The Monster in the Corner, with test train. . .
Whew. Got the helix constructed, after three attempts. It's pretty solidly built--God forbid what will happen if (knock on wood) I get a plumbing leak in the wall void this thing occupies!
After two abortive attempts at building the thing, I took it down to the bare base and rebuilt it, taking care to measure the gradient on the climb upward, a task made quite a bit easier with my Husky "Professional 9"Multi-Function Digital Level with Storage Bag." This tool really made the helix possible to construct for an idiot like myself. Besides the usual visual bubble levels, this thing provides push-button access to a display that provides level in degrees, inches of rise to foot of run, and grade in terms of percentage.
Another view of the Helix. Sorry for the mess!
Husky digital level--invaluable for building a helix. . .
The level helped keep us "honest" while laying the most important part of the structure, the sub-roadbed risers atop the base level. With the first level of roadbed secured to these at a constant 2.4% climb, it was mostly a matter of then adding level after level, separated by 3 1/2" high spacer blocks. Several blocks were held in place by clamps--including nifty one-handed clamps by Irwin--and each level's rise, in turn, could be measured and kept within limits.
It isn't perfect--you'd be amazed how little the difference there is visually between a 2.2% and 2.7% grade within an 18" run--but it is far more consistent than the first two attempts. Proof of this: a load test of a train of Auscision NGTY wheat hoppers behind a Trainorama 49 Class loco. The first attempt at the helix, complete with steep spots and a flat spot in front, found the loco barely able to take 9 cars and a brake van up the helix. The rebuilt version found it able to climb the grade with 11 cars and a van, and, with a bit of a running start, 12 cars and a van--a moot point, i'd guess, as the crossing loops will handle 10 of these cars, one loco and a van.
All that's left is cleaning up a couple of track joints, wiring track wiring feeders, and waiting for the upper benchwork to extend atop the helix towards the large circular sub-terminal. At that point, I'll secure the last 4 feet of upper level helix and work the vertical transition. Eventually, it'll all be encased by fascia panels. I'll likely add infrared detection sensors at the top and bottom of the helix for crews to be alerted when their trains are about to re-enter the visible portion of the layout.
The scene atop the helix should be visually interesting: a giant circular grain terminal, served by 2 tracks. A pair of tall concrete silo elevators will be adjacent to the circular structure, helping to hide the hole in the wall the mainline entering the helix makes. Here's a shot of the Grain terminal I'll be modeling.