Length of circumference = 2 x pi x radius (not diameter)

QUOTE The train has to climb about 8-9 inches and I would like to use a gradient of 1:50, as I have heard this is a fairly safe gradient to use. Is that correct?

That should be perfectly safe but you will probably be able/need to go steeper. I assume you are using H0/OO, but what sort of length trains will you be using? You can test pulling power of a locomotive using track on a plank of wood and adjust the angle.

QUOTE If I am climbing 8 inches at a 1:50 gradient that is 400 inches of track required. Is *that* correct?

To the nearest inch yes. Actual length = square root of (400 x 400 + 8 x 8) = 400.08 inches (2DP)

QUOTE Using all those numbers I worked out that my helix would need 3.7 complete circles to rise 8 inches. Correct?

Yes but here is a problem depending upon how tall your trains are: If you perform 4 circles then clearance between levels in the helix is 2 inches minus - thickness of board used! Unless you use N gauge it will be impossible!

__Turns__---------

__Clearance + rail height + wood thickness__

4--------------2 inches

3.5------------2.3 inches

3--------------2.7 inches

2.5------------3.2 inches

2--------------4 inches

1.5------------5.3 inches

Whether you can use half turns will depend upon the orientation of the tracks that you are connecting. Using two turns and a gradient of 1:25 sounds a better option with clearance of 4 inches but depends on your trains capability at that angle.

As an N scale modeller I don't know much about OO train power etc.

Hope this helps,

Goedel