Using a 4400-hp AC4400CW as a basis for comparison, it is rated for about 3800 tons at that speed and would have to slow slightly below 50 mph to pull 7500 tons.
If it helps the Class A had 430,100 LBS on the drivers for adhesion.
Timz has a point here. 7,500 tons at 64 mph on level track would take 10,000 to 11,000 drawbar hp, steam, diesel, electric or millions of mice. An A can’t to it on level track. Such speed would require about a -0.15% downgrade with a single A. Davis formulas aren’t perfect, but they’re very good at estimating train resistance. Timz has a working knowledge of this info - he’s done the homework, years ago.
Not the relationships in that chart-- they’ll never hold true. Take another look at his chart, everyone-- can you see why it’s worthless?
Hopefully you mean The Steam Locomotive? If so, I sure don’t remember him including anything that wacky, but I’ll check.
Any way to do the latter without first doing the former?
“Worthless,” …“Wacky”, eh?
OK, we’re up to name-calling … I had a feeling you were looking for that opportunity with this thread. Yes, the book is The Steam Locomotive: Its Theory, Operation and Economics Including Comparisons With Diesel-Electric Locomotives, Ralph P. Johnson, Simmons-Boardman Publishing Co, 1944. It was first published in 1942; reprinted in 1944, and again in 1981. Apparently it was the definitive classic.
A world-wide audience of professional engineers read the identical graph in H.F. Brown’s 1961 paper: the graph you have termed “wacky”. Brown had 40 years experience as a motive power specialist at the Pennsylvania Railroad and at Gibbs & Hill; the acknowledged premier motive power consulting firm of the era. A P.E., he also had a PhD in engineering. As a combinaton of education and practical experience, there are few people who have ever had the qualifications to comment on motive power as H.F. Brown. His article was and remains to this day perhaps the most widely and thoroughly vetted article on railroad motive power in the history of the industry. The correspondence regarding the article shows no one challenging that particular presentation, using the words “wacky” or otherwise … David P. Morgan commented on it, and missed that one; Trains missed it; General Motor’s chief of locomotive marketing who commented extensively on the article, missed that one; Railway Age editors assisted in preparing the Brown piece – they missed it too? British Rail, the veritable inventors of modern railroad locomotion, and for whom the stu
No, you have to do the former to do the latter, but you can do the former without doing the latter, which is what I meant. If you are not concerned about a fair test, I think you would have to stop after doing the former.
This is regarding your earlier comment:
“Sounds like you’re at a dead end. Far as I’m concerned you’re worrying too much about making your comparisons “fair”. Go ahead and make the comparison, doing your best to make it fair; if somebody says it’s unfair, leave it up to the reader to decide.”
I thought the whole point of a comparison was to prove something rather than to just leave the conclusion to the eye of the beholder.
I’d suggest the “Steam and diesel-electric locomotive drawbar characteristics” graph on page 406 of The Steam Locomotive In America Its Development in the Twentieth Century by Alfred W. Bruce, published in 1952. It compares a 6000-hp diesel against a 6600-hp steam locomotive and shows tractive-effort and horsepower figures on the vertical axes. Although I doubt that a 1952 diesel consist is the best subject for a current comparison, I can’t cite a graph comparing a more modern diesel against a steam locomotive.
Can you post it?
I’m afraid not. I’m behind-the-times to the point of not even owning a scanner. For whatever it may be worth, the related narrative (page 405) is as follows: “A typical 484 steam locomotive of 6,000 ihp with an axle loading of 70,000 lb will have a weight of about 280,000 lb on drivers with a tractive effort of perhaps 70,000 lb maximum. A 6,000 bhp diesel-electric three-unit locomotive with an axle loading of 53,000 lb will have a weight of about 630,000 lb on drivers and a tractive effort of perhaps 157,500 lb.” The use of exemplar diesels having four axles and 2000 hp seems strange to me.
Well, published motive power TE for a given locomotive is generally at “starting.” As Fred’s calculations show, the TE at low speeds is the Diesel-electic’s forte, unfortunately just not where the trains need it. This citation shows that that the starting Tractive Effort is identical (per lb of axle loading) at starting. Even at the overall relationship, the DE loses its TE advantage at 9 mph. And it still can’t use its advantage below that speed, whereas Steam can use its advantage above that speed. This is not inconsistent with the overall trends offered by Brown, Johnson and Fred.
|
MPH |
Diesel-Electric, TE |
Steam, TE |
|
0 |
157,500 |
70,000 |
|
5 |
94,500 |
68,833 |
|
10 |
66,150 |
67,667 |
|
15 |
50,4 |
The chart doesn’t agree with the diesel TE values that you listed. Its 70 mph value is approximately 20,000 lbs (not your 9459 lbs); and the diesel and steam TE lines cross at approximately 40 mph (not at your approximately 10 mph), where both locomotives produce approximately 40,000 lbs TE. At speeds below approximately 40 mph, the diesel produces more TE than the steam locomotive produces.
Wherever the numbers cross in regards to speed and TE, they still cross. The only other piece of information that we need to know then is adhesion.
Bruce assumes 25% for both steam and diesel.
No, the weight on the drivers of the two machines is quite different; whereas the estimation for that chart presumes they are similar. I was looking to see general relationships. That was kind of why I was hoping to see the whole chart, because rather than comparing similar weights on the drivers, this one apparently was comparing machines of similar horsepower by some measure of it at some point. It is interesting that the TE curves still cross even though the weights of these machines is so substantially different.
I hope I won’t input a fly to the ointment, but we seem to have difficulty, severally or as a group, with all the assumptions, and that is what keeps bogging down the progression of these threads. One person assumes this, another feels it isn’t right, since his biases don’t find it convenient for his purposes, and substitutes his own convenience, which raises “concerns” in the other camp(s), and off we go for another six pages of badgering each other over things that none of us appear (appear) to be qualified to deal with. I find it frustrating that we find ourselves tugged between two highly polarized views where neither side of the issue seems to accord much credence to the other.
I hope this can be settled, but I am afraid I’m pessimistic.
Sorry, I had to get that off my chest.
I feel somewhat better, but like I have just eaten a rice cake…dry…unflavoured even.
What is the weight on drive wheels of each engine?
The purpose of the chart was to compare locomotives of similar horsepower (6600-hp steam versus 6000-hp diesel) even though they had dissimilar weights (280,000-lb steam versus 630,000-lb diesel). Presumably this was because when railroads make diesel acquisition decisions they think primarily in terms of “buying horsepower”. I’m sure that a railroad could have compared the performance of a steam locomotive against the performance of a similarly weighted diesel locomotive while disregarding their respective horsepowers; however I can’t think of what operationally useful information that would have provided.
Each weight (280,000 lbs for steam and 630,000 lbs for diesel) is weight on the drivers.
I agree. The problem is in comparing two fundamentally different technologies and trying to find a common vocabulary to describe them, while dealing with a historical pattern of development in which you had a major player, General Motors Corp, trying to frame the conversation exclusively in terms which favored its products while trying to get the industry away from the older terminology, which spoke primarily in terms of Tractive Effort, but which was a metric that did not favor its products.
And this certainly fit in with a much broader, extraordinarily well-financed contemporary campaign to pursuade Americans to trade in their cars for the newest, latest, higher horsepower model. Horsepower was what it was all about. But that didn’t tell anyone much on a railroad locomotive and still doesn’t. The sleight of hand that compares two machines of similar horsepower, for instance, is attempting to compare one that develops its maximum at 19 mph; while the other reaches it perhaps around 60 mph. The problem is, in the real world, one of those machines is actually moving the train at 60 mph, while the other machine of ostensibly equal horsepower, can’t. Maybe if you cut the train tonnage in half it could, but th