Prototype Versus Model Grade Question

[wabash2800]

On real railroads, they can get by with short, steep grades with long trains, connecting between two railroads, with one on a fill, for example, because at any given time, most of the train is on the level, whether it be the front or back of the train on either line.

I've been an HO model railroader for some years and know how to calculate grades, etc., and have built them successfully. The current layout under construction has 2% as the max grade to handle all the trains I need to run, including some long ones (about 20 feet long).

Anyway, I've got this section I'm planning where my road parallels and connects with a foreign road that is on a fill (3"). If I utilize my 2% max standard, that will require about 150" (or about 12 feet) to get up to the other road (which by the way is double track and will have a long crossover to get the trains on the right-hand track.)

So, I'm wondering if the same physics as the prototype will apply if I instead use a 3% grade for a shorter section (about 8 feet) and all things being the same with train length and motive power. (Making the upper line run downhill to reduce the uphill grade is not an option, though I've used that trick before.)

Victor A. Baird

Fort Wayne, Indiana

[mlehman]

Victor,

I was pondering this very question myself a few months back when I was doing some detailed smoothing of grades to maximize the tonnage rating in several areas of my line. In general, I stuck to 2.5% max. Problem was I didn't scan it all as closely as I later did once I had an electronic level, which gives me direct readout on grades. As it turns out, I did find that many of the problem spots were as much as 3%, but most were simply in excess of 2.5%.

So my recommendation is to go for 2.5% and you'll likely be more satisfied with the results. In my case, I was trying to pull mainly passenger trains with a single steam loco for prototype reasons. Doubleheaders were somewhat rare on the Rio Grande because of buridge limitations that required them to uncouple and cross one at a time.

Maybe you're in the diesel era and it's simply a matter of adding another unit? That really helps in such situations if you must go with 3%.

[wabash2800]

Thanks Mike. Yes, I could add an additional unit but my prototype wouldn't do that. For short steep grades on connectiong tracks, like in my example, that I see on the prototype everyday, the prototype has no problem at all. And often these tracks are curved.

[mlehman]

Perhaps I can interest you in a good deal on some depleted uranium?

Sorry, don't think that stuff is legal for most civilians, although they do use it to add mass to aircraft control surfaces IIRC.

Thinking some more about it, if you're in the diesel era, you'll probably be OK if the steeper section are short. The way the trucks pivot  helps keep all wheels in contact on diesels. I was dealing with the issue with my steam, diesels did OK, but let one of those long rigid wheelbase steam locos hit even a slightly uneven spot at max tonnage and they just sit and spin.

Sometimes this involved the vertical curve transitions. Most of the time it was more about side to side unevenness, even .010" could cause a problem.

[Texas Zepher]

wabash2800

So, I'm wondering if the same physics as the prototype

Sort of, but might not be nearly as dramatic on our models as it would in real life.    What you are talking about is a "ruling grade" or "limiting grade".  Since your 8' is less than the length of the normal 20'  train then it is not the ruling grade.  For trains less than 8' it would be.

[wabash2800]

Texas Zepyhr T]that's what I was thinking too, but I guess there's one way to find out. I might have compromise and get 2.5% to work as Mike suggested. 

[doctorwayne]

wabash2800

....So, I'm wondering if the same physics as the prototype will apply if I instead use a 3% grade for a shorter section (about 8 feet) and all things being the same with train length and motive power.....

Depending on how much track you have in place, an 8' test grade should be do-able without too much trouble, although you'll need at least a few feet of level track at the top just to be sure that the train keeps moving.

mlehman

Thinking some more about it, if you're in the diesel era, you'll probably be OK if the steeper section are short. The way the trucks pivot helps keep all wheels in contact on diesels. I was dealing with the issue with my steam, diesels did OK, but let one of those long rigid wheelbase steam locos hit even a slightly uneven spot at max tonnage and they just sit and spin. Sometimes this involved the vertical curve transitions. Most of the time it was more about side to side unevenness, even .010" could cause a problem.

I add lead to all of my steamers, taking care to balance it about the centrepoint of the driver wheelbase.  On one particular grade, an ess bend with a straight section between the two curves, the locos (usually doubleheaded) occasionally exhibit some wheelslip as they enter the straight, but regain their footing once they make it to the second curve.  I'd guess that the forces which increase the cars' drag while they're in the bottom curve act equally on the locos' drivers in the upper curve, giving them more "bite". 
Another grade, also at 2.5%, leads to the second level of the layout, and it consists of two horseshoe curves (in opposite directions) also separated by a long straight section, then two wide ess bends.  I've run trains in excess of 35' in length up this one, with all of it on the grade, which is about 45' long.

A single locomotive (steam or diesel) should be able to haul your 20'-long train on level track, so your 8' test grade should give you the answer as to whether it can haul 8' of that same train up the grade.
Another factor which might come into play is the cars in the train.  F'rinstance, a 20' long train could be made up of forty 40' boxcars, with 160 axles, or 20 89' autoracks, with only 80 axles.  Even if the train weight is similar, the latter should offer less rolling resistance.

Wayne

[selector]

wabash2800

...

So, I'm wondering if the same physics as the prototype will apply if I instead use a 3% grade for a shorter section (about 8 feet) and all things being the same with train length and motive power. (Making the upper line run downhill to reduce the uphill grade is not an option, though I've used that trick before.)

Victor A. Baird

Fort Wayne, Indiana

 

Yes, the physics is exactly the same because both items, prototype and model, are operating in the same gravitational field on the surface of our planet.  However, there are differences due to curves, the types of bearings and friction, real tractive efforts at the rails for both classes of items, and the metal surfaces that are bearing...tires and rail materials.

I think our models might do a bit better than the real locomotives in terms of cars pulled on a given grade, assuming the curves are few and broad.  However, if we were to scale-weight all the cars in a scale consist to match what a proto locomotive can pull, I think the proto locomotives do better.  I could be wrong.

My models do well, with a single loco on the front, pulling about 15-20 cars up my 2.4% helix with 33" and 36" curves.  A BLI Niagara or a T1 Duplex can haul seven Walthers heavyweights plus a reefer up my helix without a pause or a slip.

In my limited experience, grades nearer to 3% and up just invite disappointment or the same complication the real roads face...added tractive power.

[ndbprr]

How will it. Affect the transitions to level? It might not save enough length to justify it

[wabash2800]

I agree on the vertical transitions as that is why qualified my distances with the word "about".

[superbe]

I realize what I am about to say has no bearing on the question at hand, but I have to say it anyway so forgive me. 

The local shortline when it had steamers had a grade so steep that it would uncouple half of the cars at the bottom and pull the first group up the grade to a "run around" track and then back down and pull the remaining cars up the grade.

Thanks for reading and have a good day.

Bob

[cuyama]

It seems that this would be very simple to mock up and know for certain with your specific equipment.

[wabash2800]

Thanks all for your replies. I may have a found a solution to the problem. I might start the Wabash grade in the adjacent room down the track from a place where my line and another foreign road cross at grade. I'll continue the Wabash grade uphill into the next room where my Wabash line finally meets the PRR on the same grade (on a fill).

That way, I can stick with my 2% max and have the tower operator control the connection btw the Wabash and PRR from the same tower located at the at grade crossing. He'll not only control the connecting switches btw the PRR and Wabash but also the signals.

Confused? Picture a cross where two roads cross at grade in one room. Make one of those two roads my Wabash Indy Branch. To the west of where the two roads cross, on the Wabash, split the Wabash into two lines with one leg going uphill to the PRR and other continuing to the at grade Wabash's Indy yard.  I just need 150" plus with vertical transition to make it up to the PRR fill with about 50"+ of track in one room and the other 100"+ or so in the room where the two lines connect. Most of the grade will be in the room where the best visual effect of the two lines connecting will be affected.

In this scenario, eastbound engines and cuts of cars can also drop down into the Wabash Indy yard to pick up and set out blocks of cars. (The Wabash ends at the Indy yard but the PRR goes into loop staging as some Wabash through trains use the PRR to access PRR Hawthorne Yard and Indy Union Station. In a roundabout way, the Wabash services a big Ford plant not far from Hawthorne Yard.)

Victor A. Baird

Fort Wayne, Indiana

[bing&kathy]

I realize what I am about to say has no bearing on the question at hand, but I have to say it anyway so forgive me. 

The local shortline when it had steamers had a grade so steep that it would uncouple half of the cars at the bottom and pull the first group up the grade to a "run around" track and then back down and pull the remaining cars up the grade.

Thanks for reading and have a good day.

Bob

  FYI, That's called doubling the hill.

[tgindy]

wabash2800

On real railroads, they can get by with short, steep grades with long trains

Horseshoe Curve (circa 1854) is one of the quintessential prototype grades at 1.45% (note the track elevation & radius stats).  Wikipedia also has a nice Horseshoe Curve article.