Helix Help?

[Frank53]

My layout plan has a number of track routes on different levels, primarily against the back wall. I know how it looks in my mind, but I am struggling with what happens after the run along the wall. I am doing 2" deep trackside industries against the back wall.

The layout is U-SHaped plus an extra leg, and I am thinking of keeping the high level and trying to drop the trains down to the base level using a helix in a mountain. Trains go into a tunnel at the top, come out a tunnel at the bottom. Ideally the difference between levels is 8"., but if it had to be six inches, I could improvise.

My layout is exclusively post war, although I will cheat by using tubular track in non-post war radii.

If I start at o-31, and keep increasing the diameter as I go from 3/4 of a complete circle on down, I would o-31, going into o-42, going into o-54. Hopefully that length of travel would allow enough travel for the trains to descend the required amount wihtout exceeding 4 percent.

Does this have any merit? Anyone have experience with this?

[lionelsoni]

The problem will be getting to that first O31 loop. The track leading to it will have to cross over the loop, which means that you will have at least a 7-percent grade of O31.

[Frank53]

well that was too obvious - hadn't even thought of it.

Perhaps I can go o27 and use a back and forth to the bottom.

[Big_Boy_4005]

Bob is correct about variable radius helixes. I had a similar discussion with someone over on the MR forum a couple of months ago. The conclusion was that the smallest radius was the limiting factor because of the need to bridge over the previous turn to exit.

Helixes are best done using a constant radius, generally the larger the better. If you don't have room for a large circle, you could use a smaller radius, and add straights to form an oval. Keep in mind from an operational perspective, it will take some extra work at the throttle to negotiate an irregular shape, whereas a circle could pretty much be left to run.

You don't need 10' diameter to make a functional helix, but it does help to keep the grade percentage down.