Helix gradients

[guest311]

the proposed changes to my plan will allow me 40" x 40" as the footprint for my helix, which needs to raise a twin track 24" to the upper level.

I'm looking at 18.5" radius for the outer track and 17" radius for the inner, and aiming to use flextrack throughout the helix.

this by my calculations gives track 'lengths' per circle of 116" and 106".

if I go for eight circles at 3" rise per circle this would give the outer track  a gradient of 1:38 and the inner one of 1:35, or if I went for 9.6 circles at 2.5" rise the gradients would be 1:46.4 and 1:42.4 respectively.

do these sound reasonable, bearing in mind that I'm aiming to run 2+7 HSTs and loco + 9 carriages as heaviest trains.

would 2.5" give sufficient clearance, I'm planning on making the helix from 3mm MDF in 1/4 of a circle segments, laminating two  lengths of them so that the joins are staggered to smooth them out.

any advice would be appreciated.

cheers

alan