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The Wright R-790 Whirlwind was a series of nine-cylinder air-cooled radial aircraft engines built by Wright Aeronautical Corporation, with a total displacement of about and around . These engines were the earliest members of the Wright Whirlwind engine family. ==Design and development== The R-790 Whirlwind began as the Lawrance J-1, a nine-cylinder air-cooled radial developed in 1921 by the Lawrance Aero Engine Company for the U.S. Navy. The Navy was very enthusiastic about air-cooled engines, which it felt were better suited for naval use than liquid-cooled ones.〔(Wright J-5 "Whirlwind" ) (PDF), by Kimble D. McCutcheon, from the Aircraft Engine Historical Society〕 Lawrance was a small company, though, and the Navy doubted it could produce enough engines for their needs.〔 Despite urgings from the Navy, the major U.S. aircraft engine makers, Wright and Curtiss, were satisfied with their liquid-cooled engines and showed no interest in building air-cooled ones.〔 Since the Navy was already a major purchaser of Wright engines, it decided to force the issue by suggesting that Wright purchase Lawrance and build the J-1 itself, while informing the company that the Navy would not buy any more of its existing engines or spare parts.〔 To keep the Navy's business, Wright was thus compelled to buy Lawrance in 1923, and the Lawrance J-1 became the Wright J-1.〔 By the time Lawrance merged with Wright, it had already developed the J-2, a more powerful version of the J-1 with slightly enlarged bore and displacement. However, Lawrance decided the J-1 was large enough, and the J-2 never went into production; only two examples were built.〔 Over the next two years, Wright gradually refined the J-1 engine, introducing the J-3, J-4, J-4A, and J-4B. The changes improved the engine's reliability, cooling, and fuel consumption, but the basic design, dimensions, and performance were unaltered.〔 The J-4 was the first engine to bear the Whirlwind name; previous engines had no name, only a designation.〔 The J-5 Whirlwind, introduced in 1925, was a complete redesign of the engine which greatly improved its cooling and breathing, further increasing its reliability and reducing its fuel consumption. Among the more visible changes were a much wider separation between the valves, for better cooling airflow, and completely enclosed pushrods and rocker arms, rather than exposed ones as on the earlier engines.〔 The U.S. government later designated the J-5 Whirlwind as the R-790, but it did not apply this designation to the older engines.〔(Naval Aviation Chronology 1920-1929 ), from the Naval Historical Center. See entries for 1928, February 1 and 28.〕 All these engines had a bore of 4.5 in (11.4 cm), a stroke of 5.5 in (14.0 cm), and a displacement of 788 in3 (12.91 L). The J-5 was the last of the original nine-cylinder Whirlwinds. In 1928, it was replaced by the seven-cylinder version of the Whirlwind J-6. Image:Wright_J-6.jpg|Partially sectioned Wright J-4B at Canada Aviation Museum Image:Wright_R790_2.jpg|Side view of the USAF museum's R-790 (J-5) 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Wright R-790 Whirlwind」の詳細全文を読む スポンサード リンク
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