Track layout for over under

[Lintz12268]

Does anyone know the maximum incline that I can design an o-scale over under layout?

 

[Selector]

In all scales, including the one you and I are in at the moment, grade is measured in percent, and the number means that, regardless of the locomotive involved, model or real, each must climb the same distance in a given length of climbing track. Said another way, grades don't scale. A grade in one scale is precisely the same grade in any other scale.

So, the grade is one variable, but like in the real world, the other major variables are the tractive effort the locomotive brings to the problem and also the trailing tonnage. An engine, even on level track, can only tow so much. The grade just limits that figure, and a curve on a grade adds even more stress to the engine.

So, irrespective of scale, a given grade is a problem. Our problem with our track plans is getting into the space we have something that will work for us. For true scales, there is a recommended minimum overhead clearance between the rail tops and anything overhead, be it a supporting member for a bridge, the bridge itself, roadbed that we can cover and hide, or the bottoms of any ties. Most of us like our railroads to look at least passably realistic, so we need to consider at the least the bottoms of girders on a bridge or the apex of a tunnel portal as the item to be concerned with.

Why talk about clearances when you had asked about grades? Because in order for you to get your over and under configuration, like a figure 8 or something, you must clear the rolling stock passing below the overhead tracks. That clearance dictates what the grade to the overpass, and then down the opposite side, must be. In turn, the grade is set also by how long a run you have to get the overhead clearance you need. If you only have 2 feet, in your scale your grade will be severe, extreme, in the order of 20%. Real trains don't do well with grades over 2%. Our toys won't be able to manage 20% any better than would their real-life counterparts. The only way to get down to 2% is to have a much longer run....much longer.

I don't know the precise figures suggested for your scale, but your minimum clearance for single stacks and non-pantograph locomotives (on level of intermodal and no overhead catenary wires needed for electric traction) would be in the order of 5.2", maybe more, maybe less. You'll have to measure from the bottoms of the tires on each model and then add another 3/4" at a minimum over head the highest point of the model measured.

Sorry for a long post, but it really is an involved question and topic.

Crandell

 

[fast_ian]

+1 on Selectors comments.

Having said that, the following is from John Armstrong:

- "O" scale, and the xover is at 90 degrees.
- Assume you need 5" clearance (his minimum for this scale.)

Min curve radius (") - Grade (%)
22 - 4.2
24 - 3.1
30 - 2.5
36 - 2.1
42 - 1.8
48 - 1.6
and so on.

He also notes that with "average" rolling resistance cars (they'll roll on 2%) the hauling capacity on a 3% grade is only about 30% of what it is on flat track!

Furthermore, "most well weighted model locomotives will haul more "tonnage" than they should on steep grades, less than they should on the level, so model grades should be somewhat exaggerated if their effect is to be accurately simulated on long trains."

Certainly, at least in my testing (in HO) a 3% grade and a little loco needed helper service - Which I think is great!

Cheers,
Ian