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The Boeing Model 40 was a United States mail plane of the 1920s. It was a single-engined biplane that was widely used for airmail services in the United States in the 1920s and 1930s, especially by airlines that later became part of United Airlines. It became the first aircraft built by the Boeing company to carry passengers. ==Development and design== In 1925, the US Post Office issued a requirement for a mailplane to replace the ex-military DH-4s then in use. The new aircraft was required to use the same water-cooled Liberty V12 engine as used by the DH-4, of which large stocks of war-built engines were available.〔Davies ''Air Enthusiast'' January/February 2007, p. 65.〕 The resultant aircraft, the Boeing Model 40, was a conventional tractor biplane, with the required Liberty engine housed in a streamlined cowling with an underslung radiator. The aircraft's fuselage had a steel tube structure, with an aluminum and laminated wood covering. Up to of mail was carried in two compartments in the forward fuselage, while the single pilot sat in an open cockpit in the rear fuselage. The wings and tail were of wooden construction, and the Model 40 had a fixed conventional landing gear.〔〔Bowers 1989, pp. 124–125.〕 The Model 40 made its first flight on July 7, 1925. Although the prototype was purchased by the US Post Office, the production order went to the Douglas M-2.〔〔Taylor ''Air Enthusiast'' August–November 1983, p. 67.〕 The Contract Air Mail Act of 1925 set out the gradual privatization of the Post Office's Air Mail routes. In late 1926, bids were requested for the main transcontinental trunk mail route, which was to be split into eastern and western sections, with Boeing bidding for the western section. Boeing revived the design for the tender, with the Model 40A replacing the Liberty engine with a air-cooled Pratt & Whitney Wasp radial engine, which was lighter than the Liberty, ignoring the weight of the Liberty's radiator and cooling water. The fuselage was redesigned to make more extensive use of welded steel tubing, and an enclosed cabin was fitted between the mail compartments, allowing two passengers to be carried as well as of mail. Boeing's bid of $3 per lb was much less than any of the competing bids, and Boeing was awarded the San Francisco to Chicago contract in January 1927, building 24 Model 40As for the route (with a further aircraft being used as a testbed by Pratt & Whitney).〔〔Bowers 1989, pp. 116–117.〕〔Davies ''Air Enthusiast'' January/February 2007, pp. 66–67.〕 The next model to reach production was the Model 40C, with an enlarged cabin allowing four passengers to be carried. Meanwhile Boeing Air Transport's Model 40As were modified by replacing their Wasp engines with Pratt & Whitney Hornet radial engines to become the Model 40B-2.〔Taylor ''Air Enthusiast'' August–November 1983, p. 69.〕 The Model 40B-4 was a new-build aircraft combining the four-passenger cabin of the Model 40C with the Hornet engine of the B-2.〔Bowers 1989, p. 129.〕 Production continued until February 1932.〔Bowers 1989, p. 130.〕 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「Boeing Model 40」の詳細全文を読む スポンサード リンク
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