PRR-S1, an Experimental 4-6-6-4 Steam Locomotive

Picture of Pensylvania Railroads locomotive, PRR-S1

Built: Built in 1937 as a collaborative effort between Pennsylvania Railroad, Baldwin Locomotive Works, Lima Locomotive Works and American Locomotive Company

Description: The PRR S1 class steam locomotive was aptly nicknamed "The Big Engine". It was a single experimental locomotive, the longest and heaviest rigid frame reciprocating steam locomotive ever built. Weight: 44.3T Length (overall): 140ft 2½in Tractive power: 71900 lbf. Building was completed in early 1939. Since its design placed more than 50% of its weight on the leading and trailing trucks (the centre large, 6-wheel units), there was a smaller amount of this actually applied to the 8 driving wheels. This increased its tendency for wheel slippage during acceleration, a situation which could destroy the engine from over-speed stress.

Duties: The S1 was so large that it could not negotiate most of the tracks of the PRR system. In its brief service life it was restricted to the main line between Chicago, Illinois and Crestline, Ohio. It hauled passenger trains such as The General and The Trailblazer. It used a 4-6-6-4 configuration. It was a "duplex" engine, with each of the two sets of 6 drive wheels driven by a separate set of pistons.

Significant Events: Displayed at the New York World's Fair of 1939 where it operated under its own steam power on a platform that had rollers under the drive wheels. It was brought to the fair via the Long Island Rail Road, a longer route than would normally be travelled, to minimise the number of obstacles in its path. Some were temporarily removed, while others were passed at greatly reduced speed.

Retirement: The engine was scrapped in 1949.

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