Does anyone know how are HP requirements calculated for specific cargo weight, grade percentage, and speed of train movement?
I mean specifically, does anyone know the formulas for those things?
Electo-ortcele: I cannot answer this question, but have seen several of your recent posts, and wanted to offer a site that you might enjoy. The other day you mentioned, I think that you were from Romania?, anyway…The site is:“Latta Laments-- Tales of the CTH&SE” by Mike Dettmers
www.haleytower.org/laments/index.html… or can simply Google- Latta Laments
Latta Laments is a series of stories by Mike Dettmers who is a night trick dispatcher on the Soo Line’s Latta Sub in nort Central Indiana, and relates his trials and tribulations as he does his job…I think it is quite interesting and funny and informative…I hope you will like it…Let me know...samfp1943@hotmail.com. Parsons, Ks.
HPT… horsepower-per-ton. Your high-priority intermodals (the Z’s, shooters, etc) usually rate @3.5hpt, or better. Your lowly boxcar manifest (the pickers) that works in, and out, of every siding will usually rate below 2.0hpt.
Total combined horsepower divided by total tons…
3 engines at 4,400hp *3=13,200hp / 8500 tons = 1.55hpt
CC
Each territory has it’s own tonnage rating for each locomotive which is a function of the grades and curvature on each territory…EVERY subdivision has it’s own RULING GRADE…the biggest ‘hill’ on that particular segment of track.
When Class I railroads obtain new classifications of locomotive power they generally test it in the real world on real trains while having a dynamometer car attached to the consist. These tests will generally be performed over the most significant grades that the railroad posses. After the data from these tests are examined and related to prior testst of other locomotives the tonnage rate for the New Class of engines will be determined and disemenated to all that distribute power and build trains.
Horsepower is only one factor in how much a locomotive can haul, the type of traction AC or DC is another factor.
On a territory where GE’s latest ES44DC’s with 4400 HP are rated for 3900 tons…the CW44AC’s also 4400 HP are rated for 5600 tons. Where horsepower does an effect is on the speed at which a given tonnage can be handled. Intermodal trains are normally powered to a level of 3 HP per ton of train. Bulk Commodity trains will be powered to a level of 1 HP per ton, or less. Intermodal train can reach ‘crusing’ speeds of upto 70 MPH. The Bulk Commodity train will be able to ‘JUST’ climb the ruling grade at the minimum continuous speed (9 to 11 MPH) that the locomotives allow and will rarely top 40 MPH on level ground.
samfp1943
thanks for the link, I’ll check it out.
The country is Croatia by the way, but you didn’t miss far 
(Romania is on the other side of Hungary)
thank you all for your imput.
But ok, let’s say I know the tractive effort the engine has at a certain speed.
How do I transform that number into the number of tons it can pull on horisontal terrain assuming the wheels don’t slip?
You use the “Davis Formula” to determine total resistance. It has components for wheel and bearing friction, air resistance, and grade. Resistance is stated in pounds per ton. For loads, as I recall from memory, figure 4#/ton wheel and bearing, air resistance at low speeds is negligable, for high speeds considerable since it increases as the square of velocity. Air resistance is also a function of the area of the vehicle. intermodal air resistance is a big deal due to higher speeds and very poor air flow characteristics. Grade resistance is 20#/ton/1% grade. This is zero on flat track, 20#/ton on 1% and 44#/ton on 2.2 %
Now we can start to answer your question assuming flat track and speed not over 10 mph our only resistance is wheel and bearings. If all loads 4#/ton.
Now we need tractive effort of locomotive at 10 MPH. Assume an SD-40 with 90,000# TE at minimum continuous speed of 9 mph. 90,000# TE / 4#/ton resistance = 22,500 tons. Since the diesel is constant horsepower, if speed doubles, TE is halved so TE at 18 mph is 45,000# and tonage rating would be 11,200, at 36 mph would be 5600 tons and at 72 mph would be 2800 tons. Actual ratings at speeds of 18 mph and higher would be lower due to air resistance. The fall off in ratings quoted has only to do with fall off in tractive effort as speed increases.
Mac
Modern roads have their system loaded into a computer program that calculates the speed, drawbar forces, fuel consumption and load on a given train. Some programs use a generic train, some allow trains to be built with specific cars or load/empty configurations. You can also specify what engine consist you are using.
They will “run” train over the route, noting where the speed falls below a minimum (or reaches zero), where maximim drawbar or buff forces are reached and giving information on fuel consumed. Some programs are text only, the output is basically a table of exceptions, some are graphic and you can watch the train move across the territory with graphs for the drawbar forces and speed.
Basically the railroad will use these tools to develop a standard requirement for power, often expressed as horsepower/trailing ton, as others have mentioned. A flat land drag freight might be .5 to 1 hp/tt. A DP coal train with AC’s might be .7 to .9 hp/tt. general freight trains run with 1 to 2 hp/tt, premium intermodal and automotive trains might get 1.5 to 2.5 hp/tt in flat areas, 2.5-4 hp/tt in mountainous areas.
Dave H.
Thank you all, I understand now.
By the way PNWRMNM I’ve done some research on this, some people say it’s 5 punds per ton for wheel resistance rather than 4
thanks adrian, great stuff indeed
" let’s say I know the tractive effort the engine has at a certain speed.
How do I transform that number into the number of tons it can pull on horisontal terrain assuming the wheels don’t slip?"
In other words, how hard is it to pull a train? You’d think we’d know the answer to that, but we don’t actually have that good an idea. There are formulas, but most of them say an engine with (say) 400 kiloNewtons of tractive effort at low speed should be able to pull 30000 to 60000 tons on the level. Is that realistic? It would be interesting to find out.
Here is some good stuff on tractive effort and HP:
Krug is the man!
Adrianspeeder