Minimum Curves for Long Freight Cars & Steam Locos

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beiland

Active Member
#21
Whale Body Tank Car

Just saw a photo posted on one of these. I've got an unfinished kit of one of these. Guess I will have to experiment with it one of these days.
 

beiland

Active Member
#22
Steam Loco, articulate Proto 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 lousy 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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beiland

Active Member
#23
....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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beiland

Active Member
#24
Broadway Ltd articulated 2-6-6-4 Class A loco

On 31" Radius Curve​



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




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





On 28.5" Radius Curve​







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







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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beiland

Active Member
#25
Bachmann 4-8-4, (Santa Fe one 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.
 

beiland

Active Member
#26
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​







 

beiland

Active Member
#27
Allegheny 2-6-6-6, by Rivaqrossi

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 separate forum posting?
 

beiland

Active Member
#28
Bachmann 4-8-2, C&O Mountain

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.
 

beiland

Active Member
#29
Bachmann 4-8-2, no operation on 18"

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
 

beiland

Active Member
#30
Very Interesting Analysis of Curve Caqpability

Brian,

I can't offer any specific answers to your question, I have an Allegheny, but as you know my curves are big......

But, I will share another basic principal of railroad physics often missed about steam locos and curves.

The most important factor for steam locos and curves is the rigid wheel base of the drivers. This controls minimum radius more than any other factor.

So, for example, the Allegheny has a very short rigid driver wheel base for such a large loco, only 11.83' for each three axle set. This makes the loco very nimble for its size. Especially considering the double swivel design of the model.

The Allegheny will work better and look better on any given curve than, for example, the C&O 4-8-2. Why?, because the Mountain has a rigid driver wheel base of 18.25'.

Here on the ATLANTIC CENTRAL, even with 36" radius curves, I limit steam loco rigid wheel bases to 21', with a few USRA 2-10-2 lights being the longest rigid wheel base.

Examples of locos prohibited due to length:

SP GS4 4-8-4 - 21.5' rigid wheel base

B&O S1 2-10-2 - 22.30' rigid wheel base

Here is an example of how driver diameter effects rigid driver wheel base:

USRA 2-8-8-2, 57" drivers, 15.5' rigid wheel base

Compared to that GS4 above, 80" drivers, 21.5' rigid wgheel base

Eastern prototypes tended to have smaller drivers and were more suited to sharper curves.

A story from the prototype: The B&O has two main routes west, one directly west from Baltimore to Cincinnati, it is very curvy, and has many up and down grades. The primary large steam on this line were the 2-8-8-0's and the EM-1 2-8-8-4's, rigid wheelbase, 16.50'. Longest locos commonly used on that run, T-3 Mountains, 18.25' driver wheel base.

The other goes north thru Pittsburg to Chicago, it has longer, straighter, fewer (but just as steep) grades, and much broader curves. The primary steam on this line were the famous S1 2-10-2's, 22.30' driver wheel base.

At one point someone thought it would be a good idea to try an S1 on the line to Cincinnati - they put the loco on its side in a curve.........and put another on the ground on a different try........twice was enough.

This is exactly why the LIMA built the Allegheny as an 2-6-6-6, because they wanted larger drivers, they knew they would get better performance with a short wheel base, so this just put the max axle load on 6 drive axles rather than spread over eight like a Big Boy. Same is true of the N&W Class A.

While the C&O had ok success with the LIMA 2-10-4's built in the 1930, notice how they did not build more, but rather opted later for the Allegheny and the 2-8-4's - because the 2-10-4's were hard on the track, and hard on themselves in the curves.........

Way before these modern locos the C&O had a fleet of nearly 300 2-6-6-2's, not much more powerful than a 4-8-2. Why have the complexity of articulation for only that much power? Because they were more nimble, rigid wheel bases all around 10'. Worked so well they build the last ten in 1949......

I have lots of these on the ATLANTIC CENTRAL as well:

All of these prototype facts apply to your models as well.

So you can have big locos, on smaller curves, just pick the nimble ones......

Sheldon
 

beiland

Active Member
#31
Very Interesting Analysis of Curve Capability

Brian,

I can't offer any specific answers to your question, I have an Allegheny, but as you know my curves are big......

But, I will share another basic principal of railroad physics often missed about steam locos and curves.

The most important factor for steam locos and curves is the rigid wheel base of the drivers. This controls minimum radius more than any other factor.

So, for example, the Allegheny has a very short rigid driver wheel base for such a large loco, only 11.83' for each three axle set. This makes the loco very nimble for its size. Especially considering the double swivel design of the model.

The Allegheny will work better and look better on any given curve than, for example, the C&O 4-8-2. Why?, because the Mountain has a rigid driver wheel base of 18.25'.

Here on the ATLANTIC CENTRAL, even with 36" radius curves, I limit steam loco rigid wheel bases to 21', with a few USRA 2-10-2 lights being the longest rigid wheel base.

Examples of locos prohibited due to length:

SP GS4 4-8-4 - 21.5' rigid wheel base

B&O S1 2-10-2 - 22.30' rigid wheel base

Here is an example of how driver diameter effects rigid driver wheel base:

USRA 2-8-8-2, 57" drivers, 15.5' rigid wheel base

Compared to that GS4 above, 80" drivers, 21.5' rigid wgheel base

Eastern prototypes tended to have smaller drivers and were more suited to sharper curves.

A story from the prototype: The B&O has two main routes west, one directly west from Baltimore to Cincinnati, it is very curvy, and has many up and down grades. The primary large steam on this line were the 2-8-8-0's and the EM-1 2-8-8-4's, rigid wheelbase, 16.50'. Longest locos commonly used on that run, T-3 Mountains, 18.25' driver wheel base.

The other goes north thru Pittsburg to Chicago, it has longer, straighter, fewer (but just as steep) grades, and much broader curves. The primary steam on this line were the famous S1 2-10-2's, 22.30' driver wheel base.

At one point someone thought it would be a good idea to try an S1 on the line to Cincinnati - they put the loco on its side in a curve.........and put another on the ground on a different try........twice was enough.

This is exactly why the LIMA built the Allegheny as an 2-6-6-6, because they wanted larger drivers, they knew they would get better performance with a short wheel base, so this just put the max axle load on 6 drive axles rather than spread over eight like a Big Boy. Same is true of the N&W Class A.

While the C&O had ok success with the LIMA 2-10-4's built in the 1930, notice how they did not build more, but rather opted later for the Allegheny and the 2-8-4's - because the 2-10-4's were hard on the track, and hard on themselves in the curves.........

Way before these modern locos the C&O had a fleet of nearly 300 2-6-6-2's, not much more powerful than a 4-8-2. Why have the complexity of articulation for only that much power? Because they were more nimble, rigid wheel bases all around 10'. Worked so well they build the last ten in 1949......

I have lots of these on the ATLANTIC CENTRAL as well:

All of these prototype facts apply to your models as well.

So you can have big locos, on smaller curves, just pick the nimble ones......

Sheldon
 



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