Hello. I’m planning a helix for my HO layout, and I’ve come up with two options for the grade/height drop per revolution, and I’m looking for some feedback.
Option 1 - 3.75" height drop per rev = 2.01% grade
Option 2 - 4" height drop per rev = 2.14% grade
I’m pretty sure I can build the helix with the 3.75" height drop. My plans are based on allowing 3" for the height of the train, 1/4" for code 83 track, and 1/4" hardboard for my base. I guess my question is, am I fooling myself by thinking I can actually squeeze trains through a 3.75" height? Is a change in grade of 0.13% worth worrying about, or should I just give myself the extra room?
Any thoughts & comments would be greatly appreciated. Thanks!
I would go for the ‘clearence’ - that .13% is not enough to worry about. Our club has a 5 turn helix with 4’ per rise - No problem with high/wide cars.
Rather than asking a bunch of strangers for advice, take a machinist’s square and stand it next to your tallest piece of rolling stock (on a piece of flex track on a flat surface.) Make sure you’re measuring the tallest point - which may be an extended pantograph if you model heavy electrics. Whatever measurement you make is your MINIMUM required clearance. Go from there.
Now, be aware that the decision you make will limit you to that clearance figure forevermore. If you don’t run stacks, triple auto racks and loaded Schnabel cars now, you won’t be able to run them up the helix in the future - so plan accordingly.
Chuck (Modeling Central Japan in September, 1964 - with helices)
You don’t state your radius, which should also be part of your concern. I have a 3 1/2 tier 33"r. helix with 4" rise per turn. It works out to 1.93% grade and this allows me to pull 25 40’ freight cars up it with a single 13 year old LL proto1000 GP7, no problems! I would go with the extra height so as to be able to re-rail cars if ever needed. Murphy says, “you will need to get your hands in there sometime when you least expect it!” The easier you make it the more satisfaction you will have in the long run. We take pains to make our trackwork bulletproof, that should include the helix, eh? John Colley, Port Townsend, WA
My concerns are also regarding problems like derailments. I would fasten a legnth of track to a surface and see how much room I needed to rerail a difficult car or engine. Let that be your guide
First of all I am concerned with he use of a 1/4 inch hardboard track base. You would need to double the supports to prevent sagging. To be on the safe side go with 1/2 inch quality plywood.
Assuming you are planning a 30 inch radius you might consider an oval helix. By adding just 12 inches to the center of the circle you will gain 4 1/4 inches of total clearance and still keep the 2 percent grade. This also will allow the use of a 1/2 inch plywood track board with room to spare.
This may not apply to your space, but I am planning a layout that is adjacent to my workshop. I am planning to put an oval helix in a corner of the workshop over storage cabinets that will be 7 x 10 feet. This will allow me to obtain 18 inches of elevation in just two tiers.
Trains will depart into the Western East Haven tunnel portal at the bottom and exit the Eastern East Haven tunnel portal at the top of the helix and proceed to Boston on the New Haven Shore LIne. The upper tunnel portal will actually be directly above the lower one.
I would suggest using a bigger radius or making it oval as Big Rusty suggests to increase seperation while decreasing the grade.
I have designed several layouts using a helix. My favorite formula is 36" min radius with 4.5" rise = a grade not to exceed 2%. It can be built with 1/2" material and still leaves 4" clearance.
In answer to your question since I am only passively interested in multideck layouts I wouldn’t! Were I interested, however, I would go with the 4" separation; you are working with a 30" radius curve–a broad curve by definition–and that radius should be long enough for lugging a reasonably long train up six helix loops. You probably will appreciate that extra quarter of an inch if you ever have to use your 12 inch to the foot fingers to rerail your 3.5mm to the foot cars.
. . . . . . . . . . and please, don’t tell me a forty plus year modeler, that you are going to be so careful in your track laying that you will never have to worry about a derailment on your helix. HEH! HEH! HEH! HEH! HEH!
The 1st picture shows how changing a circular helix to an oval helix can decrease the helix grade, and eases coupler tension for fewer derailment opportunities…
Helices are not confined to multi-deck layouts. I have one (approximately 1.3 turns) that serves only to raise one track high enough to clear several others. The rise is only 3.25"/turn, using ultra-thin construction (flex caulked directly to steel stud formed into a dodecagonal trough) to keep the grade/curvature drag within the operating envelope of the locomotives that will be using it.
After some experimentation, I’ve come up with a system that effectively makes the entire interior of that steel trough a huge curved rerailer. Even if something does climb the meticulously-laid rails, the geometry of the surroundings will put it right back on the track. At the very worst, I might have to reach into the 2" clearance and nudge everything downhill if the thing that derails is one of my teakettle tank locos and that loco is the train’s only motive power.
So, what are the radius and grade? Radius, 350mm (a tad less than 14".) Grade, 3.3%. Scale is HOj (1:80.) The ruling grade on that route is 4%, trains are very short and usually doubleheaded.
Chuck (Modeling Central Japan in September, 1964 - with steam-powered mountain goats)
Option 1 - 3.75" height drop per rev = 2.01% grade
Option 2 - 4" height drop per rev = 2.14% grade
You need a radius to track center (single track) of 30 inches, and 31 inches to helix outer edge for both options. If you have a space of at least 62 inches x 62 inches to place this helix, you are fine.
Thanks for the input, everyone. I had already planned on using an oval as big rusty suggested. I’m planning on a 24" radius with 18" straight sections between the circle halves. I know most of you don’t like to see anything near a 24" radius on a helix, but since my main layout has 22" radii, I figured that 24" should work out ok. Plus, the straight part of the oval should help to mitigate any stress on my locos. I just wasn’t sure what was more important - grade or clearance. I’m going to go ahead with the 4" clearance now, especially after thinking about how much fun it’s going to be re-railing any cars in that small space. Thanks!
Burke, my suggestion FWIW is to go with the biggest radius you can get into your space. The reason is that sooner or later you may have some modern equipment, be it 85’ passenger cars, or auto racks etc. and they will definitely look toy-like on a 24" radius. I learned the hard way by building a bedroom layout with 24" r. Needless to say I wasn’t pleased with the result, so I tore it out. My new layout in a much larger space has a 33"r. helix and 36"r. min. visible with many scenes exceeding the minimum. One busy town LDE has a 15 degree bend of 60" r. on the mainline, and had I the room I would have gone to 72"r. Been where you are and have moved on. John Colley, Port Townsend, WA
You might want to look at “Easy Helix” which uses I think 28" and 30" R curves. A little pricey but makes construction easier.
I would agree with using a bigger radius. If nothing else, you might someday build a new layout with bigger curves, and you could just ‘plug in’ the helix from the old layout, rather than having to do a new helix.
2 comments, 1/4" hardboard way to thin, takes to many supports. Go to 1/2". You can go the extra height and if worried about grade lengthen the helix to elliptical shape.
