More info required...

Dear Paul,

"Practical" is a moving target, and needs some clarification:

- What length + mix-of-lengths of equipment do you intend running?
(speaks to basic minimum radii limits)
- what's the average train length (# of cars) you intend to run?
- how many locos do you wish to run on your trains?
(tighter radii + steeper grade = need more locos for given train)
- how thick are you hands?
(bear with me, size of hands --> distance between helix "turn" layers --> grade/turn --> radii/distance-per-lap)
- do you have a preferred helix roadbed/construction method already in mind?
(speaks to "thickness" of roadbed in the helix, which also affects the grade-per-turn maths...)

and is the helix intended to be "in the middle" of the mainline run, or at the end?

Happy Modelling,
Aim to Improve,
Prof Klyzlr

Good questions all. I will

Good questions all. I will run mostly freight, usually with two locos, and a maximum of 12 to 15 cars. most of my cars are 4" and my locos are mostly sd-40 size 6 axle types.

I have big, bass player, woodworkers hands, and the helix(es?) will be t the end(s?) of the mainline run.

Does that help?

Thanks.

Exceedingly rough guess

Dear Paul,

It (the answered questions) does help, although there's still a lot of "fudge factor" to work around.

Let's start with some basic givens:
(Warning : Maths ahead! While not overly complex, if the maths below starts to make your head swim,
then I would seriously suggest considering a layout design that does _not_ use a helix.
The below is the _minimum_mandatory_ to calc a helix).

- based on one of Joe's earliest articles, a curve radii which is 3x the length of the longest piece of equipment in-play is a nice ballpark place to start. From the gear you've mentioned, a SD40 is around 65' long, or around 130mm in N scale.

130mm loco length x 3 = 390mm curve radii
= 15 1/4" curve radii.

We _may_ be able to go tighter, but this would be a good radii to aim for so everything stays coupled and runs reasonably.

Keep that in mind as we move on...

- I just checked a LifeLike SW1200, which tops out at just under 1 1/2" tall, roadbed surface --> top of cab
(That includes the track the loco is sitting on)

For the sake of the maths, lets say 2" roadbed --> "clearance" height
(might be worth checking if you intend to run excess-height cars or double-stacks!)

- Let's assume you have some known helix-compatible roadbed technique which allows all the strength the helix requires, in less-than 1" of thickness

- For no reason more than a flat-out guess, let's allow 2" between the top of the equipment and the bottom of the "next turn of the helix Up" for fingers, and to rerail cars which may come adrift in the helix.
(I have Roadie/"loader"/Sound-System-Engineer hands, and would find 2" a bit tight... )

Total = 5"

That means, each "circle" or "turn" of the helix has to achieve 5" of lift over whatever linear track distance 1x lap of the helix is.

- let's assume, for no better reason than it's a round number, that the grade is 4%, or, said another way,

1" of "up" for every 25" of linear travel.
(to keep the maths simple, we're working with sheer constant grade, and not easing it to compensate for the tightness of the curve in the helix. The tighter the helix, the more significant the drag of the train).

- Right, back to the curve maths. With our guess-timated target radii of 15-and-some inches, we get around 94" of linear run per "lap" of the helix.
(15" radii x 2 = diameter of 30"
Circumference, or "distance per lap of the helix" = diameter x Pi
Circumference = 30" x 3.14
Circumference = 94" approx)

IE for every lap of a 15" radii helix, the train travels approx 94"

- now we get to choose how we work things.

Assuming 15" radii and having to achieve 5" of "rise" per lap, the resulting grade = ???

15" radii gives 94" linear run
(see above)

94" linear run (per lap) / 5" rise = 1-in-18.8 grade, or 5.3%

(Ouch! That's starting to look like Saluda Grade territory!)

So, if we strictly stick to our desired 4% grade, (still steep, but much more acceptable),
and keep the 15" radii curves, How much "lift" or "rise" _can_ we get per lap?

Linear run / grade = rise-per-lap

94" / 25" (for every 1" of "rise") = 3 3/4"

Hmm, only 3 3/4" worth of "rise" per lap, that's _barely_ enough to allow the track, loco, and the next layer of helix, and leaves _no_ room to get your fingers in should anything go wrong!!!
(we kinda knew that already, based on the previous calc, but just to prove the point... ).

Sooo, what can we do? We obviously need more "linear run per lap of the helix" in order to get the desired 5" rise-per-lap, at a grade (estimated 4%) that the locos may actually have some chance of pulling...

There's 1 obvious, and 1 maybe-not-so obvious solution.

Obvious Solution 1 - make the helix curve bigger, so that we _do_ get the required linear-run-per-lap,
(given 5" rise and a desired grade of 4% or "1-in-25",
that calcs out to a linear run of 125" per lap of the helix,
and an extrapolated curve radii near enough to 20")

OR

Not-So-Obvious Solution 2 - keep the 15" radii curves, but cut the "circle" into 2x 180 degree "curves", and stretch the helix from a circle to an oval, effectively adding straight track and "linear run" distance for each loop.

It'd make construction of the helix a bit more challenging, but by adding a pair of 16" straights into each "lap" of the helix, you get the tight curves _and_ the required "linear run per lap" you need to make a 4% grade work...

Now, please note that all of the above "givens" are completely up for grabs. As long as you were able to follow the maths, you should be able to adjust for your preferred roadbed thicknesses, "hand space" clearance, etc etc,
and still extrapolate out a meaningful set of results...

I hope this helps!!!

Happy Modelling,
Aim to Improve,
Prof Klyzlr

Prof Klyzlr you forgot to mention something...

A helix consumes a large amount of track. If he double tracks the helix he doubles the cost of the track consumed by the helix.  This can get expensive quickly.

Now some of us don't build our helix with roadbed. There are two thoughts about this. Roadbed or no roadbed. The only real advantage of roadbed built into a helix is to quiet the train's movement through the helix.  As it is most of us run a train slowly through a helix, so the noise really isn't that much without roadbed. There are some of us who get nervous when the train is out of sight while it is climbing the helix and we can't hear it.  Several modelers will make cliff cuts into helix cover scenery so they can see the train is still climbing.

For Paul he could do a search on eBay for a helix kit. There a several out there and it will give him a good idea of what is involved.  Even an N scale helix with a 15 inch rise is going to take up a table area of about 36 x 36 inches.  That is deeper than a modern house closet these days.

I built a helix for N scale, from a kit I bought on eBay.  I had a blast building it with dual tracks.  I was surprised at how much track was consumed. However, I did make some changes to the kit.  Considering the possibility of a move I built it so the levels could be collapsed like a slinky toy.  It works out very well.  Paul really needs to plan this out before building it.

Den

Instead of a figure 8 why not an oval?

Have you thought about an oval helix in the same space as the figure 8 helix?

Den

dbl-track and figure-8s

I am beginning to think a

I am beginning to think a "Nolix" is in order. I may be better off with a long ramp, with a return loop and a staging yard.

Not a fan of two deck railroads

Don't ask me why, I couldn't exactly say why, they just never have appealed to me. I think your idea of a Nolix is a good one though. Helixes are neat pieces of work but I can't imagine standing there for an extended period of time while the train negotiates the helix. That's always been the drawback in my mind.

Michael

hence the "where is the helix" Q

Dear Michael,

It's exactly this issue which prompted the "where is the Helix?' question.
If the helix is "mid-run",
(IE run lower deck East> West,
disappear into the helix for x minutes,
then re-appear and run upper deck West> East)

then yes, the operators are going to be standing there "mid run" accross the layout,
wondering "is my train still moving?"

Many have written about the challenges if this.
- Symtoms such as trains rocketing out of the helix, as the operator had kept throttling-up the longer the train stayed out-of-view
- "herniating" one or more of the mid-helix loops into a little "shadowbox" scene, as a check if the train is still moving (Jim Provendenza's Santa Cruz Northern, IIRC???)
- deploying "crawling worm" indicator systems to trace trains as they navigate the helix
(If a "worm" of LED indicators suddenly splits in 2, you've got a break-away!)
- deploying repurposed car-reversing (default wide angle) and/or cheapo CCTV security cameras to monitor action within the helix.

In contrast, a situation where the helix represents the _end_ of the run
(The train exits the helix,
circles around the room on the "scenic section" of the layout a few times, like a _massive_ "nolix",
then ends-it's-run re-entering the other end of the helix),

can be more acceptable in some cases, and may even present an option for sequential/serial staging.

It's a legit layout planning tool, but one that is rarely reccomended unless the desired-layout-VS-space-available ratio is severely cramped...

Happy Modelling,
Aim to Improve,
Prof Klyzlr

i am thinking as much as

i am thinking as much as anything of using the helix (or nolix) to get up and down from staging. That may change things a bit.

Helix to staging or....

Helix _as_ staging? As long as you're going to be putting all that track in a helix, double or triple-track it and turn it into an extension of the staging yard. Might be able to "steal" room from the staging yard to make the helix a bit larger as well.

helix setups

I too have never been a huge fan of multi-level setups if they are both going to reflect scenery...(just my personal preference, although I have admired the skill and detail put into many fine looking, multi-level setups).  They do make the best use of a space.  I'm planning a new N scale layout with a helix at the end of my mainline run, but it is merely for the purpose of spiraling my way down to a lower level staging and storage yard.  While I hadn't thrown the math at my helix idea yet, I was formerly considering a 36" diameter unit.  The discussion above fits my arrangement as well, so now I'll be designing it around the idea of a 40" helix.  I appreciate the discussion.

I am a Surveying Manager by trade and I work a lot with highways, bridges and some RR layout, so I'm naturally drawn to the challenge of planning model layouts that demand attention to clearances, selecting an appropriated radius and developing workable grades.

Didn't mean to highjack the thread, just wanted to stick my $0.02 in .

I love the information on this site.

Coupla comments

Building a helix isn't trivial. Don't plan it solely for your current locomotives. You don't want to have to tear it out and start over if you buy a steam locomotive with a long wheel base. This mainly goes to the question of radius. To put it in perspective, I'm currently doing a helix in HO. I don't ever want to redo it, so I decided to do it to class-Ia radius standards => 39" radius with track and benchwork. So yours isn't so bad.  Though as it happens I have some steam engines that might actually need that radius.

Multi-tracking can work as a holding yard, but it's really difficult to get your hands into that helix structure. If you want to adjust the trains that are in there, you might have a problem.

In HO I'm using a helix layer-to-layer spacing of 4", giving a worst-case grade of 1.71%. You should look into what grade is tolerated by N-scale locomotives. You might not need or want to go as tight as the 2" that was proposed. At a given (fixed) grade, radius and layer height scale in inverse-linear proportion: double one and you can half the other without changing the grade.

1/2" plywood with lap joints should work well for this if you support it adequately. Lighter plywood is likely to sag.

So are we talking about a

So are we talking about a helix with a radius of 6 feet? Even for staging? In N scale?

Sorry, I meant diameter.

Thanks!

Been there, done that...

My last N scale layout had a 15" radius helix. Single track and it worked fine. It's main purpose was to bring trains up from and back down to staging. The other end of the layout had what I guess would be refered to as a NoLix.  Without all the math, I found the 15 worked well for most freight cars. My passenger cars looked a little tight, but they worked fine. A friend of mine has a larger helix that is really well done and has allowed him to do run thru staging and add two new locations on his layout. Here's a link to his blog...

http://espeeoregondivision.blogspot.com/

One of the better N scale layouts to operate on in the Los Angeles area. Feel free to ask Jeff about his design. He has photos of the construction on there.

My new narrow gauge layout will also have a helix, since I'm using shelves for the layout. Makes it easier to goto different levels.

we talking about a helix with a radius of 6 feet?

I think he said it would be 40" diameter, which is probably adequate. I;m using 22 inch minimum radius on my N layout and the curves look like they could handle trains in a helix if need be.... .....DaveB

N-Scale Helix

Last year I built two double track oval helices (I used spline roadbed) to take the trains to/from the main level and staging.  Both of them use a minimum outer radius of 22.5" and an inner radius of 21".  By the time I was done building the support structure, the width was 48" and the length, due to being oval (each turn has an 18" straight section) ending up being a minimum of 66". 

Any helix has its grade determined by its length and rise per turn.  However, while researching how to construct a helix I found an article describing "apparent grade" caused by the friction of the wheels on the track that work to increase the real grade in a fairly significant manner.  By making a helix too tight in radius and too steep to save real estate, you can really affect the ability of engines to pull trains up the helix and thus increasing the "apparent grade".  This can be compensated in may ways to include increasing the radius and/or lowering the rise per turn but that will require more room.  Another way of compensating for the "apparent grade" is to build the helix as an oval.  Remember lowering the rise may also reduce the room for hands getting access to the helix levels to put a car back on the tracks.  I have about 2 inches from the top of the track to the bottom of the turn above.  I would not recommend anything smaller than that.

My recommendation is to not use a small radius in a helix, even for N-scale, as you will not like the result.  If I could have had more room, I would have used even larger radii than I used but the radii that I did use were limited by my goal of a minimum aisle width of 36". I did not have the luxury of having another room to put the two helices that I did build.

Good luck,

John

Radius of 3'3"

Not what I was describing. First, I'm working in HO. Second, I'm looking at a diameter of 6ft 6in. The track radius itself will be 36", but some additional space is required to allow for overhang, and then to allow for the structural support on the outside edge of the helix.

As I noted above, I was

As I noted above, I was thinking about a 6 foot diameter helix. I am interested to read that some people have made a 30" radius work....

John Allen

The concept of  expressing " compensated grades" that took into account the radius of a curve on a grade was first popularized by the legendary John Allen.  At least I believe this is true. The first references I ever saw to "compensated grades" were in articles about the Gorre and Daphetid. I believe either John or someone else made a table based on his formulas for deriving grade compensation based on radius.  Unfortunately I don't have a link to give but I'm sure the information is out there if a Google search was conducted. Our favorite magazine publisher Joe Fugate learned the hard way about trying to make the curves in a helix too tight and has detailed his experiences in one of his  Siskiyou Line videos also.

MIchael

Models follows prototype...

Dear Michael,

The prototype was doing "compensated grades" long before JA adopted it...

Happy Modelling,
Aim to Improve,
Prof Klyzlr

I don't doubt it Prof....

But articles on the Gorre and Daphetid are the first place I can ever recall it being mentioned in a modeling context. That's all I meant to say.

Michael