Slap a 500 horse engine in a 2500 lb vehicle--they do that in Europe with some of those high priced sports cars; you know the ones--those with a price tag approaching or exceeding a quarter of a million smackers--with a top speed exceeding 200 MPH and turn 0-60 in 3.5 seconds--and you may be able to tow a 2000 lb tent trailer. Slap that same engine under the hood of a 5000 lb pick-em-up truck and you probably would be able to walk off with five tons in tow. In short, T(ractive) E(ffort) tells you how much work you can do; H(orse) P(ower) tells you how fast you can do it. This is why if you take a 175 HP John Deere tractor and engage with a tug-of-war with a 500 HP GMC pick-em-up truck the tractor will pull the pick-em-up truck all over the south forty . . . . . . . . . . but it sure won't do it very fast.
Steam engines did have horsepower ratings but unlike a diesel which exerts its greatest tractive effort going from stop to moving a steam locomotive's horsepower curve develops in a bell curve. I remember an article in Trains magazine of a few years back talking about the Cab-forwards on Donner. They were rated at about 4500 tons--6000 HP I would guess--but they could only develop about 15-20 MPH doing it; a 4 unit F7 set--also 6000 HP--could walk about 6000 tons uphill at 30-35 MPH. I don't care how much infatuation you have with steam is it really any wonder that GE is building locomotives in the 21st Century and Baldwin isn't?
From the far, far reaches of the wild, wild west I am: rtpoteet
Here's a good discussion on horsepower vs. tractive effort .
Wayne
I posted the following links in response to a similar thread earlier this week:
Following link has some prototype tractive effort information: http://www.steamlocomotive.com/misc/largest.shtml
Following link has information on how to convert tractive effort to drawbar pull: http://www.tpub.com/content/armytransportation/TR0603/TR06030076.htm
When you look at the second link, be sure to look at the proceeding and following pages of the document. I think a lot of good info here.
Regards
If you go to the Trains Magazine General Discussion forum and do a search in "Search Community" (right sidebar), you will find many threads dealing with this in great depth.
Here is one from 2004: http://cs.trains.com/trccs/forums/p/15592/220885.aspx#220885
-Crandell
Here are some tonnage ratings of the SP as of Oct. 1952 for between Sparks and Truckee you might use to compare.
F7 (4 units) -- 7,900 tons
PA (2 units) -- 4,075 tons
AS616 -- 2,150 tons
2-8-0 -- 1,300 tons
4-8-2 -- 1,700 and 1750 tons depending on class
2-10-2 -- 1,875 and 2,150 tons depending on class
4-8-8-2 -- 3,400 and 3,650 depending on class
As has been mentioned there are a whole bunch of variables in the mix so its not possible to directly compare horsepower and tractive effort between steam and diesel. Another factor is wheel slip adjustment. A diesel can have much better wheel slip control than a steamer had and so can pull more at low speeds, that's why AC's are so powerful, they have excellent wheel slip control.
But back to your question. The RDG used a heavy 2-8-2 or a 2-8-0 as powerful as a 2-8-2 to pull freights and they were replaced with two 4 axle diesels on flat territories or three 4 axle diesels on hilly territory. So they would replace a 2-8-2 with an AB set of F or FA units or two 1500-1600 hp road switchers on flatter territories.
Dave H. Painted side goes up. My website : wnbranch.com
It's a misleading conversation--and easily mislead me.
Tractive effort for steam engines was normally the maximum available force in pounds at the drawbar available for pulling a train--and peaked at very low speeds, then reduces as speed increases.
Horsepower is the ability to do work, and 1 horsepower is roughly equal to 746 Watts, or 550 lb-ft/second.
http://en.wikipedia.org/wiki/Horsepower
I would say it is difficult to correlate the maximum drawbar tractive effort of steam power with horsepower because so many factors enter the equation: weight, condition of rail (wet, dry, sanded), speed, etc.
From the loco test data reports I've seen for just one given steam locomotive type, it would be challenging to try to extrapolate a direct, real-world mathematical relationship between the two.
I noticed that Steam locomotives are rated in Tractive Effort and Diesels are rated in Horsepower. What "rule of thumb" can I apply to equate the two? For instance a few years ago in MR Mag I saw a photo of a Mikado 2-8-2 pulling a 75 car freight train. The Mikado is rated at 120,000 lbs (60 tons) with a boiler pressure of 180 psi and a Tractive Effort of 28,000 lbs.
If a Mikado can haul a freight train of 75 cars (overall train weight unknown), How many Diesel Locomotives would it take to do the job of 1 Mikado, on average?