A small discussion broke out on the minimum radii that some brass engines can handle, (both old and new), on the general discussion board. In general, most felt that brass locos of older vintage couldn’t negotiate tight curves the way modern model metal and plastic steamers can
The concept of prototypical curves came to mind and I wonder if the high scale brass of yesteryear could handle the tightest proto-typical curves found on their real life roads.
I realize that curves which the Big-Boy might experience in real life would be far more open and gentle than what a brass bigboy of any vintage could probably handle (24" radius?). Thus, here, the big-boy brass would do better than the real thing. Sure a Big Boy would never wander onto a curved siding to do a switching trick, but N&W Y6Bs and Z-1 mallets did switching tricks all the time.
As a narrow gauge guy, I have acquired two older United and Sunset K-28s (mikes, 2-8-2) and they do OK on my 22 radius turns and the manufacturer’s old litterature claimed 18" radius which would be about in line, barely, with some of the tightest curves on the D&RGW. The modern Blackstones, (metal, but not brass), also claim 18 radius on their K-27 mikes.
Does anyone know of a brass loco or any loco model that will not negotiate a protoypical, operational curve found on their original, real life roads? In other words, did a brass manufacturer pay a lot of attention to surface scale detail, but fail in the operational scale end of the model?
So, it looks as though you want to compare prototype and model minimum radii. Most modelers aren’t likely to know the former, BUT I’ve been interested in this for a long time, and I’ve got some numbers (in easy to understand “HO inches”). Where I have the info, I’ll note whether it’s with or without a train:
Great Northern Z-6 (4-6-6-4) 40"
Great Northern R-1 (2-8-8-2) 49 1/2"
Union Pacific 4-12-2 (without train) 50"
Union Pacific DD40AX (without train) 42" (with train) 50"
Union Pacific SD45 (without train) 36" (with train) 47"
Union Pacific SW10 (without train) 14 1/2"
Union Pacific U50C (without train) 42" (with train) 50"
Ed, Thanks for the info. So far it looks like most brass steam models can handle any minimum radius prototypical curve. I would expect Diesels to fall well within their prototypical range as they don’t have the bulk wheel sets found on steam. The biggest 4 wheel diesel trucks are about like an 0-4-0 steamer and, thus I would think any model diesel could handle any prototypical modeled curve. This not to say that a DD-40 would look OK on an 18 " radius curve.
And to the comment about dead slow in tight radius in protoype, I am well versed in the D&RGWs speed limits and narrow gauge specific issues. A look at the railroads regs even into the 1920’s shows many long stretches where the engineers were ordered to not exceed 5 mph. A lot of this was not the radii of the curves, but the nature of the light weight rail still found along the line. Another reason was the only moderately maintained right of way coupled with the ever present “soft spots” from flooding or mounded up melted and refrozen snow in winter! On the D&RGW derailments were a daily occurance and there is a reason all engines had re-railers hung on both sides of the rear of the tenders.
It was only on those parts of the road where the 30 and 40lb rail was upgraded to 55lb and above and on straight and level open plains runs during the summer where the throttle could be opened to 25-30MPH. The “Chili line”, (Antonito to Santa Fe), and Antonito to Chama had a few such “fast” stretches like this.
I doubt there was ever a brass loco model made that couldn’t take as tight a curve as the prototype it was based on. Remember our model curves are really tight. In HO 30" radius or larger curves are considered “broad”. IIRC John Armstrong in one of his books pointed out that the sharpest mainline curve you’d generally find on a real railroad would work out to be about 34" radius in HO, and speed would be restricted on that to about 20 MPH…and a number of large steam or diesel engines couldn’t do that sharp a curve anyway. In HO, an accurate model of a real mainline that allowed for high speed running would require curves around 80-100" radius.
My 2-8-8-2 plastic P2K will go places that my little brass 2-6-0 has a hard time. I also built a Bowser 2-10-0 that originally had blind drivers on 2,3,4 axles. I replaced the 2 and 4 axles with flanged drivers now it will derail on anything sharper than a 26 inch radius turn.
It would all depend on how much lateral play the manufactures put in the drives. Another thing to look at is the draw bar length from loco to tender. My brass 2-6-0 has a draw bar that is around 5/8 of an inch long from hole to hole. Anything sharper than a #5 turnout will pull the tender off the rails. I could lengthen the drawbar but it looks too good now. Overhang is one of the reasons why I don’t run big locos. My friends Centipedes look great on a tangent but anything sharper than a six foot radius they look terrible. The front trucks almost come completely out from under the cabs. That is a look I do not want to model.
Based on the chart I presented, I chose a minimum mainline radius of 48". I figured if a real 4-12-2 could make 48" (approximately), a model one ought to, also. And that should hold even with the right sized wheels spaced properly, the engine-tender gap to scale, all the little doo-dads hanging down near moving parts, and so on.
Now, since I don’t have a proper (or improper) warehouse for a layout, my trackage is stunning in its simplicity. I am, though, involved with free-mo, so every one in awhile I can “go large”. Their minimum radius is also 48", so that works out well.
One thing that may not be understood is that “modern” model articulated engines that have both sets of drivers articulated aren’t like that just to allow them to go around very sharp curves - many old model Mallets could take pretty sharp curves - but to make them look better doing it.
Just as an example (with made up numbers), let’s say a real articulated needs to have it’s front drivers able to move left or right by 10 degrees. This allows it to take the curves it need to go around on it’s railroad. OK, now let’s say the real railroad’s curves scale out to 60" radius curves in HO. So how do you make the model go around say 24" radius curves?? Well, in the past, they compromised some the accuracy of the model to allow the front drivers to swing by say 30 degrees instead of only 10. That allows the engine to go around the unrealistically sharp curves, but it looks silly doing it due to the huge overhang of the front of the boiler.
If you allow the front and the rear drivers to articulate, you can cut the swing of the each one in half, so now the front drivers are only 15 degrees off-center - much closer to the 10 pct. of the prototype.
A DD40X will make it around the loop at a coal fired power plant, one powered the Arkansas Power & Light family days special from N Little Rock to the White Bluff power plant.
It would make it around the loop but couldn’t fit thru the dumper (but then neither would the dome cars).
For the filming of Biloxi Blues they moved a 4-6-2 through N Little Rock to the fliming location. The Superintendent was concerned about the Pacific with its 70+ in drivers making it around the wye connection to the Van Buren Sub and ordered that the curve be oiled.
I pointed out to him that the rigid wheelbase of the Pacific was actually less than an SD50 truck and that the MP had run 2-10-2’s and 4-8-4’s around that same curve all the time, but he insisted.
Big Boys would make it through #9 turnouts in yards and #10 turnouts on center sidings.
The numbers that I have read for a UP Bigboy, are that they can manage(at restricted speed) a maximum 20 degree curve, which is supposed to figure out to a 40 inch radius in HO.
Thanks to all for the stimulating and well considered reponses. The prototypical nature of the real narrow gauge world prior to 1960 is far removed from modern railroading.
I have read a number of books and studied hundreds of images now on the narrow gauge and specifically, but not exclusively relating to the D&RGW and the RGS. I have been working solely in HOn3 for about 2 years after 45 years in HO. It seems that the real track was always very light rail 25-45 lb and never was upgraded to anything heavier than 70lb. Very light ten wheelers and the earliest consolidations had little trouble with this weight rail, per se. It was the road bed condition and general uneven nature of the trackage that put many of them down on the ballast.
Specific accounts of blind drivers on the “consols” entering an uneven, fairly sharp curve actually dropping over the outside rail or falling into the inside rail were not at all unusual, especially in the pre-1900 era. Even after that, all manner of derailments were the norm, but due to the light weight of the locos and cars, most derailments were actually handled by the crews themselves! No heavy equipment needed! Re-railer frogs littered the narrow gauge. Cabooses had at least four of the 100 lb items and every tender seemed to have at least two hung off the rear sides. These and a good long steel pry bar and some 6X6 timbers were usually all that was needed when a pilot, trailing or freight truck bounced off bad track. No book on the narrow gauge can avoid talking about derailments which plagued operations.
I have not really got my HOn3 layout more than 20% done, since I “run as I go”. I am really sorry that the electrical nature and especially the DCC nature of modern MR trackage will not allow me to run over true prototypically rotten track work that is deliberately set out “washboard style”. The waddling of a k-27 mudhen down uneven
A couple years ago I had the chance, through my work, to see the current BNSF design standards.
If I recall correctly, the smallest mainline radius they will actually build today (for freight service) works out to about 72" in HO scale.
Also, most rolling stock in real railroad service today would negotiate about a 41" radius curve in HO (obviously there are exceptions).
John Mock, P.E.
Civil Engineer (highway design)
P.S. A prototype “20 degree curve” based on the definition of curve used in civil engineering is indeed roughly approximate to a 40" radius curve in HO scale–So that Big Boy comment above is technically correct. However–again–that is at restricted speed.
Also, as documented by William Kratville in his excellent books, the real Union Pacific 4-12-2 #9000 operated through Cajon Pass under its own power on its way to its current location. There are photos of it with high ranking railroad officials walking alongside it through the curve near Summit, which at that time (from what I’ve read) was approximately 11 degrees, or 72" radius in HO scale. The engine derailed once at Summit but was carefully rerailed.
Prototype 4-12-2’s could not ever have operated on (HO equivalent) 48" radius–that statement is totally incorrect.
It seems to me one of the first - if not the very first - HO engine to be “dual articulated” actually had it as an option…like, the engine as it came from the factory had only the front drivers articulated. If you wanted to have both sets of drivers move, you removed a screw or two (or something) and then both front and rear drivers swiveled.
I can’t remember which engine it was - maybe the Lionel HO Challenger from about 10 years ago?? - but I always liked the idea that you had the option based on your layout and your own personal preferences.
From page 185 of Kratville and Bush’s “The Union Pacific Type-Volume 1”:
“By May 17, Gray had told Charske in New York that the test ‘has fully met our expectations,’ saying ‘they had subjected the 9000 to every possible test and put it around curves up to 17 degrees without difficulty.’”
Seventeen degrees is 46 1/2 inches in HO.
Would you like to perhaps reconsider your declaration of “totally incorrect”?
Gidday Richard, probably talking through the extra hole in my head, but, providing you kept the track in gauge, could you not try “tweaking” a single rail , alternately, in the horizontal plane to give the illusion of waddling?
Definitely not in MRs “Tip for tracks” and against the grain, but[^o)]
No, thank you. Elsewhere in Kratville’s Volume I it also states that Alco insisted upon delivering 9000 with a blind center driver, but the Union Pacific operating people did not want any blind drivers on the 4-12-2. It also states that Union Pacific replaced the blind driver(s) (if there was more than one axle blind–if I recall correctly at least one source was not totally sure regarding the number of blind axles on engine 9000 at delivery) with regular flanged drivers very shortly after delivery.
Perhaps they tested the engine on 17 degree curves, perhaps to “sell” management on why they should build more–sure–but did not routinely operate them on 17 degree mainline curves.
I’ve read from other sources that Cajon Pass at that time had 11 degree curves. It is clearly stated in Kratville’s Volume II book that engine 9000 derailed on the curve at Summit during its final run to the display location.
So, either the sources I’ve read regarding the curvature at Summit were not correct, or there is some othe
I just did a search regarding degree of curvature on Cajon, and found a post (I think it was on Trainorders, but I’m not a member…) where the poster says the 1952 track chart for Cajon Pass indicates the degree of curve at Sullivan’s curve to be 10 degrees, 01 minute and 43.5 seconds. The curve just west of Summit (where the UP 4-12-2 #9000 derailed on its final journey) was listed at 10 degrees, 20 minutes. Now, any vertical curvature at the same location may have exacerbated the impact of the horizontal curvature on that big engine, but I’m very very sure no 4-12-2 could have routinely operated on curves of 17 degrees (only 337’ prototype radius).
The UP claim (as reported in Kratville’s book) of testing a 4-12-2 on 17 degree curves, unless with blind driver(s) is questionnable and subject to doubt.
To Ja Bear… I might just try your suggestion about laying some temporary washboard track as an experiment. I would imagine it would be best done on a straight section though. Putting in on a curve might be pushing the envelope a bit.