Banking curves
- Thread starter oplholik
- Start date
Banking curves will allow you to make slightly tighter radii. I've been meaning to set up some test track for it. Banking and curving at the same time can be complex. Jannie, how did you go about doing that? I didn't spot it in your thread.
I would probably cut blue foam strips on a table mounted hot wire, first 3" x 1" x 8'
Then cut the slant so they then end up 3" x ~0.5" x 8'
Then with a hand tool hot wire cut slots 2" apart and 2" deep on each side with a 1" offset, similar to the Woodland Scenics grade risers.
You'd also have to manually make bank-to-flush transitions by hand.
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Suzuki grand vitara
I would probably cut blue foam strips on a table mounted hot wire, first 3" x 1" x 8'
Then cut the slant so they then end up 3" x ~0.5" x 8'
Then with a hand tool hot wire cut slots 2" apart and 2" deep on each side with a 1" offset, similar to the Woodland Scenics grade risers.
You'd also have to manually make bank-to-flush transitions by hand.
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Suzuki grand vitara
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Selector
Well-Known Member
Banking curves, or what is properly known as "super-elevation", is unnecessary in the hobby, and will even contribute to stringlining on tight curves. So, if you do it, do little of it, just enough to get the ooohs and aaahs, but think twice about using it on heavy trailing 'tonnages' on tight curves, particularly on a grade more than 1%.
If you can lift the outer tie ends on your curves, say by wetting and softening the ballast first, and slide thin cardstock shims under several of the rails, and let the ballast harden once more, you can achieve that look.
If you can lift the outer tie ends on your curves, say by wetting and softening the ballast first, and slide thin cardstock shims under several of the rails, and let the ballast harden once more, you can achieve that look.
Jannie
Member
^Wow! That looks super smart! My Layout's entire left side loop is banked,reason why is the radius being 1meter & I ofund trains going down it tend to derail sometimes.How I got it to work was by nailing the inside ties & then sliding paper wedges under the outside tie ends....It works wonderfull....even for trains going up that mad incline 
.......It was however a mayor pain to get it just right.....& alot & alot of testing & re-testing
So if you got the time,go & check out 'My HO Layout'......will be 1 of the top threads in the 'Layout & Construction' thread
Keep well.J
.......It was however a mayor pain to get it just right.....& alot & alot of testing & re-testingSo if you got the time,go & check out 'My HO Layout'......will be 1 of the top threads in the 'Layout & Construction' thread
Keep well.J
lmackattack
old school
I super elevated track in my hidden return loop because of the tight radius. Its 18" radius with a 3% grade. I was worried about larger locos riding up the outside rails. after I placed shims under the outside rail. it reduced derails drasticly. I only run 10-12 car trains so its not a problem. when I have pulled 30 car trains stringlining becomes a problem.
Selector
Well-Known Member
You can superelevate by putting paper shims, by glueing thin styrene strips under the outside ends of the ties or rail (less than .060) or by building up layers of masking tape undener the outside of the track. Be sure to include a "runoff" where the superelevation transitions back to level.
Some people bank the risers or cut the roadbed at an angle. That is very hard to do to keep a consistent SMALL bank. a real railroad is only going to have a couple inches of superevelation in most places, that's only a few hundreths of an inch. I have always found it easier to make the roadbed level and then raise the outside end of the track the amount I want it.
YMMV.
Some people bank the risers or cut the roadbed at an angle. That is very hard to do to keep a consistent SMALL bank. a real railroad is only going to have a couple inches of superevelation in most places, that's only a few hundreths of an inch. I have always found it easier to make the roadbed level and then raise the outside end of the track the amount I want it.
YMMV.
Sounds like my foam cutting concept is massive overkill ...
Has anyone done the maths to determine what effective radius gains are provided by increments of super elevation? For example, if you super elevate an 18" radius by 0.01" does it become 18.5" effective radius?
Also, how is super elevation typically measured? Seems to me it would make sense to measure it in % of grade so that it can be transitioned between scales and gauges. But maybe that makes it too difficult.
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Bondage Torture
Has anyone done the maths to determine what effective radius gains are provided by increments of super elevation? For example, if you super elevate an 18" radius by 0.01" does it become 18.5" effective radius?
Also, how is super elevation typically measured? Seems to me it would make sense to measure it in % of grade so that it can be transitioned between scales and gauges. But maybe that makes it too difficult.
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Bondage Torture
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It has no effect on radius whatsoever. The purpose of superelevation is, just like banking a race car track, to counter centripidal/centrifical forces of an object traveling a curved path, to reduce the tipping forces.
On a model railroad the speeds are normally so slow that it makes no practical difference. It is purely done because it looks good, it looks like the prototype.
In North America it is measured in inches, the difference in elevation of one rail with respect to the other rail. So 4" of superelevation means the outside rail on the curve will be 4 inches higher than the inside rail. On a real railroad that is a vey simple measurement to make (just need a track level and a ruler) and understand. For model railroad you just put the equivalent of a couple inches (a couple hundredths of an inch in HO) of something under the outside ends of the ties or the outside rail and you can simulate superelevation. Its purely for looks. If you go too far with it you will shift the center of gravity away from the center of the track and increase the probability of tipping over.Also, how is super elevation typically measured? Seems to me it would make sense to measure it in % of grade so that it can be transitioned between scales and gauges. But maybe that makes it too difficult.
malibu43
Active Member
Technically, by banking the track, aren't you taking the horizontal curve of the track and changing some small component of it to what would be perceived as vertical by the train?
This is difficult to explain, so let me use the extreme. If you had a train that wouldn't fall off the rails and banked the track 90 degrees, the train would not perceive any radius at all, just an increasing grade.
So wouldn't a small amount of bank have a very small (and probably insignificant) similar effect?
Please note that I'm acknowleding the effect would probably not be significant enough to make a difference. I just want to know if it is in fact happening, even at a very small level.
You are absolutely correct. It does reduce the radius by converting it to vertical curvature. Maybe later today I'll have time to mock up some visual examples.
As lmackattack pointed out, super-elevating rails has reduced derailments for them.
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BONDAGE TUBE
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I'd tend to agree with Crandell. Not necessary, and I certainly would not tear up completed trackwork to install it. It looks good on broad sweeping curves, and should be done very sparingly. One manufacturer used to make super-el track by putting little "feet" under the ties on one side. Maybe 1/16 on an inch at the most. If you have to have it, well it's your railroad. I wouldn't bother though.
Selector
Well-Known Member
Super-elevation has no effect on the real radius. The radius stays the same, as the trucks moving in azimuth will show on measurement. The only substantive effect on radius is the easement, or the cubic spiral curve it is meant to emulate.
What super-elevation does is to shift the CoG inward along the radius, thereby imparting a moment to counter centrifugal, or radial, forces that would tend to topple the cars or passengers. It also minimally drives the CoG lower, imparting a slight increase in pressure on the rails. Tilting the entire curve, as is suggested, with the intent of reducing the effective radius, would impart great forces onto the wheels, but only as the speed increased many times to keep the car from wanting to fall off.
What super-elevation does is to shift the CoG inward along the radius, thereby imparting a moment to counter centrifugal, or radial, forces that would tend to topple the cars or passengers. It also minimally drives the CoG lower, imparting a slight increase in pressure on the rails. Tilting the entire curve, as is suggested, with the intent of reducing the effective radius, would impart great forces onto the wheels, but only as the speed increased many times to keep the car from wanting to fall off.
Its still the same radius because the railroad still would be moving in a horizontal plane. So it would still be a 18" radius curve, it would just be at 100% superelevation. If you drew the plan of the train going from A to B, the plan would be the same, regardless of the superelevation. The radius is to the track center and the track center hasn't moved.
Well, what's the physical result of different radius on the train? It is directly observable in the amount of rotation of the trucks under the car body, yes? If so then what mailbu43 is saying is perfectly correct. Laying the rails at 90 degrees to the surface and bending them around would cause zero rotation in the trucks. They would quickly pitch beyond their limits, but they would not rotate.
So if you simply bank a small amount your trucks would pitch and roll (in airplane speak) but they would rotate less on their bolsters, which equates to less radius.
I don't think anyone is denying the fact that the center of gravity of the equipment is going to shift inward and eventually eclipse the inner rail. That's a given. And depending on the equipment it may happen VERY quickly. And no one is saying there is any significant gain in effective radius, just that it does change.
Now, all this is assuming that the primary affect varied radii have on rolling stock is the amount of twist it puts on the trucks. It also changes how close the corners of car bodies come to each other and how much bend there is in the couplers. Banking the rails will cause the top corners of the cars to come closer together.
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Jailbroken
So if you simply bank a small amount your trucks would pitch and roll (in airplane speak) but they would rotate less on their bolsters, which equates to less radius.
I don't think anyone is denying the fact that the center of gravity of the equipment is going to shift inward and eventually eclipse the inner rail. That's a given. And depending on the equipment it may happen VERY quickly. And no one is saying there is any significant gain in effective radius, just that it does change.
Now, all this is assuming that the primary affect varied radii have on rolling stock is the amount of twist it puts on the trucks. It also changes how close the corners of car bodies come to each other and how much bend there is in the couplers. Banking the rails will cause the top corners of the cars to come closer together.
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Jailbroken
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Selector
Well-Known Member
If the rails tilt, say 40 degrees, sort of like on a NASCAR circuit, the frame of the engine also tilts because the bolsters of the trucks will tilt, and there is a flat bearing riding on the bolster. If the frame of the engine tilts 40 degrees, and the train is made to stay in the rails on the same radius, the trucks will pivot in azimuth the same amount as they would while on the tracks laid parallel with the surface of the earth around them. No change in radius.
Also, when tracks are super-elevated, they don't also rise in unison. The difference in elevation is imparted only to the outer rail. The inner says at grade, except that it is tilted upward along its inner foot so that its running head matches the roll (and not the pitch and yaw) of the outer rail. This is accomplished by its fixture on the same ties that run transversely across the major axis of the tracks, which is the centerline.
I think there may be some confusion over what the radius would appear like if one observed it from directly overhead. Yes, the radius would appear to lessen in profile, but not from the point of view of the engine having to negotiate the same radius as it was doing when the tracks were laid flat.
You can prove this quite easily. Take a length of fixed radius trackage that is laid flat to form a curve...eased or not, don't matter. Now rotate that element so that it is at a 40 degree angle. Of course it now has a curve that is superelevated, but it is not superelevated like the railroad engineers would do it. However, that aside, have you had to change the length so that the ends of the track section will fit between the same joins as before? No. So there is no change of radius.
Also, when tracks are super-elevated, they don't also rise in unison. The difference in elevation is imparted only to the outer rail. The inner says at grade, except that it is tilted upward along its inner foot so that its running head matches the roll (and not the pitch and yaw) of the outer rail. This is accomplished by its fixture on the same ties that run transversely across the major axis of the tracks, which is the centerline.
I think there may be some confusion over what the radius would appear like if one observed it from directly overhead. Yes, the radius would appear to lessen in profile, but not from the point of view of the engine having to negotiate the same radius as it was doing when the tracks were laid flat.
You can prove this quite easily. Take a length of fixed radius trackage that is laid flat to form a curve...eased or not, don't matter. Now rotate that element so that it is at a 40 degree angle. Of course it now has a curve that is superelevated, but it is not superelevated like the railroad engineers would do it. However, that aside, have you had to change the length so that the ends of the track section will fit between the same joins as before? No. So there is no change of radius.
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And that would be the ONLY change in radius if you maintained the radius of the inside rail while rotating the outside rail up.
Change in Radius = (56.5-sqrt[3192.25-S**)/2
S is the Superelevation in inches.
For 2 inch superelevation the change would be 0.018 in. on prototype track. That's the thickness of 4 sheets of paper. If you put a scale 2" superelevation on HO scale track it would change the the radius by 0.000020 in (20 millionths of an inch).
And that's ONLY if you hold the radius of the inner rail constant. If your surveyors layout the track based on the centerline (like they are supposed to), the radius of the curve will remain constant and there will be ZERO change.
