Effective Slope caused by curves

[gregc]

The most common rule-of-thumb is that proposed by John Allen. For HO, this is expressed by the formula 32/R, “R” being the radius in inches. The result is the additional grade percentage to be added to the nominal grade. For 22" radius, the result would be 1.45%, added to your 2% nominal grade would be 3.45%.

Empirical testing is underway on this calculation and it seems to be relatively accurate. The table posted earlier doesn’t seem to relate to observed curve effects on grades.

Thanks Byron.

As I said, I’m interested in this topic wanted to see what Byron’s recommendation means for different helix configurations.

here are 3 tables for board thicknesses of 1, 3/4 and 1/2 in. Clearance above the rails is assumed 2.75" suitable for HO. The actual grade is the rise / 100. Compensation is 32/Radius and the total is the sum of the grade and compensation.

If these calculations are correct, a target compensated grade of 2% would require a radius of 46, 44 or 42" for board thicknesses of 1, 3/4 and 1/2".

clearance board radius grade(%) compensation total
2.75 1.00 18 3.3 1.78 5.09 %
2.75 1.00 20 3.0 1.60 4.58 %
2.75 1.00 22 2.7