Hi
I need to build a helix to go between 2 levels of a layout. I would like to keep it as tight as possible well not going over a 3% grade. How can I do this? All it needs to clear is diesel locomotives as far as height. As well what tips do you have towards the helix? I will decide the height later.
thanks
I am normally an adherent to the NMRA gauge for most stuff but you can get away with a slightly lower head clearance if you are not running high cubes or the like.
Three percent can get steep if you are pulling a dozen or more cars.
I worked recently with a group of modelers on the construction of a helix on a home layout. We used threaded rod for all of the risers which allowed us to run nuts up and down to adjust for spacing.
The grade is going to depend on a lot of factors........ the space between your levels and the diameter of the area allowed for the helix. For example a four foot diameter gives you 12 (for easy math) running feet of track. You can calculate your grade as if it was a straight section of track once you know the number of turns x12 feet and the height you need to climb.
The one we built took 7 1/2 turns at four feet in diameter to clime about 29 inches.
see ya
Bob
Key factors for a helix are grade and radius. A 3% grade may be OK, but in combination with a too tight radius, it´ll give you a bundle of problems. I´d consider any radius below 24" for a helix a no-no!
Gidday, Hope this is of use.
http://www.youtube.com/watch?v=ZdrXH--f41Y
Cheers, the Bear.
"One difference between pessimists and optimists is that while pessimists are more often right, optimists have far more fun."
hi,
a little bit of math could be helpful. Not mentioned by you is the modeling scale, nor the desired vertical clearance. Lets assume you are building in HO and you need at least a 3,5" distance from railhaid to railhead.
Compared with a grade on a straight part of your layout the curve of a helix adds to the drag. This could be an issue not only for your engines to climb up the hill, it can cause "string-lining" as well. Your trains might derail climbing the inside track.
The virtual grade is compensated for the curve and the appropriate formula in HO for a 3,5 distance between railheads is about : 87/R or if you like the needed radius can be calculated by the formula: Radius = 87/ grade in perc.
To give you an idea: if you want a maximum 3% virtual grade the required minimum radius will be about 29"
With a 24" radius the virtual grade will be about 3,6 %.
(for a 4" railhead to railhead distance the formula becomes: radius = 96 / grade;
for a 3" distance you'll get: radius = 72 / grade)
Smile
Paul
Information Station's (2) Guide to Helix & Staging Design PDF-downloads are worth their weight in gold. So, don't leave home without 'em! Note, how each PDF-cover picture (covers) "the how & why" staging (shooting off of the helix) is built into half of the articles.
Each PDF-download has a "tight" helix design article:
-- Vol. 1: "Silver Gate Northern" -- U-shaped in barely more than 4'x8'.
-- Vol. 2: "Union Terminal Railway" -- Multi-level in a 4'x8'.
If you can swing it -- Do a 2-track helix -- Inner track for down and outer track for up.
Remember, the steeper the climb means greater tension on couplers, and fewer freight and/or passenger cars in your consist. Also, track-joint soldering, whether sectional or flex, needs to be completed "as-you-go" before you "limit easier access" from building up each additional helix level.
Conemaugh Road & Traction circa 1956
tgindyEach PDF-download has a "tight" helix design article: -- Vol. 1: "Silver Gate Northern" -- U-shaped in barely more than 4'x8'. -- Vol. 2: "Union Terminal Railway" -- Multi-level in a 4'x8'.
It may be worth noting that neither of those layouts were actually built -- they are theoretical designs.
Radii below 24" in HO have proven unreliable for many experienced layout builders, many of whom ended up tearing out tighter helixes and replacing them with much broader versions.
If the Original Poster has never built a helix (or a layout) before, a super-tight helix is a very daunting project. I've seen a number of such attempts abandoned.
Best of luck.
Byron
Layout Design GalleryLayout Design Special Interest Group
csxbnsfbnrailwayAll it needs to clear is diesel locomotives as far as height.
Are you saying that only locomotives with no cars are going to be using the helix? That would be unusual.
Note that some cars are taller than some locomotives, so scrimping on the clearance in the helix is a path to possible future problems. especially as you acquire new equipment -- unless you already own everything that you will ever use on this layout.
csxbnsfbnrailwayI would like to keep it as tight as possible well not going over a 3% grade.
Scale? (For now I'll assume HO. ) Era? Typical train length?
Remember that grade calculations typically give you railhead-to-railhead elevation differences. That doesn't include allowance for ties and roadbed, which you need to consider.
As Paul alluded to, tight curves create friction of their own that adds to the actual grade of the helix, thus raising the equivalent grade effect on trains. I'm not sure I grasped Paul's calculations, but the general rule-of-thumb for HO curves is to use 32/R for the equivalent grade.
If you want to keep the effective grade to 3% or less and assuming a 4" railhead-to-railhead clearance, the helix becomes pretty broad. At a 32" radius, the actual grade is about 2% and the additional equivalent grade is 32/32 or 1% for a total of 3%. That well over 5 feet across for the helix and supports.
Even at a the tighter railhead-to-railhead elevation gain of 3.5" (which to me is a little too tight for building and maintenance in HO standard gauge), you are looking at about 29.5" radius (actual grade ~1.9%, additional grade from radius about 1.1%). That's still over 5 feet wide, with clearances and supports
Many folks hope that a helix negates the laws of physics -- sadly, this is not the case.
Hi Byron and others,
the math is really straight forward:
real grade = dH x 100 / circumference of the circle.....................with dH = railhead to railhaid distance
when dH= 4 you get:
real grade = (4 x 100) / (6,28 x R) = 64 / R
add the drag for HO caused by the curve = 32 / R
the virtual grade = 96 / R
When the virtual grade is 3% you have a 32" radius.
Byron mentioned it already, the length (read weight) of the train is an important factor. On a small layout with 6 car to 8 car trains, pulling power and string-lining will not be that severe; so you might be able to use a tight (18" to 24") radius in your helix. With a more normal train length however problems will surface quickly. I quote John Armstrong: "grades above 4% are an attraction in it self". Helper service or doubling the hill (read shorter trains) are mandatory.