AIRCRAFT PROPULSION — TAYLOR 259 



As the rotary engines became obsolete, the water-cooled Vee engine 

 became the dominant type. In the U.S.A. the Curtiss "OX-5" engine 

 (pi. 9, fig. 2, and table 1, page 29i) led the field until 1917, when the 

 "Liberty" and "Hispano-Suiza" engines (see later descriptions) were 

 introduced here. 



The "OX-5," a water-cooled V-8, had an aluminum crankcase, 

 cast-iron cylinders with sheet monel-metal water jackets brazed onto 

 the barrels, and overhead valves, push-rod operated. Used by both 

 Army and Navy,"^ it powered practically all U.S. and Canadian train- 

 ing airplanes and was probably responsible for training more pilots 

 for World War I than any other engine. The best-loiown trainer, 

 the Curtiss JN-4, afl'ectionately known as the "Jenny," is shown in 

 plate 8, figure 2. My first airplane ride (1917) was in a single-float 

 seaplane with the "OXX-2," the Navy version of this engine. 



The "OX-5" engine was considered very reliable for its day, but 

 few pilots completed the (very short) training course without at 

 least one forced landing. Its weaknesses included single ignition,^ 

 a rather flimsy valve-operating gear including "pull-rods" for the 

 inlet valves, and a tendency to leak water from the water pump down 

 onto the low-slung carburetor. In freezing weather the latter defect 

 accounted for many forced landings, as Dr. Stark Draper of M.I.T., 

 who owned an "OX-5" equipped Curtiss Robin airplane, can testify. 



A very important new style in liquid-cooled cylinder design ap- 

 peared in 1915 on the German 6-cylinder 180 hp. "Mercedes" engine 

 (fig. 6, table 1). This was the built-up welded-steel construction, 

 widely used for a long time thereafter in most water-cooled engines. 

 It was copied by such famous makes as Rolls-Eoyce "Eagle" (pi. 10, 

 fig. 1), the "Liberty," F.I.A.T., Renault, Salmson, B.M.W., etc., but 

 finally gave way to the cast-aluminum en-bloc construction, to be 

 discussed later. 



An important engine built in this style was the U.S. "Liberty" 

 engine (pi. 10, fig. 2, and text fig. 7), which was developed under 

 extraordinary circumstances. After a decision on May 29, 1917 (only 

 7 weeks after the U.S. entered the war) , by the War Production Board 

 to build an airplane engine more powerful than any in use up to that 

 time, J. G. Vincent, Chief Engineer of Packard, and E. J. Hall, of the 

 Hall-Scott ^lotor Co., started to design such an engine in the Willard 

 Hotel, Washington, D.C. On May 31 preliminary layouts were 

 approved by the W.P.B. and some extra help was called in. Com- 

 plete layouts were approved June 4, detailed design was substantially 

 completed on June 11, the first 8-cylinder engine was delivered to the 

 Bureau of Standards for test July 3, and the first 12-cylinder engine 

 completed the official 50-hour test August 25, 1917. The first "pro- 

 duction" engine was delivered to the Army Air Service in Dayton on 



« The Navy version was a slight modification having dual ignition and a 100-hp. rating. 



