History of aicraft piston engines

This change which allowed operation of the coolant 55

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Unformatted text preview: cylinder engine was tested at McCook Field in 1923 w ith a mixture of water and ethylene glycol at a high coolant temperature, probably near 300° F During 1 9281929 further tests were made at McCook Field with a Curtiss D -12 e ngine. After considerable development work to avoid leaks and to overcome other t roubles encountered, the use of this method of cooling was adopted for Curtiss liquid-cooled engines by 1932, and used soon afterward by Allison a nd Rolls-Royce. This change, which allowed operation of the coolant 55 a t 250° F, reduced the radiator area required by about 50 percent (fig.55). T his improvement, together with better radiator design and radiator cowling (fig. 56) brought the drag of liquid-cooled engines well below that of air-cooled radials of equal power. Their installed weight, which had b een greater than that of air-cooled radials, also came down to more c omparable figures. Schlaifer gives the weight per horsepower of the best liquid-cooled fighter installation in relation to a comparable air-cooled i nstallation as 30 percent more at sea level and about the same at 25,000 ft.18 T he fact that the Battle of Britain was won by liquid-cooled engines ( the Rolls-Royce Merlin) gave a great impetus to the Army prejudice in favor of water-cooled fighters.19 A ctually, both types were used, and it was found that the air-cooled fighter was better at low altitude both because of its lighter specific weight and its lesser vulnerability to small-arms fire. F or commercial uses, however, the elimination of the weight, complication, and maintenance requirements that characterize liquid-cooling has been a chief reason for the popularity of air-cooling for air-transport purposes since about 1932; and with few exceptions, commercial air transports all over the world have used air-cooled engines, mostly of American m anufacture, from the early beginnings in the late 1920s up to the present. A lthough today (1969) jet and turbine engines are standard for large m ilitary and commercial airplanes, there are still many more planes powered by air-cooled piston engines, because of their use in planes of smaller size, t han by all other types combined. 56 U nconventional Engines H undreds of unconventional types of aircraft engines have been proposed, b uilt, and tested. Among these the following may be mentioned. I n this type the cylinders were positioned around the crankshaft with their axes parallel to it. Its advantage was its compactness, which provided a small frontal area and allowed good s treamling. P erhaps the best known was the A lmen e ngine of 1921. N one were successful—although d uring 1929 t here were brief demonstrations of the Swiss Statex and British Redrup types, and an example of the latter, t he Fury powered a Simmonds Spartan biplane in flight. The methods of linking the pistons to the driveshaft caused lubrication and mechanical p roblems that were never solved. B ARREL- OR REVOLVER-TYPE ENGINES. T his was a 4-cylinder radial engine (fig. 57) with rollers in the p...
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