Helix spacing - What am I not getting here?

Model Railroader Layouts and layout building
1

I have been reading and reading and reading about building a helix and I can’t figure out what I’m doing wrong. I have enough space to install a 30” radius helix and I only need three levels. I was looking at a helix kit like the one listed here http://www.ashlintrains.com/servlet/the-51/railroad-model-train-ho/Detail , they clam to build a helix with a 20” radius on a 2% grade and get 4” between decks? How?

I’m working with AutoCAD to design the helix. I have a 30” radius circle with a circumference of 15’-8 1/2" on track centerline. 15’-8 1/2" drops 3.77 inches at 2% grade, if I use 1/2” material for the decking that leaves me with only 3.25” from the top of one deck to the bottom of the other and that does not include the track. The only thing fitting in there is my gondola’s! If they can get 4” clearance with a 20” radius why can’t I get 4” of clearance with a 30” radius? Please help before I bang my head on the desk one to many times!

2

LION gets 2.5" clearance on a 5’ diameter helix.

For the lowest turn I made risers each one 1/4" taller than the previous, thus the spacing of the risers controls the grade.

I set the end of the first loop at the elevation that I needed to clear trains on the lower level, and then evened out the risers until I had a secure loop. I have no clue what the grade is. What does it matter? I have so much space (5’ diameter) and so much rise required (2.5") between the top of the lower deck to the bottom of the second deck. It is what it is.

ROAR

3

The simple answer may be that the math used for Ashlin’s site is incorrect. Using a 2% grade with a 20" radius yields a between level spacing of only about 2.5". To achieve the 4" separation claimed for a 20" radius helix requires a grade of over 3% (actually their spacing between the top surfaces of the roadbed is 4.25" per the photo on Ashlin’s site, with a 4" clearance to the bottom surface of the next level, so the grade is around 3.4%).

EDIT Looking some more at Ashlin’s site, they also claim a 2% grade for their 26"/28" radius HO helix, which is also incorrect. It would appear to me like they did some sloppy cutting and pasting on their text.

4

Yep, their math is wrong - but the deck spacing is right. I have used their kit and it is 4 inch inter-deck spacing (measuring top surface to bottom surface), the deck material is a nominal 1/4 inch (BTW, its actually a MDF product). This makes for a grade around 3.4% for 20 in radii. I also found that 1/2 inch plywood ‘glue plates’ between sections worked just fine to make the assembly a bit more solid - and it still allowed sub-roadbed and track with my typical HO equipment to pass under without any problem.

Charles

5

I have designed and been involved in constructing a number of layouts with the famous “helix”.

Personaly, I don’t recomment anything less than 36" radius and I usually use a 4" rise, rail head to rail head. Built with 1/2" material, that works fine and yields a manageable grade of just under 2%.

You only need 3-5/32" abouve the rail for even the most modern equipment.

Sheldon

6

Finding how much separation you will get between decks is as simple as figuring out how a straight ramp would work…except that ours will be curved. What that means is, assuming we keep a decent consistency, and don’t have sloppy undulating ramps, if you know your maximum acceptable grade, and you then substitute a series of lengths of run, you can find out how far above your starting point, where the first overpassing takes place, your top ramp will be.

If you were dead set on 2%, as I am, how far must your train travel, either in a straight line of tangent track, or curved as in a helix, to get the minimum acceptable clearance you want? That is the key and essential question you need to answer. If you want that 2%, and no more, and can’t have greater than 22" radius to lay in your helix, then treat your ramp like a circle and use “twice Pi times the radius”, which is the formula for a circle’s circumference. Two times Pi times the radius of 22" comes to 140 inches, rounded up nice 'n tidy…it actually is 138" and a quarter.

With a nice long ramp of 140", and rising at a comfy 2%, how far above the lower starting point will the upper ramp be, on average, when it completes the first full circular ramp? Simple math says it is 140 X .02 (2% expressed as a decimal), or about 2.8". Shoot! Some items will just barely clear that, and that’s only if the ramps have that beautifully consistent grade…no sags! Double stacks haven’t a hope, and the same for some MOW equipment.

Remember, the rails have to get under the top layer, or between any two of those layers. Ideally, you would want some finger room to gather things if an emergency arises. Otherwise, you will have to tip them, and risk breaking details. Or, let them run back down the grade and try to catch them before they derail and fall or run into something.

My current layout build has helix curves at an average of 35" rad

7

Reverse engineering Crandell’s equation

2% grade =2 inch rise in 100 inches or 4 inches in 200 inches

200 / 2*pi (using 3.14) yields 100/3.14 or 31.847 inch radius (let’s round that up to 32)

The 30 inch radius will get you 188.4 or about 2.1% (rounding up); of course that is the physical grade not the effective grade in terms of pulling power.

8

Doc

I am wondering if your example is an exact comparison to Crandell’s. He states that he has 4" clearance which means, if I understand him correctly, that there is an actual 4" of free space above the track. You don’t mention taking the thickness of the sub-roadbed or track into account in your calculation. If that is added in I think your radius will increase. None the less, your mathematics are useful if the thickness of the structure is added into the rise. You also make a good point about the effective grade.

Dave

9

tbriney

Welcome to the forums!

As others have said, I think Ashlin Trains math is a bit optimistic.

My current track plan will only allow me about 25" radius for my helix in and out of staging with less than 4" clearance. Based on many others’ actual experience the effective grade will severely restrict the length of trains, so much so that I might not even bother with staging, at least on a lower level.

Dave

Dave

10

Some of Ashlin’s calculations are incorrect (overly optimistic).

I’ve emailed them twice with specifics, but they have so far not corrected the site.

11

Dave, you are correct, Crandell’s numbers work out to 4.396" from rail head to rail head, allowing 3/8" for support structure.

As I noted you only need a little over three inches for anything, that is why I use 4" rail head to rail head and because of the effects of the curve, insist of grades of less than 2% in the helix.

I know people with 30" radius helixes, they work, but you need lots of loco power to pull any amount of cars.

I also know a guy who built my discribed design, one BLI N&W Class A can pull 70 cars up an eight turn helix on that layout.

The helix is not magic, you will only get the operation you design for.

Sheldon

12

If you look at their picture, Ashlin is using a very thin material for the decking. The OP said he was using 1/2-inch decks. This will give a lower clearance than using thinner stuff. It may not be enough to account for the entire miscalculation, though.

13

Hi mr Beasley,

if you do not understand junior-high math, it might be better not to use phrases like:

“it may not be enough to account for the entire miscalculation.” Calculation is very straight forward if you know the radius, needed clearance and sub-roadbed thickness.

A 2 percent grade with a 20" rises 2,5 inch per turn. If this leaves sufficient clearance with 1/4 inch material thickness is not my problem. When a “respected” entrepreneur states this helix has 4" clearance, even after receiving comments, he is way out of line.

BTW the effective grade is about 32/20=1,6 % higher then nominal 2% grade. The curve adds drag equivalent with a 1,6% grade. The resulting grade will effect the length of your train, pulling power or/and string-lining might be causing problems.

Paul

14

LION has a four track helix. The table is 5’ wide, thus the outside diameter of the helix is 60" or a radius of 30" Fortunately, it is the outside two tracks that are going up the hill. Lets call them 28" and 26" radius, after all there is some space between the edge of the helix and the first track. The inside tracks are say 24" and 22" radius, but these are downhill tracks and work just fine. In fact there is a big fat 5.1Ω resistor there so that the trains do not go too fast.

All of my trains are 6 cars (300 scale feet) long, some have one motor, others have two. The single motor trains are treated with Bullfrog Snot on the drive wheels for extra traction.

ROAR

15

In the words of Ward Cleaver spoken to Eddie Haskell who has just overflowed Ward’s gas tank: “Eddie, one of life’s profound truths is that you can’t squeeze 19 gallons into an 18 gallon tank.”

The math for this is brain-dead simple: 4" divided by 2% gives a result of 200", the lateral distance required to rise 4" on a 2% gradient. Divide that by pi – 3.14159 or whatever – and you come up with 63.66", the diameter of the circle required to achieve that 4" rise on that 2% gradient. Divide that by 2 and you come up with 31.83/31 53/64", the radius of the circle required to rise 4" at 2%.

16

I didn’t want to go into too long and overwhelming a description of all the considerations, but wanted to provide a rough figuring method so that one’s arcs of plywood or whatever comprising the ramps to form the spirals could be cut with side clearances of a couple of inches on either side of the tracks. For a double or quadruple track, such as the Lion’s, the ramps will be quite wide in HO scale to avoid sideswping of long cars. In my case, with a double track, I have cookie cutter sections 7" wide. They allow me to drive screws into them to the side of the tracks, to keep the tracks spaced nicely, and to use bits of 1X4 to act as supportes for spacing between the ‘decks’.

One important point, touched upon by Dave on the previous page, is the thickness of the sub-roadbed, or the arcs of ply comprising the ramp sections. In my case, they are 1/2" ply with the Code 81 glued directly to the plywood using DAP Alex Plus clear with silicon. Wonderful stuff…it should be a rule in the hobby to use it because it is so easily spread and taken up if you need to remove track elements or roadbed. Try it, you’ll agree with me.

So, back to the thickness of the plywood. For the lower onset of the first level of ramp, clearance is usually not a problem… It is only when the ramp crosses itself, and in most cases continues atop its first deck with the same curvature for yet another layer that you must remember to account for four (4) things between the two:, your roadbed thickness if any, the height of the tracks themselves, the tallest rolling stock you intend to use, and then a way to get at least a forefinger between the plywood above and the tops of the cars/engine that you have to remove due to problems. When I was asking myself how much clearanc I would need, I measured the height of my MOW crane, the worst offender, and I also measured my GG1 with pantograph extended. The figure I came to was 3" with a bit of a buf

17

I think one of the discussion points was whether or not the thickness of the sub-roadbed had an impact on the radius needed for given incline. So, does it? Ashline uses 1/4" , Crandell 1/2 in. Does it make a difference?

18

There has been some mention in this discussion of the spacing of side by side tracks. It should be noted that at or above 36" radius, 2" spacing is fine for most all equipment, but as you get down into the 30" range or below, a spacing of as much as 2-1/2" may be required for the largest equipment.

Considering the effects of curvature, grade, clearence issues, etc, a helix with a radius below 30" is suiteable only for the the shortest trains and/or “old time” modeling.

As we have been over several times now, 32" is about the practiacal minimum radius for a reasonable working helix and 36" or larger provides much better operation.

Sheldon

19

Thicker is better in my view. I don’t know any wood product I would use as a subroadbed in a helix that is only 1/4" thick. It would require too many/frequent supports. I don’t what Ashline uses, but 1/4" anything is too thin in my book.

Sheldon

20

And there in lies the problem, we have done away with Junior High in favor of “Middle School”. One of the great undoings of public education in America if you ask me.

Sheldon