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As to the turnout question,.....the larger the number on the turnout the more shallow the diverging route will be. So the new Atlas code 55 #10 turnouts hooked diverging route to diverging route would look best. However, their #7's and even the #5's are designed to be hooked the same way and offer the same track spacing as the #10's, they just are sharper in curvature as the train passes through them so they don't look quite as pretty. You may want to concider them though as they take a lot less room, and if space is a concern as it is for you, you may want to make that tradeoff.
As to the track plan,........there are a few places to get ideas, but it's unlikely that anything someone else comes up with is going to meet your exact criteria. That's why making your own plan is such a popular option for most. For more on this, read this post ( http://www.trains.com/trccs/forums/961453/ShowPost.aspx ). To learn more about layout design there's an excellent site you need to see ( http://www.vetmed.auburn.edu/%7Esmithbf/BFSpages/LDSIGprimer/TOC.html ).
If you'd like to look at some plans anyways, either for inspiration or maybe to find one that will work, try these places.
Here's some I've done.....
http://s83.photobucket.com/albums/j319/pcarrell/Track%20Plans/
And here's some other addresses......
http://www.carendt.us/microplans/
http://home.earthlink.net/~mrsvc/id9.html
http://www.ntrak.org/plans.htm
I've got a couple other addresses on my other computer that I can get for you in the morning, OK?
Hope this helps!
Yard and industry based on a real location in as little as 8 square feet in N scale
This small N scale switching layout based on a real railroad was described in MRP 2005
My own small N scale switching layout inspired by real locations on the Western Pacific and Southern Pacific
Layout Design GalleryLayout Design Special Interest Group
Here's a couple more;
A bare-minimum-size shelf switching layout, five feet long and six inches wide. The cyan track is the interchange. Five industries (the white block at the right is an unloading ramp for flatcars) provide room for at least nine freight cars, sometimes by a very convoluted route.
If you can spare 5 feet in length, you could build this linear spaghetti-bender. A busy chemical works takes up the left side, while the center and right hold three more industries and the interchange track.
This switching layout is bent around a corner, so it only takes up 5 square feet. In that limited space, you still get 6 industries and interchange. The curved center gives your switch engine the chance to run a little.
A minimum-size shelf switching layout, with seven industries in a space 4 feet long and only 6 inches wide. The siding with the rerailer is the interchange track.
Here's some more that can be converted to N scale;
That should give you something to play with. Remember, any of these plans can be changed or added to.
I think you're going to find that for one deck of the helix to clear the next and fit a trail in there you're going to have way too steep of a grade.
For example;
For N scale a 10 inch radius with 2.5 " seperation between decks (thats about a thin as you're going to get) yields a 4% grade. That grade on a tight curve will offer too much resistance. You'll be lucky to get much more then a loco by itself up that.
Your best option may be a switchback to get the height you want.
Keep this in mind.
A 2% grade (good) will raise the elevation of your track from zero to four inches in 16 feet.
A 3% grade (tough) will raise the elevation of your track from zero to 4 1/2 inches in 12 feet.
A 4% grade (steep) will raise the elevation of your track from zero to four inches in 8 feet.