caple, a very clean and eminently practical inertia engine- starter. Some time before that Mr. J>Japier himself had under construction a small aero engine of low power, and it is therefore not surprising to find that the first engine from the new factory is one of 70-80 h.p., called the Cirrus "Minor." In its general layout it follows previous Cirrus engines, in that it is a four- cylinder inverted air-cooled engine. The cylinders are interesting, as they have been designed to obviate the use of long studs to the cylinder heads; our sketch explains the method whereby the heads are bolted to the barrels. The barrels, which are machined from forg- mgs, are located in the crank case by spigots and secured by four short, stout bolts. The heads are Hiduminium alloy castings, and each one is clamped to the flange on its cylinder by eight studs, a gas- tight joint being maintained by laminated copper washers. The head itself forms one half of the valve-gear box, and has an Elektron cover forming an oil bath for the mechanism. The finning around the inlet and exhaust ports is so de signed that there is an air space between them. The valve mechanism itself is similar in most respects to that simple layout which has stood the test of time in the SPECIFICATION Type : Air-cooled four-in-line ; direct drive. Rotation: Left-hand tractor. Bore: 95 mm. Stroke : 127 mm. Capacity: 3,605 c.c. Normal b.h.p. : 70 at 2,200 r.p.m. Maximum b.h.p.: 80 at 2,400 r.p.m. Cruising r.p.m.: 2,200 Compression ratio: 6.4 :1. Weight; 210 lb. appro*. Fuel consumption (normal r.p.m.): .54 pt./h.p./hr. Fuel consumption (max. r.p.m.): .58 pt. per /h.p./hr. Oil consumption: .5 pt./nr. Oil pressure : 45-50 lb./sq. in. (25 lb./sq. in. minimum.) Oil in circulation : i gall. Overall length : 932 mm. Height: 641 mm. Width: 433 mm. Bearer feet bolt centres (front to rear): 402 mm. Bearer feet bolt centres (between front feet): 380 mm. Bearer feet bolt centres (between rear feet): 429 mm. The crank case of the Cirrus "Minor" with cover removed, showing the sturdy big-end bearings and the five main bear- ings ; there is also, of course, a thrust bearing. "Hermes Mark IV A" engines. Tie pistons, which each carry two compression rings and one scraper ring, are of the slipper type with fully floating gudgeon pins. The connecting rods are also of light alloy, being forged from Hiduminium and having white- metal bearings Particularly robust, the crankshaft is a steel forging and is carried in five plain bearings with a ball thrust bearing at the front end. The rear end carries a gear for (Left) This view of the " Minor indicates its small frontal area and shows the camshaft-drive casing, from the induction side. (Right) The eop*
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