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In the Whyte notation for the classification of steam locomotives by wheel arrangement, a is a Garratt articulated locomotive using a pair of engine units back to back, with the boiler and cab suspended between them. The wheel arrangement has four leading wheels on two axles, usually in a leading bogie, eight powered and coupled driving wheels on four axles, and two trailing wheels on one axle, usually in a trailing truck. Since the type is generally known as a Mountain, the corresponding Garratt type is usually known as a Double Mountain. Other equivalent classifications are: * UIC classification: 2D1+1D2 (also known as German and Italian classifications) * French classification: 241+142 * Turkish classification: 47+47 * Swiss classification: 4/7+4/7 up to the early 1920s, later 8/14 ==Overview== A Garratt locomotive is actually two separate engines combined in a double articulated format, thereby providing multiple powered axles over which the total locomotive weight is spread. This results in a more powerful locomotive since, compared to a tender locomotive of similar total mass with tender included, a much larger percentage of the locomotive’s total mass contributes to traction.〔(Beyer, Peacock Garratt Locomotives )〕 The Double Mountain was probably the optimal Garratt wheel arrangement, with the four-wheeled leading bogies and the two-wheeled trailing trucks on each engine unit ensuring stability at speed and with sixteen coupled wheels for traction. More coupled wheels would inhibit the locomotive on tight curves, while the only advantage of more non-coupled wheels would be to reduce the axle loading. The largest steam locomotive built in Europe was a Garratt, built by Beyer, Peacock and Company for the Soviet Railways in 1932. The most numerous Garratt class in the world was also a , the Class GMA and GMAM of the South African Railways, of which one hundred and twenty were built between 1954 and 1958.〔 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「4-8-2+2-8-4」の詳細全文を読む スポンサード リンク
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