This is my first HO layout and I need to build a Helix to go from and Elavated Train to Table top and to a Subway level (3 levels). However, I need to know if there is a formula to determine the amount of rise per turn. I am thinking of a 36 inch dia Helix
Any help would be greatly appreciated.
davidmbedard Not worth while with 18 in radius. Your grade will be too high (close to 5%) and your tight radius will amplify that. David B
Not worth while with 18 in radius. Your grade will be too high (close to 5%) and your tight radius will amplify that.
David B
Beg pardon! According to my cheap calculator 1 turn of 18 inch radius equals 113+ inches of track. At 3%, this gives NMRA clearance plus the thickness of a minimum-depth railhead-to-bottom upper level.
I've just finished the design work for a 350mm radius 520 degree helix. Using steel stud (12 segments) 'rain gutter' upper level support, I held the grade under 4% (which is the ruling grade for the route.) For the metrically challenged, 350mm is just under 14 inches (and well within the capability of a Mantua HO scale Uintah 2-6-6-2T.) Needless to say, the longest car which will ever travel this route is shorter than a 40 foot AAR HO scale box car.
With short trains of short cars, a 18 inch radius helix is doable. If you want to run big diesels and long trains of humonguboxes, it isn't.
Chuck (Modeling Central Japan in Septeber, 1964)
For mere mortals, an 18"R helix in HO is only theoretically possible, not really practical, in my experience. Especially for a first layout.
Unless you plan for very short trains of fairly short cars, the extra friction of the tight curve radius when combined with the grade of the helix is just not reliable. More importantly beyond grade, the alignment of forces across the center of a helix that tight will lead to a tendency to stringline the train (pull the cars straight across the helix and derail).
No less an accomplished modeler than Joe Fugate found that even a 24" radius HO helix did not work well and replaced it with a 40" version. The story is in Layout Design Journal #14, published by the Layout Design SIG. He noted that the 2.65% "inherent" grade of the 24"R helix acted more like a 4% grade in practice due to the relatively tight radius. And yours would be even tighter.
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The recomended minimum radius for a helix is 24" anything else is just too tight fact not theory.
I duplicated the helix that Cliff Powers used on Mississippi, Alabama & Gulf railroad his three level layout he emailed me the exact specifications and it works perfectly. It takes up about a 5'x5' area so I located mine in the next room.I have provided a link below to a website that has a lot of useful information concerning grades and elevations and scale very very useful site.
Thanks for the help.
My experience with a helix was in 'N' scale but the laws of physics still apply. The larger the radius the better off you are. As the train goes up the helix, your engines are pulling alot harder than on a straight track.The constant curvature is the problem. If you have the space, make the helix as large as possible.
I redesigned my old layout to us a constant grade to get from one level to another. There is nothing wrong using a helix. If you build the helix, make sure you have enough room to get your hand between the levels in case you have a derailment.
Check out past issues of Model Railroad on how to build a helix. Don't rush into building the helix until you are sure this is the best way to get from one level to another.
I hope this helps!
madmodeler