290 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1962 



drawbacks for aircraft use, principal among which are its high 

 fuel consumption when used with a carburetor, and its tendency 

 toward misfiring and stalling at light loads. Most of the proposals 

 have been for small, low-cost engines, but so far none has been 

 developed with the characteristics necessary for a truly successful 

 aircraft engine. 



6. Finally there should be mentioned in this category two engines 

 with unconventional cylinder arrangements.^^ The first is the Napier 

 "Lion" (pi. 26, fig. 2) , the only W-type engine to see extensive service. 

 This engine was liquid-cooled with its 12 cylinders arranged in 3 

 rows of 4 each. Brought out in 1918, it was quite widely used in 

 British military and commercial aircraft, and won the Schneider 

 Trophy, a race for seaplanes in 1927. The second engine in this cate- 

 gory is the Pratt and Whitney R-4360, 28-cylinder air-cooled 

 radial with 4 rows of 7 cylinders each (pi. 16, fig. 2). This is the 

 largest (but not the most powerful) successful piston-type aircraft 

 engine ever to reach the service stage. It has been used in many 

 large military aircraft and in the Boeing "Stratocruiser." Besides 

 the large number of cylinders and their unusual arrangement in 

 "staggered" radial formation, unusual features include machined- 

 all-over cylinder heads of unusual shape and an ingenious arrange- 

 ment of the push-rod valve gear. This engine would undoubtedly 

 have been more fully developed had it not been for the advent of jet 

 engines and turbines. 



SUMMARY OF PISTON-ENGINE DEVELOPMENT 



Figure 20 shows performance parameters for piston aircraft engines 

 since 1903. 



Brake mean effective pressure (bmep) is a measure of an engine's 

 ability to withstand high cylinder pressures and to produce power 

 with a given speed and size. Starting at 62 pounds per square inch 

 (Manly, 1902), it rose to 130 by 1925, which is near maximum for 

 unsupercharged engines. With the introduction of supercharging 

 and improved fuels in the 1930's, bmep was increased to takeoff values 

 up to 360 psi (Rolls-Royce "]\Ierlin") and 300 psi (U.S. large radial 

 engines) , where it has stopped since the advent of jets and turbines. 



Mean piston speed (mps) at takeoff rose steadily from 750 ft./ 

 min. in 1903 to a maximum of 3,000 ft./min. in 1935, where it has 

 remained. 



Specific fuel consumption has improved from near 1 pound per 

 horsepower-hour to current minimum values of less than 0.40. This 

 gain has been achieved partly through improved design and partly 



" Obviously, the sleeve-valve Napier Saire and the Junkers Diesel also had unconven- 

 tional cylinder arrangements. 



