Off the Rails host Gerry Leone has re-railed and is gaining traction in this Trains.com exclusive series, Back on Track. From his new home in the Upper Midwest, members can follow Gerry as he walks, talks, and works his way through planning and building an all-new, double-deck model railroad in HO scale. First order of business? Figuring out how to handle the rise and fall of a helix!
Back on Track: Track planning with a helix, Episode 2
By Jenny Freeland | March 18, 2021
| Last updated on April 19, 2021
One thing was forgotten in the calculation of railhead-to-railhead height. Yes, you were right to deduct the thickness of the subroadbed from the railhead-to-railhead distance, and also the thickness of the plywood.
However, you forgot to deduct the thickness of the upper piece of track – namely the tie thickness and the code of rail – which for code 100 snap-track as an example, is approximately 0.175 inch total.
That can put a fly in the ointment in terms of space for the rolling stock. I think that the height you’re really looking for is distance between lower railhead and upper railhead minus (thickness of upper track plus subroadbed plus plywood). As an example, using 1/8th inch cork sheeting and 5/32 plywood, the thickness to be subtracted from the railhead-to-railhead height isn’t 0.125 plus 0.156, but 0.125 plus 0.156 PLUS 0.175 – a height reduction over 60% greater than just the plywood and subroadbed sandwich.
Janet — Well, here’s the thing: let’s say railhead-to-railhead was 3 inches between two turns of the helix. That means that top-of-subroadbed to top-of[subroadbed is also 3 inches, because the track on the lower level is the same thickness as the track on the upper level. Taking it to an extreme, that means that the bottom of the upper deck subroadbed to bottom of the lower deck subroadbed is also 3 inches. “Railhead-to-railhead” is just an expression; the track thickness and subroadbed thickness remains the same regardless of where you put your ruler (or calipers).
Thanks Gerry, Very very Interesting, and helps me a lot.
Forgot to answer your second question, Randolph. Yes, the helix is 68” wide. But if there’s a derailment you can easily climb under the helix benchwork and stand up in the middle to fix any problems. There’s a 30” aisle on two sides of the helix, which makes accessing the inside of the helix easy.
Ok, let me explain the 0” to 7” comments. Most modelers will build a layout perfectly flat (no grade), then have a helix to get the train to the upper deck. It may have to go around the helix, say, 5 times to get there.
In MY case, I realized that if I put the lower deck on a slight grade — starting at 0” and rising to 7” by the time it reaches the helix, I could eliminate one whole turn of the helix because the mainline is already up 7” by the time it gets to the helix. When the train comes out of the helix it’s at, say, 25” high for the upper deck. In order to maintain a constant 18” separation between the decks (and remember the lower deck goes from 0” to 7”) then the upper deck has to go from 25” to 43”.
The 7” I used in the video was just an example, IN REALITY, my lower deck goes from 0” to 4” (a grade of only 0.5%). But that 4” was enough to eliminate a whole turn of the helix and still give me an 18” separation between the decks.
Make more sense now?
I am also confused by the 0″ to 7′ and 18″ to 25″ statements, perhaps a perspective or edge on diagram of the helix with these values shown would help. Also, is your layout really 68 inches wide at the helix location? I would think it impossible to reach in and fix a derailment on the back part of the helix.
Great video otherwise.
Interesting. I’m sure that Gerry, as a very experienced modeler, realizes that a 34″ radius curve adds nearly 1% grade worth of rolling resistance to his 1.5% real grade in the helix, giving him a “compensated grade” of nearly 2.5%…
Very informative and I have to admit that even after your presentation I cannot understand the part about 0″ to 7″ or the upper part I cannot visualize what the helix looks like. I thought you entered at one level and exited at some higher/lower level after going around so many loops.