So I’m gonna be going to DCC control on my layout which gives me the ability to easily add loco’s to a train. Cool! But when does extra units go from functional to excessive? I mean 2 C628’s pulling 5 boxcars is excessive, but 2 f3s pulling 4 passenger cars may be underpowered. I know things like grades and curves come into play, but does anyone have a rule of thumb they use? I gues something like X tons per 1000 hp or somthing like that.
It depends on the train length that you can physically run on your layout. Grades, passing sidings and the length of your yard tracks will dictate that. On my layout, I’m set up for trains that max out around 25 cars. In N scale, this gives you a train roughly 6’ long, which is decent enough. I also have my scenery designed so the trains run through a series of vignettes, so you don’t see the front and back of the train at the same time very often.
To give the illusion of a longer train, I use a general rule of 1 engine per 10 cars. (12 cars would get 2, 23 cars would get 3 etc.). This gives me enough power to mount the steepest grade on the layout, and a good visual as the longer trains pass by.
Lee
Hi,
different members have different ways of doing this. Myself, I use the rule of thumb of 300 hp are required per freight car to be pulled across the road. This allows a SD90 to pull 20 cars while the GP38 will pull 6. Here is a link to a previous post about the subject. http://cs.trains.com/forums/1159026/ShowPost.aspx
Hope it helps
Frank
Railroads often run 2 engines back-to-back, even for small trains. This gives them the ability to run in either direction without having to either turn the engines or run backwards.
You really won’t like the answer but here goes.
Easiest rule of thumb (and prototypical too) is horsepower/trailing ton (hp/tt). If Have 2 SD70’s and am pulling 4000 tons of cars then I have 2 hp/tt.
8000 hp/4000 tons = 2 hp/tt
Normal flat land general merchandise and bulk trains get 1 hp.tt. In mountains 2 hp/tt.
Premium trains get 2-2.5 hp/tt (auto and stack) and high speed intermodal trains get 4 hp/tt.
Coal or other bulk trains with AC’s might only get .5-.8 hp/tt.
Generally a train needs to have the same hp/tt as the ruling grade. So on a 2% grade, a train needs at least 2 hp/tt. All of these are very general.
The problem comes on a model railroad on how to scale that down. A real loaded car can weigh 6 times what an empty car weighs. You have to scale down your train size to match your layout. You can use a hp/carfigure. I would start at the largest train with the biggest engines you can handle. So if the largest engine you have are SD70’s and the biggest train you can handle is a 25 car grain train with 3 engines then you figure from there.
12000 hp/25 cars = 480 hp/car. Rounding to 500 hp/car. That means a GP38 could handle 4 cars and a single SD40 6 cars.
For an intermodal train you want probably double the hp so figure piggyback train is rated at 1000 hp/car (platform). So five 5 packs you would need 25 cars x 1000 hp/car or 25000 hp or 6 SD70’s.
Like I said, you won’t like the answer.
So the best way may be to just pick which set of engines looks right for the train and use that. So you might have 3 6 axles on a coal or grain train, 2 six axles or 3 4 axles on a freight train and one or two 4 axle units on locals.
Dave H.
I’m not sure real railroads have a rule of thumb anymore. If they do, they don’t follow it too closely these days. During the auto changeover last summer, NS 17J went south out of Detroit with 2 light C9-40s, and no cars. One of the train watchers with us that night, was an NS conductor. He said if the train is scheduled, it goes, with or without cars, and added that they probably needed the power on the other end to bring a train back the next day.
Friday night, 29k, an empty auto rack train, came north with a single CSX AC4400, and over 90 empty auto racks. Likewise, an empty coal train of over a hundred cars went south, pulled by a single IC SD40, on the CN River Sub. That same night, 69T, a heavy Detroit to Chicago steel train, went south with a single GP50, and a bunch of coil steel cars, which I didn’t count.
A week earlier, a GTW train came north, with 7 units of various liveries, but 3 of the units were shut down, and being taken somewhere for service.
I have noticed a trend toward using a single unit on some fairly long trains, probably due to the cost of diesel fuel these days, and the much greater power of modern units.
On my own layout, I run 25 to 30 cars and two or three units. My rule of thumb, whatever looks good.
If one is modeling a prototype with a reasonable degree of accuracy, do whatever your prototype does.
If you want to be obsesso about the whole thing, determine each locomotive’s tonnage rating (pre HP/ton thinking) and each car’s weight (light weight, plus weight of lading if any,) then assign as much power as necessary to move the total weight of the train over the division.
If a train stalls on a grade, you haven’t assigned enough power.
If there seem to be too many locomotives, I have seen a BNSF freight westbound out of Barstow (headed toward Mojave) with a half-dozen units and fifteen assorted freight cars. Sometimes the railroad moves units to balance power or to prepare for an expected rush.
As for me, I run prototype-length trains behind the locomotives the prototype would have assigned, and keep a C12 class 2-6-2T or DD13 class diesel-hydraulic at Haruyama for pusher service - just as my prototype did at Agematsu.
Chuck (modeling Central Japan in September, 1964)
Flatland or grades?
According to a UP engineer friend he’s given a Consist Horsepower vs. Tonnage figure to say ‘yay’ or ‘nay’ to. Stalls then are then are his fault.
Empties are tacked onto the far end.
MODELING cosists of pulling empties, so ‘tonnage’ and ‘horsepower’ ratings become imaginary. Train length becomes a matter of length of your passing sidings. An 8’ passing siding holds about 5’ of train, including engines. That’s 5 85’ passenger cars (w. no engines).
What’s the length of your’s?
This is basically what other people have said, but this is the easiest way. (I’ll put it in an equation so you can just plug in the numbers)
I’d first decide what your longest train you want is. Let’s make L the length of the longest train. Then find your two highest HP locomotives, it would make it easy if they where the same type. Find out what HP rating the two locomotive are, and add them together. Let’s make that H for Horse Power for two locomotives. Then divide L by H and you should get the about of HP per car (C). L/H=C
For my layout my max length is 15 cars. So with 2 SD45s making a combined total of 7200 HP. Divide that by 15 and you get 480HP per car. This means that one GP40 can haul 6 cars. But this can make problems, as a SW1500 can only haul 3.
Other variables can also be what I car is hauling. Like a loaded ore trains weighs a lot more than a piggy back.
I usually run two locos (both powered) pulling a minimum of ten units.
The minimum would be the number of locomotives to keep wheels from slipping.
You’ll want to have two cab units pointed in opposite ends of the chain of locomotives if you want to avoid turning locomotives.
Even with the prototype there will be times when more locomotives are used than necessary. It may not be worth the effort to breakup a set of locomotives, or more power is expected to be needed for the return trip. Perhaps the locomotives are unreliable so spares are there for the ride to backup a failed unit if needed. There could be an imbalance of locomotives and they need to be moved to another location. And so on. Also, a batch of helper locomotives may be returned en masse to their starting point.
Do what looks good, and if it becomes seemingly rediculous, have a ready excuse (see previous paragraph).
Mark
It also depends on the pulling ability of individual locos. For example, my 2 Bachmann Berkshires can pull a 50 car coal drag up the grade with an Atlas GP7 helper on the rear, while my Proto 2000 E6 can do the same thing by itself.