Has anyone ever experimented to see what the absolute minimum working radius is for, say, 40-foot cars? I'm no talking about what looks good, because obviously the bigger the radius, the better the appearance. I'm just wondering what would be the absolute minimum for short rolling stock.
The work of John Allen got me thinking. I recently reread an old issue of MRP that had a brief bit on his first Gorre & Daphetid, which I believe featured 13" radius curves, IIRC.
Anyone have experience with anything that tight?
That depends entirely on your rolling stock.
I have some equipment that works just fine on 15" radius, and I have some others that are touch and go on 22" radius.
Most freight will go around 18" radius, most passenger should be bigger.
Dave
Lackawanna Route of the Phoebe Snow
I think the smallest radius I ever used was the 15" snap-track that came with my first Mantua set, about 1956. The Booster and a trio of 40' cars with Talgo trucks and the old Mantua hook and loop couplers seemed to have no trouble with the curves. I did have derailing problems with X2F body mounted couplers later on with the 15" curves. I imagine most of the old Pre-WW1 era rolling stock could take a smaller radius, as well as some logging equipment, maybe shorty ore cars and the slag cars. The old Penn-Line company advertised a 4 wheel diesel switcher going around a circle that used a Silver Dollar for the inner track.
Almost everything I have will work on 22" radius, and a lot of it on smaller radius, except for a couple free lance articulated passenger cars I bashed from Athearn kits, and an old Amboid 1 in 5000 Tobacco Hogshead 95' box I built over 30 years ago. Those three need about 24" or 25" minimum.
JTGHas anyone ever experimented to see what the absolute minimum working radius is for, say, 40-foot cars? I'm no talking about what looks good, because obviously the bigger the radius, the better the appearance. I'm just wondering what would be the absolute minimum for short rolling stock. The work of John Allen got me thinking. I recently reread an old issue of MRP that had a brief bit on his first Gorre & Daphetid, which I believe featured 13" radius curves, IIRC. Anyone have experience with anything that tight?
The NMRA Layout Design Special Interest Group (LDSIG) has conducted some research into a formula that could be understood and used. This was described at length in Model Railroad Hobbyist magazine - the Jan 2009 issue of an on-line magazine.
Since an HO 40ft box car is 6 actual inches long, 2.5 times the car length is 15" radius. You will be successful most of the time with 40ft cars on 15" radius, even with body-mounted couplers. There will be occasional cars where the couplers don't have enough swing or the wheels contact details on the underframe. Long trains may string line on 15" radius curves.
When you get down in the 2X range (12" radius), generally truck mounted couplers become necessary. Less detail can be included on the underframe due to likely interference with truck rotation or coupler swing.
Our O27 cousins successfully use ratios down around 1.2 (radius =13" for an 11" long car). They succeed with extreme overhang, truck mounted couplers, car underframes with no detail and mounted unrealistically high to avoid interference with the trucks and couplers. Trucks may be mounted unnaturally close to the end of the car, and of course coupling distances are multiples of the prototype. Stringlining is expected on O27 curves with trains of significant length.
Which says to me that 2-5 car trains of 40ft cars could possibly be run on about 8" radius. It would take significant tweaking of the rolling stock to make it happen. Only 4 wheel locomotives are likely to work. But again - what reason do you have for going to that kind of effort for what you admit is not going to a very realistic appearance? To me, it would have to be a very good reason - perhaps a coffee table layout - to justify the extra work in laying track and adapting rolling stock.
There have been plans in MR for a 2x4 ft HO layout that used 10" radius curves. And a layout with 12" radius curves was featured not too long ago. But again, unless there is a good reason I would stick with no less than 15" and preferably 18" radius curves for a minimum for 40ft rolling stock and similar length locomotives.
my thoughts, your choices
Fred W
My Tomikawa Tani Tetsudo (HOj, 1:80 scale) has an absolute minimum radius or 350mm, just a little less than 14 inches. The normal rolling stock operated over it includes a modified Mantua/Uintah 2-6-6-2T (cosmetic modifications, no change to drive geometry,) a motley collection of teakettle tank engines and cars about the size of ore jimmies. JNR locos and passenger equipment are embargoed, as are some unusually long JNR freight cars.
The absolute minimum radius I have ever seen operated in HO was a silver dollar with a rail (on ties) circling it. A Varney 'Little Joe' dockside 0-4-0T ran around it in a really tight circle at very low speed.
Chuck (Modeling Central Japan in September, 1964)
With my Pizza layout I have only 8.7 ''. It works without problems even with 40' cars. You have only to manage to couple the cars.
Wolfgang
Pueblo & Salt Lake RR
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I know built-to-scale HO streetcars will do a 6" radius curve, so I wouldn't be surprised if a freight car of similar length couldn't go around the same curve. I would think the limiting factor might be keeping cars and engine coupled together...although as noted above, trains of small engines and short cars apparently can successfully navigate very sharp curves!!