# of loco's req'd for a given weight

Is there a formula for deciding how much hp is needed for pulling trains of varying weights ie: hp per ton etc,

Scott W Leon-Guerrero

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RE: # of loco's req'd for a given weight, plainsman, Dec-02-02, 08:56 PM, (1) RE: # of loco's req'd for a given weight, sniper297, Dec-02-02, 10:08 PM, (2) RE: # of loco's req'd for a given weight, Mrscotti, Dec-02-02, 10:16 PM, (5) RE: # of loco's req'd for a given weight, Mrscotti, Dec-02-02, 10:15 PM, (4) RE: # of loco's req'd for a given weight, plainsman, Dec-03-02, 00:24 AM, (8) RE: # of loco's req'd for a given weight, kevarc, Dec-02-02, 10:10 PM, (3) RE: # of loco's req'd for a given weight, Mrscotti, Dec-02-02, 10:19 PM, (6) RE: # of loco's req'd for a given weight, kevarc, Dec-02-02, 10:23 PM, (7) RE: # of loco's req'd for a given weight, mjcoyne, Dec-03-02, 01:31 AM, (9) RE: # of loco's req'd for a given weight, OhioRailFan, Dec-03-02, 01:48 AM, (10) RE: # of loco's req'd for a given weight, Mrscotti, Dec-03-02, 06:33 AM, (11)

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This is really a lot more complicated question than it seems. Some of the questions that first need to be answered are:
1 How fast do you require the consist to move, to not impede your track's other traffic?
2 What is the nature of the train being pulled? unit coal, piggyback, autoracks, reefers, merchandise, scrap metal, local, passenger? Lines with almost all dedicated ore traffic are able to use low HP heavy six axle locomotives on very heavy trains, as they do not need to maintain much track speed. The prime consideration is starting pull (tractive effort) which is related to weight and adhesion, not HP. A 370,000 pound SD7 or a 390,000 pound U25C can start a very heavy train, even though they are meager to modest in HP. Once moving the number and current capacity of the traction motors may be more important than HP in determining whether a consist will make it over a grade. Since a SD40-2 has the same traction motors as a SD45, and the benifit of better computer control, a SD40-2 is able to generate slightly more continuous pull than the higher HP SD45. Now as speeds rise, the higher HP locomotive will prevail, and above 45 mph, the SD45 is clearly superior. Some trains like piggybacks require very high HP but not a lot of starting pull, because not onlyu do they operate at higher speeds, but they are very inefficent moving through the air. This creates a lot of drag at high speeds, so a lot of HP is needed to maintain speed and overcome air resistance. It used to be hat these trains were the domain of units like the B36-7, the B40-8, and the GP50 and GP60. Now it is more common to see high HP six axle units on these trains, such as the AC6000. The modern unit coal trains of 14,000 tons, are usually handled by modest AC units like the AC4400 and SD70Mac, and SD90Mac/43. The 6000 HP versions rarely see coal service.
I have to go, but will finish the answer a little later.
Bob Boudoin

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In addition to that, player or AI? AI traffic trains cheat on physics.
Try making a route with a 4 or 5% grade (or download PO&N v6 and start at Johnsburg wye going up the South Pass), start the default 2xGP38x35 mixed car consist at the bottom and see if you can drag it to the top. No way. Now do an AI traffic train with the same consist, slow but steady the little beggar climbs all the way to the summit. Most of the default MSTS heavy consists (2x Dash9, 49 mixed, etc.) will NOT climb the South Pass on the PO&N without adding more helpers when the player is driving, even with a running start. All of them will climb that hill as an AI train.

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Guess MSTS does that so at least something works...heh heh

Scott W Leon-Guerrero

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Interesting! I was thinking about a coal drag as you mentioned approx 12,000 tons pulling over Raton Pass from the Las Vegas side with 5 ac6000, It went over but it sure was dragging it's hiney about it, Maybe I'll try it w/SD70m and see how it goes......Thank you for your quick answer

Scott W Leon-Guerrero

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I did not mention grades and curves. Obviously, it takes a lot more pull to get a heavy train across a steep grade than to get it down a gentle downgrade. Very curvy routes also demand extra pull to overcome train resistance.
Now on a reasonably flat straight route, the 14,000 ton coal train might get by with .75 HP/ton. A 6,500 ton merchandise freight might require 1.5 HP/ton to maintain 45 mph, and a 3,500 ton piggyback might need 3.0 HP/ton to maintain 55 mph.
I did not mean that an SD70Mac or AC4400 will out pull their 6000 HP counterparts, just that 6000 HP models won't necessarily do any better at slow speeds. The reason these are not frequently seen on coal is not that they wouldn't pull the coal train, but that their extra HP can't be put to use, they are more expensive to operate than their 43-4400 HP relatives, so they are usually allocated to functions where the extra HP will accomplish something, and this occurs at high speeds.
Hope this was helpful,
Bob

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Many RR's have charts for each subdivision. It will list grades and tonnage for the different engines. The BNSF site is a good place to get timetables that list the requirements for grades.
http://www.bnsf-ttc.com/bnsftime/index.html
Kevin Arceneaux
It is time for Amtrak to become a fallen flag!

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Thanks Kevin! That'll really help! That's more or less what I was looking for..................Damn..3 answers in quick succession..wasn't expecting that.........Thanks a lot Fellas..really appreciate it

Scott W Leon-Guerrero

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You can get the Raton timetable there and you will see the axle requirements.Kevin Arceneaux
It is time for Amtrak to become a fallen flag!

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you can get RR FORCES CALCULATOR at AL KRUG's site www.vcn.com/~alkrug/home.html cheers

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OK you guys, how many 50 ton coal hoppers do you think a 2-8-2 could reasonably be expected to haul up a 1.5% to 2% grade, with a few curves in it?

>OFFICAL MEMBER OF THE EXTREME PARALLEL PARKING TEAM<

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Thanks everyone! You were all very helpful! All the information will be put to use. Thanks again!

Scott W Leon-Guerrero

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