276 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1962 



Figure 14. — Evolution of Wright Cyclone engine valves. 



1940. 



From Journal of S.A.E., Colwell, 



Figure 14 shows a sequence of development in exhaust-valve 

 design. Much ingenuity has been displayed by valve manufacturers 

 in fabricating the modern hollow-head-with-hollow-stem valve, and 

 filling it (partially) with metallic sodium. 



The automatic lubrication of valves by engine oil, introduced to 

 liquid-cooled engines by Hispano-Suiza (1914) and to air-cooled en- 

 gines by Pratt and Wliitney (1932) has also been an important con- 

 tribution to the present long life and reliability of aircraft-engine 

 valves. 



Another method of attack on the valve-cooling problem was to elim- 

 inate the poppet valve in favor of some form of sliding valve. This 

 method has not met with success, with one exception. The Bristol 

 Aeroplane Co. developed its single-sleeve-valve air-cooled radial in 

 the 1930's to the point where it was used to a limited extent in 

 World War II. 



FUELS AND DETONATION 



One of the most important developments in aircraft propulsion has 

 been the improvement m, and control of, aviation gasoline. This 

 development is a long and complex story, and only a bare outline can 

 be given here. 



