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Reply to "PRR K4 Top Speed"

That dyno figure at Altoona would not have included the wind resistance or flange friction of the engine, nor the weight and friction and wind resistance of the tender, so something in the 2800-2900 drawbar HP range would be the result at the tender drawbar, and assuming that the engine had a mechanical stoker.  So if the max drawbar HP peaked at 60 mph, the weight and increasing resistance of the trailing train would intersect with the declining drawbar pull curve,  and this would be the terminal or balancing speed of the train with that locomotive.

It is significant that railroads' max speeds for light engines was low...usually 25-35 mph.  There were at least two reasons for this limitation:

1)  An engine with a train acts a lot like a kite with a tail in that the train makes the entire consist more stable, so higher speeds can be used.

2)  A light engine is severely limited by the ability of its braking system to stop in a short distance.  An engine with a trailing train can stop in a short distance, mainly due to the weight of the trailing cars and the much more numerous contact points of all of the wheels on the rail.

Any locomotive can reach high speeds if the train is light with fewer cars, subject to the mechanical design elements of the locomotive such as cylinder diameter and stroke, driver diameter, valve gear capability, and size and weight of the rods and pins.

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