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Model Railroading > Super-Elevation on my Spiral Easement Curves


Date: 11/11/20 19:51
Super-Elevation on my Spiral Easement Curves
Author: wabash2800

I thought I'd post this here since the subject was brought up in my 42 in. Radius Curve post, and I didn't want this to get buried in the thread.

For my super elevation, I used 1/16 in. wide striping tape under the outside rail under the ties. (I would suppose it is about .005 in. thick.) The first strip starts from the beginning of the spiral easement on one end through the full arc of the curve to the end of the easement on the other end. The next strip starts a little in from the first strip and ends the same distance in from the other end of the easement. Every strip in stacked on of the other and is a few inches shorter, but centered in the arc. So in effect, you have a very elongated pyramid profile, with the lowest elevation on the ends of the curves and the highest in the middle of the curve. By using the easement and laying out a pyramid, the super elevation gradually builds up as the train enters the curve and gradually flattens out as the train leaves the curve. I use a printed track line from my 3rd Planit software to know where the easements start and end and also the track centerline itself. It has been a while since I did this, but I think my maximum elevation on the outside of the curve is about .060 in. (1/16 in.) for HO. By experience, anything less and you can't see it.

Victor A. Baird
http://www.erstwhilepublications.com

 



Edited 4 time(s). Last edit at 11/11/20 20:00 by wabash2800.



Date: 11/11/20 20:44
Re: Super-Elevation on my Spiral Easement Curves
Author: railstiesballast

You have the concept of gradually increasing superelevation correct, "warp" or the change of superelevation over distance can be a derailment cause for big or little trains if it exceed certain limits.
A common prototype limit is not more than 1" change in 62 feet, or about 0.011" in 8.5" in HO scale.  For models we can be a little more severe.  My spirals go from level to 0.030" in 18" and they work fine.
Prototype track design shuns too much superelevation where trains run too slow to benefit from it such as struggling with low horsepower up steep grades.  This is because it become easy to "stringline" or pull cars off to the inside of the curve if they are leaning that way, and models can do that too.
The 0.030" superelevation I use, as built in to the Precision Scale flex track, is about 2.6", which is almost exactly what the SP used for decades on the 10 degree curves on the Tehachapis and other mountain passes, this was good for 30 MPH passenger and 25 freight.
I find 0.030" is almost invisible unless seen alongside level track, it is very subtle.
Your 0.060" would be about 5" on the prototype and would be typical of a 60 MPH 3-degree curve, provided most trains could run close to that speed.
Books have been written on this, but I wanted to congratulate you on knowing how to gradually increase superelevation; if you like it you've done it right.



Date: 11/11/20 21:00
Re: Super-Elevation on my Spiral Easement Curves
Author: wabash2800

Thanks. I think I got some of the idea from an outstanding modeler, Bill Darnaby, who was an engineer for EMD before he retired. IIRC, Bill uses masking tape.

As I said in my other post, modeling is an illiusion. I am aware that the real track forces use specs derived from the engineering department's mathematical calculations. I feel that anything larger than a 42 in. radius curve or a No. 8 turnout in HO is a waste of space. The model super-elevation works, but again, it's an illusion. My spiral easements are an illusion too.  If you provide curves with spiral easements and super-elevation, it sure looks beautiful. It is sight to behold and not that much extra work.

Victor A. Baird
http://www.erstwhilepublications.com



Edited 2 time(s). Last edit at 11/11/20 21:15 by wabash2800.



Date: 11/11/20 23:06
Re: Super-Elevation on my Spiral Easement Curves
Author: tunnel88

While I agree it's an illusion, I have a slightly different take on this! I'm planning an HO layout focused on the 80-90's era after many years without one and have a fairly decent space available finally. Initially I assumed 42" radius curves were a good start and sketched a number of concepts maximize run length but when I mocked them up with 89' flatcars after reading an article on another site regarding curves I found the overhang on curves shockingly excessive from what I recalled with tighter inside curves on my prior layout (36"). Progressively broadening the curves, I found 60" radius to give the right visual appearance for my taste on inside curves and anything beyond that gravy. Outside curves were obviously much worse and 72" was what I deemed the minimum curve radius for any fully visible outside curve. Yes, shorter cars could use tighter curves and look great but the 89' flatcar is a very tough metric that I'm assuming many simply ignore how bad they look on tighter curves, simply don't care or save these for the club with broad curves. Operational radius was a different story, with 38" a good radius for hidden track or turnback curves in my opinion. Moving your viewing height to close to 60" above finished floor can probably change things, but these were my observations around the low 50s and match RailThunder's photo examples in your other thread. I may post some photos at some point for reference. Turnouts I would probably agree with the #8 as modeled turnouts of higher frog numbers look way too heavy or exaggerated compared to prototype but I can't put my finger on why.

Now this may seem extreme and completely changed my trackplanning concepts and probably wouldn't work for most but at the same time it also simplified the trackplans which actually fits more with what my modeling style will probably be, which is a relaxed combination of through train running mixed with enough local or interchange operation to be keep things interesting with a focus on scenery and realism. Very broad curves also promote open space between scenes which will allow me to attempt to recreate a few memorable vignettes and images that have stood out to me over the years. Not that long ago I would have considered multi-deck and as much track as possible but now I've realized my modeling time is finite due to other life priorities and interests. My biggest problem now is choosing a track plan out of a handful that I've focused on so I can put these concepts to the test.

Not to get too off topic Victor, did you ever find your photos of your visit to Freeburg, MO? That location is one stands out to me, and one I'd like to take inspiration from as a way to hide a tighter turnback curve with an unexpected tunnel burrowing under a small rural town in gentle hills.

-Benjamin


wabash2800 Wrote:
-------------------------------------------------------
> Thanks. I think I got some of the idea from an
> outstanding modeler, Bill Darnaby, who was an
> engineer for EMD before he retired. IIRC, Bill
> uses masking tape.
>
> As I said in my other post, modeling is an
> illiusion. I am aware that the real track forces
> use specs derived from the engineering
> department's mathematical calculations. I feel
> that anything larger than a 42 in. radius curve or
> a No. 8 turnout in HO is a waste of space. The
> model super-elevation works, but again, it's an
> illusion. My spiral easements are an illusion
> too.  If you provide curves with spiral easements
> and super-elevation, it sure looks beautiful. It
> is sight to behold and not that much extra work.
>
> Victor A. Baird
> http://www.erstwhilepublications.com



Date: 11/12/20 05:58
Re: Super-Elevation on my Spiral Easement Curves
Author: AVR3001

That sound's like a great way of doing it Victor.  Thank you, I plan to try it.  At the railroad I work at, the spiral length is based upon how much superelevation is calculated for the curve segment.  For main lines we use 1/4" of  elevation per 31'.  For example a curve calculated to require 3/4" superelevation will be designed to be 93' long.  If constrained on available length we go to 3/8" per 31' of length.  In industrial sidetracks we allow 1/2" per 31' which is the maximum and which is the 1" in 62' mentioned elsewhere in this thread.  The formula we use to calculate elevation of the outside rail in a curve is as follows: .0007 x speed x speed x degree of curve.  For example a 4 degree curve operated at 25 MPH would have superelevation as follows:  .0007 x 25 x 25 x 4 = 1.75" (1 3/4")  3/4" divided by 1/4 per 31' would be a spiral length of 217' (1 3/4" / 1/4" per 31' = 7 and 7 x 31' = 217')  This elevation is for equilibrium where the centrifugal force and the gravatational force in the banked curve combine to create a force perpendicular to the railhead.  Many railroads where there is a significant variation in train speed at the curve (for example slow loaded coal trains upgrade and fast Amtrak) deduct a certain amount of elevation from the equilibrium elevation to underbalace the curve.  Of course the curves in model railroading are so sharp that this information is irrelevant to modelers, but nonetheless it may be of interest to some.



Date: 11/12/20 06:01
Re: Super-Elevation on my Spiral Easement Curves
Author: mamfahr

> I thought I'd post this here since the subject was
> brought up in my 42 in. Radius Curve post, and I
> didn't want this to get buried in the thread.

Hello all,

That's an interesting way to do it, seems to work well.  I did things in a slightly different way and also had great results.  I just purchased strip styrene and glued it to the bottom of the ties (on flex track) under the outside rail of each curve before laying it down.  I checked actual track charts and converted the inches of elevation to the correct thickness in the styrene for each curve.  I tapered the styrene at each end of curves to provide nice, long "elevation runoff" (aka "spiral") transitions so it looks good and accommodates the longer equipment I run without "warp-off" issues (crosslevel deviation-caused derailments).  With this method track goes down quickly, provides exact prototypical elevations, and provides for trouble-free operation.

Take care,

Mark  



Date: 11/12/20 07:01
Re: Super-Elevation on my Spiral Easement Curves
Author: SPDRGWfan

tunnel88 Wrote:
-------------------------------------------------------
> the 89' flatcar is a very tough metric that
> I'm assuming many simply ignore how
> bad they look on tighter curves, simply don't care...

I care, but like so many, I don't have enough space to get beautiful scenic curves for long rolling stock AND build a layout with more than a giant loop of track that only may provide a few scenes.but no sense of really going places.  On a previous layout, I did include a scenic curve (or whatever John Armstong called it) to provide a spot where longer equipement looked visually decent - it was 56"R.

> Not that long ago I would have
> considered multi-deck and as much track as
> possible but now I've realized my modeling time is
> finite due to other life priorities and interests.
>
> -Benjamin

A mulit-deck layout would allow for more operation and run length with broader curves.  My modeling time is also finite so I've come up with a track plan the I feel I can live with and hopefully get to a decent state of operation and scenery - building a model RR after all, involves a lot of compromise by it's very nature.

Cheers,
Jim



Date: 11/12/20 10:24
Re: Super-Elevation on my Spiral Easement Curves
Author: tunnel88

I think I remember your scenic curve, if you posted photos of the CZ or a similar streamliner on it. I have done a lot of reading across many forums (I recall your track plan as well) on trackplanning, curve radius and appearance and you are absolutely right on the compromise aspect. Building a layout set in the mountains can go a long way and I'm sure getting your head buried in operations can take the focus off that as well. Of course that may open another can of worms such as how much detail is enough on rolling stock and personally for me, even though I have many fond memories of the DRGW from growing up in Denver, I don't think I want to model those mountain crossings!

-Benjamin
 



Date: 11/12/20 10:26
Re: Super-Elevation on my Spiral Easement Curves
Author: SPDRGWfan

Some like to model the mountain crossing due to the nice scenery.  In my case, I'm breaking from the norm and planning to model the desert environs of Grand Junction CO and into eastern Utah.  For some reason I've always found it visually appealing.

Cheers,
Jim



Date: 11/12/20 10:36
Re: Super-Elevation on my Spiral Easement Curves
Author: wabash2800

Benjamin:

The Freeburg photos were posted here on Trainordrers:

https://www.trainorders.com/discussion/read.php?11,1563998,1564195#msg-1564195


tunnel88 Wrote:
-------------------------------------------------------
>
> Not to get too off topic Victor, did you ever find
> your photos of your visit to Freeburg, MO? That
> location is one stands out to me, and one I'd like
> to take inspiration from as a way to hide a
> tighter turnback curve with an unexpected tunnel
> burrowing under a small rural town in gentle
> hills.
>
> -Benjamin
 



Date: 11/12/20 17:12
Re: Super-Elevation on my Spiral Easement Curves
Author: RailThunder

Great stuff and thanks for sharing!



Date: 11/13/20 09:56
Re: Super-Elevation on my Spiral Easement Curves
Author: wabash2800

I forgot to add that since striping tape comes in different colors I use a different color for each layer or alternate them, that way I can tell where I left off. The 1/16 in. width is narrow enough to stretch and curve. I also mark the location with a line on my Homabed with a jig to know where to lay the tape under the outside rail.

Victor A. Baird
http://www.erstwhilepublications.com



Edited 2 time(s). Last edit at 11/13/20 18:30 by wabash2800.



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