True, an equivalent radius will be smaller than the closure radius.
The minimum radius of the closure rail in a normal US AREA turnout will be the following formula:
n= frog number
g= gauge in inches
R= radius of closure rail center line
R= 2*g*(square(n))
Thus for number 6:
N=6 (6*6=36)
R=(2*56.5*36)
R= 4,068” (4068 /160 = 25.43” radius of closure in N) - about 645,92mm
Thus for number 10:
N=10 (10*10=100)
R=(2*56.5*100)
R= 11,300” (11,300 /160 = 70.63” radius of closure in N) - about 1794,0mm
You only need to divide the prototype by your scale factor and any scale will give the proper minimum radius.
-ed-
_________________
-ed mccamey-
COSLAR RR -
http://www.coslar.us/NMRA Standards and Conformance Department
PROTO & FINE Scale Coordinator
I estimate I have about 5 pounds of coupler springs somewhere in the vicinity of my workbench.