I plan to have an s curve on my layout a bit ahead of some super elevated curves. But then I realized that might not be prototypical/safe on the prototype to have trains flying straight from super elevatated trackage into an s curve. Would they super elevate the s curve too? Or would trains HAVE to slow down...
My other alternative is to just scrap the s curve and leave that track straight. I'm perfectly open to that too if thats my only choice...
I'm beginning to realize that Windows 10 and sound decoders have a lot in common. There are so many things you have to change in order to get them to work the way you want.
IMO, leave the track straight. Unless you have short switchers and rolling stock, ess curves are a disaster waiting to happen, as far as derailments. Avoid them at all costs...or make them less gradual by placing as long a straight section of track between the curves as possible.
Tom
https://tstage9.wixsite.com/nyc-modeling
Time...It marches on...without ever turning around to see if anyone is even keeping in step.
Depends on how big is the S curve.
Superelevation is dependent on the speed and how long the curve is. EVERY superelevated curve has a transition from the tangent to the full superelevation.
For an S curve it would be level, transition to superelevation, superelevation, transition back to flat, trainsition to superelevation, superelevation, transition to out of superelevation, flat. If your S curve is a total of 10 ft long or more you will have room to do all that. otherwise you will have to start cutting out the superelevated parts, then the transitions. If the S curve is real short then you might only get a fraction of the superelevation in before you have to back it out.
Dave H. Painted side goes up. My website : wnbranch.com
Well...
I have about 5-6 ft to play with. The question is, is it protypically logical to have a train hit an s curveal most directly after a super elevated curve? And if yes, would there have to be super elevation on the s curve as well to continue to handle the speed the train is at?
To avoid having to construct a tunnel, possibly, but it doesn't sound like something you'd see just 'cuz. Are you contemplating this on level ground, no prominent features through or around which the tracks must go? If it's on flat ground, nothing nearby that can't be blown up, excavated and removed, or simply rolled/slid out of the way, why have the S-curve at all?
And yes, absolutely, you'd have to provide the same super on the S-curve as on the gradual curve in the way of super if you wish to maintain the same speed, and if you need the same effect on objects borne by the cars. However, methinks you're going to have the galley awash in soups and gravies, salads and crockery strewn everywhere, and some peeved passengers if this were the real world and you expected to run through it all at speeds higher than about 20 mph.
IOW, what is your aim or objective with the S-curve? What need or requirement do you have for the final product that would make such a curve, placed close to a super-elevated curve, necessary?
So quite honestly, the only reason I want it is because curvy track like that can squeeze in an few cars per train versus having straight track. I see now with all of the prototypical problems that would be encountered, its best to leave the track straight and not make matters worse for passengers, like the prototype passenger train company which shall remained unamed...
Most of the curves on my layout are superelevated to some degree, but speeds are relatively low, so it's unlikely that passengers will be wearing their soup.Other than in the towns through which the track passes, most of my track is curved and I also like the look of a train gliding through an ess-bend, too.
In the photo below, the track at the distant left is curved and superelevated, as is the track on the distant bridge and the curve leading to the straight track climbing the hill. The track in the foreground is also superelevated...
...here, the curve continues, superelevated...
...and further along...as the track nears the right edge of the picture below, it begins to curve in the opposite direction....
....with the superelevation shifting...
Here's an overview...
...and as seen from the top of the hill...
If your track is on risers (it doesn't have to be on a grade) it's easy to add superelevation.
Draw a pencil line on each riser where they attach to the crossmembers of the layout structure - this is to ensure that the risers will be at the proper height after the superelevation is imparted.
Place (or run) a train onto the curve - it should extend completely through the entire length of the curve, even if you'd never run a train of that length. Next, unscrew, from the crossmembers, all of the risers supporting the curve. The roadbed will likely sag somewhat, depending on the thickness of your sub-roadbed - I used 3/4" plywood, so the sag was minimal. Now, select the riser closest to the mid-point of the curve, raise it so that the pencil line aligns with its crossmember, then push the bottom of the riser towards the outside of the curve, thereby imparting some degree of superelevation to the track. Manually adjust the amount of offset until the train looks good to your eye...a noticeable tilt that you'd consider appropriate to the speeds at which trains would pass through that curve. Line-up the inside point of the pencil mark on the riser with the top of its joist, and then clamp or screw it in place. The outside end of the pencil mark will now be somewhat above the joist.
Next, pick a riser mid-way between the one you just attached and the beginning or end of the curve. You'll notice that the pencil line on it is now also not-level, as the entire sub-roadbed of the curve has twisted with the re-positioning of the riser at the mid-point of the curve. This twist diminishes as it gets farther away from the mid-point of the curve, which imparts the vertical easements into and out of the curve.Without applying any outward force, carefully lift it until the inside end of the pencil line aligns with the top of its riser, and fasten it in place. Repeat this procedure for the riser on the mid-point between the first-done centre one and the other end of the curve. You should then be able to repeat this operation for all intermediate risers, taking care to only lift until the pencil line on the inside of the curve aligns with the top of itts joist. Do not apply any force outwards.Each portion of an ess-curve is done in the same manner, and as long as the distances are great enough between the changes of direction, the superelevation will automatically transition to suit the curves.
It's a pleasure to watch a train snake through the curves, tilting in and out as they respond to the superelevation.
Wayne
BNSF UP and others modelerThe question is, is it protypically logical to have a train hit an s curveal most directly after a super elevated curve?
From a prototypical standpoint there is no difference between a "super elevated curve" and an "S curve".
They are all curves. The question is how long are they and how much curve there is. Are they all the same radius? Are they all the same length? Do you want the track speed the same on all the curves? Is the S curve just a left hand curve followed by a right hand curve or is it a crossover?
The short answer is sure, there can be a series of curves where left hand and right hand curves follow each other. Happens all the time.
In his second post, our asker states the space in which he wants to do all this. If it's in HO, it will be a royal pain...
A lot of it depends on the radius of the curves. I don't see why it would be a pain.
Lets say the superelevation in the main curve is 1/16" (a HUGE amount of superelevation). If you have an S curve after it and each other curve is 3 ft long then you might get to only 1/32 or 1/64 of an inch or so and only over the middle 6-8 inches of each subsequent curve.
I like to use masking tape for superelevation, building up to maybe 3 layers at most. Each tape layer is offset from the next about a foot or a quarter of the curve.
dehusmanI like to use masking tape for superelevation, building up to maybe 3 layers at most. Each tape layer is offset from the next about a foot or a quarter of the curve.
I, too, use masking tape for superelevation. I have an ess curve on the double mainline, with each curve superelevated. I have not any problems. I love the look of the cars as they go through the curves.
York1 John
I guess my question has been answered. Thanks eveybody! Even though I'm almost definitely going to keep that track straight, I'll probably just tinker with seeing how an s curve looks anyway just because why not...
previous threads explained that superelevation is necessary to add a lateral force to the wheels/trucks so that they follow the curve at a specific speed without relying on the flanges to keep the trucks centered
and easements provide time for the trucks to actually pivot the slight amount to track the curve properly
both of these principles suggest that there would be approriate easements both before and after an s-curve on a prototype.
greg - Philadelphia & Reading / Reading
General 'rule of thumb' with S-curves is to have a straight section of track between the curves that is at least as long as the wheelbase of your longest piece of equipment. If you're superelevating curves, you'd want at least that long a straight section between where the superelevation starts for each curve.
p.s., Unless it's a very gradual curve, trains would normally have to slow down even if the curves are superelevated. Our "broad" radius curves, like 30-36"R in HO, would be considered sharp mainline curves on a real railroad, requiring trains to slow down to like 10-20 MPH.
gregcboth of these principles suggest that there would be approriate easements both before and after an s-curve on a prototype.
The method which I outlined in my previous post provides those easements into- and out of- superelevation automatically. The maximum amount of superelevation appears to be about .047" on that 34" radius curve. Pretty-well all curves on the layout have easements for the curves themselves, whether they're superelevated or not.
wjstixGeneral 'rule of thumb' with S-curves is to have a straight section of track between the curves that is at least as long as the wheelbase of your longest piece of equipment. If you're superelevating curves, you'd want at least that long a straight section between where the superelevation starts for each curve.
That may be so, but I didn't deliberately bother with any straight track within most my S-curves. If there's straight track within an S-curve it's there simply to place the rest of the curve where it needs to be. I certainly wasn't aware of the need for straight track within an S-curve when I was building the layout.The one S-curve which has absolutely no straight track within it also performs flawlessly, whether with a freight train or 85' passenger cars, and regardless if it's being pulled or pushed. It's part of the long grade shown in the photos, where many trains use pushers, too.
doctorwayneThe maximum amount of superelevation appears to be about .047" on that 34" radius curve.
curious how you came up with 0.047"?
Fundamentals of Railway Curve Superelevation provides a detailed explanation of the physics and math behind the values for superelevation along with a tables of values.
one table (see Superelevation, A.R.E.A. Manual of 1929) indicates the max elevation of the outside rail of 8 1/8" (HO 0.095") for a 20 deg 286' (39" HO scale) curve for a train going 25 mph. Less elevation is required for slow speeds. The table shows no elevation values of 9" or more, or for curves > 20 deg (< 286').
the physics for superelevation doesn't scale. The centrapedal forces depends on velocity squared. a max 1/64" (0.017) is required on a 19" radius going a scaled 70 mph.
so it appears easements and superelevation are for purely aesthetic reasons on model railroads
but the question about superelevation around an s-curve made me think that while easements which allow trucks to pivot would be required, it is highly undesirable to stop a train on a curve. That prototypical signals requiring a train to stop would always be on straight section of track (at least for freight service). And this is impractical on most layouts.
gregc...curious how you came up with 0.047"?....
Well. that's the measurement I got a few minutes before posting that entry.When I originally decided to add superelevation, I actually did put a train on those curves, then marked and tilted the risers beneath the subroadbed until it looked good to me - a purely subjective decision, not at all based on mathematical formulae or on prototypical practices.
gregc....so it appears easements and superelevation are for purely aesthetic reasons on model railroads....
Yup! If we really required superelevation on our layouts, I'm guessing that speeds would be quite a bit faster than what I'm running.
While most of my curves are superelevated, that long, multi-curve grade shown has an upbound speed limit of 35mph for freights and 45mph for passenger trains. In reality, only a light engine move or a very short train would be able to sustain those speeds for the entire 45' (3/4 of an HO mile) to the top. Instead, the thought is that a train will enter that grade at the posted limit if the engineer has any hope of making it to the top without either a helper or having to double the hill.
The downbound trains are limited to 20mph for freights, 25mph for passenger trains. Since passenger trains are seldom more than four or five cars, controlling speed isn't all that difficult. However, downbound freight trains can often be longer than upbound ones - sometimes double the length, and even with two locomotives on the point, controlling train speed (due to slack run-in) can require an engineer's full attention.
gregcThat prototypical signals requiring a train to stop would always be on straight section of track (at least for freight service).
Say what?
You have obviously never traveled very much on a real train.
gregc said: "... The centrapedal forces depends on velocity squared. a max 1/64" (0.017) is required on a 19" radius going a scaled 70 mph..."
Did you mean 'centripetal?' And there's no requirement for any super on any curve in our scale models. The super, if we have it at all, is entirely for aesthetic reasons, as you guessed in your last post.
Here is a photo I took at the Bonaparte River 700 yards east of Ashcroft, BC, on CN's main in the Thompson River Valley. The curve continued behind me for about 200 meters.
dehusmanYou have obviously never traveled very much on a real train.
i don't travel on freight trains
i think stopping on curve may be less of a problem on relatively short passenger trains. Of course, subways have a different set of rules.
selectorDid you mean 'centripetal?' And there's no requirement for any super on any curve in our scale models.
yes (at least I didn't say centrifugal).
i was curious if there were scaled values that made any sense.
BNSF UP and others modelerplan to have an s curve on my layout a bit ahead of some super elevated curves. But then I realized that might not be prototypical/safe on the prototype to have trains flying straight from super elevatated trackage into an s curve. Would they super elevate the s curve too? Or would trains HAVE to slow down...
From my railroad experience every curve has a speed restriction..You don't fly into a curve.
Larry
Conductor.
Summerset Ry.
"Stay Alert, Don't get hurt Safety First!"
gregci don't travel on freight trains i think stopping on curve may be less of a problem on relatively short passenger trains. Of course, subways have a different set of rules.
Obviously. There are absolutely no restrictions on stopping on a curve. There are absolutely no restrictions on having signals that could require a stop on a curve (other than sight distance but that has nothing to do with what you are implying). There is no attempt to put signals on straight track. In 37 years of railroading, I never saw a derailment merely because a train stopped on a curve.
Its not an issue.
dehusmanThere are absolutely no restrictions on having signals that could require a stop on a curve
my understanding is that superelevation balances the centripetal force causing a train to go straight when on a curve with the elevated outside rail that causes the train to "fall" toward the center of a curve. This allows the wheels to ride between the rail, as they do normally without flanges contacting the rail.
so my take is if a train is operating at less than the speed the superelevated curve it is designed for, flanges will rub against the inside rail. And this results in extra friction when a train starts from a stop until it gets to the speed the curve is designed for.
again, while this may be less of an issue for a relatively short passenger train and perhaps unavoiadable in urban areas, i think it would be more of a problem for a long frieight train.
of course it can't be prevented. I'm suggesting it is undesirable.
I'm sure the calculations can be done, and it will vary based on the type of car and how it's loaded, but I doubt very mouch that the superelevation puts more of the weight, or the center of gravity at any rate, of the car outside of the inside (lower) rail - otherwise the car would just tip over. Since there's still plenty of the car's mass pushing down against the rail, I'd think the conic section of the wheels will keep the flanges off the rails. The purpose of superelevation is to lower the CG relative to the outside rail, reducing the tendency to roll to the outside of the track. On a passenger train it helps keep the passengers from feeling liek they're being flung agaisnt the outside side of the car, but superelevation alone is not enough for the high speed trains, that's why they often have tilting systems to actually tilt the cars, further than would be safe to do via superelevation alone.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Greg, it would be 'centrifugal' force if anything. Think of it this way: an object in motion stays in motion. Also, they don't change direction. If you push something on a rail, it will keep going if it's in good running order and if the rails are level, or on a down grade. Now put the rail car in space. You push it and it keeps going. It is going to follow a curved path, but only due to gravity. If we place the item well away from the nearest large mass, it will still follow a curved path in space, but much less curved. If there were no gravity to deal with anywhere, the item would move in a straight line. In our real world, rails curve at the ends of tangents. But the car wants to continue straight, to follow a tangential path all along the curve. The wheel profile, the track head's profile, and /or flanges keep it on the rails, but it really wants to go 'outwards', or tangentially on that curve. That comprises a centrifugal force, not a centripetal one.
The super neutralizes that tendency to want to wander outward along the curve, something that would cause the flanges to abut up against the flange face of the rail head and squeal...and wear. The super incline makes the car want to continue to follow the curve more evenly by moving the centre of gravity inward and adding a 'tug' down the radius of the curve toward the pivot point, wherever it is. You have called it 'falling' inward, and that's not a bad way of looking at it. But it's the centrifugal force we wish to couneract, not centripetal. The latter is what we add to balance the forces to the exent possible when we build in super-elevation.
I'm probably not entirely correct, certainly not using correct engineering/physics terms, but that's the gist of it for our purposes.
selectorI'm probably not entirely correct, certainly not using correct engineering/physics terms, but that's the gist of it for our purposes.
thanks for the science lesson. yea i guess its centrifugal
did you read the link i posted earlier
gregcFundamentals of Railway Curve Superelevation provides a detailed explanation of the physics and math behind the values for superelevation along with a tables of values.
as I said, the elevated outside rail provides a force to pull the train toward the inside of the curve. The centrifugal force results in an apparent force toward the outside of the curve.
the inward force depends on the weight of the train. The centrifugal force depends on the speed. They are only equal at one speed!
so when stopped, they at not equal and the force pulling the train inward dominates and flanges rub.
gregcThe centrifugal force depends on the speed. They are only equal at one speed!
True. And trains in most likelihood would be operating at less than the superevelvated speed. If there are passenger trains, the speed would be balanced for the passenger speeds, for passenger comfort. Which means that all freight trains would be operating at less than the balance speed and since most freight trains operate at less than track speed, freight trains would be operating way less than balance speed.
There is no force applied by the outside rail.
Tilting something causes it to want to "fall" in the direction its tilted. It has a horizontal component towards the center. Going around a curve there is a force that wants to keep the motion in a straight line. It has a horizontal component away from the center. By tilting the track the horizontal force trying to make the car fall toward the center can offset the force trying to make the object move in a straight line away from center.
If you tie a string to a ball and swing it around, the ball will want to move in a straight line, with an outward force, and thus pull on the string, keeping it taut. The string will apply a force inward and keep it going in a circle. If you cut the string at the ball, the ball will move in a straight line, because there is no inward force from the string. The string will go limp because there is no outward force from the ball.
gregcso when stopped, they at not equal and the force pulling the train inward dominates and flanges rub.
When moving at less than balance speed, the forces aren't equal. In that case the horizontal force caused by the tilt will cause the cars to move towards the center and rub the inside rail of the curve. If there is no superelevation then the force trying to make the train move in a straight line would be there and the cars would rub the outside rail. Its not necessarily the force "pulling the train" that makes it move toward the inside rail its gravity. If there was no superevelvation in the curve, the train moving through the curve would go tothe outside rail. That works whether its a car being pulled or you just roll a car free (not being pulled).
dehusmanWhen moving at less than balance speed, the forces aren't equal. In that case the horizontal force caused by the tilt will cause the cars to move towards the center and rub the inside rail of the curve.
wouldn't running at less than the correct speed for the amount of elevation, allowing the flange to rub the inside rail of the curve be something to avoid (or at least minimize)?
gregcwouldn't running at less than the correct speed for the amount of elevation, allowing the flange to rub the inside rail of the curve be something to avoid (or at least minimize)?
Some curves are equipped with flange greasers before the start of the curve.This is to cut down on the rub of the flange against the rail. It also lowers the flange squeal.
Its not a huge concern. The reasons trains aren't running the speed the superevelvation are either for cost or safety. Even if you added millions of dollars of engines to increase the speed there would still be slow orders, speed restrictions, approach signals and speed restricted cars. If the trains hit the speed great, if they don't the rail wear is not the largest of the concerns. If the train has an approach signal, I don't really care what the rail wear is, I want the train to reduce speed and be prepared to stop at the next signal.
Its also possible to have one train on multiple curves with multiple degrees of curvature and multiple speeds, the train will travel the lowest speed.