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[quote user="MichaelSol"][quote user="Bucyrus"]What would the comparison look like if you compared a 5,600 HP diesel to a 5,600 HP steamer, assuming that they both were capable of delivering their full HP to the rail?  [/quote]I'm going to change this to a 3,000 hp Diesel and a 3,000 hp Steam engine to come a little closer to the reality of the era since a 5600 hp Diesel-electric didn't exist then and statistically isn't much of a presence now.A relatively big diesel is being compared to a relatively small steam engine. As the steam engine gets larger, its ability to continue to develop horsepower continues to extend to higher and higher speeds.The physics of the whole thing changes when you take a relatively small steam engine and compare it to a large diesel-electric. In this example, equal horsepower means that the steam engine has about one-third the weight on the drivers as the Diesel-electric and yet -- above about 18 mph, their Tractive Effort is identical. And the maximum horsepower output of the Steam locomotive is reached at about 28 mph -- not all that different than the Diesel-electric. So in your 30 mph train example, it's wrong with locomotives of equal horsepower because they are, at that point, generating the same tractive effort and the same horsepower. The Diesel-electric has zero advantage.So, you don't really gain the clever comparison that you expect, because the smaller the steam engine relative to the diesel-electric, the more it actually does start to look like the diesel-electric. So, for locomotives of "equal maximum horsepower", when the Diesel-electric reaches its peak, the Steam engine has already developed 83% or more of its total capacity -- at about half the purchase cost per horsepower, by the way -- and that's really what this is all about; if you want to spend equal dollars, you are buying a much larger capacity with the Steam engine all the way round. Another way of looking at it is by trying so hard, as you have been doing, to limit the Steam engine to what the Diesel-elecric can produce, you lower the power scale of the Steam engine so that it gets to full power much earlier than a large Steam engine. And so the comparison between a Diesel-electric and a Steam engine of equal horsepower becomes pretty much of a big "so-what" because the maximum power of the smaller steam engine is developed much earlier and is within a few mph of the top output of the Diesel-electric. And the Tractive Effort of the Diesel-electric still drops like rock so that those are equal as well after about 18 mph but if the train is still moving at 18 mph, then both motive power types had the tractive effort to get it there.The problem for your argument is that the Steam engine scales up differently than you apparently expected -- and I didn't look at it as close as I should have either, or I could have put this tangent out of its misery much earlier. And it is pointless to say that somehow the Diesel-electric develops its power "earlier." The Steam engine can develop the same power at the same speed -- and that is what railroads look at for "comparability." It's "earlier" only if you intentionally underpower the Steam engine and then set an artificial rule that it cannot exceed the Diesel-electric. And that rule comes strictly from baseball cards -- nobody plays this game in the real world. The real rule is that, for the cost, you buy the Steam engine with equal weight on the drivers.It is useful when a heavy train is being moved to have the capability to move it efficiently at 15 mph. Both types can do that and that is really what the real world is looking for.The problem comes at 30 mph, when that Steam engine can continue to develop additional power as the train requires more power. The key is that these genuinely comparable engines -- same weight on the drivers, pulling the same load -- is that this large Steam engine has a much longer scale distance over which it continues to develop horsepower compared to the little same-horsepower steam engine -- and which provides an additional advantage over both the Diesel-electric and the "same-horsepower" Steam engine used in what still remains to me an artificial metric standard desperately in search of a purpose or point.However, we can now maybe put this to rest:[quote]Not only is this ability to reach maximum horsepower early not a disadvantage, in some cases it is actually an advantage; for instance, when pulling a drag freight that requires the locomotive's maximum horsepower, but is so heavy that its balance speed will be say 30 mph. A diesel can deliver all of its potential horsepower at that speed whereas a steam locomotive cannot.[/quote]And this wrong. By imposing a maximum hp limit, at 30 mph, both motive power types develop the same hp and same TE.   Case closed.[/quote]I am still trying to digest this topic of HP/TE curves.  I am not wedded to any particular position, but I am only developing and posing my positions and questions largely upon the information you have provided.  You have made the point several times that a fair comparison requires the locomotives to have equal weight on the drivers.  When you said the following about two locomotives of equal horsepower, are you referring to a size disparity stemming from differing weight on the drivers? "A relatively big diesel is being compared to a relatively small steam engine. As the steam engine gets larger, its ability to continue to develop horsepower continues to extend to higher and higher speeds."You said:"In this example, equal horsepower means that the steam engine has about one-third the weight on the drivers as the Diesel-electric and yet -- above about 18 mph, their Tractive Effort is identical. And the maximum horsepower output of the Steam locomotive drops down to about 28 mph -- not all that far above the Diesel-electric."You have indicated that there must be equal weight on the drivers in order for the test to be fair, and yet in citing the weight-on-driver disparity (one-third the weight), you go on to say that above 18 mph the TE is identical.  So with equal horsepower producing mostly equal TE in the compared locomotives, how is the unequal weight on drivers making the comparison unfair?  You said:"...the smaller the steam engine relative to the diesel-electric, the more it actually does start to look like the diesel-electric. So, at equal horsepower, when the Diesel-electric reaches its peak, the Steam engine has already developed 83% of its total capacity""The problem for your argument is that the Steam engine scales up differently than you apparently expected -- and I didn't look at it as close as I should have either, or I could have put this tangent out of its misery much earlier."Well that is certainly a surprise and it does indeed reverse the point of my previous post.  But it also reverses your counterpoint about steam locomotives fundamentally continuing to increase horsepower during acceleration while, as we agree, diesels reach their maximum HP very early during acceleration.Or to be completely accurate, it reverses both of our points once a steam locomotive drops below a certain size.  What is the reason for this performance reversal that you say occurs when steam locomotives change in size?  I cannot imagine an explanation.  And what is the rate of this reversal as the locomotive size changes?
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