270 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1962 



first result being the Wright J-5, essentially a Lawrance-type engine 

 with Heron-type cylinders (pi. 14, fig. 2). This was a successful en- 

 gine of 200-hp. class as evidenced by its use in Lindbergh's New York- 

 Paris flight, May 20-21, 1927, and in a number of early transport 

 airplanes. 



Although Wright Aeronautical had been experimenting with air- 

 cooled radial engines having cylinders larger than those of the J-5, 

 whose bore was 4.5 inches, the first really successful engine in this 

 class was the Pratt and Whitney 425-hp. "Wasp" of 1927. 



The merger with Lawrance having involved a management change, 

 in the summer of 1925 a considerable fraction of the Wright Aero- 

 nautical staff, including the chief engineer, George J. Mead, resigned 

 from Wright to form Pratt and Whitney Aircraft, of Hartford, Coim. 

 In a time almost as short as that for the Liberty engine, this new group 

 produced the "Wasp" shown in plate 15, figure 1, the first large radial 

 air-cooled engine of what may be called "modern" design. The nota- 

 ble features of this engme included : 



Rating, 425 hp. at 1,800 r.p.m. 



9 cylinders. 5.75 x 5.75 inches. 



Built-in geared centrifugal supercharger. 



Fully enclosed valve gear with rocker boxes integral with cylinder head 



(pi. 15, fig. 1). 

 Forged and machined crankcase (pi. 15, fig. 2). 

 Domed-head, 2-valve cylinders, basically of the Heron design. 

 Divided crankpin with one-piece master rod (pi. 15, fig. 3). 



While most of these features had appeared previously, their com- 

 bination here was an eminently rational and successful one, and set a 

 high standard for future radial-engine development. 



The only important basic improvements to be developed later for 

 radial air-cooled engines were : 



1. The forged and machined aluminum cylinder head, pioneered by 

 Bristol in England and Wright Aeronautical in the U.S.A. (Gnome 

 had pioneered the forged and machined steel head for air-cooled 

 engines) . 



2. The automatically lubricated (by engine oil) valve gear, pio- 

 neered by Pratt and Wliitney in 1932 (first used in water-cooled aero 

 engines by Hispano-Suiza, ca. 1914) . 



3. The vibration-absorbing counterweight, introduced by Wright 

 Aeronautical in 1935, which will be discussed later. 



4. Second-order balancing weights, to reduce vibration. 



The basic features of the "Wasp," with the addition of the above 

 improvements, are used in all modern large air-cooled radial engines. 

 This type, of course, has dominated transport and much of military 

 aviation until the recent advent of the jet and turbine engine. Plate 



