One point not mentioned so far: If the line you are bridging goes down while the line you bridge with goes up, the grades inside the helix do not have to be any more than what is necessary to separate the trains. Now, apply Utah Mark’s idea but in reverse – the lowest level is the tightest curve, so that succeeding levels do not have to stack atop one another. For a few turns more, the grade becomes much reduced, and access is a snap provided you are not an old fart like me with sore knees and a hesitancy to spelunk inside a plaster mountain.
I agree, however, that 18 inches is far to tight to start with if you are running a Hudson – the four-wheel trailing truck will make the locomotive hang over so much that the clearance problems will leave you drunk, and the forces tending to push your consist toward the center well could leave a lot of your equipment smashed on the floor.
Do remember that even a helix is subject to what railroads call a ruling grade. In the early exchanges, you spoke of running 40-50 car trains. A standard 40’ car in HO is about 6" long, so 40 cars is about 21-23 feet (including engines and caboose). To the extent any of these cars are not actually going up the helix, the grade for them may be zero. On the (real) Union Pacific, the top of Cajon Pass was 4 per cent, but that section was short and did not control what was needed to pull a mile-long freight up the hill. The ruling grade actually was two something, depending on how long the train was.
And yes, pulling up a curve does increase the ruling grade, and the sharper the curve, the more the increase.
Other than just cosmetics, you have to look at operation reliability. I have operated on a large home layout with a beautifully mountain scene. In order to fit this into the space and double back into an adjoining room there is an 18" curve partially in a tunnel. I can not remember an operation session when operations came to a halt to rerail a train(s) and fish out derailed cars in this section of track. The rest of the layout runs smoothly. The derails seem most common with 6 axle diesels, auto racks and long trains. Any two of these and it is almost a guaranteed derailment. In short I would highly recommend you look at increasing the radius or look at other ideas to fit in your trestle.
I like the idea of a test track. A 4x8 sheet of plywood would be a good test bed to experiment with various radiuses to determine operational characteristics.
Joes comments about the drag in turns is dead on. He helped me as well as John Collie when I built mine. thanks again to you both.
In a nut shell my openions now about building a helix. Start with a solid foundation, any sag will defeat operation and any work on it from there on.
Soder all connections with a track jig to get perfectly aligned joints, both vert and horz. Trash any joiner that fits loose, this helps to prevents any offset rail joints. use a magnifying glass to inspect and file each joint dead smooth, if not, cut the bad joint out and rework them at that time. Drag a penney over each sodered area, wire connectors and joiners, this will magnify any imperfections. Run trains both pushing and pulling, seems a backing up a train will show your bad track in a hurry, as well as bad cars.
Then test each level of your helix as its being built, this prevents surprises and flustrations, imaginine testing a helix after its compleatly built, not much vert room to re soder a wire or file a bad joint or even drive a track nail. I left only enough nails to hold a radius account of my seasonal temp changes( 113 to 25 degrees), Has been one year now and not one derail…other then my gravity car test to see how much drag, a few cant handle the grade… LOL
My double track helix is 23 and 25 3/4 radius, run 25 to 30 cars. Now is the time to know if your going to run double stack cars, Lots of luck, email me if you wish,…John
i had a helix on one of my layouts and it was 36"radius… the area inside the helix was to be the dispatchers area… with a 2% grade and a large radius i still had problemswith trains trying to stringline the cars… this resulted in quite a few damaged cars until i super elevated the track to lean the cars outwards… ps do not be tempted to put helpers on the end of the train you will get away with it a couple of times then disaster… believe me i have tried it…pps… try having two grades in the one helix 2% going up and 4% going down…peter
We have a helix on our club layout that is 5 feet in diameter and are able to take 45 hoppers up grade with two stewart locos with no problems. We use all other locos with 10 to 15 car trains and never have problem with pulling power. BUT that doesn’t mean there are not problems with derailments. We have thought of enclosing the helix but come to the conclusion that the rerailing of cars and seeing the problems out weighs the inclination to cover it up. We also find that the public are facsinated with the open helix and never think about it not being sceniced. We also double tracked it as it was the bottle neck on the layout. We raise 18" in 7 loops. We kept the spacing to a minimum between layers but now wish we had given more heght to them as there is little clearence for rerailing cars, let alone a 4-6-6-4 loco.
Has anybody used guardrails (like those found on bridges and with turnouts) with helixes that use a radius that is also the minimum radius of the layout?
An alternate suggestion that may have already been alluded to. I thought about a helix, deciding against it due to the amount of time that the train would be hidden to raise the 20" that I wanted on a 30" radius. Instead I eliminated one wall run, widened the pennisula and brought the track around twice on it climbing1.7%. With the length of my pennisula (about 20’) I was able to climb the 20+ inches with only the short sections where the track overlaps hidden inside the mountain. I love to watch trains run and this gives me what I want, more time with trains in view. The helix must be accesible, both physically climbing in the middle (18-22" radius may be tight for some) and between the levels to rerail any cars that have derailed. One more thing that others have hinted at. Physically when a real engine or a model one pulls a train the pulling force is in a line strongest in a straight line behind the locomotive, so the tension is pulling the cars inward on a curve, the danger of an S curve as well. With a small radius and taller grade this makes the engine work hard, thus multipling the force, the engine trying to pull the cars into a straight line, thus derailing the cars, or at least wearing the wheels on the cars, or if you have metal wheel sets, the cars and the rails. I am not trying to discourage you, just want you to go in “heads up”.
good look to you in whatever you decide
Randy Johnson
One of my helixes is an oval shape. This allows me to keep the same headspace and the same min radius where it curves but the run length for each loop is increased as much as I’d like simply by how long the straight section is. And this length directly reduces the grade percent. You can maintain your aisle space as well, just use a longer mountain along the wall or peninsula.
I’m actually planning to do this at the base of a long peninsula but to hide the turnback “blob”. I figured it would look better to see a long coal drag’s caboose disappear before the power appeared across the aisle. So I’ll be putting a 1 1/2 turn helix behing the backdrop at the base of the peninsula, even though I don’t need one in that area.
I saw an N-scale helix like this over the weekend, and had never heard, thought of, nor read about the concept before. It was genius! The helix was cone shaped with the widest radii on the top and the sharpest on the bottom. Supports for each turn where stair-stepped shape. The layout owner stated a couple advantages to the construction – unlike a conventional helix, it could be built first, and then track added after it’s finished. You also didn’t have to worry about car/hand clearance between levels because each level had nothing directly above it limiting access. This also makes it much easier to clean track.
If I had the room in HO on my layout, this is DEFINETELY how I’d build MY helix.