Helixes

[Anonymous]

I have a recess in my basement wall under the fireplace that is 46-1/2" across. I want to use this area for a 22" radius helix as a way to change levels on my new layout. I'm working in HO. Is this radius generous enough to use for this purpose with reliable operation? I operate mostly diesel units but have a 2-8-2 Mikado and an Amtrak pasenger train.I figure it will be okay for the diesels, but I'm not sure about the Mike and the passenger train. I run this equipment now on 22" radius curves with no problems. Also my longest freight is 25 cars. I anticipate a rise of about 1-1/2%.

Opinions, please!

[Anonymous]

Hello,

The radius shouldn't pose a problem, especially with 1.5 percent gradient. Make sure to use transition curves into and out of the helix.

Regards,

Paul Schmidt
Contributing Editor
Trains.com

[Anonymous]

Paul--are you sure about that? The diameter of a circle having a 22" radius is 44" X 3.1426 or about 138 1/4 inches. At a 1.5% grage that would transalate to about a 2" rise per revolution. I thought that for HO scale you neeed at least 3.5" per revolution, which at a 1% grade would mean that the distance travelled per revolution is around 233 inches. It may be possible to use a 22" radius curve if the helix were oval or oblong shaped and had a straight section totalling about 50 inches between each half circle. I am missing something or did I do my math wrong?

I seem to recall when I built my previous layout with a helix that I used 28" radius w/ a 2% grade. That gave me about a 3.5" rise per revolution.

[Anonymous]

Your math is pretty close, Jim, and your logic correct. No way a conventional circular helix can utilize 22" radius without having 2.6% or more for a ruling grade.
The thickness of the track used ( Atlas is about 3/16" thick overall ), plus the total thickness of the roadbed used, must be added to 3" to give a logical clearance, and one that pretty well conforms to NMRA standard in HO.
So, to keep the 22" radius, keep the grade to 2.6%,and use Atlas flextrack, you have to use roadbed no thicker than 5/16", with the track fastened directly to it.
If you want to use cork roadbed over 1/2" plywood, you'll need to go to a 2.8% grade.
(I factored the circle down on these calculations to 43 1/4" diameter, since the inside rail is the determinate radius for vertical clearance).
I have one spot in my layout where I 'squeeze' passenger cars around a 22" radius, but it is easy to get to, and fairly level. I would be reluctant to do so on a 2.6% grade or where any track is hidden, but it may be possible if track is perfectly laid.
Compliments of the Season & best regards / Mike

[Anonymous]

Is your recess under the fireplace 46 1/2 square both in length and width? What is the total rise from your current level to the second level? What kind of Amtrak passenger equipment are you running... any high level stuff will require more overhead clearance. What kind of material will you mount the track to? If you have 46 & 1/2" open the radius up to 23". 23 will be the radius to the outside of the tie. That 1/2" should keep you from hitting the wall. Good Luck!

[Anonymous]

There were a couple of very helpful earlier threads in this forum about helix construction and operating issues/parameters. Try a "helix" search. John Armstrong's Track Planning book is also an excellent resource. You may also try www.trainstyles.com which has a helix product. Good Luck.

[Anonymous]

Hello Jim and Mike,

You're both correct and I'm wrong! I got fixated on the 22" radius and entirely negelected to consider the rise per revolution in HO scale with a 1.5 percent grade. Sheesh, ever after coming back to HO scale after all those years in N scale I still should know better.

So, our questioner will have to employ the steeper gradient, 2.8 percent, as Mike correctly points out. And that in turn raises the issue of degree of curvature. Broader is better in that case.

I owe you both one.

To the question poster: I'd look elsewhere to put that helix. The location is tempting but you'll likely find having the helix there is source of frustration. The space is too small to allow for a more generous radius (which would enable a grade that's less steep).

Paul

[dknelson]

I had the chance to inspect Trainsyles "EasyHelix" at this years's Trainfest/MRIA show in Milwaukee. It is very durable black plastic and good looking. The radius is a bit bigger than you want perhaps but essentially all the work has been done for you. It ships in two large boxes (a friend has already bought one after seeing it at the show). The product is advertised in MR
Dave Nelson

[Anonymous]

EasyHelix is shipped in three 30 pound boxes and weighs in at over 90 pounds when complete. We appreciate your kind words. Hope your friend is satisfied. Happy Holidays.