Superelevation vs minimum radius

[yippy]

Does superelevation appreciably affect minimum radius of engines?

Due to space constraints, I am going to have an 11" radius turn around in the main line for the inner track as part of my n-scale Kato Unitrack layout. A few of my engines (like my Kato GS-4) have a minimum radius of 11" and I am trying to figure out if it is a good, bad, or doesn't matter, idea to use the Kato 11/12 3/4" superelevated double track for this.

[PRR8259]

I'm going to go with "no" but I'm an HO guy and do not have N.  By itself, the presence or absence of superelevation has relatively little to do with the ability of an engine to go around a curve of a given radius.

Superelevation will affect whether some trains stay on the track, as for example, if you want to run large 4-8-4's, at least in HO, some of the big-drivered ones will tend to lift the front axle out and over the outside rail of a curve, so having a little superelevation may help keep them on the track more.  That can also be an engine weight balance versus sprung or not sprung drivers issue, and not purely a trackwork issue.

However, I can attest that in HO any sudden vertical kink within a horizontal curve can be a challenge and can cause big steam to derail.

Also if one is going to run very long trains, having a slight amount of superelevation can be useful.  If there is none at all, "stringlining" can occur where cars may fall inward off a curve--if the weight of the train behind the cars becomes an issue.  I saw this in HO when running 70 car trains, many years ago, with horn hook couplers, on 22" radius curves, that were flat in the vertical direction.

In prototype railroading, during the late 1960's Santa Fe found that (long) empty autoracks on the front end of trains on Cajon Pass became an issue and caused stringlining.  They fixed the issue by realigning the tracks at Summit, and lowering the tracks via a roughly 200' cut, to the alignment that exists today.  I do not know and cannot confirm what changes were made in horizontal curvature at that time, though previously they had curves in the 10-degree to 11-degree range (573' radius down to 521' radius).

John

[mbinsewi]

I'm also in HO scale, but becareful with "super" as in too much, elevation.  I have a curve that I hesitate to run double stacks on, because I thought I was giving it a little elevation, for fast passenger trains, but it turned out a little too much for double stacks.  They "lean" more than I like, when being pulled through the curve.

Mike.

[yippy]

My elevation amount is fixed by the track manufacturer as it comes pre-elevated from Kato (http://katousa.com/N/Unitrack/concrete.html) 

Both answers sound like it probably won't make it worse (ie, an engine that can go around a flat 11" can go around a superelevated 11")

[BigDaddy]

Somebody recently posted a link on a real world study on superelevation and track wear.  The ideal amount is different for up hill and down hill trains.  Interesting in a nerdy sort of way.

I don't think we can extrapolate rail wear on the Cajon Pass to n-scale friction. 

[wjstix]

To the extent it would have an actual affect on the trains (i.e. beyond the cosmetic) I believe superelevation would make it easier for trains to go around curves, not harder - that is, if there's any affect it would be to make the curves act like slightly larger curves, not like tighter curves.

[dknelson]

I think it is generally agreed that in common modeling scales, and assuming trains are run at something like realistic speeds, super-elevation is largely a cosmetic virtue -it seems more realistic to see a train leaning into a curve -- rather than an operational benefit/necessity as it is for the prototype.  If you have ever seen Lionel train "train races" at a train show (or if you recall the 200+ scale MPH Athearn Hustler locomotive) then you'd see actual benefits to super elevated curves.  Otherwise, just for looks (and it doesn't take much to give it a nice look).

This is NOT the case for another matter that is sometimes confused for super-elevation, and that is the genuine benefits to be gained by having easement curves.

Dave Nelson

[selector]

Super-elevation has the effect of moving the rolling stocks' center of gravity inward toward the center of the arc of travel, or down the radius if that makes more sense to you, and counteracting centrifugal forces.  It helps to stabilize loads and platforms. Super-elevation helps to control lurch along with easements as well.

Easements are what make curves more easily handled by allowing the mass to change directions more gradually, thus preventing 'lurch'.  Lurching is what happens with sectional track when the train goes from tangent to fully curved over the distance of the gap at a joint.

[mlehman]

selector

Easements are what make curves more easily handled by allowing the mass to change directions more gradually...

Selector has a pretty good summation. This works well assuming the trains are moving through the curve. The problem is that superelevation can be a problem if too severe (shouldn't be an issue here with the Kato track having it built in.

However, if a train stops and backs, or does other slow speed maneuvers that result in this force shifting, it's possible that it could cause more limited traction on the uphill side or even having the uphill-side drivers losing traction or simply derailing.

Consider how your trains will use the track.

[carl425]

wjstix

if there's any affect it would be to make the curves act like slightly larger curves, not like tighter curves.

Actually, it is slightly larger.  A 30" radius curve superelevated 2 degrees will have an actual radius of 30.02".

[Pruitt]

Superelevation is, if anything, an aggravating factor in stringlining.

Since the cars are already leaning a bit into the curve, it's just that much easier to pull them on over. The effect is generally minor and not of concern unless you're close to stringlining your trains already, then superelevation can push you past the tipping point (pardon the pun).

I would be leery of superelevating any sharp curves (below 12" in N; about 24" in HO), and would have to think about it carefully for 12-13" in N (24-26 HO). Beyond that I w3ould have no hesitation, and I use it on all mainline curves on my 30" minimum HO layout.