Depending on how "tall" the 8

Depending on how "tall" the 8 is wouldn't that be just a really big S curve? I admittedly have no experience in helix construction or use, but that seems like a lot of different forces on the train. Again, I suppose that would depend on the length of train versus length of helix.

Curves

At first thought the 8 would put more drag on the train than a circle, but that's flying by the seat of my pants

cheers, Leo

8 issues

I would think that a figure 8 would be no worse than a constant circle, and maybe better since it would even things out between left and right curves.  As for a giant S curve, I would assume you would have a length of straight track between the curves.

Twice as big

with no gain in clearance at the crossing.  Maybe some use as a herniated helix with special scenic treatment? 

Herniated Helixes

Dear Rick,

Herniated Helixes not only give an opportunity for a "vignette" of mountain railroading half-way up the helix climb, but also act as a valuable "is my train still moving?" viewing portal. IIRC Jim Provendenza's Santa Cruz Northern had just such a vignette? (I recall seeing such in an old MR, which I have in my head as being the SCN...)

Happy Modelling,
Aim to Improve,
Prof Klyzlr

No perfect solution

That's true, Rick, but there's plenty of clearance everywhere else.  It's not too difficult to reach onto a narrow tight spot, moving a car to one side or the other if you need to to gain access.  It would certainly be better than a straight helix with no clearance.

The more I think about it, the more the alternating radius helix makes more sense to me - provided there is access to the inside.  It would not take up anywhere close to the space of a figure 8, but you could still have the clearance and lower grade.

Like all brilliant ideas

this one makes me go "I wish I thought of that."

While it seems to me a figure 8 helix would solve the access problem by limiting the limited access point to just the crossing, I think there are some drawbacks to consider carefully.

1. Support structure. How will you support the levels? How will it attach to the benchwork, L girder or open grid, in a manner that allows easy stand up access from inside the helix? Not only would the straight section interfere, but supporting that "bridge section" could be problematic.

2. Train forces. The length of the straight track should be carefully measured to insure no S curves, and so that car weights or helper service doesn't result in too much slack action or  force issues that could derail cars.Helper ops would be very tricky.

3. Square footage. While the footprint isn't any larger than an oval shaped helix (They all spiral, BTW.), the lack of center access needs careful consideration. Also, in many places making a helix longer in one direction may impact other features of the layout, reducing room for nearby scenes.

It seems to me a wedding cake helix with gradually decreasing radii as you climb could also eliminate the access issue with low overhead clearance. So could alternating the radii of curves in an oval helix. I've seen one of these built with a masonite stiffener with plywood shelves of subroadbed coming off the Masonite alternately on each side. Might be easier to construct.

All these obstacles can be solved. If so, maybe it's an article.

CP Rails, Spiral Tunnel

The prototype CPR Spiral Tunnel here in the Canadian Rockies is basically an elongated figure 8 Helix.

This is an actual example of the prototype using what amounts to a helix to take a previous 4%+ grade down to a 2.2% grade.  And the vignette suggestion has a prototype example here too as there is a roadside turnout on the highway to allow spectators to actually see the head of the trains cross over themselves as the engines come out of the tunnel before the end enters (I say spectators rather than railfans as most days there are more people there just too see it then there are railfans watching).

It is quite awesome to here the big diesels at the lead of the train go quiet as they enter the tunnel and then you strain to see the helpers come around the bend.  Shortly after they appear, they enter the tunnel and the valley goes quiet.  Suddenly the air explodes as the big diesels roar out of the tunnel, crossing over it's own tail.

Definitely too large to model full size, but a figure 8 helix would provide many of the exciting parts of the real thing.

And yes, if you must, you can get the same feelings with steam...the CPR used too .

Therefore, my opinion is a properly planned and constructed figure 8 could be awesome.

Wedding cake

I like the idea of a wedding cake helix.  It even has the advantage of allowing a lower grade, since the tracks do not need to rise enough to cross over one another.  However, I can see its usefulness being somewhat restricted by space.  Each turn of the helix would require a larger diameter circle, and after a few turns, that could get big in a hurry.  At a minimum of 2" per turn, an additional 6 turns would add 2' to a helix that is already 5' to 6' in diameter (assuming HO scale, of course).  If you've got room for an 8' diameter helix, then I envy you, and you could probably do a lot more interesting things with that space!

Silverbackman

My Dad's dream layout was always to include a modeled version of the spiral tunnels.  I've done several design plans for doing it in N scale, but haven't pulled the trigger on it.  Perhaps one day...

Figure 8 helix? Really?

There is no way a figure 8 helix will take anything less than twice as much space as a round one, and there will be no savings in gradient, as well as making it more difficult to access and build.  I don't see the point.

helix space between tiers

Just a note food for thought. My original helix was 24" radius, 5 tiers, and it worked fine for '50's diesels and 40' cars. What a shock to discover that 85' passenger cars roofs jammed on the joint bars! I got so disgusted I did a Joe F.'s  solution to the "Helix from Hell"! So do your planning BEFORE building, and even make a mockup to test your largest rolling stock. Sometimes learning the hard way is the best, but if you can benefit from other's mistakes it will save you grief. John Colley, Port Townsend, WA

How about an oval

With a figure 8, you still need clearance on the line below when you crossover. 

If you make the helix an oval, you gain distance on the tangent portions to minimize the number of levels of the helix or to keep the overall grade manageable. An oval could be also be kidney shaped in order to fit an available space. A circle is a space eater but a squeezed oval may fit the needs better.

Eric

Offset Helix

I designed/planned an offset helix in that it changed radius so that some parts of the helix track would be over each other and some part the track would be next to each other. But this was done to create a two or three turn helix to gain some elevation while keeping as much of the helix track exposed, while trying to disguise the helix. In some areas the tracks would be next to each other and would not be high enough to clear one another if they crossed. I have not yet build this helix, but have it as a Layout Design Element as I am planning our clubs new layout if I need to climb quickly.

Has for a true helix to traverse a large climb, say 16 inches, the best way to go is either with a traditional round helix or if you have the room to conceal it, an oval. Or you could do part oval and part circle. The minimum radius I would use is 28 inches for a circle. A 28 inch radius is a track run of 175 inches per turn and at 2% will climb 3.5 inches per turn.   

Kidney-shaped, you're talking

Kidney-shaped, you're talking s-bends are you not? OR are you assuming a straight between changes in direction. Either way, ovals and kidneys would take up a lot of real-estate.

I've been fooling around with Anyrail to see if an alternating radius helix is feasible using Unitrack. So far, it looks doable, but I haven't accounted for framework to support the tracks.

wedding cake alternative

i built a 4 turn oval  helix with only the back wall tracks were over lapping each other.  the lower level was the widest and as each level was narrower and narrower in the front that became the climbing mountain scene.

It has been done!

A figure 8 "helix" has been done and in LBG no less.

The Sumpter Junction Restaurant in Baker City Oregon has an LGB display layout which circles the dining area. Two helixes are used to get the train from the overhead portion of the layout to about table level one is an oval helix and the other is a figure 8 helix.

It runs, completely unattended, during business hours!

George

Sumpter Junction ride-along

One helix (descending) is "rectangular" of a fashion, so sort of traditional, but the other is definitely "herniated".

Take a ride aboard!

Figure 8 helix? Really? Mon,

Echt?!!!! 

I'm with you on that Jurgen!

my helix is set at 27 in rad

my helix is set at 27 in rad ( i know it is tight). and there is just enough room inside for me to get in there. a figure 8 would not allow any room to gain access.

and yes i use a double stack high cube container and a auto carrier car to make sure there is room for everything to get through. but will only be running mostly older 40, some 50 foot cars. 1900 - 1950 steam, i have a good roster of 2-6-0's mostly 2-8-0's to play with. couple 10 wheeler's. (if they play right in the helix).

On the freeway

No wonder I haven't been inside Sumpter Junction, it's next to the freeway. Usually I stay next to the mainline and where the Sumpter rolled into Baker City. Was in Sumpter last month, sure love that part of the Blue Mountains.

I think the figure eight helix is one cool idea if a modeler has the room to pull it off, my layout room is too small unfortunately.

Helix

Helix(es) have been kind of a fad so examine your reason for wanting one.  Often the problems can be solved in other ways. 

That said, our club layout has two.  One is a constant radius 3-track jobber (31" minimum radius) that climbs five feet to connect the west and east ends of the railroad.  It uses pre-cut 3/4" plywood sub-roadbed supported by metal strapping and threaded steel rods.

The other is a single track oval with similar radius that is stretched into an oval with eased curvature, sitting below our main deck. It allows a branch line to drop to a lower level.  Same threaded rods and plywood are used here.

A figure 8 sounds like an access nightmare, and a problem with usable grades unless you are using cog-drive rack locomotives and have quite a lot of space.  At any rate, if you build a helix, your very best track work needs to be in there. Our main helix is more or less a six-foot cube. A figure 8 would take up 12 by 6 in HO.