Any experience with 5" radius curves?

[dem34]

The MILW's BiPolars could take ridiculous curves.  Reportedly one went through a 12 inch kink, caused by a fallen tree, with the rails bent into a "U", without derailing.  This was while pulling a passenger train, and the front truck of the first car also made it over, before the train could be stopped.

page 117, "The Milwaukee Electrics", Noel Holley

So what you're saying is, I have enough room to run a 1:1 Bi-Polar. 

[nkalanaga]

You might actually be able to run a true 1:160 model on 5 inch curves.  Remember, these were articulated locomotives, with the bodies "floating" on the trucks, not diesels with trucks pivoted to the frame, and the body was in three pieces, so it could bend with the trucks.  Also, with the motors in the trucks, gear bind wasn't a limit on sharp curves.  Finally, they had a surprisingly short rigid wheelbase, since they had four trucks. 

[ChristianJDavis1]

You might actually be able to run a true 1:160 model on 5 inch curves.  Remember, these were articulated locomotives, with the bodies "floating" on the trucks, not diesels with trucks pivoted to the frame, and the body was in three pieces, so it could bend with the trucks.  Also, with the motors in the trucks, gear bind wasn't a limit on sharp curves.  Finally, they had a surprisingly short rigid wheelbase, since they had four trucks.

If you use the only "readily-available" models of the Bipolar out there, the 80's run NJI/Kumata model, they will probably not be happy on so tight a curve. On the 7~ish inch curves of a minitrix micro layout, the engine will make it all the way around, but it pushes the boiler room off to one side, and probably if done enough tomes, just right off of its posts. I can't imagine it would be any happier at 5 inches. If I had a piece of flex track handy I would test it for you.

[wm3798]

Obviously, you're not going to use a BiPolar or a Centipede to swap out a few covered hoppers, so lets dispense with that nonsense off the bat.

Many thousands of years ago I built an N trak module with the three tracks in front, which left about 16" between the inside line and the skyboard, and in that space I wanted to show an urban switching district.  In order for it to all work on a 2x4, I had a fairly tight radius that swung off the inside line, did a 180 toward the back, where it was about 3" in front of the back board... this allowed room for the requisite runaround track at the rear.  So in all, probably about a 12" diameter turn.

Now mind you, this was the 80s, so I was working with what was available...  I took a Bachmann Plymouth, already a dreadful engine, and found that I had to either blind the middle axle, or take it out altogether (I pulled off the wheels so the gear became an idler).  This was the only way I could get it to navigate the bend.  I suspect that while the drive may have improved over the years, the geometry may be about the same.  The smaller flanges they use now may make it want to creep over the rail even more.

You could probably use a more modern two truck switcher, which will give you better pick up and better adhesion, being a bit heavier, but you may have to nick the bolsters that swivel with the gear tower so they can swivel that tiny bit more that you'll need.

The surest thing you can do is get a piece of flex, the desired locomotive and rolling stock, and see where the limits can be pushed to before you finalize your installation.

The other thing that you could do is build some transition modules that bend out toward the aisle so your module can be a few inches deeper.  I've only been involved in T-Trak for about 15 minutes, but it appears that while the back edge is a fixed point in most set ups, the front edge can wander out quite a bit.  (I added a couple of inches to the front of my modules to provide for some foreground scenery that wouldn't fit on a standard depth module).

Just my two cents.

Lee

[CRL]

The Peco code 80 “short” turnouts have a 9-1/2” departure radius and work good for modeling sharply curved industrial sidings. I would not go any sharper than that for N-scale standard gauge. You’re asking for trouble if you go any sharper.

If you can’t model what you want with that minimum radius, then you need to make adjustments elsewhere.

[nkalanaga]

Christian:  No, I wouldn't even attempt 5 inch curves with an N scale model of a Bipolar, and probably nothing bigger than a small three-axle locomotive, say an 0-6-0T or a diesel "critter".  Two axles would be much better, and I doubt that unmodified freight cars much longer than an ore car would well run on it.

Even on the prototype, I doubt that a Bipolar would like a long curve of that radius.  A short kink is much easier to handle, especially with a flexible articulated design.

I wouldn't want to run most of my Nn3 on that sharp a curve, although much commercial Z will do it.  All of mine is tested on Marklin 220mm curves, between 8 and 9 inches, and my minimum radius is 10 inches.

[randgust]

My friend Lee Farnsworth took a couple decent photos of my "McCabe Lumber" T-trak module under development at Altoona, which is also my Nn3 test track to demo my Nn3 Climax kits.

This is 5" radius in operation.  The sectional track is Rokuhan,  the switch is Rokuhan, the spur track is Mark Graulty's ("Narrowminded") printed tie strip with code 40 rail on it.     The locomotive is my Nn3 Climax (RTR) , behind it are two of Mark's little mine cars.  In front of it are log cars from Showcase Miniatures, flatcar from Shapeways, and my converted Bachmann old time boxcar to Nn3.   That train made it quite nicely around 5" radius all day with no issues.

This also shows how tight it is that I had to even go to the back edge of the skyboard to get clearance.   That back edge is only accessible from the back, that's a 'holding spot' for the finished module.   This is be a very small circular sawmill served by narrow gauge, which was McCabe Lumber in West Hickory, PA 1904-1908.   The Class A Climax ended up resold and I have a good photo of it.





So this is what it looks like, it's not impossible to do on Ttrak geometry and make reliable.

When Mark gets his switch development done (which is mimicing Rokuhan geometry) I'll pull all that sectional track and replace it with his switch and ties and Code 40 rail.

The standard gauge in the front is Peco C55, unpainted at this point, but it will be.

[vekelly09]

From actual experience with operating a variety of N scale standard gauge on <5" radius turnback curves I can report that much more equipment can run than you might guess, but there are severe trade-offs.  I was using Kato Unitrack, which at 4.625 radius is actually a bit tighter than what you specified.

As long as the equipment geometry can actually negotiate the curves, the real enemy becomes friction (drag).   The good news: with the right engine, trains of 4-6 cars can be pulled reliably (but not pushed).  Pushing one or two cars works pretty well.  You need an engine with some serious traction.  The Arnold/Hornby SW-1 with decent weight and traction tires worked the best for me, assuming you want a switcher.  Double-head a couple of these and you're really in business.  But if you limit yourself to only 4 cars, several other switchers can work: Kato NW2,  Life-Like SW1200, and even the old Arnold S2 are usable.   What doesn't work well are lightweights like the Bachmann 44 and 70 tonners.  They slip with just 2 car in tow.  Bachmann S4 is also marginal due to light weight.  I'd be curious about an Atlas S2 but I didn't have one of these.

Traction to the max?  Try an A-B-B-A all-powered lash-up of Life-Like split-chassis FA/B1's (not the spring-drive FA/B2's)! They are heavy and can really pull, so hard that you might stringline a train on the turnback before you run out of traction.  But those are the only non-switchers that I found that worked reliably.

I echo the earlier posters who suggested shorter cars, 40 feet or less.  I have been able to sneak one 50-footer into the middle of a train, but stringlining gets much worse with longer cars.

Other things that help:
-  easements if you can spare the space
-  place a short car with body mount couplers between a body-mount engine and any truck-mount cars.

[squirrelhunter]

Thank you to everyone who took the time to reply and share their experience. Based on the way the prototype facility operates and what I'd like to do operationally, I'm going to shelve this idea for now. I've still got 2 quad T Trak modules kits to hand, I'll keep think about the best way to utilize them...