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The BMW 803 was BMW's attempt to build a high-output aircraft engine by "coupling" two BMW 801 engines back-to-back, driving contra-rotating propellers. The result was a 28-cylinder, four-row radial engine, each comprising a multiple-bank in-line engine with two cylinders in each bank, which, due to cooling concerns, were liquid cooled.〔Gunston 1989, p. 27.〕 ==Design and development== One problem with scaling up any piston engine design is that eventually a point is reached where the crankshaft becomes a major engineering challenge. This was a problem that affected almost all engines of the class, including BMW's own 18-cylinder BMW 802 project. For the 803 the engineers decided to avoid this problem by simply not using a common crankshaft, and driving a set of independent contra-rotating propellers. The front engine drove the front propeller directly, while the rear engine drove a number of smaller shafts that passed between the cylinders of the front engine before being geared back together to drive the rear prop. This layout resulted in a rather large gearbox on the front of the engine, and the front engine needing an extended shaft to "clear" the gearbox. With no common crankshaft it became more practical for all of the accessories to be powered by one engine alone, in this case the rear engine. The supercharger itself used up several hundred horsepower, so the rear propeller delivered considerably less power than the front one. The 803 had two valves per cylinder and overhead camshafts.〔Christopher, John. ''The Race for Hitler's X-Planes'' (The Mill, Gloucestershire: History Press, 2013), p.83.〕 Displacing 83.6 litres,〔Christopher, p.83.〕 and using the same 156 mm bore and identical stroke mesurements as each cylinder of the 801 used, the four-row 803 engine weighed 2,950 kg (6,490 lb) dry, and 4,130 kg (9,086 lb) fully loaded.〔Christopher, p.83, puts it at with propellors.〕 For all this weight it delivered 3,900 PS (3,847 hp; 2,868 kW). Although this made it the most powerful German engine design, its power-to-weight ratio was only about 0.98 kW/kg (0.60 hp/lb), comparing rather poorly with other large designs like the Junkers Jumo 222 at 1.7 kW/kg, the primary powerplant design for the advanced Bomber B design competition, which was designed to use only two engines of over 1,500 kW (2,000 hp) output. Specific power of the complex BMW 803 was likewise poor, at about 34.4 kW/l, compared to the 222's 40 kW/l, as was specific fuel consumption, at 380 g/kWh (0.63 lb/hp·h), comparable to late generation turboprops. As with most coupled engines, like the earlier Daimler-Benz DB 606 and DB 610, the 803 was not a success on the test-bed, and did not enter production. About twelve prototypes were built.〔Christopher, p.83.〕 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「BMW 803」の詳細全文を読む スポンサード リンク
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