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HO Minimum Curve Radius Problems

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HO Minimum Curve Radius Problems
Posted by Redhawk95 on Friday, October 30, 2020 6:35 PM

Hey guys so I am starting my second layout and this is my first serious layout. I am planning on this layout taking up a whole building on my property and the building is 16x19 and am planning a walk in layout with a peninsula in the middle. I am using anyrail to design this layout as I plan on this layout being something I work on for quite a while. The one thing I absolutely want to have is a double mainline and be able to run passenger cars. 

So right now I have mainly just designed the size I want my benchwork to be and tried to find my curve restrictions. It looks like the minimum curve radius I will be able to get away with is 26" on all the mainlines. There is no way with the current bench work design I have I could make it any larger and I do not want to have an around the wall layout. Now I have done a lot of research and it seems like people are all over the place with what size curves you need to run passenger cars on. Obviously everyone says the bigger the curve the better but my main concern is that I do not want derailments. I do not care as much about it looking prototypical as much as I do the whole layout working flawlessly. Right now my only passenger set is a 5 car MTH Norfolk and western Powahatan arrow set pulled by a MTH J class.

 

So my real question is what do you guys think about having a minimim curve radius of 26". Will it work fine? Will I have restrictions on other passenger cars? Will I have any restrictions on other Steam or Diesel engines? I am going from a 4x8 layout with 18" curves and unfortunately don't have any clubs within 3 hours of me.

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Posted by dknelson on Monday, November 2, 2020 10:57 AM

A few observations. 

1. Minimum radius can be a shifting concept.  If you had a perfect circle of 26" radius there might be cars that could easily handle that curve without derailing.  But introduce a tangent (straight) track to that 26" radius curve and you could have a sudden derailment because the transition of perfect tangent to perfect radius curve creates a pinch point (the "coefficient of lurch" as John Armstrong phrased it).  That is why easement curves are important but particularly important when you might be challenging your equipment with a tight curve.  And 26" is frankly still a tight curve in HO.

2.  Similarly, a passenger car might roll fine on a 26" radius curvedf, and even be fine with curve and tangent without an easement curve, but couple that car to a locomotive (where due to wheelbase and other factors its coupler may swing outward toward the outer rail) and you have a sudden problem.  Ditto for coupling two or more passenger cars together - you might have a sudden problem that did not exist with one car.  Even the prototype railroads had issues combining short cars, such as a 40' express reefer for example, with full length passenger cars.

3.  Spacing of double track.  The more you challenge a passenger car (or other long car such as an autorack, auto parts hi-cube boxcar, and so on) with a radius curve, the more you may have to widen the spacing between double tracks on curves.  Recently I posted (can't recall where) that when I was planning my layout I took a piece of plywood, made a trammel so I could draw curves of various radiuses (?) while maintaining the 2" spacing I had on straight track.  Laid track of various curvatures using old brass flex track.  I found that to avoid having two passenger trains interfere with each other if they met on a curve, I needed a radius of 36" at least.  I finally chose 38" and 40" radius to be safe, and prefer 40" and 42" (again to maintain the 2" spacing).  I could have gone smaller radius had I been willing to increase the spacing between double tracks.  If it was 26 inch radius I suspect the spacing between double tracks would have to be pretty considerable to avoid problems when both tracks have passenger trains.  In fact that might use up more space than would using a larger radius curve! 

I should also add that I have that radius using benchwork dominos of 2' width meeting at a 90 degree angle, so it is surprising that you feel you have no room for a larger radius than 26".  

I think it is worth while doing an experiment using real track and real cars and real locomotives.  And again now is the time to find out if you need easement curves leading into that 26" radius.

Dave Nelson

 

 

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Posted by mlehman on Monday, November 2, 2020 11:02 AM

Many full length passenger cars will be OK on 26" Min R. However, many will not, including some that claim a 24" Min R.

Since you have a specific consist you want to run, I'd suggest testing it on such curves.

Keep in mind that if you have double track, then you'll need to widen track spacing on the curves a bit to avoid overhang interference. Since it's a double main, you'll want to have the inner track set at your Min R with the outer track being a larger than Min R curve.

Mike Lehman

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Posted by Doughless on Monday, November 2, 2020 11:14 AM

Hmmmm. 16 feet of width is pretty generous.

With an around the room plan and one center peninsula, if I read your comment right, creates only a small area "pinch point" where you have to scoot past the outermost part of the benchwork to get through the pensinsula blob.  Careful planning could narrow the ailse' on the adjacent walls to accomodate a larger radius for the P.

Assuming 18 inch shelves for the adjacent walls, and generous 30 inch scoot paths on both sides of the pensinsula, that leaves 8 feet for the peninsula itself.  Placing the track a generous 3 inches off of the edge of peninsula, the remaining 90 inches provides a 45 inch radius for the outer most main line.  

Or 24 inch deep benchwork for the adjacent walls, and similar other measurements provides for about a 39 inch radius on the peninsula.

Maybe you have other restrictions.

Broader is better for passenger ops. 

Edit:  Okay, I see you said walk in.  That makes three blobs and not one, but still seems like you could do better than 26 inch if you staggered the blobs a bit.

Thought about a duckunder or liftout?

- Douglas

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Posted by York1 on Monday, November 2, 2020 11:29 AM

Redhawk95
Hey guys so I am starting my second layout and this is my first serious layout.

 

Welcome to the forums, Redhawk!   Welcome

Your first posts are moderated and may not appear immediately, but after several posts, everything will be normal.

There are a lot of experienced, knowledgeable modelers on this forum who will give very good advice, so check back often with any other questions.

York1 John       

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Posted by IRONROOSTER on Monday, November 2, 2020 11:41 AM

dknelson
I think it is worth while doing an experiment using real track and real cars and real locomotives. And again now is the time to find out if you need easement curves leading into that 26" radius.

I agree.  Set up a test oval and see how your equipment works.

Some different things you can try for 26" radius curves.

1.  Limit passenger cars to 70' or less.

2.  Use truck mounted couplers (some passenger car brands may still come this way).  This can be a problem backing up, but adding a little weight to the cars will help.  This may require removing details at the end of the car.

3.  Mount the trucks close to the end of the cars to reduce overhang of the ends - again may need to remove details at the end of the car.

Good luck

Paul

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Posted by wjstix on Monday, November 2, 2020 11:53 AM

A lot depends on whether we're talking about what will go around a certain radius curve, or what will in someone's opinion look good going around the curve. The old 80' AHM/Rivarossi passenger cars with truck mounted couplers will go around 18" radius curves, as will Athearn's passenger cars (some of which are full length, some are shortened). Many passenger cars like Walthers, say they can 24"R curves, but may need some adjustments to actually do it.

Stix
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Posted by Trainman440 on Monday, November 2, 2020 12:11 PM

I will tackle this in a different perspective. Instead of modifying the layout, I will modify the equipment. 


STRICTLY SPEAKING OPERATIONS, 26" will work. I got 22" radius with a single piece of 19" radius as my mainline. My Walther's super chief consist looks AWFUL on it, but it DOES work. You gotta work with what you got right?

That being said, my passenger cars needed some mods. In particular, the front end cars needed additional weight. The coupler heights and trucks and screws had to be tightened perfectly, not being too loose or tight. The Vista observation and Pleasure Dome car needed a bit of material removed on the underframe for the trucks to turn more. I removed as little material as possible so they still look fine. 

Here's another vid of a consist of Walthers AND Branchline heavyweights modified to run seamlessly around my 22" oval. I intentionally dont film them on the curves cause they looks awful, but hey they dont derail!

From my experience, the Athearn Shorty passenger cars look best on these curves. But I like my Branchline Heavyweights.

On the other hand, certain steam engines of mine will derail, such as my I1sa, and ATSF 2-10-2. My 4-8-4 also is pushing it. I reserve those to run on my club layout. Generally, I stick with 4-6-4s and 2-8-4s being my largest engines. I think anything larger than that doesn't look good anyways. 

If I had the space and resources, I'd get 40" curves. But you gotta work with what you got!

Charles

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Posted by doctorwayne on Monday, November 2, 2020 12:26 PM

Unless I'm misunderstanding your post, and without a picture of your trackplan, this...

Redhawk95
I am planning on this layout taking up a whole building on my property and the building is 16x19 and am planning a walk in layout with a peninsula in the middle.

...seems to be in conflict with this...

Redhawk95
There is no way with the current bench work design I have I could make it any larger and I do not want to have an around the wall layout.

A walk-in layout and peninsulas in the centre generally suggest that the layout is an around-the-room design.

My layout is a walk-in with a peninsula, as the crude drawing below illustrates

...and the area shown in grey is double-decked.  A track plan is not shown because it was built without one.  I set my minimum radius at 30", but the only place it was used was for a turning wye in the upper left corner of Dunnville.
The rest of the layout uses mostly 34" radii or larger...a couple are in the high 40"s.  Wide curves are one of the strong points of an around-the-room layout, while another is the ability to limit the depth of the layout, so that most of it is easily reachable.

If you could add a diagram of the building and layout, we might be able to offer more assistance, or at least have a better understanding of your goals.

Wayne

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Posted by jjdamnit on Monday, November 2, 2020 12:32 PM

Hello All,

Welcome

As is usually asked...

Can you post a track plan?

DC or DCC?

Running large steamers, 6-axle diesels and longer passenger cars requires more than just "large" curves- -30+ inches or more.

Have you considered the length of turnouts required for relialbe operations?

Are there any reversing sections, loops, turntable(s) or wyes that will require shifting track polarity?

Will the passenger cars be using track power for illumination?

These questions will factor into your track plan(ing).

As is usual, the more information you can provide will allow the great folks on these forums to assist you in the best way possible.

Hope this helps.

"Uhh...I didn’t know it was 'impossible' I just made it work...sorry"

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Posted by rrinker on Monday, November 2, 2020 12:38 PM

 16' width should easily fit 30" radius on a 3 blob walk-in design. Even as much as 4' wide aisles alongside the center peninsula blob. That's with making the blob 6' wide, which is more than enough for a 30" radius/5' diameter loop of track. 

  Lengthwise, that gives somewhere around 7 feet of straight between the curves on the sides and potentially near that for the center blob even with setting it back a bit to allow clearance.

                                     --Randy

 


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Posted by dstarr on Monday, November 2, 2020 1:35 PM

You could do worse than 26 inch min radius.  I was only able to fit in 22 inch curves on my layout.  I can, just barely, run a streamliner of an AA pair of Proto 2000 E9's and a bunch of 80 foot IHC streamline cars. I had to do some Dremel work on the undercarriages to permit the trucks to swing all the way. And go with truck mount couplers.  I weighted all the cars up to NMRA recommendations and replaced the plastic snap on truck mounting pins with 6-32 flat head machine screws. I am thinking if I had your 26 inch curves this rig would run perfectly.  

I like the Athearn heavyweight passenger cars.  They look right to my eye, like what I used to ride in long ago when I still traveled by train. And they run happily on 18 inch curves. Give them a coat of dark gray auto primer on the roofs.  Mount diaphrams on the ends.

Double track main line is good.  You can run two trains at once with out getting into DCC.  Meets are cool.  With a double track main you don't really need passing sidings. 

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Posted by SeeYou190 on Monday, November 2, 2020 1:52 PM

Welcome

I hope to see may updates on your layout in the years to come.

-Kevin

Living the dream.

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Posted by RR_Mel on Monday, November 2, 2020 2:14 PM

Welcome

 

My plan was 26” minimum radius mainline but I did end up with one 24” do to a Mel error in planning.  The Athearn 72’ passenger cars negotiate my yard 18” radius curves and turnouts at yard speeds.  All most all of my steam is heavy steam and all negotiate the 24” radius at running speeds easily.
 

Mel



 
My Model Railroad   
http://melvineperry.blogspot.com/
 
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I'm beginning to realize that aging is not for wimps.

 

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Posted by Overmod on Monday, November 2, 2020 2:35 PM

Lastspikemike
a plan that includes broader radius curves. If you can get out to 24" or even 22" you will enjoy running so much more.

He edited this out, so comment withdrawn.

No one has reiterated so far in this thread that if he lays these curves 'from the middle' with flextrack he can easily approximate a smooth transition curve at both ends, as described in recent threads... which I think solves any operating issue that careful common-sense surgery on his passenger-car center sills wouldn't.

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Posted by Overmod on Monday, November 2, 2020 2:45 PM

Lastspikemike
I've tried that surgery route on a Walthers  heavyweight. It doesn't gain you very much.  Part of the issue is those long wheelbase trucks, body mount couplers and coupler gearboxes which limit the truck swivel range. 

I think it depends on the car and maker type more than the discussions about the approach so far indicate.  I suspect that a judicious choice of truck pivot point vs. "editing" the center sill at the truck ends plus any step detail or coupler box placement might give remarkable 'curve rounding' ability -- e.g. raising the coupler box height and using a vertically-offset coupler shank to get NMRA gage height.  It may not be rivet-counting prototype fidelity but then again running Pullmans around any real-world layout curve isn't either...

Does anyone model full brake rigging on cars intended to negotiate these curves?

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Posted by rrebell on Monday, November 2, 2020 3:45 PM

Doughless

Hmmmm. 16 feet of width is pretty generous.

With an around the room plan and one center peninsula, if I read your comment right, creates only a small area "pinch point" where you have to scoot past the outermost part of the benchwork to get through the pensinsula blob.  Careful planning could narrow the ailse' on the adjacent walls to accomodate a larger radius for the P.

Assuming 18 inch shelves for the adjacent walls, and generous 30 inch scoot paths on both sides of the pensinsula, that leaves 8 feet for the peninsula itself.  Placing the track a generous 3 inches off of the edge of peninsula, the remaining 90 inches provides a 45 inch radius for the outer most main line.  

Or 24 inch deep benchwork for the adjacent walls, and similar other measurements provides for about a 39 inch radius on the peninsula.

Maybe you have other restrictions.

Broader is better for passenger ops. 

Edit:  Okay, I see you said walk in.  That makes three blobs and not one, but still seems like you could do better than 26 inch if you staggered the blobs a bit.

Thought about a duckunder or liftout?

 

Or you could use sa larger radius on all but the pennisula and do minnimal radius there with a bypass for the passenger stuff.

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Posted by wjstix on Monday, November 2, 2020 4:37 PM

BTW the OP did say he wanted a "double mainline" which I assume means a double-track mainline, so he'd actually be doing 28" radius curves on the outside of the 26" minimum radius. That might be why it seems he's shorting himself on what can fit; he has to allow for the larger curve.

BTW best bet is go to the LHS and get some Kato Unitrack or Bachmann E-Z track with 26"R curves and do some real-world tests to see what works with what you have, and how it looks.

Stix
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Posted by selector on Monday, November 2, 2020 5:00 PM

Two considerations that are often missed, even though I agree with what has been pointed out so far:

a. are diaphragms involved?  And, if so...

b. Backing a train with long pax cars, especially with diaphragms, causes a whole nuther set of problems often enough that it becomes a royal pain you wished you'd foreseen months ago.  This pertains to running curves near or at claimed minimums.

I bought the 2000's era Walthers Pullman Heavyweights, really nice cars, back when I was planning my second layout 14 years ago. I fashioned what I thought were sufficient curves at just over 24" radius, the claimed minimum by Walthers.  I learned, to my deep regret, that 'somebody' had been quite a bit optimistic.  Oh, not me...I was a naive and trusting fool...or so I found out.  No, the optimist was the person writing up the specs for those cars. (I'm not obtuse, I'm.........nice.)

I eventually found a way to broaden the affected sites with curves just under 28", whereupon all my troubles went away.  I still had the odd backing accident in the yard, where speeds were slow, but where the cut of heavyweights began to rise at about 1.5%.  Between the rolling resistance, them infernal diaphragms, the curves, and the gradient's effects, I would derail at least one of the cars about every other time.

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Posted by doctorwayne on Monday, November 2, 2020 10:44 PM

Overmod
Does anyone model full brake rigging on cars intended to negotiate these curves?

These are the old Rivarossi passenger cars, with a little tweaking...

By the time I get the major underbody details in place, there's not much room left for fully modelled brake rigging.   If it looks busy enough underneath the car, most viewers notice only what they see, not what's missing.

Wayne

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Posted by riogrande5761 on Tuesday, November 3, 2020 6:11 AM

So the OP has a 16x19' room.

The track plan I designed below is in a 15x33 foot room, but if shortened, could be adapted to fit a 16x 19' room and my minimum radius is a more comfortable 32 inches which would be a big help to passenger cars and might avoid surgery to the undercarriages.  There is no duck under.

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Posted by richhotrain on Tuesday, November 3, 2020 6:48 AM

riogrande5761

So the OP has a 16x19' room.

The track plan I designed below is in a 15x33 foot room, but if shortened, could be adapted to fit a 16x 19' room and my minimum radius is a more comfortable 32 inches which would be a big help to passenger cars and might avoid surgery to the undercarriages.  There is no duck under.

Yep, in my experience, 32 inch radius curves will avoid derailments of 85' passenger cars, 6-wheel trucks, and bigger steam engines. Anything less than 32 inch radius, in my experience, is not trouble free.

Rich

Alton Junction

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Posted by riogrande5761 on Tuesday, November 3, 2020 10:56 AM

I'm pretty sure the OP can have a walk-in layout with 32" minimum curves in a 16x19' room using an e configuration.  A turnback lobe at the tale of the e and another at the left middle inside of the e.

Rio Grande.  The Action Road  - Focus 1977-1983

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Posted by SeeYou190 on Tuesday, November 3, 2020 11:09 AM

Overmod
Does anyone model full brake rigging on cars intended to negotiate these curves?

All of my equipment has my "Fakey Brakie" brake rigging system underneath.

It looks good from normal viewing, but will not interfere with truck swing. All my equipment will pass through a 22 inch radius S-Curve with no tangent.

-Kevin

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Posted by jjdamnit on Tuesday, November 3, 2020 2:36 PM

Hello All,

Lots of great speculation!

No real answers from the OP.

Have we been "ghosted" again??

Hope this helps.

"Uhh...I didn’t know it was 'impossible' I just made it work...sorry"

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Posted by riogrande5761 on Wednesday, November 4, 2020 10:49 AM

Lastspikemike
How do you take 14' out of the length? It's the walk in part I'm having trouble visualizing. The peninsula has to stick out from the U, it's the centre bar in the E shape. The turnback radius is the hard one to find the space for unless you have length to fit the turnback loops in line, walking in at right angles and then turning down the aisle as in you're diagram. Without the overlap length the width limits your radius severely.

The lower middle part would have to be shorted upward and the bottom lobe pushed up into that area.  Not knowing where the entry/door is would matter as well.  I'd have to draw it out but it looks like it would work.  I'm not in a place where I can do that right now.

Rio Grande.  The Action Road  - Focus 1977-1983

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Posted by wjstix on Thursday, November 5, 2020 4:17 PM

What I've done on a lot of my passenger cars with diaphragms (like Walthers) is to replace the couplers with Kadee long-shank ones. Yes they don't look as good, but you can back them up OK. I've found on my layout with 30"R curves I can designate one end of the car the front and one the rear, and just the long-shank couplers to the front. That seems to be far enough to allow backing up, but looks better than using just long-shanks on both ends.

But it's a trial-and-error thing, everyone's layout and cars are a bit different so may need different solutions.

Stix

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