train lenght vs curves

[Anonymous]

Let me start again. We have an around the cellar layout; 4 scale miles. We easily run 90 car freights on very gentle curves. We have nicely weighted cars, metal wheels, good couplers (mostly Kadees, not junk stuff) excellent motive power (again, not junk). We would like to deviate from our 2 loops around with a large expansion. This is what we plan and my question to everyone. We would like to have a curve of 10' diameter on a 1% grade and the curve would approach about 200 degrees, more than double back on itself. We want to be able to continue to run large freights. However, we're concerned about the lateral forces and are very concerned about "shoestringing" a long freight. I suppose mid-train helpers might be the answer, but we were wondering if anyone has dealt with such a situation and how many cars can be run successfully on such a curve without difficulty.
Thank you very much.

[Anonymous]

A 60" radius is very broad and a 1% grade would be less of a grade than a typical helix. I have never tried pulling that many cars up a curved grade, so I couldn't tell you what would happen. You probably already know not to mix car length, short cars between long cars (what are the length of the cars you're pulling?). I think you could have derailing problems if you super-elevate your curve. But I don't know of a formula that can determine how many cars can be pulled up a curved grade.


Just my [2c] worth

[tomikawaTT]

Somebody certainly has dealt with something like that - a little outfit originally known as the Southern Pacific! The Southern Pacific may have faded into the mists of history, but the Tehachapi Loop is most emphatically still in service - with well over 360 degrees of curvature on a grade a good bit steeper than 1%.

The La Mesa club layout in San Diego's Balboa Park is a very good representation of the route over Tehachapi Pass, runs prototype-length trains and (to the best of my knowledge) has had few or no derailment problems. Perhaps a member of that club might be willing to add to (or correct) this information.

[Don Gibson]

YOUR CURVES are finite. Your grade is the limitation on weight to be pulled at any one time.

AT some point you will exceed the limit of the (a) grade and (b) curve.
When that limit is reached, start pulling off cars.

HOW can you predict when cars have different lengths, weight, and using different trucks?
I'm assuming you are not wasting your time pulling identical cars on identical trucks - (or conducting a test on how fast you can go before things fly off).

What railroads do is calculate the weight to be pulled, and the horsepower needed, and put the heaviest cars forward and emptys on the rear. If anything goes wrong, trains stall, etc, jobs are at stake.

YOU do what you want.

EDIT: For the record the Tehachapi loop ballparks around 84"r. in HO and 2% grade, anyone got room for a 14' X 28' 'M' shaped centerpiece?

[dinwitty]

your curves are very broad, if for HO, be any curve, level or grade a curve introduces a little more friction. But like any railroad, its an operational problem to enjoy solving.
Other model layouts arent so generous in curves or grades. I dont see major problems in what you want to do, go for it and see how it works out.

[Texas Zepher]

QUOTE: Originally posted by cnvan
We easily run 90 car freights on very gentle curves. We have nicely weighted cars, ... We would like to have a curve of 10' diameter on a 1% grade and the curve would approach about 200 degrees, more than double back on itself. We want to be able to continue to run large freights. However, we're concerned about ... "shoestringing" a long freight.

If the cars are NMRA weighted as you have implied, there should be no problem. That is the purpose of that weight. I've run 65 cars up hill on an S-curve much tighter than that (36") with no problems at all. The cars filled both curves and the caboose was at the bottom of the hill.

[jimrice4449]

I have a test helix, it doesn't go anywhere it just makes 2 1/2 turns and ends at a bumper post. The radius is 42" and the grade is 1 1/2 per cent. My test trains are a 50 car frt train made up of cars wieghted to 3 1/2 oz and the psgr train is an 11 car Cal Zephyr(brass). I've never had either train pull off of the inside of the curves. Of course there've been times when not all of the train made it onto the grade, but they've never pulled off of the inside of the curve.

[johncolley]

Do what the big guys do! If your engines start to slip, add some helpers either pushing or 2/3 back. As for stringlining, well they do that once in a while, too, but not often. The word "empirical" means knowledge gained from experience! Keep trying until you find the limit, then let the rest of us know!

[cacole]

On our HO-scale club layout with 26" radius curves and 2% grades, we have pulled up to 60 assorted pieces of rolling stock with no derailments, using 3 or 4 diesels on the front end.

I, too, always thought that no prototype train would ever put an empty car at the front and loaded to the rear, but one day last year when I was out video taping trains east of Benson, Arizona, where there is a 5-mile long 2% grade with numerous tight curves, a Union Pacific train pulled by 4 diesels had an empty TTX flatcar at the front followed by 90 autoracks. Even if the autoracks were empties, that was still a lot of tonnage to pull up such a long grade and the numerous curves.

[moparman48]

Being a semi-veteran model railroader, I still learn new stuff every day. Can some one elaborate on the effects of mixing short cars with longer cars? My rolling stock represnt cars from the '40s to the '60s, so I have various lenghts.

[canazar]

Mopar Kid,
If you ar running trains in 20-30 car range, and they are wll weighted well, and good equipment, I dont thingk you would have nay problems.

Often I run a train to one section of the layout where I will have a concrete and plastic peelt operation, along with others. For that train, (the Monday Pain" I call it) I wll have 6 2 bay 70 hoppers, 5 54' covered hoppers, and 2 or 3 65' covered hopppers, one lumber car, (which are pretty long I think 65') and a 3 or 4 40' and 50' box cars. I have run them all in different orders, over 2.2 grades, 24" to 34" radiuis turns, in and out of the yards... and never had a problem.

That is biggest mix of mismatch sized cars I know of. Hope that helps you a little.[:)]

[Anonymous]

QUOTE: Originally posted by moparman48

Being a semi-veteran model railroader, I still learn new stuff every day. Can some one elaborate on the effects of mixing short cars with longer cars? My rolling stock represnt cars from the '40s to the '60s, so I have various lenghts.

It's explained better and in more detail in John Armstrong's book Track Planning for Realistic Operation, but basically car length affects the overhang or the amount of swing the coupler makes around sharp curves. Problems can accrue if you run a 40' box car between two 87' flat cars with body mounted couplers. The long cars will swing out more than the short cars. You might have never notice a problem because some, if not most, manufacturers equip long rail cars with truck mounted couplers to eliminate this problem.
It's not a problem with prototype railroads because the curves are so broad. We scale modelers usually don't have a scale 40 acres to turn a train.

[modelmaker51]

I think the most important factor will be the transitions from straight to curve. My minimum mainline curve is around 36" but the transition is twice the length of the curve, which results in something more like an elipse than a radius. We have no trouble running 60-75 car trains of varying lengths. We've run as many as 86 cars. Except for passenger cars, our max car length is 70-75' as we are modelling the 50s-60s, so no 85' autoracks etc.

We only use KDs and all cars are weighted to the nmra standards.Wheels are only changed if they are causing problems, so about half the wheel sets are metal.

With nearly double the radius I don't think you should have any probs running 100+ car trains, just make sure the transitions are gradual and smooth. We used an 10' long piece 1/2' trim to lay out our transitions and curves.

[Leon Silverman]

Since you invested in metal wheels, properly weighted cars, kadees, and good engines, it is likely you also invested in good quality power control for your layout. A prototype 90 car train, even if the cars are emptys, will start up slowly and gently. As long as you start the train in a similar manner, you should have no problem. One thing you might want to do is the check run the the expansion line with just the engine(s) to make sure there are no dead spots that might cause the engines to stop momentarily and then start up again. Then you will have shoestringing.
Midtrain helpers couldn't hurt as long as they start moving just before the leader locomotive(s). This would mean they would have to be either DCC operated or in a different electrical block than the lead engines. Having the helper locomotive start just befor the lead locomotives will generate some slack in the couplers and make it easier for the lead engines to start up. However, if the lead engine does not start up within a second of the rear engines, you will probably then have a "baloon" derailment where the cars fall off the outside of the curve. For this reason, your helper engine should be the weakest puller of your locomotive set. If you are using diesel engine helpers, all but one unit should be a dummy to avoid overpower the lead locomotives.