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Aviation History
1940
1940 - 0387.PDF
FEBRUARY 8, 1940 119 PLANTS (CONTINUED) 3. Daimler-Benz DB 600. 4. Napier Dagger. 5. Bristol Taurus. Junkers), though despite their claims it is difficult to see where, even in "ideal" installations—much less in present-day examples—this arrangement scores. The engine of H section as exemplified by our Napier Dagger will doubtless establish itself even more strongly. The Dagger, which may be the prototype for more powerful units, is virtually two engines in one, being in effect a combination of a pair of "flat twelves" joined by a common crankcase and driving through spur gears a single airscrew. Another method of obtaining in- creased power is exemplified by the Fiat AS-6 racing engine which is nothing more than two twelve-cylinder vee-type units placed back to back with a gear box between them. There are two concentric airscrews, one for each engine, driven through off-set gearing and con- centric shafts. A French bomber has been designed to utilise two sets of Hispano Suiza Series Y engines joined in similar fashion. Cooling "--•; . The air- versus liquid-cooling controversy continues, and is likely to do so. Mr. Fedden, the Bristol designer, maintains that friendly rivalry is beneficial to both and the competition afforded stimulates engineers to greater achievement. In this connection Mr. Fedden depre- cates the opinion expressed by Mr. F. R. Banks that for powers in excess of 2,000-2,500 h.p. the liquid-cooled engine will be more generally used. Air-cooled engines of the multi-bank radial types and of the X and H lay- outs are possible in large sizes, and the problems involved, he states, are no greater than when liquid cooling is employed. The provision of cooling gills and cf sufficient cooling surface can be obtained, and the installation can be arranged so that the drags of both types of engine are almost exactly comparable. Moreover, the cooling ot a cylinder by air is a problem which is still Ueing actively pursued, and further developments in this direction are much more likely, according to Mr. Fedden, than in that of the more fully developed liquid-cooled cylinder. In this connection Mr. Fedderi quotes the recent N.A.C.A. experiments with cylinders of large cooling surface. This states : "By increasing the fin area of a standard head six times and by doubling the pooling surface of a barrel, the power obtainable from a cylinder of given size has been trebled without increasing the cooling loss or the temperature." Although it is recognised that engine weight contri- butes to aerodynamic drag by its influence on wing area, power plant weight is not such an important con- sideration as in the past. Mr. Mead points out that weight alone is not a true criterion, but rather its effect on the overall efficiency of the aeroplane. Illustrative of this is the constant-speed airscrew which, though it weighs anything from 60 to 80 per cent, more than the fixed-pitch type, permits take-off at a 10 to 30 per cent, greater gross weight. Direct Injection A popular and topical controversy is the "petrol- injection or carburetter" argument. A well-known American engineer when asked for his views on the benefits of fuel injection compared with the carburetter stated that if the aero engine, as developed, incorporated fuel injection instead of a carburetter there would have been people just as anxious to fit the carburetter as they The injection pump unit of the Junkers Jumo 211A engine shown dismantled. A centrally disposed camshaft with six cams actuates the twelve injection pumps.
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