264 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1962 



ENGINES, 1917-1940 



In this period hundreds of new engine types appeared. From 

 the technical point of view, the period is marked by tlie following 

 significant developments : 



1. Further development of the liquid-cooled engine of the all-cast 

 type, chiefly for military purposes. 



2. The development of the air-cooled radial engine to a place of 

 dominance in all but fighter-type military and small civilian aircraft. 



3. The advent of 4-cylinder vertical in-line, and later, opposed- 

 cylinder, horizontal, air-cooled engines for light aircraft. 



4. First trials of rocket and jet engines. 



LIQUID-COOLED ENGINES AFTER 1918 



By 1920 the success of the "Hispano-Suiza" engines by that time 

 built in both the original size and a larger size (300 hp.), had con- 

 vinced most designers that the welded-cylinder construction was 

 obsolescent. 



The Curtiss Company, in the U.S.A., took up the cast-aluminum 

 engine, generally based on the "Hispano-Suiza," with successive 12- 

 cylinder designs known as the K-12," C-12, D-12 (pi. 12, fig. 1), 

 and V-14:00 models. These were all of the 12-cylinder Vee type, 

 with four valves per cylinder, instead of two as in the "Hispano- 

 Suiza." The two early models had steel cylinder heads like that of 

 the original "Hispano-Suiza," but cooling was greatly assisted by 

 an integral stud, in the center between the valves, by means of which 

 the head was held tightly against the water-jacket casting (fig. 10, 4). 

 In the D-12 the steel head was abandoned, and the valve seats were 

 bedded directly in the aluminum head, as in the Wright version of the 

 "Hispano-Suiza." 



The great success of the Curtiss engines in racing (first to exceed 

 200 m.p.h. in the Mitchell " Trophy race, Detroit, 1922, and winner 

 of the Schneider trophy in 1923 and 1925) led the Rolls-Royce com- 

 pany to develop aluminum V-12 engines of similar type. The first 

 was the "Kestrel" of 1927 soon followed by the racing or "R" type 

 which attained theretofore unheard of output in proportion to its 

 size and weight and won the Schneider trophy in 1929 and 1931. 

 The "Kestrel" was followed by the Rolls-Royce "Merlm" (pi. 12, 

 fig. 2), winner of the Battle of Britain, and also by the Allison 

 V-1710 ( a fairly faithful copy of the "Merlin"), and the German 

 "Daimler-Benz" (fig. 9) and "Junkers" V-12 liquid-cooled engines, all 

 descendants of the "Hispano-Suiza" and Curtiss. In all these engines 

 the valves were seated in inserts embedded in the aluminum head, 

 and thus had better valve cooling than the original "Hispano-Suiza" 



"The K was for Chas. B. Klrkham, who conceived the basic design for this series and 

 was also consulted in the design of the earlier Liberty engine, q.v. 

 " Named for brother of Gen, WUliam ("Billy") Mitchell. 



