Hi all. I'm a new poster at this forum, and I can see that my question has been asked in one form or another before. I am designing a 4x8 N-Scale layout (this very dimension seems to have been a topic in its own right). In the quest to keep the layout interesting, it definitely is a little bit of a "bowl of spaghetti." In particular, I would like the mainline to go on for longer than is possible on just two levels (which essentially would be two loops around the layout or some variation thereof). This has led me to a design with three levels, where in order to also accommodate some yard areas, sidings, and industries, I want to build a single-track helix rising from "ground" level to my top-level (Level 3). In its first incarnation, I had designed a helix with a 13.75" radius--something which many threads dismiss as too tight. In its current incarnation, I have been able to compromise and modify the plans to accommodate a 15" radius. Obviously, any layout features some sort of compromise. Going larger than 15", however, would seriously impact the rest of my trackplan, making it all but impossible to retain the somewhat more gracious curves and easements on the trackage that is visible. My intention is to model late 1950's AT&SF, which means I would like to operate my Kato ALCo PA/PB with a (not exactly prototypical) 4-6 car SuperChief consist, as well as Freight trains under Geep and EMD F3 (or F7) motive power. Has anybody here actually constructed (or operated on) such a tight-radius Helix? Am I setting myself up for failure? I figured I would construct the helix using 1/4 plywood held in place with threaded bolts and nuts, and use no corkbed, so that a 2" rise per revolution would be possible on such a tight radius (this yields a 2.12% grade which, in itself, seems manageable). This, however, begs the question of whether it is possible to achieve the necessary level or rigidity on the plywood under the helix track. How do I stiffen the plywood where two pieces are joining without adding bulk that interferes with the vertical clearance above the track? Any insights are much appreciated.