Scale?

Dear Joe,

What scale are we talking? 18" radii may be tight for a HO helix and gloriously-large for N scale...

I'd also reccomend having a cruise thru the following...

http://model-railroad-hobbyist.com/node/4205

http://model-railroad-hobbyist.com/node/9982

http://model-railroad-hobbyist.com/node/14742

http://model-railroad-hobbyist.com/magazine/mrh-2011-07-Jul/building_helix

Happy Modelling,
Aim to improve,
Prof Klyzlr

Helix

 A helix is a combination of several parameters, the primary two are radius and height between turns.  You can compensate for tight radius a bit by decreasing height/vertical separation between turns.

The choices depends on the scale, the equipment being used and the material used for the helix (since that is part of the vertical separation).

If you wan to be able to run double stacks, dome cars and autoracks you need more separation than if you are running 1900 equipment.

Grade is rise over run, radius determines run and separation is rise.

18" radius with 4" separation = 100*(4"/(2*18*3.14))= 3.53%

18" radius with 3.5" separation = 100*(3.5"/(2*18*3.14))= 3.09%

24" radius with 4" separation = 100*(4"/(2*24*3.14))= 2.65%

24" radius with 3.5" separation = 100*(3.5"/(2*24*3.14))= 2.32%

Depending on the radius and separation the grade can vary greatly.  Choose wisely.

I apologize it is HO.   I was

I apologize it is HO.   I was hoping and may just have to try for a 24" radius, that would fit and the other good thing is that the height that it will have to climb is only abou 14" inches.  Worries that nay be a little tight for 6 axle locos.

Joe 

24 inch

Mine is 24 inch radius and it handles 6 axles SD70, F45, C628 and RSD-15 engines with no trouble.

What is the longest rolling

What is the longest rolling stock you will be running on the helix?

The longest car is 86' auto

The longest car is 86' auto parts boxcar and auto racks.

Joe

I think 24" too tight for 86 foot cars.

Our modular club has a standard requiring 36" minimum radius on the mainline, but the first wye we built into the staging yard had some 24 inch radius curves, and 86 foot passenger cars would consistently derail trying to get through those tight curves.  Also, some of the 86 foot boxcars have a long overhang on the ends from the truck centers to the couplers.  This results in serious overhang on the outside of curves which will tend to derail as well.

I would recommend reading the article in the first issue of MRH, Jan. 2009, titled "Powerful new curve radius insights for any scale."  It is a real eye opener about how a piece of rolling stock will behave on various curve radius. 

What might work better for you is a "nolix" which uses the entire room, or in your case all of the room except the door way like a helix.

HO Auto-box cars are 86'

HO Auto-box cars are 86' long, but all the HO auto-racks I am aware of (Accurail, Athearn Genesis, Walthers etc. are 89' long.

I'm going to have to agree with Russ, 24-inch for running 89' cars up and down a helix is a recipe for trouble.  Unfortunately this may be a situation where the proverbial eyes are bigger than the plate of food they are looking at.  An 11.5 x 11.5 foot room is very small for an HO layout and much better suited for N-scale. 

Ten to twelve car trains are modest enough, a helix is a space swallowing beast and will eat up a relatively huge part of that 11.5 x 11.5 foot room.  Even if you squeeze in a 28-inch radius helix, that will eat up a 5 foot diameter space, effectively wiping out almost a quarter of the room in one corner.  And 28-inches might be barely broad enough to handle trains with long cars like auto racks, auto box cars, passenger cars and TOFC flat cars under more ideal conditions where there is no helix.

Keep in mind that the physics of a helix due to grade + curve = drag, means that the effective curve in a helix is actually smaller than a same radius curve on a ordinary part of a layout.  So if a someone can get smooth reliable operation using a minimum 29 inch curve, that same 28 inch curve may not give smooth reliable operation when in a helix, which is why modelers often go a bit larger than some might think is fine.

About the only way you can get away with a helix is if you by some chance have space in an adjacent room (such as a garage) you could run through the wall, out and back in.

In my case, I have a fairly small 10x18' room and even in that space I opted against a space eating helix, so I did went with Russ's "nolix" option and have a 2.9% grade, which carries trains from a staging yard up and over to a main yard with some sorting and industry tracks.

I would recommend reading the

I did go ahead and read the article and of course it's, as you say, an eye opener and not in a good way.  Basically this:

2.0 x car length - Some equipment may track reliably but 2x is generally considered pushing it.
2.5 x car length - Most equipment will track reliably if everything is of similar length
3.0 x car length - All equipment should track reliably; coupler performance ok if altered to allow 50% car width swing
3.5 x car length - Equipment will look less toy-like when viewed from inside the curve
4.0 x car length - Equipment will look less toy-like when viewed from outside the curve

Ok, so here is where I fit into the above scenario.  In my small 10x18' basement room, I am using 32-inch minimum curves and I have lots of 89' TOFC cars, autoracks etc.  By my caculations for HO, these cars are roughly 12.3 inches (maybe a bit more over the coupler faces).  With my curves, that puts me slightly over the 2.5 car length category only tracking reliably if those long cars are coupled to cars of similar length - yikes!  Well, I've found I can operate fairly reliably if those 89' cars are coupled to 50' car too but I guess I'm "pushing it".

My "take-away" is that if you are in Europe or the UK, abandon all hope for HO trains and just go to N-scale - but they already know this.  There are a few stubborn UK folks who model HO, like Mr. Brian Moore but he runs on modular layouts mostly and seems to limit his freight cars to 50 and 60 footers.

Even if you live in the US, many still don't have "wide open spaces" to fit in say 44 inch curves if they want their long cars to look "less toy-like when viewed from inside the curve" hah hah.

Getting back to the original poster.  Those 24-inch curves, when viewed from the perspective of the MRH article in Jan-2009 page 45, those autoracks and auto box cars would be at the top (or bottom) of the chart setting in at the 2.0 Ratio where "Some 86 or 89' equipment may track reliably, but 2x is generally considered pushing it".  Russ's club found that out when they installed 24" curves in the wye leading into the yard and found long cars deraililng.

I think the general wisdom over the years from reading many articles in MR magazine, I've concluded that 30-inch radius is an absolute minimum for most HO layouts which include long cars, but only operationally.  Anything you can manage that is broader than 30-inches is a plus and gains further improvement in operation.  That said, even V&O author Allen McClellan chopped down a Walthers 89' auto-rack by one panel because he thought it looked too toy-like on his 30-inch curves.  Really you have to get up into the mid-40 inch radius range to get longer cars to start looking decent.

Them are the apples - IOW, you needs real estate!

Since I'm

Since I'm the one that's going to be helping build this, I'll follow this thread along.

My prior layout had a 24"

My prior layout had a 24" radius helix built using overlapping 1/4" Luan plywood. The rail-to-rail separation was 4".  I was able to run 80' passenger car trains up/down reliably.

So 80' passenger cars

So 80' passenger cars operated successfully, however, the OP listed 86' auto box cars and auto-racks (which are 89') so those are longer than Onewolfs test case.  If I were the OP, I'd try to get a larger test sample and build a consensus before building a 24" radius helix to hopefully save on some possible grief.

That is exactly what i am

That is exactly what i am doing.  I also am willing to make some concessions on car length if i have to.  Space for helix is not problem since it is going below bench work and will be going into staging.   I appreciate all input and look forward to reading more.  

Joe

Space for helix is not

Below or above, a helix will bulge out into the room by whatever size it is.  I say that because most people size bench-work such that they can reach to the back of it - which is typically in the range of 24 to 30 inches.  With a helix under the bench-work, that is going to drive the width to double that so you'd be reaching across a good 50 inches to get to the back fo the bench-work where that helix is hidden underneath.  I have long arms, but not that long!  =P

Anyway more food for thought.  I look forward to seeing it all take shape - please post photo's.

As far as the room

Well as far as the room, I get inspired by Rob Clark who's room is only 11 x 8 with a big helix. Joe's got half again the square footage. Plus from the layout plan we've looked at so far, it's going to be in the back corner anyway.

Do you have a helix on your

Do you have a helix on your layout Jim?

Joe

Another approach

Another approach was discussed here that was intriguing. A spiral cut from a single piece of plywood would start with the smallest radius and wind outward. The grade could be kept to a minimum since clearance is not an issue. Obviously this may take more space but is worth looking for - wish I could remember who was doing this. Anyone? 

Do you have a helix on your

Copy/pasted from an earlier post I made in this topic:   

I have a fairly small 10x18' room and even in that space I opted against a space eating helix, so I did went with Russ's "nolix" option and have a 2.9% grade, which carries trains from a staging yard up and over to a main yard with some sorting and industry tracks.

I've posted layout progress photo's over at Atlas Rescue Forums here if you want to see what I've squeezed into a 10x18' space:

http://atlasrescueforum.proboards.com/thread/3737/jims-layout-progress?page=1&scrollTo=62156

80 Foot Passenger Cars

On tight curves one of the keys to reliable operation is not so much the length of the car as it is the distance between the center of the trucks and the couplers. This distance will be, in general, shorter for a passenger car than it will be for a flat car or auto rack. That is probably why the aforementioned 80 foot pax cars played well with others on the 24 inch curve, but the 89 foot auto racks would not.

George

Good point George.  And

Good point George.  And realistically, if one is going to design and operate a helix, it's going to need to accommodate the variety of rolling stock going through it.  It makes the most sense to design it so you don't have to bar certain rolling stock, if at all possible.

"Another approach was

      Hi Neil,  I've thought about this in the past, but I stop when I get  to the point of figuring out how to draw a spiral on plywood :> ) .......DaveB 

Inspiration

Check out this link for inspiration:  https://forum.mrhmag.com/post/new-meaning-to-the-word-spiral-track-12196284

@daveb - I haven't tried this but a string tied to a 3/4" diameter dowel set at the middle should give you an offset of almost 2-3/8" with each revolution. If the smallest radius is on the top of this wedding cake spiral then portions of the line could be brought out into daylight to be sceniced and allow operators a look at the train along the way. 

" I haven't tried this but a

     Hi Neil, That sounds like it should work. One could calc the dowel diameter to suit the roadbed width they need. I guess after the first revolution is drawn the rest could be just drawn with a compass set to the roadbed width, following the previous edge around the circle. One benefit I see is the grade could be made less steep if desired since the levels don't overlap.....DaveB 

Train Lift

Hve you considered using a train lift. Your trains are probably too long but  train lift is a good way of moving trains from one level to another and also of storing them. It's essentially a vertical acting traverser. They needn't be straight.

Archie