Create helix

A helix takes the track from one storey to the next within a small footprint. The dialog builds it from a curve you selected beforehand.

The dialog for creating a helix.

How to go about it

Select exactly one curve with one end still free. It is the element the helix repeats, and it grows out from that free end.
Call up Create helix… in the context menu.
Set the turns and the rise per turn.

No Create helix… in the menu?

The entry only appears for exactly one curve with a free end. With several tracks selected, with a straight track, with a turnout, or with a curve that has track attached at both ends, it is not offered at all.

Inputs

Turns: how many full circles the helix makes.
Rise per turn: the height gained per turn. The preset is 5 m at prototype scale, around 57 mm in H0.

From these the dialog calculates and shows:

per turn: how many curves make a circle. This follows from the curve itself — 12 pieces at 30°, 16 at 22.5° — which is why the dialog never asks for a radius.
elements: how many track pieces the whole helix needs.
total rise: what it climbs in total.
grade: as a percentage, calculated as the height gained per element over its plan length — the number that decides what a locomotive can still pull up.

400 elements is the limit

So the helix cannot accidentally overload the system, it is capped at 400 elements.

Clear height

Choose the rise so that enough room remains between the turns for track, train and baseboard. If it drops below 5 m at prototype scale, around 57 mm in H0, the display changes color and reports "Less than the height a train needs below" as a hint that it is probably getting tight.

Check the numbers before you build

The warning is a rule of thumb. Check it against your own equipment: rail profile, the tallest vehicle, the thickness of the board plus its underlay and, if you have one, the catenary.

Raily builds the helix even with the warning showing. See also Technical limits.