Try Again

[loathar]

[#ditto] I think there's too many variables to use a nice, neat formula. (car weight,coupler spring force, axle friction,wheel flange friction.car length) I think your probably stuck with the trial and error method. A real train engineer might know this better for figureing how much power they need to haul a train up a curved grade.

[fwright]

I saw a while back on a forum - might have been Yahoo layout constrution group - someone quoting John Allen as saying to add about 1.3% to the grade for the effect of the curves. Don't remember what radius was being discussed, but it was for a helix. That figure was from the '60s, so one would have to assess the impact of using RP-25 wheels, which were not common back them.

The newer wheel profile is much more free rolling than the old on straight and "moderate" curves, where the tread taper does the "steering". But there will be a sharp increase in friction when the flange starts rubbing against the rail head. At what radius does the flange come into play? I don't know.

But looking at the situation logically, there would be little increase in friction from helix curves until the radius decreased to the point where flanges come into play. I don't think the relationship between extra friction and radius of curve even begins to look linear. I think the extra load curve would be small at large radii with a slow increase to the critical radius, where there would be a sharp "knee" upward. What the critical radius is and what the shape of the added friction curve is beyond the knee is beyond my limited knowledge of wheel and rail mechanics.

Similar to the impact of grade on train length, the impact of curves is going to best be determined by individual experiments. I would try a train on a circle of track of the desired radius, and compare it to performance on a straight track at different grades. You will need a loco of limited pulling power to keep train length viable for the experiment. If you do the experiment, please publish your findings as another data point for all of us.

yours in mad science
Fred W

[Anonymous]

The question is clear, but I don't know the answer. I think it is also going to depend on the length of the train. A loco alone isn't going to notice the curve near as much as a 30 car train. I think (a dangerous sport) that if you keep the helix as wide as possible, and keep the grade to the standard that you use on the rest of your layout you probably survive. You might slow down, but I'm guessing you make it. Without an experiment, I don't think you are going to really get a good answer.

[jawnt]

Earlier I asked for a rule of thumb on figuring effective (equalivant) grades on curved track ie a helix where the actual grade is known.

Such as a 24" radius at 2% actual grade --- what would be the effective grade in terms of engine pulling power. I've read here about the effective grade would be considerably more due to the curve.

Lothar pointed me to the curve calculator, which is fine and appreciated, But I can figure grades with my handy pencil and envelope back[:p].

What I'm looking for is some sort of rule of thumb such as: for a given radius at a given grade add x% to your grade figure to arrive at an effective grade.

I hope it is clear what I'm seeking. If not, I'll try to re-word this another way.

Thanks for any help --------- John T.