I was running at my MR club tonight and finally figured out what the phenomenon where my cars would tip inward going up the helix with a long train was called. Apparently that was stringlining.
The club member who I asked for advice suggested making sure the cars were at least NMRA weight, but I remember weighing them up to that. IIRC, the inside track on the helix is a 24 inch radius (min radius on the club layout is 22) on a 3% grade. My train had four locos and about 34 more modern (Accruail, Atlas, and Athearn Centerflows; MDC and Athearn RTR FMC hoppers, and few other varieties thrown in) grain hoppers, all with Kadees and Metal Wheels.
I’ve always had issues with stringlining on the inside loop, but I’m beginning to think it might be the track. I’ve been staying away from the inside loop going up with a long train just because I think it’s too sharp of a radius for that.
My question is does a tight radius have anything to do with strinlining? Should I re-check my equipment? Would moving one of my locos to the rear of the train help (they are all speed matched really closely)?
Edit: Also, this same train has issues with uncoupling and derailing when going down this same helix on the outside track (which I think is a 28" radius). I can’t figure this one out either, but it seems to happen when I slow down. It doesn’t seem to happen when I’m going a decent speed. Perhaps slowing down is causing all the slack to come together in one point or something?
I agree, that’s a pretty tight radius for kind of grade.
Your problem coming downhill is no doubt due to the grade as well - if your cars are free rolling, that’s going to be a lot of weight bearing forward on your engines. Instead of stringlining, your train is buckling due to the excessive downgrade pressure of the train.
You’re either going to have to start running shorter trains, or have the club members take a serious look at making the helix bigger with a softer grade.
Hmmmmm, Centerflows seem to be more wobbledy than other cars. Is the weight in the cars as low as you can get it?
Stringing occurs when the latteral force on a car is greater than the downward force holding it on track. Perhaps you could put a reverse super elevation on the track and see if that help. In racing it would be called an off-camber curve.
Absolutely. The sharper the curve the greater the sideways force on the car.
Yes,That could be a factor in your string lining problem.
While adding weight helps it also causes problems the extra weight with free rolling wheels will shove against your engines while going downgrade and resist going upgrade.
Now if you are running modern cars of various lengths RP20.1 can become a problem in train make up since a 8" car will weight slightly less then a 9,10 or 12 inch car.
Speed…Yes speed can be a factor in running long trains on steep down hill grades and around sharp curves.
My solution would be to slow down and if you are using modern cars I would weigh the cars evenly or run shorter trains on the 22" inside loop.
For issues coming downgrade, I’d recommend watching the locomotives closely to see whether they buck or jerk coming downgrade.
On one friend’s layout, we had to retire some older Proto 2000 diesels which had mechanisms that we just couldn’t keep from jerking and bucking coming down a 3.25% grade. There was more slop in the drive train than we could correct with shim washers.
Hobo9941, That’s what I’ve always though. That’s why when I build a full-size layout, the minimum mainline radius will be around a 28" and probably max out at a 2% grade (IDK if 28" with a 3% would work well)
Mark, The problem coming down hill seems to usually be around where the Atlas cars (2 Centerflows and a Thrall) meet up with the MDC cars. The MDCs aren’t nearly as free-rolling, and I don’t think I used the truck tuner on them.
Texas Zepher, I’ll re-check the cars next time I go there (bringing a postal scale and several stick-on weights). As far as the centerflows, on the Athearn BB and RTR ones I add weight above the trucks on top of the existing ones (also helps in securing the weight to the frame), The Atlas ones I haven’t been able to get apart, and the Accurail ones are glued shut (not by me, I never glue snap-together cars shut). I doubt the club members would consider that as I’ve brought up having superelevation on the modular layout (which has 36" radius). I’ll try sseeing how well it works with one (or two) of the locos moved to the rear next time I go, kinda gves me an excuse to stick sound in the 2nd F45.
Brakie, Point taken. Now that I think about it I don’t recall anything longer than 30 cars going up that grade.
Fmilhauput, I’ll watch the locos as well. I’m using 2 Athearn Genesis F45s flanked by 2 modfied P2K SD45s. I’ve managed to about about half an ounce of weight to the SD45s, and when I redid the electronics in the sound/DCC F45 (was an MRC unit, now has a DH163 for motor control but retains the sound system) I added a couple ounces of weight. The other F45 is stock weight, but all have DH163 for motor control. I could try it with other engine groupings to see if the problem still occurs.
Is this happening when the all the cars are on the helix? I have that problem on my layout on a slight downgrade into a curve when running about +/-25 cars- it seems to be the magic length for me of when all the cars on the downgrade and the engine has just made the curve and the slack action pushes the first car off the rails. Any longer and there is enough cars on the higher flat section keeping the rest of the cars from slacking up against the engine and a few cars shorter and it is not enough weight to push off the car in front.
Yes, a too-tight radius has everything to do with stringlining. Even experienced modelers have torn out tight helixes and replaced them with 28" or broader in HO.
Note that a 24" HO curve adds about 1.3% to the grade (32/R), so a “3%” helix is really well over 4% effective grade. And as you’ve seen, the build-up of oblique forces when the full train is on the helix causes trouble.
Turns out the minimum radius is between 26" and 28" (varies in spots). I took a close look at the cars that kept derailing and noticed they didn’t roll too well. Turns out on these MDC FMC hoppers, the axle on the Walther’s wheelsets I used in them were rubbing on the screw for the coupler. Switched them to branchline wheelsets and they roll great now, and no rubbing.
First time I tried it going up the helix with 2 engines at the back and 2 up front. Seemed to be a little too much push, and the newest engine in the group starts a bit faster than the other 3 (still need to work on speed matching, and I think weighing it closer to the other one would help*).
After trying the newer F45 to the back unsuccesfully, (started too fast), I changed it to a P2K SD45 and the 2 Genesis F45s on the head, and a P2K SD45 on the tail. Worked fine, even with an addtional 15 or so cars (club cars). Tried it with all 4 engines on the head, and worked fine. So I definately think it was the axle rub causing my problems…
I added weight to the F45 that came with the MRC decoder. I used tire weights to mount a DH163 for the motor. I wound up adding around a good bit of weight to it, so it’s just under 27 ounces. The P2K SD45s are around the 28 ounces IIRC. But the newest (only a few months old) loco is a DCC-ready F45 that I didn’t add weight to, so it’s around 23 ounces. The other locos are a few years old…
new question: Would adding weight to the newer F45 help it run closer to the other locos?
It was fine when I matched them I first got it and ran it for a few hours each way. Then it was too fast a few weeks ago and I corrected it. Now it starts out a bit faster than the other 3, but at mid-throttle it’s fine. I’m thinking a few more ounces would slow it down a bit…
Our club has a 5 turn helix with 33/36" radius curves with a 5" climb each revolution. We insist on metal wheel sets and highly suggest proper weight and the use of a ‘Truck Tuner’. Whenever folks have problems, it is usually one of the following:
Not weighted correctly
Trucks do not swivel correctly
Wheels barely turn in the trucks
Slowly folks are buying a Micro-Mark ‘Truck Tuner’ and using it. Weight can be a real issue as some cars(like tank cars) are sealed and it is hard to get weight in them. And a lot of folks do not use a digital scale to weigh the car - They just add pennies/BB’s/washers/etc and many time have the car weighted too much!
It is indeed probably the tight radius and steep grade, if your cars truly are weighted. Due to people not paying attention, we sometimes have sections of the layout shut down due to a short, and that can even be when a train is on a curve. When the power comes back, the train instantly jumps back to the previous speed, no gentle acceleration - and I have yet to stringline any of my cars (all to NMRA weight, or as close as practical. Also, no truck-mounted couplers). That’s on a 28" radius flat though, no grade other than what might exist in a particular venue where we set up. I cringe every time I hear the snap of the entire train havin the slack removed instantly, always expecting to see a good cunk of someone’s train on its side, but it doesn;t happen.
Jim, I use a digital scale and get them as close as possible. I even go as far as to have count half an inch over a full inch increment as an extra 1/4" ounce (i.e. a 7.5" car should weigh 4.75 ounces). I have a few cars that are a bit over (Atlas centerflows are about 5 ounces, and my modified bachmann cylindrical is 5.25) but I’ve had no issues with either of the “overweight” cars. I may be over-using the truck tuner lol. I use it on almost every car I run…
Randy, it was an axle rub that seems to have been the culprit. I keep near my train and if I hear it loose power, I set the throttle to stop. Maybe overkill since I made the speed curves on my engines kinda slow (half throttle is about 25-30 scale mph) so jerking isn’t really an issue.
Jim,I think the best thing a club can do is toss RP20.1 and come up with a better weight system especially with modern cars that varies in length from 7-12" and add the various styles of intermodal cars.
RP20.1 was good in its day of short freight cars and still is for steam era cars but,I seen some issues with modern cars due to difference in weight because of the length…
Well, we have some 200 coal hoppers in our breaker yard, and those ARE all too heavy - by a lot. I’m sure many of the sideframes have been reamed out from the weight, although most of them are only for show and only get shifted around a little when I feel like shuffling cars in the yard, or we occasionally run the 100+ car coal train, which even with the FULL layout set up at 160’ long, clogs most of the main, so it makes a few laps and then gets broken down again.
The guys running modern stuff with the spine cars and whatnot don’t seem to have trouble with their trains either.
I’ve seen 50’ cars string line because the 60’,72’ and 86’ cars weigh more then they did and these cars was weigh to RP20.1.Then there’s the 52,53,57’ and 65’ cars to add to the list of possible string line derailments.
I am of the opinion metal wheels help tremendously since they put weight on the rail.
A thing to watch for with spine cars is members putting weight in the trailer and can make the car unsteady.
Longer cars have more of a tendancy to stringline, because the sideways force component at the couplers is greater than on shorter cars. You can pull longer trains up the grade without stringlining if you put the shorter cars at the head end of the train.
I’m glad you solved the problem - rolling quality has a big impact on stringlining tendancy!
But the biggest issues is the 24" radius and 3% grade. You could probably pull as many ore jennies up that as your locos can handle, but safe train length with 50’+ cars will be limited.
Stringlining is caused by the angle between cars on a curve. When the inward forces are larger then the “weight” of the car, the car will climb the inner rail.
The forces on couplers are enhanced a lot by grades. So the best recipe for stringlining is a combination of long trains (more drag), long cars (larger angle), tight radii (larger angle) and steep grades (more drag). Adding weight to cars is a two sided sword. The pushing down force will be a bit larger, however it is adding drag at the same time.
The yardmaster could fight stringlining by placing the heavy though shorter cars directly behind the engine and long lightweights at the end of the train. Adding extra weight to those cars just behind the engine might be helpful. If complicating the yardmaster’s job is advisable on a specific layout is a completely different question.
Anyway as the previous poster stated with different words: in critical situations tiny issues of trackwork and / or rolling qualities will easily lead to derailments.