The Helix Part I …
It’s been a while between posts. The main reason for this is since the last bit of spline was done, I soon realised that I needed to think about the construction of the helix before I went any further with benchwork or spline construction. I didn’t want to have spline in place around the next peninsula and then realise that things would be in the way when I came to build the helix.
So, things had come to a halt.
For a while now, I have been gathering information on helix construction. There are certainly many ways of going about it, but which method to choose?
I eventually settled on an all timber design, based on an article in the online magazine Model Railroad Hobbyist. In the July 2011 issue, Art Houston presents a 13 page article on how he built his 10 turn helix. What a monster!! The article starts on page 61.
But first, a bit of background on my helix requirements.
The basis of the the whole layout’s design, was to have a rising grade against UP (loaded) trains so as to enable the working of bank engines and to take advantage of features of modern DCC sound decoders that can simulate ‘load’ on a locomotive ie, to have the loco sound as if it’s working hard but just crawling along.
The ruling grade on the layout is 1 in 84 from the bridge at Chilcotts Creek right through to a point midway through Ardglen tunnel where it levels out at an elevation of 70 inches. The line from the tunnel right through Pangela to the helix remains at 70 inches. In the real world, it is a falling grade of 1 in 40. I had to keep this section level to obtain deck clearance at the crossover point just near the helix. I have ended up with 12 inches between roadbeds which should give enough clearance for things like lighting etc.
The details of the helix as shown in 3rd PlanIt can be seen in the right hand side panel of the screenshot above. The helix has a radius of 36 inches, which is less than the minimum specified for the layout, but since it will be hidden trackage, I wasn’t too concerned. This radius also was a factor in determining the size of the helix structure as it had to fit in behind any future backscenes.
3rd PlanIt makes it easy to design a helix. Once the radius is set, and the top and bottom elevations, it automatically calculates the grade, clearance between levels and how many levels there will be. Any of these values can be changed to suit and the others changes respectively.
This helix has 5 levels with a clearance between levels of 4 & 1/8 inches. My original design had the bottom level of the helix at 42 inches which gave a level run back to the storage yards. But this design had seven levels, so Andrew came up with the idea of setting a grade from the storage yards up to and continuing through the helix, which could reduce the number of levels and hence the length of run and hence the amount of track required. The first design required 129 feet of track in the helix alone. I managed to reduce it back to the 5 levels and ended up with a new track length of 92 feet – a saving of 38 feet of track.
Well, that’s a bit of background to the need for the helix and to how it was designed on paper. The next instalment will detail on how it will be constructed.
Cheers for now.