James Wrote:
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> I'd like to know how your discussion partner
> figured the horsepower because horsepower is in
> essence force times speed. The number he gave you
> is really low unless you're talking about
> virtually no speed.
I would like to know as well, the number defenitly didn't seem right at all.
An automobile engine can
> generate high power when the vehicle is standing
> still due to the ability to leave the transmission
> in neutral with the engine itself revving fast. A
> steam locomotive can't do that. The engine is
> tied to the wheels--the axles are basically the
> equivalent of a crankshaft A steam locomotive,
> the faster you go, the more power you make--to a
> point.
>
> The catalogue page linked by BCP omits one crucial
> detail (which if I recall is mentioned in a
> different page of that same catalogue): Beyond
> low speeds, steam locomotive tractive effort
> decreases as speed increases. If you forget this
> and multiply the rated tractive effort at say 40
> MPH, you get an absurdly large number. Tractive
> effort for steam locomotives is usually discussed
> in terms of starting tractive effort because in
> the old days railroads were mostly concerned with
> how much load an engine could start or lug up a
> division's ruling grade at 6-8 miles per hour.
> You'll note at starting--meaning .5 or 1 MPH--the
> horsepower generated is indeed very very low.
> This is because at such a low speed the cylinders
> cannot use much of the steam the boiler can
> provide, and all that happens is the safety valves
> pop and the extra potential power goes to waste.
> As speed increases, the cylinders can use more of
> the potential power, and hence horsepower also
> increases and keeps increasing until you reach a
> speed where the boiler can no longer keep up with
> cylinder demand and cutoff has to be shortened or
> throttle reduced. That's when you've reached
> maximum horsepower. You can not even
> "guesstimate" the maximum horsepower of a steam
> locomotive without at least knowing the details of
> its boiler and heating surface, and can't know for
> sure without having access to something like
> indicator cards or dynamometer tests. Even then
> "horsepower" is a bit of a weasel word for steam
> locomotives because boiler horsepower, indicated
> horsepower, drawbar horsepower, and plain
> horsepower are all different.
Thanks for your very detailed response James.
