History of aicraft piston engines

In a conference with jones over the design board i

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Unformatted text preview: d the propeller in place were the c rankshaft and the two camshaft housings. In spite of this condition, and t he loss of all its cooling water, the Liberty engine was still r unning! A serious difficulty with the supercharger shown in figure 65 was the failure of turbine blades due to inadequate cooling of the turbine. In 1922 E rnest T. Jones, in charge of superchargers under Major G. E. A. Hallett, chief of the power plant section at McCook Field, was asked to redesign t he General Electric supercharger to overcome this difficulty. In a conference with Jones over the design board, I suggested placement of the t urbine wheel on the nacelle surface, using an overhung turbine wheel as in figure 66. This suggestion was adopted for the new design. Turbine 69 Figure 65.—a, General Electric turbo-supercharger installed on Liberty engine (NASM 1966-43) of the type which held the world's altitude record for 1920, 1921, 1922. Tubes conveying air from compressor to carburetor serve as an aftercooler. b, Night view of turbo-supercharger in operation. The exhaust manifolds and the nozzle box are white hot (about 1500° F) and the turbine, operating at over 20,000 rpm, is surrounded by hot exhaust gas. (Photo A-3092, A-3193) wheels of this type have been used on all subsequent installations of turbosuperchargers in the United States, including the Martin biplane bombers u>a of the 1920s a nd the B -17 a nd B-24 bombers and P-38 and P-47 fighters of World War II. The Boeing Stratocruiser and the B-29 and B-50 bombers used essentially the same system, although in these airplanes the turbine was located inside the nacelle and the overhung wheel was cooled by air p iped in from outside. Beginning with the B-17 the engines w ere also e quipped with gear-driven superchargers acting as the second stage. Figure 66.—Side-type turbo-supercharger installed on Curtiss D-12F 460-hp engine in Curtiss P-5 Hawk, 1927. This exposed position of the turbine wheel was effective in reducing the blade temperature as compared to the earlier arrangement shown in figure 65. (Photos A-3094) F igure 6 7.—NACA R oots-type supercharger, coupled to Pratt & Whitney Model A Wasp engine, 1 9 2 7 . B ypass valve, lower right, controls inlet pressure. A w o r l d ' s altitude record was established in 1927 w ith t h i s installation in a Wright Apache a i r p l a n e . (Photo courtesy Pratt & Whitney) T he only service use of turbo-superchargers on foreign-built airplanes a ppears to be that of the German Junkers diesel-engine high-altitude p hotographic plane shown in figure 60. It is remarkable that this very effective device received so little development outside of the United States. I n 1927 the official world's altitude record was taken by Lieutenant C . C. Champion, Jr., USN, with a Pratt & Whitney Wasp equipped with a N ACA Roots-type supercharger acting as first stage to the engine's own 72 g eared centrifugal equipment (fig. 67). This is the only important use of a n oncentrifugal supercharger in aircraft.24 Aftercoolers,25 t hat is, devices to co...
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