Maybe you’re suggesting that by reducing the grade on the prior to last turn the grade would be less because the circumderences is less and more of the train ould be on the prior turn with no grade. but regardless, that last turn needs to clear that prior turn and the grade would be substantial because the radius is so small
again, not seeing it.
that last turn can’t increase in radius or become more oval because the prior turn is horizontal to it.
this is what is looks like from above with adjacent tracks less than the clearance height required
i plan on doing a vertical cliff with trestles. i am using a Proses Smart Hobbey. i choose the Marklin C4/C5 for the largest turn. I plan on using a big boy and passenger train line on it.
It looks like starting with a 29” radius, 3” rise (including deck) and reducing 2.5” per level I can only get 4 loops equaling 12” rise before the inline hits 2.2%. If I expand the diameter to 6’ I think I can get 2 more loops totaling 18” rise.
No wonder you don’t see folks doing these.
what do you think the required clearance is between tracks?
from RP-7.1 the recommended height is 1.28". Add to that the height of the track and benchwork. And don’t forget the thickness of fingers when rerailing cars. I assumed 2.8"
And the required clearance will change, perhaps dramatically, with sharper curvature toward the top.
I can see why the ‘window into tunnel’ approach with a more conventional helix geometry is used instead. It occurs to me that there are stretches of Swiss mountain railroad that are built in galleries carved in vertical mountain faces – that might be an interesting thing to adopt.
There may be an interesting approach in Creon Farr’s ‘switchback’ railroad that was built from the rim of the ‘Grand Canyon of Pennsylvania’ down to Tiadaghton… steep and curving enough that people didn’t want to ride it.
to exit the loop at the top, it needs to clear the 3 previous turns. Please look at the diagram. The black line represents that trackage exiting the helix and the blue line the clearance require any tracks it crosses
This is more what I will be doing. I have bought 2 prebuilt HO Proses Helixes and which limits what I can do. I was thinking to do it like the Chinese villagers did and “carve” out a space. I will be doing a canyon type bridge to connect the two.
