Helix Radius

[TomDiehl]

Our club built a helix on the HO layout several years ago. This one is 4 tracks wide, 5 levels, and radiuses are 36 to 46 inches. We used 1/2 inch plywood, no road bed, code 100 flex track. We made the supports out of threaded rod with nuts and washers above and below the support point to hold it in place and to allow for the inevitable adjustment for aging. The operation has been relatively reliable for the several years we've been operating it. You have to take a GREAT deal of care in the construction stage. Pay particular attention to smooth joints, steady turn to the track, flat roadbed, and TEST AS YOU BUILD. We have almost 4 inches between the levels and sometimes this is too tight for rerailing items. Remember, Murphy's Law is strictly enforced in model railroading.

Our club is located in Stockertown, PA Our website is http://nasme.tripod.com

[johncolley]

To the best of my meager knowledge a switchback is like a "Z" sometimes with several layers. it works like this: you proceed to the end of track, the switchman or brakeman throws the switch (turnout)behind the train, you back uphill to the end of that leg, the head end brakeman throws the next switch in front of the loco and you go forward uphill, repeating as many times as it takes to get to the summit, over the ridge, or up to the mine. It is rather like a skateboarder going back and forth to get from one end to the other, eh? Only up the side of a hill.

[Anonymous]

Thanks for the optimistic view John, I appreciated it . What exactly is a switchback?

[Anonymous]

I don't want to sound too much like the SecDef here, but when bldg a model rr, you use what you have. If you have space for 19" radius (38" diameter) then do it. BUT, do it well. Our clubs new helix has a couple low spots where the flanges of certain engines and cars lift off the rail and go on the ground. We are relaying some rail inside the helix to correct this problem. Be very careful in all things - quality counts.
Now - steep grades. An operating problem or a fun thing to deal with. Double a too long / too heavy train. Real railroads do it. Run more short trains. Its the ruling grade for most of us. Make use of it.
ANother possible solution if you have the length: Switchbacks. We have several. They are fun and impose operating problems.
Unless you are just running trains around and around, operating problems to overcome are a big part of the fun. JOHN

[johncolley]

I have been learning operations on a friend's layout with stacked helixes. The 3 tier lower is double track and the 3 tier upper is singletrack line, all main is code 83. It is almost all 2% with a minimum radius of 30". We have no troubles at all as the trackwork is flawless. No Kinks, checked and double checked with 3 point guages. we routinely have 16 up to 20 cars pulled by 2 units. Even have started from dead on grade.

[ckape]

When my club built a helix, we found that it's hard to prevent kinks in the track at joiners, so a lot of cars that should make it through the radius don't because the curvature is greater at the kinks. We've had to go through with 6-axle equipment and a soldering iron to smooth out the kinks, and it's getting pretty good now.

[cefinkjr]

Saw a 29" radius helix once as part of a club railroad. That curve limited train length so severely that it could only be operated one way -- down.

[Anonymous]

Again thanks for all the suggestions, I've decided to redesign for a 29" R which I calculated at 1.8 % per revolution with a double track . That will get me down to the staging area below which are going to be 12" underneath.
Just to add another question, I'm doing L-girder (1x4 " & 1x2)construction, with joists (1x4), would it be best to support the staging with the joists and have risers go up the 12" or should I have the staging supported with some cross pieces underneath cosidering the will not be much weight in that area. I realize it is a tough question without getting into the logistics of my layout.
[:D]

[Anonymous]

I have a five level helix with an approximate 28" radius (the enclosure has 60" dimensions). For roadbed I used my regular 1/2" plywood/Homasote sandwich because of the sound factor and also because it is so hard to spike into plywood. I used code 100 flextrack and worked pretty hard getting the joints smooth. The top circle is double-tracked with a homemade curved switch (made from a stock #6 Atlas where I cut out every other spacer between ties underneath, as per an MR article years ago), and the whole thing works remarkably well. I am glad to have the double track section, because it is good for staging. The one innovation is the use of of threaded rod and nuts as the support system. I was having a terrible time figuring out the necessary height of the various supports until I hit on that (another MR suggestion, I think). The helix eats up a lot of track (14 feet for every circle) and the drag factor is serious (15 car trains have to be double-headed), but I would do it again because it effectively doubles the amount of railroad that can be gotten into a room. I do wonder about a 7'x11' room, though. You are going to be taking about 20 sg. ft. out of a total of 77 sg. ft. Can you afford to lose that much? My room is 10 x 20 and the helix box, even with turning loops above it and below it takes a lot of room.

[Anonymous]

Since you have a small space and helixes consume so much space, consider this instead: build the second level, but don't build a helix at all. Instead, use railroad carfloats to transfer cars between levels. This consumes much less space. I read somewhere about a model railroader that built a bookshelf style four or five level model railroad that used carfloats to move cars between levels. Walthers made railroad carfloat and carfloat apron kits, but they are now out of production. You can still buy them on eBay.

Larry

QUOTE: Originally posted by claircreekrr

I am looking to double the size of my current layout by adding a second level on top of the first one. The track would need to climb somewhere between 18" and 24" The layout is in a room 7.5' by 11 feet with benchwork between 24" and 30" deep along the walls. For added interest, the room is a former solar heat collector which means walls that are about 6" of reinforced concrete so going outside the room is not an option.

The space that I have currently set aside is a 36" by 36" corner section. My rail line is a branch line where trains are not likely to be more than a half dozen cars pulled by one engine.

Are there any recommendations for what is the minimum radius for a helix? I'm thinking that I can likely accomodate something slightly larger but the bigger the helix, the less room I would have too move in the centre operating space. What about ovals? Are they any better for these types of places?

Can anyone offer directions to a good source on building a helix in a really tight space?

Thanks,

Neal

[Anonymous]

QUOTE: Originally posted by claircreekrr

I am looking to double the size of my current layout by adding a second level on top of the first one. The track would need to climb somewhere between 18" and 24" The layout is in a room 7.5' by 11 feet with benchwork between 24" and 30" deep along the walls. For added interest, the room is a former solar heat collector which means walls that are about 6" of reinforced concrete so going outside the room is not an option.

The space that I have currently set aside is a 36" by 36" corner section. My rail line is a branch line where trains are not likely to be more than a half dozen cars pulled by one engine.

Are there any recommendations for what is the minimum radius for a helix? I'm thinking that I can likely accomodate something slightly larger but the bigger the helix, the less room I would have too move in the centre operating space. What about ovals? Are they any better for these types of places?

Can anyone offer directions to a good source on building a helix in a really tight space?

Thanks,

Neal

[Anonymous]

Radius is definitely one of the key parameters, and naturally as larger the radius the longer the route and less stiff the grade.
But there's a second parameter to consider: space between levels. Here often '4" for each loop' seems to be the common standard, but I have made good experience with 3" (7,5 cm to be exact) instead, even if you run Dome cars (3 level autoracks are the most critical ones).
Who cares if there are only one or two milimeters between the roof and the next level.

This makes a roughly 30% difference in grade. For example with 18" radius the grade drops from 3.5% with 4" spacing to 2,7% if you use 3" spacing.

Since living in Europe means also living in tight spaces my Helix uses only a 24" radius but 3" spacing resulting in a 2,0% grade. I regularly run 40 car trains with 4 F-Units both upwards and downwards without problems.

Greetings from the old Europe [:)]

[nobullchitbids]

One point not mentioned so far is that, as a curve gets tighter, sidereal thrust on a truck generated by overall train weight is increased and accentuated by our relatively more top-heavy cars -- why superelevation commonly does not work for models --; this has a tendency to pull the whole kit-n-kaboodle into the doughnut hole.

I would not lay a helix so tight as the one proposed, definitely would opt for some kind of "around-the-room" helix; however, that said, to the extent an escalating doughnut is what has to be, might I suggest that their builders (1) use code 100 rail to maintain rigidity and strength; (2) handlay the track at maximum allowable gauge to minimize drag on the trucks; (3) spike the rail heavily to insure it stays in place and in gauge, and (4) install at least one guard rail against the inside of the outside rail.

Oh, yes, do remember to put the track in as you do the benchwork, don't plan to run 4-12-2s, and test clearances for that Northern first, since the cab overhang will be quite excessive and likely to foul benchwork or passing equipment.

[Texas Zepher]

QUOTE: Originally posted by johncolley

Consider making the rest of the helix double track? 30 inch outside and 27 1/2" inside. Then you could pass or stage on the helix, too! Check a mockup with your largest equipment to be sure 2 1/2" gives enough clearance for end and center overhangs, eh? If you do it with silicone adhesive you can easily salvage the track for the final design.

Here, here! I was going to say the same thing. The design of every helix I've ever been involved with are eventually questioned, "Why didn't we double track it". If at all possible double track especially if it is going to be hidden. The single track helix at the club has become the bottleneck. Almost impossible to change it now.

[Anonymous]

Not only the drag, but as higgsy has stated, he has long equipment, SD75's and heavyweight passenger cars...I can guarantee that those cars will never stay on the track at 19" radius...and the end swing on the engines will derail cars for sure. I've track tested some walthers cars on a single section of 22" radius EZ-track connected to straight either side. The walthers will derail on THAT. If a wider helix is out of the question, you might want to consider an around the walls run that gradually climbs, essentially making the radius of the helix the full size of the room.

[jfugate]

I discuss the effects of tight radius curves on a helix in the "helix from hell" segment of volume 2 of my Siksiyou Line video series.

I originally designed a 24" radius helix for my layout even though the minimum visible radius elsewhere was 30" (the branch) or 36" (the mainline). I figured since the helix would be hidden trackage, it would not be a problem. WRONG.

I neglected to consider the drag effect of curves ... the tighter the radius, the greater the drag effect. The grade in my helix was 2.65%, but it acted more like a 4% grade because of the tight 24" radius curve. In HO, 24" radius adds the equivalent drag to a grade increase of about 1.3%. This made my 2.65% grade equal about 3.95% in drag! The visible trackage on my layout had a maximum grade of about 2.65%, but putting this grade in a tight radius helix made this hidden trackage the steepest grade on the railroad (equivalent) and operationally, it was awful.

I've included a curve radius drag table developed by the late John Allen and published by Don MItchell in his now out-of-print book Walkaround Model Railroad Track Plans on my video.

Needless to say, the helix operation was a pain and my crews hated it. They constantly pleaded with me to replace the helix with something better. Some discussion lead us to an option to replace it with a 40" radius helix on a 1.75% grade.

Once my crew convinced me the old helix had to go, they tore it out in a single afternoon. They couldn't wait to get rid of it. The new helix that replaced it is *wonderful*. The difference was like night and day!

The moral of the story is to steer clear of a tight radius helix that has an equivalent drag grade that's greater than visible trackage on the layout. You have been warned![B)]

[Anonymous]

That's a good idea John, I've got some long heavyweight passenger cars that I'll have to check that way. Looks as if final design is in, I'm off to get some wood today to start the benchwork, more headaches to come as well I'm sure!!

[johncolley]

Consider making the rest of the helix double track? 30 inch outside and 27 1/2" inside. Then you could pass or stage on the helix, too! Check a mockup with your largest equipment to be sure 2 1/2" gives enough clearance for end and center overhangs, eh? If you do it with silicone adhesive you can easily salvage the track for the final design.

[Anonymous]

I'm going to be running mostly Diesel through the helix, such as SD75I's etc, but the occasional steamer will head through. The largest I have so far is the Genesis Challenger (articulated ) and I'll probably running some railfan excursions with some 4-8-4's. Due to limitations I cannot go beyond the 24" radius for the first turn but would it be worthwhile increasing the radius for the second and third turn to lets say 30" as I go down towards my staging which will be approx 10-12 inch's under the layout?

[TBat55]

Some of the magazines advertise a storage shelf system that goes up and down (www.RO-RO.net). I've been thinking of modifying on of these elevators since my trains are relatively short. Still researching an automatic control system. I have more length than width for my layout and a helix seems to waste a lot of space, not to mention grade problems.

Anybody else thought about this?

[Anonymous]

just remember the larger the engine the larger the helix due to the forces exserted on the whole train as it winds thru the helix.At the club layout we run a thirty and have no major problems running articulated engines with long strings of coal hoppers behind.But if i were building one today it would have a min.inside track radius of 36 in or better.With all the big solid frame engines on the market bigger is better as they say.

[Anonymous]

Thanks everyone for the comments and I have redesigned the helix to use a 24" R. I would like to use more but this is the limit of space available. I'm making a fullsize drawing on construction paper on the floor. It's amazing how one change affects other areas, I've been pulling my hair out for a week now. Probably not a good idea to start so close to Christmas (as the wife points out) but I'm anxious to get going.

[bruce22]

because of size restraints i was limited to a 22" rad. Ironically it was a great operating addenda as I now usually have to "double" the hill if train consists exceed 8 to 10 cars.

[johncolley]

Neal, there is a difference between the degrees of arc and degrees of railroad curvature. A circle is 360 degrees and an arc can be any part of that. Also a line can be any number of degrees direction from another line - example 30 or 45 degrees.
Railroad curves were developed because there is usually no place to stand to swing a string from a radius point. Surveyors coming along a straight section of track (called tangent) would measure curves in increments of 100 feet. so on the centerline they would swing their transit 1 degree, or more and the rodman would put a stake 100 feet out. then they would move the transit and maybe add another to make the next swing 2 degrees offset. Increasing the curve based on the terrain and the speed to be run. When they got halfway they would start decreasing until they were on the next tangent section. 5 degrees of curvature is a good curve, 10 degrees is pretty tight and calls for slow speeds. As an example an industrial spur minimum curve specification on one railroad was 12 1/2 degrees. Very tight, this equalled a 459 foot radius which scales out to 63.3" radius in HO. so you can see our usual model railroad curves are very tight indeed. That's why I recommend going the biggest you can fit in your space.

[Anonymous]

Thanks for the various comments. Of course, the one key bit of information that I left out is that I'm modelling in HO. With a room that is only 7 by 11 feet, a four or five foot wide circle will take up a lot of space.

I have since decided that the only way to gain some height to another level is to run the track along the walls of the layout and circle the room a couple times. While it may not be the most sightly, I can always cover those tracks with a backdrop if it bothers me.

I am interested in Jim' s comment about degree curves, how does one find the degree of a curve, especially a full circle? For the degree of the curve, is it the degrees in a circle that an arc travels (ie a semi-circle would travel 180 degrees, a quarter-circle 90, etc)?

Thanks,

Neal

[jwar]

As johncolley stated go as large as possable. I have a 25 and 27.5 double track helix and the rise is only 3 7/8 per rise. So far its working ok for me, however the most importent thing in my personal openion is a very strong bench work to prevent any sag in the future.

I made a straingh line sodering jig to hold perfect track alignment and an magnifiying glass to examan each joint, test ran (forward and reverse) each loop before mounting the next layer. Works flawless if you dont get in a hurry, is worth the effort to make this the best track on your layout, as its difficult to repair after. I too applied track directley to the plywood and routed a 1/2 1/16 deep groove for the wires to run under the track. Prevents the wires hanging down and is a neater wireing job.

There are other post you can search for, that have great information.

E-mail me if you wish....John

[Anonymous]

I am currently building a 30" and 32" radii double track helix. The trains are not having any problems so far. 18" radius won't travel far enough around in one revolution to keep the grade mangeable as another poster pointed out. At 2.0 % the tracks travel 3.75 inches above each other in one revolution with 30" radius. I am using 1/2" ply with track tacked diectly to it, no roadbed. This is by far the least fun part of the layout, but it will be great when it is done.

Guy

[johncolley]

By all means make it as large a radius as you can fit with minimum clearance to the walls and supports of 2" to 2 1/2" to accomodate the overhangs of your longest expected equipment. Another thing to consider in the planning stage...you will really appreciate it in the future if you make it a double track. That way you can use the easiest (largest radius) for going up and the inner one for coming down. Also, if starting a train from dead stop on a grade isn't a problem you can even use the helix as staging.

[jrbernier]

The biggest issue with a helix(other than maintaining it) is grade as it will need to climb about 4" for each loop of the helix. An 18" radius helix will travel 113" for each loop - that is about a 3.5% grade! And that does not count any compensation for the curve itself. IIRC, I read in an old railway engineering book that you add .05% for each degree of curve. 18" radius works out to a 45 degree curve, so 45*.05 = 2.25% - That works out to 3.5% plus 2.25%, or a 5.75% grade all the way to the top. I think this would be rather stiff grade. I have operated on layouts with a 36" radius helix, that is a 2% grade with another 1.1% compensation - about 3 % total - very managable.
The biggest operational problem I have seen is going down the helix. This can vary from the train coming in on the engines, to the engines 'hunting' due to gear lash in the drive train. Unless you are running a small logging pike, I think the 18" radius helix will become an operational headache....

Jim Bernier