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Aviation History
1930
UNTITLED0 - 0072.PDF
FLIGHT, JANUARY 3, 1930 figure, but was probably between 0-7 and 0-8 ipint per h.p./hour. The weight of an engine depends to a considerable degree on the arrangement and number of cylinders. The Gnome engine had its seven cylinders arranged radially and in order to ensure cooling the cylinders rotated while the crankshaft was stationary. A disadvantage of the engine was chiefly that its rotational speed was limited by the centrifugal stresses set up in the cylinders. In spite of this, the rotarv engine remained popular for a number of years. The horse- power increased by easy stages up to the BR/2 engine of 200 h.p., which did good service in the latter part of the great war. Since then the rotary engine seems to have been entirely abandoned in favour of the fixed, radial engine. Another early engine which •came into use very soon after the 50 h.p. Gnome was the 60 h.p. Renault. This was an air-cooled engine, but with 8 cylinders in Vee driving a 4-throw crankshaft. The engine had cast-iron cylinders and was rather heavily constructed, but it had the advantage of running at 1,800 r.p.m. and working at a brake mean effective pressure •of 90 lbs. per sq. in. On account of its higher speed, the airscrew was driven through a spur re- duction gear at half the speed •of the engine, which made it possible to use a very efficient -airscrew. This type of engine was further developed at the Royal Aircraft Establishment in the 100-h.p. R.A.F. 1/A engine, and afterwards in the 150 h.p., 12-cylinder engine known as the R.A.F. 4/A. Both these engines were somewhat similar in design to the Renault, but the brake mean effective pressure was appreciably higher, due to improved cylinder design. The petrol con- sumption of both the Renault and the R.A.F. engines was not very good, partly because the compression ratio was still -comparatively low and also because, owing to the low con- ductivity of the cast-iron cylinders, it was not possible to run with the best possible ratio of air to petrol without risk of overheating. The average petrol consumption was about 0-65 pint per H.P./hour. In the two years from 1915 to 1917 a great deal of experimental work was carried out on the use of aluminium alloys, first of all for pistons and after- wards for cylinder heads, while at the same time the design of cylinder head wae improved by the use of overhead valves, At the end of 1916 an engine was made, known as the R.A.F. 4/D, which was similar to the R.A.F. 4/A in general design but had cylinders of the newer design in which full advantage was taken of the high conductivity of aluminium alloy. This •engine gave upwards of 200 h.p. with a petrol consumption AL R The first engine to cross the English Channel: The "fan type" Anzani fitted in Bleriot's monoplanes was an air-cooled engine. (FLIGHT Photo.) ..;.;;/. of less than 0-6 pint per h.p.-hour, and a brake mean effective pressure of 115 lbs. per sq. in. Only a few of this type of engine were made, but it showed the way to further developments in air-cooled engines because for the first time an air-cooled engine was running with cylinders that were as efficient as the best water-cooled cylinders of that time. The R.A.F. 4/D seemed to be the high-water mark of Vee air-cooled engines and, like the BR/2 it seems to have been the . last of its type. The advantages of arranging the cylinders round the crankshaft became apparent and resulted in the development of the fixed radial engine. Going back again to early history, the engine that Bleriot used when he made his first Channel flight was a 3-cylinder Anzani, which may be con- sidered as halfway between a Vee-type and a fixed radial. The engine was very soon followed by a large number of true radial engines made by the same firm, and others designed by Viale, who had formerly been connected with the Anzani firm. These engines were not, on the whole, successful, partly, I think, on account of a number of special difficulties connected with radial engines which had not then been solved, and also on account of the comparatively poor design of cylinders. It was not until after the end of the war that the radial engine began to come into its own, particu- larly in the larger sizes. The Bristol "Jupiter" and the Amstrong-Siddeley "Lynx," " Jaguar," and other engines are so well known that a description of them is unnecessary. It is interesting to know that both the " Jaguar " and the " Jupiter " started as comparatively slow-speed engines, and that the improvement in weight per horsepower has been gained very largely by increasing the rate of revolution, which has eventually involved the fitting of a reduction gear for the airscrew in order to permit of still higher engine speeds. The latest engines of both companies give upwards of 500 h.p. at less than 2 lbs. per horsepower on their normal rated output. The Armstrong - Siddeley company have, in addition, made an engine of similar type which gives 800 h.p. at very nearly the same power/weight ratio. Before leaving the fixed radial engine, mention should be made of the radial water-cooled engine, particularly those made by the SallilSQn company during the great war. While the engine undoubtedly gave good service, the type has gone out of favour because it had neither the simplicity of the air-cooled type nor the small frontal area of the water-cooled engine. Water-cooled engines went completely out of fashion in 1909 on account of the success of the Gnome engine. TWO EARLY ENGINES WHICH HELPED GREATLY TO MAKE FLYING POSSIBLE: On the left the Green, a four-cylinder in-line water cooled, and on the right the famous 50-h.p. Gnome rotary air-cooled. (FLIGHT Photos.) 72
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