The track gang has completed work on a second helix on the PRR Middle Division in HO Scale. As with the first helix, this is also a kit from Ashlin Designs.
It doesn't get any easier than using these kits, if the specs work for you. This helix has two tracks -- the inner with a 32" radius and the outer with a 24" radius. Over2.5 turns the track rises 10 inches.