Bending Flex Track Vertically/Horizontally

[NewConductor]

Hi All, just new to this hobby and switched from HO scale to N as it seems I will have more room to be creative in a smaller space.

I was wondering if anyone has ever bent a single piece of Peco flex track vertically/horizontally, meaning, making a smooth curved bridge. Kinda like this

___-------____

but out of one piece of flex track if you get what i mean.
the track seems to be able to flex that way to some extent, just wondering if anyone has actualy done it.

[skipgear]

It can be done but not sure you would want to, at least nothing drastic. Verticle curves are usually a bad thing when laying track. You want to keep them to a minimum. When changing grade to go up a hill you want to draw out the change as much as you can to keep from lifting drivers off the track, especially with long wheelbase steam loco's. Try to keep grades below 2% and the transitions smooth and you shouldn't have any issue.

[NewConductor]

thanks. in a 36" piece of track, what's the best way to calculate the grade?

[Desertdweller]

Grades are calculated on percentage of rise.  A 1" rise in 100" of track would be a 1% grade.  This is true in all scales and in full-size track.

Skipgear is correct that you want to make vertical changes as smooth and gradual as possible.  The term for this is "run out".  It also applies to outside rails on superelevated ("banked") curves.

In your bridge example, even if you have smooth approaches on both ends of the bridge, you would still have a vertical curve at the points where the tracks level off at the bridge deck.  Your options would be to level off your grades gradually before you get to the bridge, or lower the bridge deck so there would be no need for approach grades.

Les

[NewConductor]

Les, at what height does one not need "run outs" with N scale track?
under an inch in 36" of track? or even less than that?

[Desertdweller]

That is a very good question.  I don't know if there has been much written about this, but a one-inch rise in 33 1/3 inches would make a 3% grade.  This would be considered a stiff grade on a full-size railroad, but not excessive for a model railroad.  If you start your grade at 0" elevation and reach one inch elevation at 36", you should find it to be quite workable.

If, on the other hand, you introduce a rise of 2" in 33 1/3" you now have a 6% grade.  This would be extremely stiff on a full-size railroad, and is enough to seriously reduce the number of cars you could pull on a model railroad.

Vertical curves on a model railroad will affect equipment with long fixed wheelbases the most.  Steam locomotives would probably suffer the most, followed by eight-axle Diesels, then six-axle Diesels.  Four-axle Diesels would be the least affected.  In this respect, model railroads would probably be affected more than full-sized railroads, because full-sized railroad locomotives used individually sprung axles that can ride up and down in their frames.  This is true for steam locomotives, too.

A 4 in 100 grade (4%) is usually considered the steepest practical for main-line operation of both full-size and model railroads.  Notice this does not change with scale.  In N scale, you need about 2" vertical separation to pass one track over another.  This refers to clearance between the top of the railhead and the bottom of the overhead structure supporting the upper track.  So you would need 5 1/2' of linear track to get a track over itself in N scale (and another 5 1/2' to get back down to 0" elevation, if that is what you want to do.

Les

[NewConductor]

Thanks Again.
Yes you're right, i'm hoping to get a 2 inch tunnel so i can run rail over another train that is passing underneath. So wow, 11 feet of track to get over a 2 inch uderpass? am i reading that right?

[Desertdweller]

Yes, that's right.

Having said that, I'll probably get a bunch of replies from people who have done that in less distance.  If you have a small layout, and can't run trains more than a few cars long, you could probably get away with a steeper grade.

Keep in mind that curves will reduce the number of cars you can pull.  Model railroad curves are much tighter than full-size railroad curves.  Full-sized railroads build "compensated" grades, where the gradient is reduced slightly to allow for more rolling resistance where curves are located on a grade.

Curves on a grade can actually be a good thing, as they stretch out the distance when climbing a hill.  And, when descending a grade, curves impart rolling resistance that lessens the amount of braking force needed to hold a desired speed.

Les

[NewConductor]

Good pointers there Les, thanks for the info, it will help a lot in my desing process.