IÂ’m well aware of the differences between tractive effort and horsepower, and why horsepower ratings arenÂ’t used with steam locomotives. But as those of you who work at museums know very well, this doesnÂ’t stop the visitorsÂ’ questions about how much horsepower that locomotive over there has (or had). Trying to explain tractive effort vs. horsepower, of course, usually leaves them cold and feeling that nothing very helpful has been offered by the museum guide (which is me). So may I ask you who are wiser in museum savvy than I: How do you answer the horsepower question? (Or could you point me to some internet info which might already address this question?)

More specifically, the 1903 Baldwin 2-8-0 we have on stationary display had a maximum TE rating of 39,453 lbs, with 200 psi boiler pressure, 21” diameter cylinders, 57” drivers, etc. (I have more specs if they’d be helpful.) Any advice on a specific HP figure we might offer as a ballpark answer to satisfy our visitors?

Many thanks, in advance, for any help you can provide! And thanks, too, Hume, for accomodating us Netscape users! :-)

My guess would be around 1200 HP or so, but my guess would also be that the engine probably has the equivalent HP of a GP-9 Diesel (1750HP). The Black River and Western RR in NJ has an Ex. GW 2-8-0 rated at around 33,000 lbs TE. I have heard estimates of it having around 1000 HP. Engineers have told me stories of pulling upwards of 30 freight cars with it which is about the limit of one of their GP-7's rated at 1500HP. Remember that where a steam locos HP is measured at the rail Diesel HP is measured at the prime mover. Generally 1/3 of the total HP is lost in the drive train of a diesel. Also, there is a much sharper drop off in TE on diesels at higher speeds than on steam engines. That is to say that a 3,000 HP diesel may be able to start a heavier train and pull it at low speeds, but a 3,000 HP steam locomotive will be able to pull a heavier train at 50 or 60 mph. Ron Ziel's book "Twilight of Steam Locomotives" has some actual numbers on this in the last few pages which might be of some interest.

jmonty@vt.edu

My suggestion is to be honest. If you don't know, you don't know, or tell them you'll find out. It's likley that the visitor doesn't understand what horsepower really is, but that doesn't stop them from asking. This is an opportunity to offer some realistic info like how many cars the locomotive can pull, weight of the cars, on what terrain, and at what speed, etc.

I recall a show visitor asking a guy I know who owned a steam tractor how fast it goes. with out skipping a beat he said they used to get it up to "50" and after a short pause, he followed up by addding "miles per day".

It boils down to people usually equating horespower and speed in their heads with what their car/truck has, and automobiles and locomotives are rather different animals.

The old standard calculation for HP for a simple steam engine used in industry was 2PLAN/33,000.

2 (number of power strokes per revolution, or two in a double acting cylinder) x P (average pressure on the piston, usually +/- 1/2 boiler pressure) x l (length of stroke in feet) x A (working area of the piston, in square inches, subtract the area taken up by the piston rod) x N (number of revolutions per minute)
Now, since there are 2 simple cylinders, you would find the HP number for one and then double it. The problem with a locomotive, of course, is not only isn't the boiler pressure constant, neither is the rotation speed. The HP output goes up as the piston travel speed increases...that, of course, is why a steam lokey can easily pull a train that it cannot start.

There was also a simple way to figure boiler horsepower based on the number of square feet of heating surface. As the equation was formulated when operating pressures were less than 100 psi, this was rather less accurate t(by anaverage factor of 3) than figuring the other way.
This is why some old steam tractors had a hyphenated number for HP. For instance a large A.D Baker engine (yes same fellow who developed the valve gear) could be a 21 or 23HP under the boiler rating and 75 and 90HP based on the cylinder output (so they were then sold as a 21-75 or a 23-90.)

BTW: the XPLAN/33,000 equation was also used to figure the HP of very early infernal combusted engines. They used a factor (X) of 1 for 2 cycle engines and 1/2 for 4 cycles, and then assumed an average cylinder pressure of 75 psi.

Amazing, the useless bits of trivia that rattle around in the dustbins of your mind. Isn't it?

> More specifically, the 1903 Baldwin 2-8-0 we
> have on stationary display had a maximum TE
> rating of 39,453 lbs, with 200 psi boiler
> pressure, 21” diameter cylinders, 57”
> drivers, etc. (I have more specs if theyÂ’d
> be helpful.) Any advice on a specific HP
> figure we might offer as a ballpark answer
> to satisfy our visitors?

Professor Francis O. Otuonye at Michigan Tech has published some relevant material on Rail/Locomotive Haulage that may answer your question on the relationship between horsepower and tractive effort.
http://www.mg.mtu.edu/~frotuony/mg336/chap02.htm

The relevant equation is:
HP (ft-lb/min) = [Tractive Effort (lb) * mph] / [375 * Efficiency]

Efficiency is that of transmission between motive power and driving wheels.
For spur gears, efficiency = 0.95 or 95%
single reduction, eff = 0.95
double reduction, eff = 0.90
worm gears, eff = 0.90 - 0.96

In the particular example of your 1903 Baldwin 2-8-0:
TE = 39,453 lbs
Efficiency chosen = 0.95

And solving for HP,
1107 HP @ 10mph;
2215 HP @ 20mph.

If there's no given value for TE, it can be calculated from this formula found at:
http://www.sps700.org/prpalogo.html

Tractive Effort (lb) = B^2 * S * BP * 85% / W
Where:
B^2 is the square of the bore of the cylinders (in inches);
S is the stroke of the cylinders (in inches);
BP is the boiler pressure (in lb/square inches);
W is the diameter of the driving wheels in inches; and
85 percent accounts for typical operations with the steam cut-off valve at 85 percent.

I hope that I've done my arithmetic correctly and that the information is useful.

Cheers.



kalbran1@NOSPAMsan.rr.com

When someone asks me how much can it pull, I tell em' we don't know. It has already pulled everything here!

Brian



bhebert@rypn.org

I can try a ballpark figure if this would help. If your 2-8-0 has 21x30 cylinders (guessing at the stroke, but 30" will give 39,458 lbs TE, very close to your figure), 200 psi boiler pressure, no superheater, and 57" drivers, horsepower would look something like this. Using formulas from several sources (however, Ralph Johnson's book, The Steam Locomotive, is an excellent single source for all kinds of formulas for estimating steam locomotive performance), drawbar HP at the tender coupler would probably be around 1,400 to 1,500 at 20-25 mph. Any estimate of steam locomotive HP must be taken with a large grain of salt because of the number of variables involved (heating surface, tube length, grate area, type of fuel, type of valves, drafting, the list goes on and on).


drs5260fr@yahoo.com

Ralph Johnson's book, The Steam
> Locomotive, is an excellent single source
> for all kinds of formulas for estimating
> steam locomotive performance)

Does anybody know where one might obtain a copy of this book? I've been looking for a long time and never seen it anywhere.

Railway Preservation News
hkading@rypn.org

Many thanks to all you good fellows for your replies to my questions! I figured this was the best way to get the info I need, and youÂ’ve been very encouraging with not only that but even more that I can use myself and whenever we have visitors with technical aptitude and questions. HatÂ’s off to you all.

Hume -

I believe I got my copy several years ago from Depot Attic in Stasburg, 717-687-9300. At that time, they told me the book is not particularly rare, and shows up occasionally. Other than that I've had good luck with other old locomotive texts from ABEBOOKS.COM, ALIBRIS.COM AND BIBLIOFIND, a subpart of AMAZON.COM.


drs5260fr@yahoo.com

I want to thank all the people who showed how easy it is to loacte copies of the referenced book.

Now that I found it, sorry, I can't afford it. $350-500 for a book is out of my acceptable range.

Railway Preservation News
hkading@rypn.org

"$350-500 for a book is out of my acceptable range."
A lot of the actual value depends on how often you'll actually use it, and why. A brand new copy of Machinery's Handbook, or the ASME codebooks are outrageously priced too, unless you happen to NEED them for your job.
Best advice? Keep looking, they'll eventually turn up at a better price. I found a dogeared 10 year old copy of Machinery's Handbook for $10, and sections I, II, V, VIII, and IX of the ASME code for nothing from an insurance inspector that was required to update his copies

steamnut@ptd.net

At the link shown below, you will find a review of the wonderful text book on Steam locomotives by Andre Chapelon. Probably the greatest expert on steam locomotives in it's waning days as a integral part of the World's railways. This is an English translation of the premier text on this subject. And, since it is newly in print, copies should be easy to get, though certainly not cheap, it is worth every penny!
Sincerely, Keith Taylor

Camden Steam Services

> When someone asks me how much can it pull, I
> tell em' we don't know. It has already
> pulled everything here!

> Brian
"How fast can it go?" Is the question I hear the most often. When the Shay was running the answer was "Top recomended speed 12mph, slightly more over a cliff!"
When asked how much will she pull, we just pointed to the 240 ton Lidgerwood Skidder and say that.

crisolite@aol.com

We need a different horse power calculation. Strangely enough the horse in the photo is rated at about 8 horse power. Horse power was based on welsh ponies, while we use Belgian draft horses. In more conventional railroad terms the horses are rated at about 3,300 lbs of tractive effort.

Randy Hees



http://spcrr.org

hees@ix.netcom.com