Model Forum / General / Railroads / February 2006

Decide the maximum gradient for your trains and halve it to allow for
curves friction.  Decide how thick the baseboard will be and how much
clearance you need between the stock and the bottom of the baseboard.
That and the rail height will determine how many circuits you can get
into the six inch rise.  Knowing that and the gradient will determine the
total length and diameter of the spiral.   To keep the diameter down you
could use a coil rather than spiral,  where the diameter starts small and
gradually increases by one track clearance (about 50mm.) each circuit.
That is also easier to build using foam boards.

Ken.

I would not go smaller than 3rd radius curves. Mine is just over and
older DE models struggle compared with more modern Heljan, Bachmann and
Hornby. Of the three brands the Hornby 50 is the only one that does not
stall with longest train possible on the curve. The gradient works out
at @ 1 in 30.

Chris

I have a helix on my garden railway, and it is 4 foot radius. My 0-6-2Ts
have no trouble traversing this with 40 goods wagons.

Helixes have been used for several years over here to connect two levels
of layout. Experience shows that in HO/OO you need about 3" rise rail to
rail to allow for the substructure. It's the grade of one turn of the
helix that counts. Also, you need at least 1-1/2" from track center line
to nearest obstruction. The following table will tell you more (numbers
rounded off):

Radius    Length 1 turn    Grade        Diameter of helix
15"    94"        3.2% (1 in 31)    33"
18"    113"        2.7% (1 in 37)    39"
20"    125"        2.4% (1 in 42)    43"
24"    151"        2%   (1 in 50)    51"       
30"    188"        1.6% (1 in 63)    63"
36"    226"        1.3% (1 in 77)    75"

Keep in mind that a curve adds drag. IMO, an 0-6-2T trailing 20 or so
wagons will have some difficulty on a curving grade greater than about 2.5%.

HTH