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All very interesting. I don't know if Isambard's ever got the answer he was looking for. I think the answer is, there is no simple formula because both TE and power (HP, watts, etc.) change with speed. The only way to find them is to measure them in most cases. TE can theoretically be calculated for steam engines from things like steam pressure, piston area, driver diameter, etc. for startup only. After that, you have to measure it and special test equipment is required. The simple equations are: TE is a force (F) measured in lbs, etc. Force x Distance = work or energy (ft lbs, etc.) Energy/Time = power (HP, watts) We can calculate output power from a generator or alternator, but there are losses, so the only way to get HP at the drawbar is to measure it and you have to do it with the train moving. Hope this helps somebody. Oh, any two variables can be plotted on a chart. However, that does not imply causation. If we look at the equation above, power = f x d / t and we know that distance/time = speed so TE x speed = power EMD plots power vs. speed because that makes a useful chart for RR engineers, etc. Also, while it may be possible theoretical to increase power out of a system without bound, in reality something will break before you can get to infinity. We call that a non-linearity. jerry
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