Author Topic: N Scale "Long train" minimum radius?  (Read 1594 times)

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w neal

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N Scale "Long train" minimum radius?
« on: January 08, 2020, 12:50:18 PM »
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What is the consensus on a minimum radius for "long" trains in N scale? Say like a minimum of 50 cars, (I mean, its N scale right? 😉)   I.E. How large do the curves need to be to prevent such a train from pulling itself over on non - super elevated track? I'm thinking here of a train making a 180 degree or 360 degree turn. Tell me of your experiences.

Ta very much!
Buffering...

Missaberoad

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Re: N Scale "Long train" minimum radius?
« Reply #1 on: January 08, 2020, 12:55:56 PM »
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I've run longer then 50 car trains on the mountain line back in my N-trak days... IIRC that was 12 inch radius...

It required a body mount coupler next to the engine and was a tad bit sketchy, but it worked...
Ryan in Alberta

MK

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Re: N Scale "Long train" minimum radius?
« Reply #2 on: January 08, 2020, 12:59:41 PM »
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We do it all the time in T-Trak.  Inside radius 11" and outside radius 12-3/8" Kato Unitrack.  You just have to have enough loco power.

Maletrain

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Re: N Scale "Long train" minimum radius?
« Reply #3 on: January 08, 2020, 01:14:49 PM »
+4
That is probably going to depend a lot on how much drag there is in each of your cars in the train, and even how that varies from the front to the back of the train.  Also whether there are any grades on the curves involved.  Real railroads have the same problem, as demonstrated on Pennsy's Horseshoe Curve and maybe at Harper's Ferry on the B&O, recently.

Try putting the heaviest cars in the front, and the cars with the least drag (lightest weight and or/or lowest rolling resistance) in the back of the train.  If you use track cleaning pads on cabooses or other "last" cars, you should probably take them off for this train.

You can also use mid-train locomotives to increase train length.  Basically, you are coupling together 2 (or more) trains that can make the curves on their own. 

Pushers are another possibility, if you have cars that can traverse your layout "in reverse".  Basically, you are coupling two trains together with one in reverse.  Sometimes steep down-grades make for derails when you try that, though.  You want the slack to shift back and forth between the front and rear of the train as it sees varying resistance from grades and curves, without being taken completely out by the pusher nor getting so far back that the lead engine is trying to pull the pusher locomotive.

There are prototypes for just about any locomotive distribution in trains.  In modern times, there are typically head-end and mid-train locomotives, all controlled from the front cab.  In older times, there were often pushers on grades that did not continue down grade past the crest.  But, there are examples like the Western Maryland that would put 7 (or even 9) big 2-8-0s on some coal drags, with distributions like 3 up front, 2 in the middle, and 2 on the rear, to deal with some heavy branch line grades.

wm3798

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Re: N Scale "Long train" minimum radius?
« Reply #4 on: January 08, 2020, 01:36:33 PM »
+2

I ran this fairly regularly, min. radius was probably 14" or 15", and included grades. 
Atlas hoppers are fairly heavy, so they tracked really well, and of course, they're short. 

Never tried that length with longer, lighter cars, though, so your mileage may vary.

Lee
Rockin' It Old School

Lee Weldon www.wmrywesternlines.net

jagged ben

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Re: N Scale "Long train" minimum radius?
« Reply #5 on: January 08, 2020, 02:37:27 PM »
+1
My SWAG would be 15" on flat, 21" on a 1% grade, and 24" on  a 2% grade.  You could certainly get away with less if you engineer your cars and trains just so, but if you want to run more or less anything you please including 89ft cars, it's probably something like that.

Rossford Yard

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Re: N Scale "Long train" minimum radius?
« Reply #6 on: January 08, 2020, 03:08:33 PM »
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On a former layout, I had an incline to a coal hopper staging yard.  It had about 15" radius and over 2% grade, and I tended to weight cars slightly above NMRA standards.  String lines were common on the portion with Atlas Code 80 flex.

On my last layout, I had a 22" R helix, flex code 80 Atlas track, and 2.2% grade or so.  While very well built, I think there was one piece of flex with a very slight nick, dip or twist in the rail, and my autoracks tended to derail at that one point when going up hill, and sometimes uncouple on the way down.  I think it needs to broaden out if 89 foot cars will be run, especially high cubes.

I agree with the generalities the broader the better (unlike my waistline.....) but would also suggest Kato Unitrak if hidden, and maybe even if not.  I had some of that around the back of the water heater and it worked well on the grade mentioned in the first PP.  Under those circumstances, the rigidity of the Unitrak I believe will contribute to some stability and lead to better ops and greater satisfaction.  Unless you are a real good carpenter, I would also consider the WS grades, again because it seems any small dips can lead to problems of slack, uncoupling, etc.

learmoia

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Re: N Scale "Long train" minimum radius?
« Reply #7 on: January 08, 2020, 03:28:05 PM »
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It all depends on grade and wheel resistance...

In my N-Trak days I could do 120+ all day long on any line (RYB)..
That is with Micro-Trains coupler with no resistance springs..  I did NOT weight cars to NMRA standards..


FF to a few weeks ago.. I was running on a T Track layout.. Inside loop.. And was running 78 cars.. (MT trucks and couplers).. no issues..
But add 15 vintage Atlas cars.. NOPE.. too much resistance and it stringlined..

~Ian


thomasjmdavis

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Re: N Scale "Long train" minimum radius?
« Reply #8 on: January 08, 2020, 03:38:33 PM »
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The unmentioned variable is "how fast do you want to go?"  Which is to say, minimum radius for a 50 car coal drag will likely be a lot less than minimum radius for a 50 car Super-C hauling COFC flats and slowing down to 70 when it hits the curve.  Also, in my experience, easements do help.  Which reminds me I need to dig out my John Armstrong book....

I don't remember counting cars, but tightest radius I have run long trains on is about 15" (with easements in and out) or 17" (no easements).

Tom D.

propmeup1

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Re: N Scale "Long train" minimum radius?
« Reply #9 on: January 08, 2020, 04:01:08 PM »
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Not much help here. I run 19.5" smallest rads but, you'll want to make sure your heaviest cars are up front. That may have already been mentioned. Just look at horseshoe last summer. Twice in two weeks derailments.

NtheBasement

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Re: N Scale "Long train" minimum radius?
« Reply #10 on: January 09, 2020, 09:10:45 AM »
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Gotta add just in case: don't superelevate your curves.

Glenn Poole

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Re: N Scale "Long train" minimum radius?
« Reply #11 on: January 09, 2020, 11:37:30 AM »
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I run 40 plus cars including 89" flats and box cars up a 2 % grade and around a 24" radius or 4' diameter 360 degree curve. I will tell you that the 89' flats have to be MTs with truck mounted couplers.  The new 89" body mounted coupler cars such as Atlas will stringline on the curves.  I generally run 4 SD 80's/90's on the front and one or 2 SD40-2's pushing.  The train will overlap itself on the circles.





Glenn

randgust

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Re: N Scale "Long train" minimum radius?
« Reply #12 on: January 09, 2020, 12:55:21 PM »
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Amen on the 89' post - I've got 13" on 2% curve on one location - 30 car trains headed uphill.  Everything worked find even with a full train of 89' cars until I got the Atlas 89', and it constantly pulled over.  Coupler shank is too short, and located too far from the bolster with not enough swing.  But MT's with truck-mounts work fine, as well as Trainworx and BLMA.   I also had issues with the MT low-profile wheels climbing up on the inner rail face if on the front of a train - just too much stress, but the medium-flange wheels work fine.   When you start pushing the envelope, strange things can happen where all the small issues multiply.

I had a good friend who regularly ran a 100-car train of MT 34' hoppers behind a Rowa 2-8-8-2, and he snuck that through a 12" radius reverse loop at one end of the layout, dead flat, and it never derailed.   Car length has a lot to do with it for sure.   The other thing that will 'nail you' in a helix or nolix situation is a sudden force increase or decrease in speed - I have a rather notorious spot on my layout where the reversing loop gap is right at the bottom of a nolix hill - no choice.   If you have a heavy train headed down around that curve and it the polarity conflict resulting in a jolting stop, the train force behind it is enough to knock everything off.   Same hill headed back up will NOT tolerate excessive acceleration on the curves headed back up, just let it run.

My dynamometer spring car has proven to me just how much dirty wheels increase drag as well, it's about 25-30% when it really gets bad, and I'll start to see power struggling, but it's not proving to be more derailment prone.

If you want to see this issue for real, visit the Tacoma Rail hill just west of the Freighthouse Station (Station Square) that swings up that miserable hill around a disturbingly tight curve with an absolute stop signal at the bottom.   An engineer with a heavy train headed down from Fredrickson onto the main better not have to make an emergency stop on that curve on the hill either!
« Last Edit: January 09, 2020, 12:57:15 PM by randgust »

mmagliaro

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Re: N Scale "Long train" minimum radius?
« Reply #13 on: January 09, 2020, 01:50:27 PM »
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I don't have any scientific tests, but I do have an example.

My layout has an 18" minimum radius.  Most curves are 20 - 24".  There is a 1.7%,  18" radius, curved grade that wraps 300 degrees around a hill (you can think of it as a "almost one turn helix"), so that is probably the most brutal curve.

I have run 60-car trains over this layout, pulled by a single engine on the front (no pushers).  The train was all 40-foot freight cars with FVM wheels, a mix of MT and several other brands, some have body mounts and some not.  So this was a pretty brutal test, I think.

It never "clothes lined" in any of the curves, but it always looked to me like it might be on the hairy edge.

CRL

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Re: N Scale "Long train" minimum radius?
« Reply #14 on: January 09, 2020, 02:13:08 PM »
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Gotta add just in case: don't superelevate your curves.

Just a thought, but wonder if a slight reverse super elevation of the track in a helix would help offset any tendency for the cars to string line. 🤔