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What’s the REAL minimum radius of locomotives and rolling stock?

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Posted by ATLANTIC CENTRAL on Monday, March 12, 2018 5:16 AM

TheWizard

 

 
rrinker

 

 
ATLANTIC CENTRAL

I understand not everyone has the room for large curves, but we all make choices. If I did not have the room for large curves, I think my choices would not include long cars......

Sheldon   

 

 

 

Exactly. No, not everyone has room for 36" radius curves. So they make do with the space they have. But then you also have to not expect to be able to run giant articulated locos and 85' cars. It's not an appearance issue, it's not an issue of elitism. It's physics.

                                    --Randy

 

 

Kato makes Superliners and P42's that negotiate 15" curves. It's only physics until you overcome it, as the Japanese have. Then it's just laziness on a manufacturers' part.

 

Respectfully, not universally true.

Because all compromises to get long cars around sharp curves require greater spacing between cars.

Spacing that many like myself find unacceptable.

I prefer that my little HO scale people not have to jump a scale 3' gap between diaphragms when moving from car to car.

OR:

All attemps at complex coupler systems to address this fail to hold up long term, fail with long train lengths, and fail to back up well.

And, special systems like KATO uses have issues with compatablity with other cars.

Most HO modelers are not interested in being restricted in this way.

Sheldon

    

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Posted by Overmod on Monday, March 12, 2018 12:24 PM

railandsail
I was just looking to determine a bare minimum fit.

But it turns out you need to know more to get an actually meaningful answer to the question you asked.

As noted, overhang at slow speed under 'ideal' conditions is no guarantee you can actually run equipment through curves.  At a minimum you will have to perform empirical testing, and only a fool would not take note of what was contributing to subsequent derailments or other issues ... and start deciding to address the causes.

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Posted by railandsail on Tuesday, March 13, 2018 10:44 PM

Steam Engine, articulated Proto 2K 2-8-8-2

I have so far 6 'questionable' steam locos that I have placed on these curves.

The first one is a Proto Heritage 2-8-8-2,..

1) On 31" Radius Curve

 

 

 

 

It would appear that this loco can fit within both the 1" outer and " inner clearance boarder markers,...both the leading truck platform, and the aft cab roof,.....31" radius curve.

 

 

 

2) On 28.5" Radius Curve

 

Sorry for the lousey angles of these overhead shots, but again it appears as thought this loco just barely fits within those 1" clearance boundries while on the 28.5" curve.

 

 

 

3) On the 24" Radius Curve

 

 

 

On the 24" curve it appears as though we need a little bit extra clearance for the cab roof to clear.

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Posted by rrinker on Wednesday, March 14, 2018 7:48 AM

 Articulated locos are where a compromise has been made in almost every model. On the models, the engines are arranged like 3 and 4 axle diesel trucks and both swivel. On a real articulated loco, that is not the case. The rear engine is fixed to the engine bed, and the front pivots off a drawbar connection to the read engine, with a sliding bearing under the boiler. Built like this, you'd never ever get a Big Boy around an 18" radius curve. You wouldn't get one around a 36" radius curve, for that matter.

 There is no way physically possible for a full length 85' passenger car with proper scale width to the car body, coupled at anything resembling prototypical distance, to negotiate an 18" radius curve, no matter how slow you to. The ends of the cars with physically touch and push the cars off the rails. The Kato ones work becauyse hey made that compromise and the distance between the cars is excessive. Others have done similar things with their couplers, which keep the cars closer on straights but expand on curves. Sometimes, even with large enough radius and cars that are "scale distance" it's still a bit far comared to how closely prototype cars actually are coupled. And it's not just modern equipment that is close coupled, walk car to car on a tourist line using vintage cars and take note of just how small the gap is between them.

                            --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by Overmod on Wednesday, March 14, 2018 12:48 PM

rrinker
On the models, the engines are arranged like 3 and 4 axle diesel trucks and both swivel.

Of course, it might be mentioned right here that a great many modern prototype diesel trucks don't 'swivel'; they are bonded to the chassis rails or other 'hardpoints' eith the modern equivalent of Fabreeka springs and have very limited rotation compared to what models in many scales provide.  There is a parallel in electrics for the designs with long outboard secondary springs.

I confess to being highly irritated at models of PRR duplex locomotives that have been 'articulated' to give tighter minimum radius ... in at least one notorious case putting BOTH engines on pivots with embarrassingly convenient gaps in the steam piping.  This is not quite as awful as the way the Berk in the Polar Express movie was made to go around short radius... but you could see it from there.

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Posted by rrinker on Wednesday, March 14, 2018 5:44 PM

 Which is exactly what MTH did to make their UP 4-12-0 get around curves. A PRR T1 is another one that wouldn't work on most model curves if it were built like the real thing.

 Yeah I don't do modern, I model diesels when they were actually unique and there were more than 2 models to chose from Big Smile

                                        --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by ricktrains4824 on Wednesday, March 14, 2018 10:13 PM

And herein lies the biggest issue - Compromises must be made otherwise everything would become a shelf queen.

While I am all for realism, I am also all for reliable operation, as I am a model railroader, not a model train collector. 

So I still don't see why manufacturers can't place the real operating radii requirements on their products.

I will point out one point with the tests being pictured - Make sure that you also can operate things coupled together with these tests. 

Just sitting a single model on the curve will be of no help if it can't move connected with another.My 2 Cents 

Ricky W.

HO scale Proto-freelancer.

My Railroad rules:

1: It's my railroad, my rules.

2: It's for having fun and enjoyment.

3: Any objections, consult above rules.

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Posted by railandsail on Thursday, March 15, 2018 9:34 AM

....very interesting link from another forum,....lots of dwgs and understandable, readable text



For the technically minded, one of the available "free" references that covers railway design is Railtrack and Associated Equipment for Use in Underground Mines. by the UK Health and Safety Executive. The relevant standards of railroad rolling stock design are usually only available at a significant cost and many of the other "free" references like Google Books etc have arbitary page limitations that may hide the relevant pages on rolling stock design as applied to curves.

In the link I quoted, check out the curved track section. This section gives:

    Minimum radius to prevent flange climbing and subsequent derailment Pdf page 19 to 21/84
    Endthrow formula for the end of vehicles on curves - Pdf page 31/84
    Centre Centrthrow formula for the centre of vehicles on curves - Pdf Page 31/84

Notice that the weight of the wagon plays no part in flange climbing.at the minimum radius. Simply adding weight will not help if your wheelbase is too long. Other topics covered are reverse curves, superelevation and gauge widening and checkrails.

For those that open the link, make yourself a cup of something. You might be there a while. This is not mainline stuff but the geometry of overhangs on curves is scale independent provided that you keep your measurement units consistent.

Regards,

John Garaty

Unanderra in oz
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Posted by railandsail on Friday, March 16, 2018 10:59 AM

Broadway Ltd articulated 2-6-6-4 Class A

 

1) On 31" Radius Curve
 

 

Requires at least 7/8" at front of loco.

 

 

Requires at least 1+1/4 inches at rear cab roof

 

 

2) On 28.5" Radius Curve

 

 

 

Requires 1" at frt of loco, and 1.25" at rear cab.

 

 

 

 

3) On 24" Radius Curves

 

 

 

Requires 1+3/8 inch clearance for rear cab roof.

**I believe I have successfully run this BLI loco around many 22" curves of my old Central Midland layout.

 

 

 

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Posted by rrinker on Friday, March 16, 2018 4:38 PM

ricktrains4824

And herein lies the biggest issue - Compromises must be made otherwise everything would become a shelf queen.

While I am all for realism, I am also all for reliable operation, as I am a model railroader, not a model train collector. 

So I still don't see why manufacturers can't place the real operating radii requirements on their products.

I will point out one point with the tests being pictured - Make sure that you also can operate things coupled together with these tests. 

Just sitting a single model on the curve will be of no help if it can't move connected with another.My 2 Cents 

 

Because for a mass produced model, if they came out and said you need 30" miniumum radius to run it, they wouldn't sell many. For limited production brass it's not as big a deal as probbaly half of them go to collectors who never run the things anyway, and those that do tend to already know that there are fewer compromises than with plastic locos and they already know it needs a pretty generous radius to operate properly.

That said, I haven't had anything that wouldn't work on the suggested minium radius. It's more like 'works with other cars' or 'works with other brand equipment' on the minimum radius. That's why many steam models have multiple holes in the tender drawbar. Yes it will run on the specified min radius, but only if you put the drawbar in the furthest hole, leaving a Grand Canyon size gap between the engine and tender. 

                              --Randy

 


Modeling the Reading Railroad in the 1950's

 

Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.

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Posted by cuyama on Friday, March 16, 2018 5:34 PM

It's not clear (Edit: to me, at least) what the point is of all the photos and "tests" in this thread.

But in case someone might be following along and be tempted to use this as a guide to their own layout construction, none of these address a key issue with track-to-track spacing in curves: what happens, for example, when a longer piece of equipment on the outer curve overhangs to the inside and an articulated engine on the inner track overhangs to the outside and they side-swipe.

That’s why track-to-track spacing guidelines like the NMRA’s S-8 are very helpful – as they address not only the limited set of the equipment one owns and can test today, but something one might buy in the future.

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Posted by Drumguy on Friday, March 16, 2018 8:58 PM

I don’t think the real minimum radius has to be quite so technical. Get your biggest loco and you longest car (preferably several). Find you tightest curve—already physically in place on a layout or a mockup. Chances are with modern gear, it will negotiate anything over 18” at a creep. Emphasis on creep. There in lies the rub. Now comes the easy part: factor your preferred running speed with you acceptable level of silly looking overhang, and there’s your minimum (For me it comes out to 28—with easements).  And don’t be ashamed of you personal level of overhang acceptance. For the folks who have the luxury of 40” minimums, there’s probably a few snobs who look down on them thinking anything under 60 is a sin. Whatever floats yer boat.

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Posted by hegedusmj on Saturday, March 17, 2018 4:59 AM
In the past month or so, I saw a lengthy table of min radius of a wide variety of equipment, perhaps 15 pages or so. I think it was on another forum. Does anyone know where to find it?

Mike

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Posted by railandsail on Saturday, March 17, 2018 12:32 PM

Bachmann 4-8-4 (Santa Fe model w long tender)

 

 

On 31" Radius Curves

 

 

 


Requires 1+3/16" at rear cab roof
 

 

 

On 28.5" Radius Curves

 

 

 


Requires 1+1/4 inches at rear cab roof.
 


Requires 1" at front
 

 

 

On 24" Radius Curves

 

 


Requires 1+5/16 inches at rear cab roof.

 


Requires 1" at the front.

 


 

 

 

On 18" Radius Curves

 


Requires 1+3/16" at front

Not sure that this 4-8-4 Bachmann will run on 18" radius curves, but it does fit on them.

 

 

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Posted by railandsail on Monday, March 19, 2018 9:42 PM

Broadway Ltd Big Boy 4-8-8-4

So now we come to a biggy, the infamous Big Boy

On 31" Radius Curves

 

 

 

 


Requires 1+3/16" clearance at the rear cab

 

 

On 28.5" Radius Curves

 

 


Requires 1+1/4 "clearance at the rear cab roof

 

 


The Big Boy is one of those long locos that actually reaches out to the 1" clearance line at its inner midpoint.

 

 

 

On 24" Radius Curves

 

 

 

 

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Posted by railandsail on Wednesday, March 21, 2018 1:15 PM

Allegheny 2-6-6-6, by Rivarossi

 

I have several of these built/marketed by Rivarossi. One in particular is a heavily weathered one. They are beautiful plastic locos, rivaling the looks of the brass ones.

I've never had a layout since owning these as I sold my previous layout just about the time I acquired my first one. So I am real interested to see what sort of minimum curves they might be operated on?

 

On 31" Radius Curves

 

 

 

 

 

 

 

On 28.5" Radius Curves

 

 

 

 

 


You can see that the rear cab of this Allegheny loco sticks out fully to the mid point between these two tracks. That track spacing is 2+1/2" between CL's. Thus this loco requires a minimum of 1+1/4" clearance at its outer side on this 28.5" curve.

Note that another Allegheny, or one of the longer freight cars, could be traveling on that outer track and still NOT interfere with this inner Allegheny.

 

 

 

On 24" Radius Curves

 

 

 


The overhang is now 1+3/8 inches on this tight 24" radius curve

 


The mid girth of this loco is at the more extreme of the longer cars and locos,...a full 1" from the centerline of the track it is on.

I wonder what minimum radius curves that many owners of these locos have experienced as operational? I may have to ask this question in a seperate forum posting?

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Posted by hegedusmj on Saturday, March 24, 2018 7:24 AM

Sometime in the past several weeks I ran across a post that attached a product by product listing of perhaps 15 pages showing the minimum radius of each one. Does anyone recall where the listing is?

Mike

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Posted by railandsail on Saturday, March 24, 2018 7:35 AM

It would be interesting to find that reference. have you looked back at your 'history' of sites visited, or how you came about finding it??

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Posted by railandsail on Saturday, March 24, 2018 7:36 AM

Bachmann 4-8-2, C&O Mountain Loco

I chose to experiment with this loco as it was the very first steam loco i ever purchased when I first got back into the hobby, and it had an 8 main driver arrangement. There were two main plastic models of this loco, the first one an IHC one, and then the very nice Bachmann one. 

I still have my 2 IHC ones that I often ran on my Central Midland layout that had mostly 22" radius curves. And I ran them double-headed. I also have several of the Bachmann versions that I plan on running on my new layout, likely often dbl-headed as well.

On 31" Radius Curves

 

 

 

 

 

 

 

 

On 28.5" Radius Curves
 

 

 

 

 

 

 

On 24" Radius Curves

 

 

 

 

 

 

On 18" Radius Curves

 

 

Note: The IHC models had larger flange wheels on them than the newer Bachmann ones do, so it might make a difference in the tightness of the curves they could run on. And it is not clear of these locos will operate on those 18" curves.

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Posted by ATLANTIC CENTRAL on Saturday, March 24, 2018 7:47 AM

The Bachmann C&O Mountain will not run on 18" radius, 22" is really pushing it, but Bachmann says that is the minimum.

I have ten Bachmann Heavy Mountains, 3 in C&O, the rest various versions for my ATLANTIC CENTRAL.

I can also tell you they will not run through #4 turnouts, or even Atlas #4 Cunstom Line which is really a #4.5.

I suspect even a #5 would be tight, but I have not tried them on a #5, I don't own any #5 turnouts.

They run fine through Atlas Custom Line #6's. And I only run them on 36" radius and above........

I have a set list of mods I do to them to improve their performance, most notably I add weight to the tenders and modify the drawbar with a "dip" to better clear the wires.

If you look closely in the second picture you can see the dip bent in the drawbar.

Sheldon

 

    

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Posted by railandsail on Saturday, March 24, 2018 8:03 AM

Thanks for that info Sheldon. I suspected that might be a problem when I placed the static loco on that 18" curve

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