282 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1962 



1920, 1921, and 1922. Supercliarging was hard on an engine not 

 originally designed for it, and I remember when Major Schroeder, 

 who made the 1920 record, returned from a flight with the Liberty 

 engine and its nacelle cut in two by a failed connecting rod at the 

 third crank from the front end. The only elements holding the four 

 forward cylinders and the propeller in place were the crankshaft and 

 the two camshaft housings. In spite of this condition, and the loss 

 of all its cooling water, the Liberty engine was still running ! 



A serious difficulty with the supercharger shown in plate 22, figure 

 1, was the failure of turbine blades due to inadequate cooling of the 

 turbine. To overcome this difficulty, I suggested placement of the 

 turbine wheel on the nacelle surface, using an overhung turbine wheel 

 as in plate 23, figure 1. This suggestion Vv'as adopted and used on all 

 subsequent installations of turbo superchargers in the U.S.A. includ- 

 ing the Martin biplane bombers ^^ of the 1920's and the B-17 and B-24: 

 bombers. The Boeing Stratocruiser and the B-29 and B-50 bombers 

 used essentially the same system, although in these airplanes the tur- 

 bine was located inside the nacelle and the overhung wheel was cooled 

 by air piped in from outside. Beginning with the B-17 the engines 

 were also equipped with gear-driven superchargers acting as the 

 second stage. 



The only service use of turbo superchargers on foreign-built air- 

 planes appears to be that of the German Junkers Diesel engine in a 

 World War II high-altitude photographic airplane. It is remarkable 

 that this very effective device received so little development outside 

 oftheU.S.A. 



In 1927 the official world's altitude record was taken by Lieutenant 

 Champion, U.S.N,, with a Pratt and ^Vliitney "Wasp" equii^ped with 

 an N.A.C.A. Koots-type supercharger acting as first stage to the 

 engine's own geared centrifugal equipment (pi. 23, fig. 2). This is 

 the only important use of a noncentrifugal supercharger in aircraft. 



Aftercoolers,^^ that is, devices to cool the air after leaving the super- 

 charger, have been generally used with turbo superchargers, and with 

 two-stage geared types. Such coolers are shown in plate 22, figure 1, 

 and plate 23, figure 1. The "Merlin" engine (fig. 16) used a water- 

 cooled aftercooler with its own separate radiator and circulation 

 system. 



The culmination of the supercharger art is represented by the 

 Wright Turbo- compound R-3350 engine shown in plate 17, figure 2. 

 This engine, introduced about 1947, has three exhaust-driven turbines 

 geared into the power system, as well as a two- speed centrifugal 

 geared supercharger. In normal operation the turbines deliver more 



" A squadron of Martin bombers was the first combat group ever equipped with turbo 

 superchargers (1923-24). 



^ When the cooler is used between stages of supercharging, it is called an "intercooler." 



