Rule of Thumb

Model Railroader General Discussion (Model Railroader)
1

Hey Guys,
I need a rule of thumb for figuring the effective grade on a curve that has a known actual grade. I’m thinking of designing a helix and need to know how to estimate the effective grade.

Even tho I live in a sandfield, I don’t want to use all that sand in my engines[:p]

Thanks -------- John T.

2

http://www.fortunecity.com/westwood/beautiful/819/HeliCal.htm
This might help. If you do a search for helix on the forum you’ll find tons of stuff.

3

Thanks loathar!!!

4

On the prototype, according to the army corps of engineering, a one degree curve is equivalent (in resistance) to 0.04% grade.

So recalling that a degree of curve on the prototype is based on a 100 foot cord.

The radius (in feet) = 5729 / degree of curve

A 22" radius curve in HO = 159.5 scale foot radius = 35.9 degree curve

So 35.9 degrees times 0.04% grade/degree = 1.4% effective increase in the grade.

However - I seriously doubt the physics of a toy train drag through a curve are the same as that of the prototype.

5

My ARA track engineering guide mentions .05% for each degree of curvature. But my tables show that a 22" radius HO curve is about 40 degrees(actually just a little less). The NMRA web site also lists a 22 " radius HO curve at about 40 degrees…

Jim Bernier