History of aicraft piston engines

Photo a 44092 h aving cylinders larger than those of

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Unformatted text preview: st-aluminum cylinder head and internally cooled exhaust valves have been retained in modern practice. Cylinder section is shown in figure 36a. (Photo A-3086) Figure 40.—Wright W hirlwind J-5 engine (NASM 121) of 1927; 220 hp at 1800 rpm, 510 lb. This is t he type used in transoceanic flights by Lindbergh, Chamberlin, B yrd, and others. Cylinder section is shown in figure 36e. (Photo A-44092) h aving cylinders larger than those of the J - 5 , the bore of which was 4.5 in., b ut the first really successful engine of the larger type was the Pratt and W hitney 425-hp Wasp of 1927. " S ubsequent to the merger of Wright and Lawrance, a considerable fraction of the Wright Aeronautical staff, h eaded by the chief engineer G eorge J. Mead, resigned to join Frederick B. Rentschler in forming the 45 P ratt & W h i t n e y Aircraft C o m p a n y of Hartford, Connecticut. In a time a lmost as short as t h a t for the Liberty engine, this new g r o u p p r o d u c e d t he W a s p (shown in fig. 41), the first large radial air-cooled engine of w h a t m a y be called " m o d e r n " design. T h e notable features of this engine i ncluded: R ating, 425 hp at 1,800 rpm 9 c ylinders, 5.75x5.75 in. bore and stroke Built-in geared centrifugal supercharger Fully enclosed valve gear, with rocker boxes integral with cylinder head (fig. 41) F orged and machined crankcase (fig. 42) D omed-head, 2-valve c ylinders, basically of the Heron design D ivided crankpin (fig. 43) with one-piece master rod W hile most of these features h a d appeared previously, their combination h ere was an eminently rational and successful one, and set a high standard for future development of radial engines. T h e only i m p o r t a n t basic improvements to be developed later for r adial air-cooled engines w e r e : T he forged and machined aluminum cylinder head, pioneered by Bristol in England and Wright Aeronautical in the United States a bout 1940 (Gnome had pioneered the forged and machined steel h ead for air-cooled engines) T he automatically lubricated (by engine oil) valve gear, pioneered by P ratt & Whitney in 1932 (first used in water-cooled aero engines by Hispano-Suiza, ca. 1914) T he vibration-absorbing counterweight, introduced by Wright Aeronautical in 1935, which will be discussed later S econd-order balancing weights, to reduce unbalanced forces T h e basic features of the W a s p , with the addition of the above improvements, are used in all m o d e r n large a ir-cooled r adial engines. This type, of course, has dominated transport and m u c h of military aviation until t he recent advent of the j e t a n d turbine engine. Figures 44-47 show the o utstanding modern air-cooled radial engines which are basically descendants of the G n o m e , b u t with greatly improved detail design, including the composite steel and a l u m i n u m cylinder construction pioneered b y Gibson, H e r o n , and L a w r a n c e . Figure 36 shows the evolution of W r i g h t c ylinders from a b o u t 1920 to 1930, in comparison...
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