Tilting outwards is an interesting idea, but I think you'd need to tilt at least five to ten degrees to get any significant relief from stringlining a long train. Stringlining occurs when the inward component of the pulling forces on the couplers exceeds the force necessary to turn the car over around the inside wheels on the trucks. Adding outward tilt will increase the force required, but one to two degrees would probably net you only a very small improvement. The most effective thing you can do is increase the radius of the curve. Even a small increase (a couple of inches) will reduce the inward component of the coupler forces significantly. If that's impractical, you might try lowering the center of gravity of your rolling stock. That will make the car more resistant to rolling over, and so increase the required inward force to stringline. You can do that by putting the car weights as low as possible. I've heard of people wrapping solder around wheel axles to gain very low CG weight.
I haven't done any calculations - I'm just visualizing component forces on the cars here, so if I'm wrong sombody please tell me...
Mark P.
Website: http://www.thecbandqinwyoming.comVideos: https://www.youtube.com/user/mabrunton
Brunton wrote: Tilting outwards is an interesting idea, but I think you'd need to tilt at least five to ten degrees to get any significant relief from stringlining a long train. Stringlining occurs when the inward component of the pulling forces on the couplers exceeds the force necessary to turn the car over around the inside wheels on the trucks. Adding outward tilt will increase the force required, but one to two degrees would probably net you only a very small improvement. The most effective thing you can do is increase the radius of the curve. Even a small increase (a couple of inches) will reduce the inward component of the coupler forces significantly. If that's impractical, you might try lowering the center of gravity of your rolling stock. That will make the car more resistant to rolling over, and so increase the required inward force to stringline. You can do that by putting the car weights as low as possible. I've heard of people wrapping solder around wheel axles to gain very low CG weight.I haven't done any calculations - I'm just visualizing component forces on the cars here, so if I'm wrong sombody please tell me...
Bruton's suggestion about increasing the radius of the helix can provide a secondary benefit. A larger radius means you can achieve the same height gain with a flatter grade. E.G. An 18" radius helix might require a 3.5 % grade in order to rise 4'' per revolution since the circle is only 113 inches long (2 x pi x r). This is a steep grade on even a straightaway. Expanding the radius to 24" gives you 151 inches to rise 4'', resulting in a 2.6% grade. At this grade, as long as you avoid sudden (unprototypical) starts, stringlining should not be a problem with freely rolling trucks.
I am planning a 30" radius so that was never the problem but since
I am modeling the region of the coal fields of western Viginia to include
N&W, C&O, NS and CSX in various ages as time frames suit me was
wondering if there might be an advantage to an outward banked track
for this type of operation and wondered only if anyone had tried this
concept.
bnobob wrote: I am considering a helix and am wondering has anybody tried tilting the track slightlyoutside by 1 or 2 degrees to try to mantain trains remaing on track if they are long versus tilting toward the center as real life train track does. 1 to1 are lots heavier than 1 to 87. Or are there better ways (other than short trains) to not dump everything to the center?
As was already stated, stringlining occurs when the drag of the cars behind exceeds the force needed to tip the car inwards. Ways to prevent incude:
- increasing curve radius, as was already stated. If your curves have a radius less than 3 times the length of the longest car, then the CG of the car gets perilously close to the inner rail, and reduces the force needed to topple the car inwards. The 3X radius rule of thumb seems to work well from all reports I have tracked with helii (sp?). In your specific case, a 30" helix radius should work fine unless you are running 80ft passenger or freight cars.
- reducing rolling drag of your cars. Consistently free-rolling trucks are critical. As Bob said, keeping the CG of the car below the coupler certainly helps. Ensure cars are consistently weighted, preferably to the minimum weight that tracks well. Remember, that increased weight means increased drag by itself on an uphill grade. You also won't want significant weight disparities between your loaded and empty hoppers if they will be in the same train. But remember that free-rolling trucks and weighted cars will create bucking and bunching issues going downhill because of the inability of our model locomotive mechanisms to free-wheel. By the way, if our locos did free-wheel with a load behind, then we wouldn't be able to stop the train on or at the bottom of a grade since we have no model braking systems!
- negative super elevation could increase the force required to tip the car inwards. But as was stated, the amount of tilt required to make a significant difference might be more than you want to deal with. Any super elevation requires transitions, which give fits to our generally rigid-frame, non-equalized trucks and rolling stock. These transitions must be over a car length long to work. The prototype can run on proportionately rougher track because of their equalization systems.
Finally, prototype weights should be reduced by 87x87x87 because it is a volume, not a length. Our model weights are not as far off as you might think. What is really different about our models is that rolling friction is so much higher proportionately than the prototype. This becomes even more of an issue in N and HOn3 than in HO.
my thoughts, your choices
Fred W
Bob,
I was in a club that had a 30" radius helixon about a 2% grade. We ran 100 car iron ore trains up and down the helix without any problems except for an occassional coupler letting go and causing a runaway. (I always stood inside the helix with super long trains as a precaution.)
Eric
Would putting the couplers much closer to the ground than the standard 33 inches above the ground to prevent stringlining. During transition a lower and higher coupler on each rail car could be installed until the lower becomes the global standard. Would 20 inches above ground be a reasonable height for the new standard?
Why was the current standard for coupler height set at the height it was?
Engineering and economy. The frames, to which the draft gear is affixed, and which should be quite robustly affixed, ride above the trucks, and they on the 33" wheels, or larger these years. You don't want draft gear pulling off axis in either axis, not high, not left, not right, not below the center of gravity if you can help it. It's best to integrate the draft gear as close to the centerline of the frame as possible rather than create a box that's welded below the frame, and still have all the draft gear and mounting dragging 10K tons and it's attendant resistance, more on grades.