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Aviation History
1921
1921 - 0828.PDF
|HBHHj ^* ^_ ^sfei.^ *^'JM *«Is iS?"" '••_-• ^~*&0^gaHBS^^ i^&Bl r j- • •* & '* .^^^^^^1 HHflei^'''-'' IBBI . - jf^K 9flHflHflHflHflHflHflHl HflflE&iiil''' MHB •'"».•• MB :'* flBHYAYAYAYAYAYJ Hi': «i •#• B ::- HHHHHHHI Fig. 5.—Rear view of Bristol "Jupiter" engine. weighing 2 lbs. per horse-power complete, the lecturer was of the opinion that the static air-cooled radial is the most promising type. In the radial engine, he said, each set of cylinders being disposed round their own crank, there is a consequent economy of both material and space, affording remarkable opportunities for saving weight. Among the advantages of the radial, Mr. Fedden enumerated the following :— (a) In multi-cylinder, single-row radials, owing to the connecting rods all coming on to one common crank, the inertia torque is practically eliminated. DECEMBER 15, 1921 (b) It may be geared without coming up against the main inherent problems of gearing, and the problem of attaching a-body such as an airscrew, which has a large flywheel effect, is very much simplified. (c) It dispenses with the radiator, piping and water, with Fig. 7.—Crank shaft, connecting rod, andassembly of " Jupiter " engine. piston Fig. 6.—Cylinder and rocker mechanism of " Jupiter " engine. its attendant troubles, apart from the corresponding saving in weight. (d) In very hot climates ^air-cooled engines have been found to give better service, because an air-cooled cylinder will maintain full power if the mean temperature of the fins does not exceed 1750 C. On the other hand, if the mean temperature of the cooling surfaces of a radiator exceeds 8o° C. evaporation losses become considerable. IJence in hot climates, where the air temperature may vary from 0° C. to 45" C, the temperature difference available for cooling may diminish 56 per cent, in the case of the radiator, whilst the diminution is only 25 per cent, in the case of the air- cooled cylinder: When these same conditions are repeated with great change of altitude, the air-cooled engine is even still more at an advantage. (e) The static air-cooled radial can be made the shortest and most compact power unit it is possible to develop for an internal combustion engine working on the four-stroke cycle. (/) From a manufacturing point of view, the radial has great advantages. Nearly all the parts are symmetrical or round, and a considerable proportion of the machining is in the form of large multiples, while there are fewer numbers of parts than in the " straight line " or " V " type of engine of equal power. Mr. Fedden mentioned that the actual number of different parts in a 380 h.p. radial of his design is 370, which is, he says, 25 per cent, less than any other known proved engine of equal power. (g) The air-cooled radial can be dismantled, overhauled and reassembled more quickly than any other type of equal power, with the exception of the rotery. (h) Provided the aeroplane fuselage is properly designed, the radial is ideal for mounting. It can be so arranged that the engine may be taken out or put into the machine in very much shorter time than is possible with the vertical or " V " types. Some Disadvantages of Air-Cooled Radials, and SomeSuggestions for Remedying Them All design is a matter of compromise, and Mr. Fedden called attention to certain special problems peculiar to the radial, which, he said, were worthy of weighty consideration. It is Mr. Fedden's opinion that these problems are not insuper- able, but that designers of this type have not realised the amount of " new ground " that had to be broken. He then proceeded to discuss some of the problems in detail. (1) Regarding the air-cooling of large cylinders, Mr. Fedden pointed out that, on the whole, the design has been poor and entirely inadequate to deal with the mean effective pressures demanded. 828
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