I have found a method for my model railraod that actually is pretty close to the protype figures. What I do is take the continuous tractive effort of the locomotive (e.g. 82100 lbs for an SD40-2). Divide that by the scale (N scale - 160). N scale it is 513.125. That is the total train weight in grams that the train can pull on staight and level track. Now for my N scale railroad I have a maximum ruling grade of 2.65 percent on the mountain division. For N scale it would be 193.632075472 grams or 6.915431267 ounces. A 600 gram train would need 3 SD40-2's leading and one other engine DPU on the rear to get the train up the grade. Actual tests show the numbers for various locomotives are good and work. The reason that I would want the 4th engine DPU is to avod uncoupling due to excess pull on the couplers going up the grade.
Real railroads had to be concerned with the "ruling grade" which is the worst grade across an entire division. The effect of a sustained grade of many miles in length has much more to do with tonnage ratings than the simple calculation of horsepower.
During the steam era Santa Fe had the longest helper district in the country of more than 122 miles in the western Arizona desert! Contrary to popular belief the desert is not flat but a series of significant grades with horizontal curves. The big 2-10-2's were preferred here over the 2-10-4's which with high horsepower approaching 6000 (indicated at the cylinders in actual road tests, as reported by S. Kip Farrington) were a little bit slippery. Actual drawbar hp peaked somewhere around or above 5600 for those monsters of steam.
At the end of the Santa Fe, this was known as the Seligman Subbdivision. I dont know what they call it now.
Got it from the Google Archive. I have been able to download it. I will have a good read.
Thanks for pointing me in that direction.
This is getting interesting! Not bad for a University project?
David
Long Haired DavidA.K.A. David Penningtonmain man on the Sunset and North Eastern R.R.http://www.gmrblog.co.ukfrom the UK
Dave H. Painted side goes up. My website : wnbranch.com
John Droge may have covered this in Freight Trains and Terminals. I will have to read a few chapters and get back to you if your interested. The info is from the early 1920s.
There used to be (and may still be) a very good treatise on this subject by, I think, a locomotive engineer by the name of Al Krug. The article was Tractive Effort vs. Horsepower, and I found it extremely enlightening.
For my layout, I run each locomotive over a curving track on a 3.5% grade. The test train is a number of loaded hoppers weighing 8oz. each, along with a 4oz. caboose. Hoppers are added until the loco can no longer readily move that train and caboose up the grade, and with each hopper and the caboose rated at a nominal (and arbitrary) 70 tons, the loco is assigned that tonnage rating. There are many such curving grades on my layout, so a loco good for this grade should be good anywhere on the layout.In actual operations, most trains may have only one or two, or even no such heavy cars, but each car is nevertheless given a value of 70 tons, and the locomotive will get no more than its assigned rating (well, maybe one or two if there are no hoppers ). For longer trains, locomotives (all steam) will be added, and their tonnage rating will be added to that of the original loco.
While this isn't very scientific, it at least sets a common standard which generally assures that a train will be able to move to its destination without difficulty. However, there is a variable which hasn't yet been factored in, as most trains will be required to "switch" the towns through which they pass, and will pick-up or drop-off such cars along their way. I'll decide how to put that into the equation once operations become commonplace, as there's much yet to be done on the layout.
Wayne
FWIW, on my line the GP9's were rated for 1200 tons on a ruling grade of 1.64%.
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while there might be rules of thumb, i think its clearly and easier to understand in term of drawbar force or tractive effort and the friction coefficient for a ton of load. you also need to consider grades
http://cs.trains.com/trn/f/741/p/258901/2905505.aspx
suggest you use google to search for "tractive force" and cs.trains.com
greg - Philadelphia & Reading / Reading
No, it is my description that is wrong It is 0.5 per hp therefore 1800hp = 900 tons. Sorry for being unclear.
I've got zero expertise on this but suggest Googling train tonnage hp requirement or the like.
Doing so, I came upon items such as the following. I would think grades encountered and minimum acceptable speed at those grades would be one key consideration.
http://hm.evilgeniustech.com/alkrug.vcn.com/rrfacts/hp_te.htm
http://hm.evilgeniustech.com/alkrug.vcn.com/rrfacts/RRForcesCalc.html
http://www.republiclocomotive.com/locomotive-power-calculations.html
Interesting topic, glad you surfaced it as I have not paid attention to such subjects before.
A total tangent, I wondered what my HO loco's typical HP might be. The following calculator yields (approximately!) 0.005227882037533512 HP when I input 12v and 0.5 amps.
https://www.easycalculation.com/unit-conversion/amps-to-hp-calculator.php
Paul
Modeling HO with a transition era UP bent
As part of my university project, I need to decide on the number of cars that can be pulled by any loco on the railroad. As an example, I have a GP9 which, I am told, had 1,750 HP and Tractive Effort 64,750. It has been suggested the a local freight would work on 0.5 so that on a local it could pull 875 tons @ 50 tons per box car = 17 box cars. If on a rolling manifest (say for my railroad example from Boston to Hartford) with a factor of 1.0 it could tow 35 cars (including the caboose) - with adjustments for open tops and tanks (too early for covered hoppers on my railroad). Would that be about right?