# Prototype Question

Discussion in 'Getting Started' started by Cannonball, Apr 29, 2007.

1. ### CannonballMore Trains Than Brains

How many cars can a single loco pull before it starts to need a second loco? Or should I say how many can a single loco pull without looking silly? I'm starting to stock up on some rolling stock and when I get done with this round on eBay, I'll have about 20 cars under the same road name. (Burlington Northern) How many more can I add before I'm gonna need a second engine in the power consist to be at least semirealistic?
2. ### Mountain ManActive Member

Steam or diesel? Tractive rating of locomotive? Level track or gradient? Type of cars and gross weight of each?

The NMRA website has info on this and many other things.
3. ### CannonballMore Trains Than Brains

Diesel
Not a clue
Both
The NMRA is a dark and scary place to me.
They've turned model railroading into quantum physics.
4. ### SquidbaitRecovering ALCO-holic

The simple answer is: it depends!

Other than that, there is no simple answer. Things that affect how many cars a loco can pull are a) the weight of the loco; b) the number of wheels the loco has in contact with the rail; c) the horsepower of the loco; d) the number and weight of the cars; e) how fast do you want them to move; f) the grade of the track; g) is the track dry/wet/snow-covered?

A diesel loco can start and move a train longer than it is capable of controlling once it's moving (if that makes any sense... ). I saw a clapped-out GP9 lift over 100 empty hopper cars and pull them on a slight downgrade to the next yard down the line. He wasn't moving very fast, but he moved them.

Also, if you think about it, yard switchers aren't very large or heavy or powerful (hp), but they can move huge cuts of cars, just not very fast. Gearing also comes into the equation (just to complicate things), it's a bit like how grampa's 30 hp tractor can out-pull your 300 hp pickup (for things like stumps and plows), but you wouldn't use it to tow your trailer down the highway at speed.
5. ### TriplexActive Member

In real life, with big AC-traction diesels, I have (very rarely) seen 100+ cars behind one engine. For most modellers, the issue is "How long does my train have to be so I can justify more than one engine?" or "How few cars can my engine pull without looking silly?"
6. ### SquidbaitRecovering ALCO-holic

You'll need a bigger layout. Arena-sized, most likely.
7. ### CannonballMore Trains Than Brains

I need a bigger layout anyway.
(Doesn't everybody? )
I just have no space.

Either way, thatnks for the input, guys.
8. ### doctorwayneActive Member

And don't forget that, in general, model railroad curves are much sharper, and our grades are often much steeper than those of the prototype. If an overly steep grade halves your locos pulling power, putting that grade on a sharp curve will halve it again.

This is true, but the saying that "there's a prototype for everything" is also probably true. Two weeks ago, a CN train went through town with 120 cars, pulled by a single unit (something modern, looked like something from GE, but I'm not "up on" the newer locos). The line has no major grades, and many of the cars appeared to be empties. I'd guess-timate the speed to be about 30 mph. Yesterday, five modern locos, with about 15 cars. I didn't count the cars because I was driving on the highway parallel to the tracks, and I wouldn't even hazard a guess at the speed, as I was moving in the opposite direction, at about 125 kph. (Headin' for the hobbyshop!:mrgreen: )

Do you ever notice that when Model Railroader does a loco test, they give the drawbar pull in ounces, then give an equivalent number of cars (free-rolling, no less!:lol: ) that the loco would pull on "straight, level track"? Who the heck has much straight, level track? Even most club layouts don't have long, uninterrupted stretches of straight track.
I checked a number of test results, and, based on the testers' observations, concluded that many good-quality locos will pull about 14 of those "free-rolling" cars, on "straight, level track", per ounce of loco drawbar pull. Based on those figures, my most powerful loco would pull 116 cars: trouble is, not much straight track, waaaay too many steep grades, and not very many of those "free-rolling" cars. :mrgreen: I run what I need to get each particular train around the layout, but, when the mood strikes me, I run what I want! By the way, Cannonball, even if you're modelling BN, your train can, and usually should, include cars from other railroads, as all common carrier, standard gauge roads in North America interchange cars with one another.

Wayne
9. ### nachomanGuest

in the model world, we often do things to what "looks right" rather than what is prototypical. Diesels used to be almost always run in groups of two or more for other reasons besides horsepower. 1) If there was a breakdown of one unit (common in early diesels) the train was not completely stranded. 2) added braking ability. 3) If the units were MUed so that the cabs faced opposite directions, the group of diesels did not need to be turned at the end of the line. This may be important on branches, where they would lash up two units even for short trains, so that on the return trip, they had a short hood at the front of the train.

For models, I would always pair up F units or first generation diesels. For all other trains, I think >15 cars probably looks better with more than one unit.

kevin
10. ### RalphRemember...it's for fun!

I concur with Nachoman about using two units for 15 cars or more...in HO it looks "right" to me at least.
Ralph