Re: Exploring the White Pass & Yukon - Part Two

> [deleted comment about power because I'd rather
> review older discussion on here about TE,
> horsepower, etc before I go sayin' stuff about
> engineering I scarcely understand, lol]

With steam, tractive effort is pretty much tractive effort. On grades, you have to remember to deduct the working weight of both tender and engine from any theoretical tonnage ratings.

Where steam gets interesting is starting a train, and on poor rail conditions where the adhesion is less than 25% ( easily down to 20% under poor conditions). Also, that maximum tractive effort rating is based on optimal conditions at lower speeds. As your speed increase, at some point the cylinder horsepower exceeds the boiler horsepower which means you're outrunning the boiler. That means "hooking up" the engine which limits the portion of the valve stroke that steam is admitted to the cylinder allowing the expansion of steam to come into play versus just raw boiler pressure, and a resulting decrease in tractive effort being created.

A diesel-electric on the other hand is an entirely different beast when considering tractive effort compared to steam....