# Minimum curve & helix size in N scale

Discussion in 'N / Z Scale Model Trains' started by P-40, Jul 21, 2008.

1. ### P-40New Member

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After wanting to build a layout for many years, I finally have room for a small shelf layout and I was wondering what the minimum curve size can be used in N scale? The largest locomotive that would be used would either be a Mikado or a Northern, but I would most likely use a locomotive smaller than that. I am mostly interested in some mainline running and have never been interested in a lot of switching although I will have a couple switches on it.

The longest the shelf can be is 72 inches, one end could be 24 inches wide, maybe a little more, the other end probably around 18 or 20 inches wide.

I have been going through the threads for a while and have learned a lot and gotten some very good ideas.

To get some practice at scenery, I will try a couple dioramas first. One will be in HO and I will use the Monogram Big Boy and a couple cars by it, a Tucker and a 1948 Plymouth business coupe, just waiting to get them from eBay. The other will be an old bridge from my home town in southern Minnesota (Red Jacket bridge) which is part wooden trestle and part metal and goes over a river and a road.

I have picked up a number of books and quite a few Model Railroader magazines that are also a big help.
2. ### seanmMember

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Congratulations on taking the plunge P-40! You will have al ot of fun!

As to minimum radius.. this is an ongoing discussion in N-Scale. Minimum radius is "traditional" in the 9.75 inch range.. Some real short wheel based engines can go around significantly smaller radii, but it is not practical at all. You may have problems with some longer wheel based engines at the 9.75 inch range. I am not sure how the Miks perform on short radius curves as I donâ€™t have any.

As to a Helix, you add in another variable... Lets say you want a 12" radius (24 is your max width)... If you rise 2 inches per revolution you have a run of 2*3.14*12=75.36" Slope is rise over run... so 12/75.36=15.9 %. That is way to steep to be usable, so it looks like a helix is out of the question at that radius.
3. ### TriplexActive Member

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Err... you just made an error there. The rise is 2", not 12", so in that case the grade would be 2.65%. Fairly steep, but well within sanity.

And in a 24" wide space, the largest you can fit will be about 11" radius. And remember that the whole grade being on a curve will add friction. In general, a helix of this radius - or the equivalent radius in any other scale - is barely practical. With helices, the usual restriction on radius is not what curve the equipment can handle, but the resulting grade.

A Northern is much larger than a Mikado. I'd recommend a bare minimum of 13" for a Northern and preferably 15" or more. A Mikado will normally take 9.75".

If one end is restricted to 20" wide, continuous running is probably impractical.
4. ### P-40New Member

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I had tried searching with Google and the opinions were all over the place about the radius of a curve. I had bought a Northern a long time ago as that is my favorite engine and I was hoping for a larger layout, but I kind of figured it would be too large now. I'll have to check, I might be able to go 24 inches on each end. There's also a slight possibility I could do a layout on a table in the spare room that would be between 5 and 6 feet long and around 30 inches wide.

My favorite railroads are the Great Northern and that Northern Pacific, I will look what's available (new and on eBay) in the smaller engines.

Looks like the helix is definitely out for me, not a bad thing as it will keep things more simple for my first layout.

About the bridge diorama I am planning, it scales out to be a little over 41 inches long, it will fit on top of my entertainment center and I thought it would be a nice way to display an engine and some cars.
5. ### seanmMember

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Geez! Where did my math skills go. I need to be sure I have my coffee before posting next time. wall1

Thanks for the correction.

SO can you check the math on my helix?

22" radius.. 2.5" rise per revolution... 2*3.14*22=138.16 2.50/138.16 = 1.8094962362478286045165026056746%

Ya, better with coffee!!!:thumb:
6. ### 60103Pooh Bah

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The original N gauge trains came with 9" radius curves. However, they were cruder than today's models -- more like toys. As models became more detailed and scale, the radius had to go up. When passenger cars (and freight cars!) were made close to scale 85-90' long, they looked really awkward on tight curves, although they would go around them, usually.
So you may be able to run your trains on the tight curves, but you may not be happy with the appearance. Lots of modellers do it by having he loops hidden.

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