Helixi....

[daniel_leavitt2000]

Started to sketch out what would be needed for bench work on the Boston line. I will need at least three helix for various parts of the layout. Each will need to drop about 18" to the lower level. Since this will be a picture-box style layout, the "wall" needs to conceal each helix.

Right now I'm thinking 36 outside diameter would be best. I want to keep the elevation around 2-2.5%, and this would mean that I would need to bring the layout room "wall" out about 40".

Any thoughts? I'm new to helixes.

[ednadolski]

Helix geometry is always a matter of trade-offs.  When deciding on a grade be sure to account for the vertical separation between levels, and leave enough room for the 0-5-0 to get in there to right derailments and such.  Be sure to also account for the thickness of the roadbed as well as any thickness contributed by roadbed joints.

An 18" vertical transition sounds relatively high - say 6 levels at 3" climb per level.  If your curve radius is say 17.5" then one lap is 3.14 x 35" = 110" which comes to a 2.7% grade.   To lessen the grade you could (a) add more levels (which decreases clearances)  and/or (b) increase the curve radius (which creates a larger footprint).

Of course more levels and larger radii also increase the amount of time needed for a train to traverse the helix. The example above works out to 55 feet of track or about 1.7 scale miles.  So a helix can become a bottleneck on a single-track mainline, depending on how it fits into the trackplan.

Accessibility is also something to consider.  In my case, I made it all reachable from the center, but I have to crawl into it from underneath.

These are just some of the considerations,  but it's always best to address as many of the design considerations up-front (as you are doing here) ).   Helixes have their challenges, but are certainly tameable.

Ed

[mighalpern]

But if you don't want to have you helix stick out so much you can  use a straight section of say 18 inches or more to make ovals. That lets you decrease the radius needed and reduce the climb angle to keep it around  2% and have good separation between levels.  I'm using 18 inches as am example, because 2x18 is 36 inches gained which would be about 1/3 of 100 of a 2 % grade means that the .66 degrees  would be alleviated .  With the above example you would equal that with a 22 in radius circular helix.
accessibility will be an issues by making tighter ovals, but make the track as bullet proof when building and it should work.
My old layout had a helix that was 4 laps with 14 inch straights and the first 2 radius was 17 inches and then i made the last 2 14 inch to stagger the the helix, like a wedding cake, but I made the back of the helix against the wall all even over each other.  used code 80 track, worked very well.  the other helix on the layout was 2 separate circular ones, one going up and an inner going down,
hope that helped

Miguel     I got pictures if you want 

[daniel_leavitt2000]

Pictures would be very helpful.

[Lemosteam]

Paging @eric220

Dan if you look at Eric's layout thread, he mad an oval helix.  not sure the dimensions, but it had several turns. 

This post shows the track plan, but he will have to clue you in on its radii, etc.

The video shows it in this post:

[daniel_leavitt2000]

How tight can helix get before stringlining a train? This part really worries me as I may need to back up a 20-40 car TOFC or autorack train up the helix in some operations.

All my cars are being converted to body mount couplers and metal low profile wheels. Weight is being added to a lot of them as well.

[Smike]

TOFC are the most sensitive to run in a helix. As far as stringing, I've been running a 16.5" radius with code 80 and have been able to consistently run TOFC trains about 30 cars long. Longest is mixed freight with 50+ cars. Backing up with be another story and different forces, as stringing would not be the issue, but friction resulting in buckling. Not sure 16" radius or so would get you much past 20 without issues regarding backing up TOFC.

The biggest issue I have so far is rail joints. The only way to keep things moving smoothly is to have perfect joints. If I had to do it over again I would use unitrack without question.

[mighalpern]

Im storing Eric220's helix right now.  I think it was an 18 and 20 inch radius.  It's pretty massive. 
He used code 55 sectional track to keep the radius consistent and soldered every joint.  Very strong and glued down.  Not going to move
when I built my helix I used code 80 atlas flex and would solder thru the turn and if the joint was on the straight section, just rail joiners for a little expansion capacity
I will try and dig up some old pictures
sorry Eric didnt mean to cut in

[Cajonpassfan]

Any thoughts? I'm new to helixes.

Yes. Hate them. With a passion. Not just because they're space hogs (they are), a pain to build and maintain (they are) or hard to get to and into (they are) or prone to derailments (not necessarily if done right), but because they are so boooooring to run on and take forever to navigate at anything near scale speeds. Helixes ruin the joy of running for me (as does most hidden track longer than a train). I hated mine so much I took it out out and redesigned the layout with added open running because of that.

I understand that a helix may be a necessary evil under some circumstances, but I would think really hard about the  amount of hidden track in an 18" vertical climb; at 2%, about 75' or 2 1/4 scale miles, or almost seven miles in three helixes? By comparison, how many scale miles of open running do you plan to have? Will half of the run or more be inside hidden trackage?

If you absolutely need a helix, I would minimize its length by open approaches or even an open midsection (it doesn't have to be round or oval or fully stacked, and I would make sure I can get to it in relative comfort. I would also think hard about necessary deck separations and grades, again to minimize length of hidden running.

Did I mention I hate them...?
YMMV, as may your hidden trackage
Have fun,
Otto K.

[eric220]

If memory serves, i used 18.75” and 20” radii with a 13” straight section in the middle. Add those lengths up, and you get 151” of travel on the outer loop per turn, which at 3” of rise per turn comes out alomost exactly to 2%. I soldered Atlas sectional track together and put rerailers in on the straight sections. (The straight sections were actually long enough to do a crossover, although that just seems like an act of unmitigated masochism.) I glued the track directly to the plywood to eliminate the possibility of cork introducing any undulations, and to give the 0-5-0 just a little more room to get in there.

My experience with my first helix was not a good one. I had some severe reliability problems because of the way I put the plywood deck togetether. The joints buckled, and the engines would walk right off the track. The aluminum straps you see in the photo were an attempt to force them back into alignment. The one thing I think I did right was to engineer it so that the outside was open. I intended to do vignettes on each level so you could follow your train as it climbed. Even so, this beast sucked up 2.25 scale miles of track. Trains would be in there almost as long as they would’ve been on either visible deck.

I’m not intending on using a helix on my next layout, but we’ll see.

[mighalpern]

ok could not find the helix pictures, must be on my old old laptop.
but like otto hates the long travel times hidden, i exposed about 1/2 of the helix and added scenery.  i had a Big Boy going up on the outer and a Challenger on the inner going down with no problems.  Only issue was the tunnel portals with the long wheel based engine.
Miguel

[mighalpern]

ok found the old laptop and got it running, using XP 
so here are a few shots of the helix.  i like it a lot and made for great meets and interesting scenery.
sorry about posting, just getting used to the new way
Miguel

[ednadolski]

How tight can helix get before stringlining a train? This part really worries me as I may need to back up a 20-40 car TOFC or autorack train up the helix in some operations.

All my cars are being converted to body mount couplers and metal low profile wheels. Weight is being added to a lot of them as well.

There is no hard/fast answer to the "how tight" question since there are so many factors - radius, grade, train length, car length/weight/overhang, body- vs. truck-mounted couplers, and more.

One thing that should generally help is to improve the rolling resistance by installing metal wheelsets.  I noticed about a 20% improvement in the number of cars that one loco could pull uphill with all-metal wheels, vs. pre-conversion where the train was mostly plastic wheels.  I also prefer low-profile flanges as a way to further reduce friction/drag.

Be careful about adding weight as a general rule. Ask yourself, what problem(s) am I trying to solve by increasing car weight?  If the answer is to keep cars on the track, that's often symptomatic of an underlying geometry issue. In that case, added weight is a matter of treating the symptom rather than the real issue.  A heavier train is of course harder to move up a grade (whether pushing or pulling) so it's easy for added weight to become a case of diminishing returns.

Autoracks having a lot of overhang are a 'worst case' situation on tighter curves.  Body-mount couplers make them even less forgiving, in that case a larger (22" - 24") minimum radius really is your friend.  But of course, that makes the helix even more of a space hog.... (that tradeoff thing again )  OTOH, on a train that is long/heavy enough, truck-mounted couplers (esp. on autoracks) will make pushing the train upgrade an exercise in futility.

One issue that I've had with autoracks on my helix: With the train going downhill at a low speed, the autoracks with the slinky couplers would tend to pogo, to the point where they would actually uncouple.   The helix was hidden, so an operator would not see it happen until the tail end of the train emerged from the helix, minus a few autoracks from the back of the train.   The slinky couplers were the root cause of the issue, but the helix just happened to be a place with the right set of conditions to make it happen (with unfortunate consistency).

Ed

[GaryHinshaw]

I'm not sure which is worse: 3 concealed helices, or an ops concept that relies on backing a TOFC train up a (concealed) helix.  Maybe you could start a Layout Engineering thread with specific track plan proposals and we'll help you figure out a way to avoid at least 2 of the 3 helices.  Until then, I've moved this thread out of the Eng. forum because that board is intended to chronicle member's layout builds, not general layout construction topics.

FWIW, I have a 3-track oval helix that serves as one of my staging yards (I would never put a helix this large in the middle of a mainline run):



The inner track has an 18" minimum radius, a 3.25" deck separation, and a 2.1% grade.  I used 1/4" baltic birch plywood for the roadbed to maximize finger space when derailments need to be managed.  Fortunately, those have been pretty infrequent.  I strongly recommend making the helix at least quasi visible - guests get nervous when there is a lot of hidden track.

[jereising]

A big thumbs up to Maestro Hinshaw for the correct use of the plural for helix, helices.  And just to continue the pedantry, the oval version of the helix would more properly be called a nolix....

And now, back to our regularly scheduled asshatery (sp?)