258 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1962 



opened until firing started and maximum propeller speed was at- 

 tained. Since the reverse process was difficult, "throttling" was ac- 

 complished by temporarily cutting the ignition, keeping the engine 

 going by short "bursts" of power. Oddly enough this technique was 

 easy to learn and pilots seemed to like it. 



Important engines of 1909 included the following (see also table 1, 

 pages 294 and 295) : 



"Wright 4- and 6-cylinder vertical, water cooled. 



Curtiss 8-cylinder Vee, water cooled. 



ABtoinette 8- and 16-cylinder Vee, water cooled. 



E.N.V. 8-cylinder Vee, water cooled. 



Darracq 2-cylinder opposed, water cooled. 



Gnome 7-cylinder rotary, air cooled. 



Renault 8-eylinder Vee, air cooled. 



R.E.P. 7-cylinder fan, air cooled. 



Anzani 3-cylinder fan, air cooled. 



These engines accounted for nearly all important flights in 1909, 

 including the winners of the first official aviation contests at Rheims. 



The "Darracq" engine, used by Santos-Dumont, was important for 

 being apparently the first aircraft engine to use mechanically operated 

 inlet valves. All the others used automatic inlet valves, o]3ened by 

 suction. Since automobile engines had been using mechanically 

 operated valves for many years before 1909, it is hard to understand 

 why this important feature was so late in coming into use for aircraft 

 engmes. 



ENGINES, 1910-1918 



This period, including World War I, saw such rapid developments 

 of aircraft engines that only the important ones can be described here. 

 By "important" I mean those which pioneered successful new design 

 features or which were particularly notable in service. 



Early in this period the "Gnome" air-cooled rotary engine was 

 dominant and was built in many countries and in several modified 

 designs, including the "LeEhone" and "Clerget" (French) the BR-1 

 and BR-2 (British) and the "Oberiirsel" and "Siemens" (German). 

 It reached its height early in the war and was definitely obsolescent 

 by 1918. Reasons for its demise were chiefly a limitation on speed 

 due to centrifugal stress, the considerable wmdage losses, design limi- 

 tations imposed by rotation of all parts but the crankshaft, and a 

 rather strong gyroscopic effect on the airplane during turns. How- 

 ever, the rotary-type engine set a pattern for the later development of 

 the modern air-cooled radial engine. It was a forged-and-machined- 

 all-over engine, and it was radial and air-cooled, features which are 

 now characteristic of most large military and commercial piston 

 engines. 



