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Aviation History
1919
1919 - 0431.PDF
APRIL 3, 1919 bombing aeroplane, while the Bristol Triplane used four of these engines two in tandem on each side of the pilot. Some Engine Test Results The Puma engine has been subject to many remarkable trials on the test bench, in addition to its work in the air. At the R.A.E. a Puma engine, taken at random, was run for 180 hours with no involuntary stops. Power curves taken at the beginning and the end of the run were practically- indistinguishable. The average power maintained through out this period was 249 b.p., and the rate of revolution 1,600- 1,700 per minute. In the Siddeley Works similar engine tests have been carried out, and the test recorded at the Aircraft Establishment is by no means exceptional. The petrol consumption on test varies slightly with the carburettor setting, but a consumption of 55 pints per horse power can always be obtained at about nine-tenths power. Hf 26* On^absolute maximum power the consumption is a trifle above this. The oil consumption in the air is generally about 1 gallon per hour, varying somewhat according to the temperature. Leading Particulars of the Puma Engine No of cylinders, 6. Bore, 145 mm. Stroke, 190 mm, B.H.P. at 1,500 rp.m., 260. B.H.P. at 1,700 r.p.m., 290. Petrol consumption, .55 to .6 pt. Oil consumption, .03 to .045 pt. Weight dry, 630. Compression ratio, 5.4 to I. Length over all, 1,775 mm.—70 in. Height over all, 1,108 mm.—44 in. Width over all, 612 mm.—24 in. Bearer centres, 436 mm.—17J- in. THE " TIGER' TOWARDS the end of the year 1917 the need for bombing aeroplanes of larger power was realised by the R.A.F. ; as a consequence the demands for engines of greater horse power became urgent. At the beginning of the year 1918 the Siddeley Co. were asked to undertake the design and manufacture of an engine to give at least 600 h.p. In view of the success of the Puma engine it was decided to continue the use of aluminium cylinder heads, and for the large power required, a 12-cylinder engine was adopted. The Tiger engine has run for a large number of hours on experimental tests. The results given have been very encouraging, the horse-power that could be maintained continuously being as high as 650, while rather greater horse power can be given for short periods. A fresh series of engines is now under construction, in which various small improve ments suggested by tests have been made, and the makers feel so confident of the engine that they are prepared to guarantee a continuous horse-power of 650 from every engine. General Description The Tiger engine has two lines of six cylinders, inclined at an angle of 60 deg. Each cylinder is 160 mm. bore by 180 mm. stroke, and 15 a separate unit. The valves are in the cylinder heads, and are worked by two overhead camshafts. The object of the designers has been to make a robust engine with the absence of small parts, which will be able to run for long periods without requiring overhauling. As the engine was intended for use on aeroplanes making long-dis tance journeys into Germany, extreme reliability i s essential and to determine this, very long duration trials have already- been carried out. Cylinder Construction The cylinder construction is similar to the Puma engine. but in this case the cylinders are separate units and are fitted with four valves instead of three. The valves are worked by an overhead camshaft through rocking levers. The cylinder head and water jacket are cast in one piece, and the cylinder is completed by a steel liner which is screwed and shrunk into the cylinder head. The valve seats are of special bronze alloy, and are ex panded into the cylinder head, after which they are machined into position. Each line of six cylinders has an overhead camshaft working the two exhaust and the two inlet valves on each cylinder. The camshaft can be slid axially so as to introduce a special set of cams which form a half com pression device, thus making the engine very much easier to start. Pistons and Connecting Rods The pistons are made of die-cast aluminium alloy, fitted with cast iron rings. The gudgeon pin floats both in the piston and in the connecting rod, and is held from moving sideways in the piston by means of expanding .steel rings. The connecting rods are tubular. The rods on one side are forked, and are clamped to the bush surrounding the crankpin, while those on the other side take a bearing on the bush between the fork of the corresponding rod. THE SIDDELEY "TIGER" AERO ENGINE.—Side view 431 II
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