280 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1962 



mechanical embodiment. This type of device has been used in large 

 radial aircraft engines ever since, and also in many nonaircraf t power- 

 plants. After testing the first engines so equipped, it was found that 

 these inventions had been anticipated in France, but the credit for 

 practical application should go to Taylor and Chilton. 



Another important torsional vibration problem was that of the gear- 

 driven supercharger rotor. Various types of flexible coupling have 

 been used in the gear train to avoid serious trouble. 



Further consideration of vibration problems is included under the 

 heading "Propellers." 



ALTITUDE PERFORMANCE AND SUPERCHARGERS 



The fact that reduced air density, as altitude increases, reduces en- 

 gine power must have been realized before it became obvious in 1909, 

 when airplanes began to try for high altitude flight. The advantage 

 of altitude in military work was very apparent in World War I. 



The only attempt at improved altitude performance used in World 

 War I was embodied in the German BMW and Maybach engines, 

 which were desigTied to be partly throttled near sea level, the throttle 

 to be opened only above about 5,000 feet. Both engines were designed 

 to be lighter in weight than would have been required for full-throttle 

 operation at sea level, and the BIVIW also had higher compression ratios 

 than could be used with full throttle at sea level without detonation. 

 In these cases the advantage in altitude performance over an engine 

 capable of full-throttle operation at sea level was quite small. 



Measurement of engine performance at altitude was first seriously 

 undertaken when the U.S. Bureau of Standards completed its altitude 

 test chamber in 1918. Subsequently a considerable literature on this 

 subject developed. 



The Swiss engineer Buchi suggested the turbo supercharger for 

 aircraft in 1914. This type was then developed in France by Rateau, 

 and experimental models were tested during the war, but none was 

 put into service use. Laboratory work on gear-driven superchargers 

 was conducted during the war by the R.A.F. at Farnborough, Eng- 

 land. Intensive development of supercharging equipment began both 

 in England and the U.S A. in 1918. 



Many types of compressors have been considered, but only one, the 

 centrifugal type, ever got beyond the experimental stage. The Royal 

 Aircraft Factory had Armstrong- Siddeley build a radial engine with 

 built-in geared centrifugal supercharger in 1916, but the design was 

 unsuccessful, probably because of torsional vibration in the drive sys- 

 tem. Siddeley did not produce a successful geared supercharger 

 until that used in 1926 in the "Jaguar." 



Geared superchargers were built experimentally by Curtiss and 

 Wright Aeronautical Corporation in 1925, but the first U.S. produc- 



