Fair enough. I use 18" radius for spurs.
Good point. Many model railroaders make the mistake of seting a min radius for the main line and using it everywhere. On spurs and in industrial areas the prototype may have curves that modeled in scale would make many model railroaders cringe.
Ah. I see you are going with prototype curves!
A Baldwin 660HP diesel switcher could do 16.5" with train (presumably 40’ box). And 6.9" by itself, FWIW.
A UP SW10 could do 14.5". That’s probably without train.
A BNSF GP15 is 16.5 singly. And 23.5 with a second unit coupled.
Ed
40’ cars or less and 44ton/0-6-0s/HH660s and Alco S1s. 18" for pier tracks, other sidings between 18-22. Largest planned radius at the moment is somewhere around 55" in one or two places. Layout plan is being professionally critiqued.
Creative Layout Design, by John Armstrong covers this whole curve radius thing well. As does Track Planning for Realistic Operation, also by John Armstrong. The latter is in print. The former I stumbled upon on consignment in my LHS. Paid original cover price. Even had the original sales slip still in it. I should find mine and put it in there for posterity.
Paul Mallery, another great from back in the day, had a little different take on radius than Armstrong in his Trackwork Handbook.
He lobbied for much broader curves for HO trying to represent Class I mainlines, with 48" being the desired goal for mainlines.
A target I am getting close to with my current layout rebuild, with 36" as my minimum mainline.
Sheldon
Well, the OP hasn’t chimed in since his first post on Feb. 27. Hopefully, he’s read some of this, and decided accordingly.
Mike.
I’m sure you don’t mean to imply that Armstrong was a proponent of tight radius curves. This is not the case. He was about understanding your options, how one choice impacts others, and finding the best compromise that would allow you to satisfy as many of your desires as possible while dealing with the reality of available space.
OTOH, like we have in all evdeavors where human males participate, there are those in this hobby who are always looking for the opportunity to say “mine is bigger than yours”. …and BTW, I do not mean to identify any specific individual as a member of this group.
We could debate this till the cow’s come home. BMMECNYC’s advice is sound and rather than the starting point should be the end point. Recommended Practice 11 very clearly indicates appropriate rolling stock for what ever radius you have. Seems simple enough that once you know what your limiting radius is, you know what type of railroad you can model. If there’s a disconnect between what you have and what you want your choices are to either change scales or find a larger space.
Ray
No, it is not a criticism of Amrstrong, just pointing out that other leaders in the hobby had somewhat different opinions.
And even 50 years ago or longer, a fair number of people did understand that better operation and better appearance was acheived with larger curves.
And, it plays along with a concept I support, there is a difference between a large layout and a complex one. A layout may occupy a somewhat larger space to allow larger curves, longer yard and sidings, etc, without being anymore “trackwork intense” than a layout others would have in a smaller space.
Sheldon
Paul Mallory was oriented towards club layouts (and very large home layouts). John Armstrong was oriented towards the folks who had smaller spaces and the attendant tradeoffs between things like curve radii and railroad like operations.
The first edition of Track Planning for Realistic Operations included several examples of how to modify some of the published plans of the day to improve their operating capabilities.
Sure 36" or 48" minimums are nice. But the reality for most of us is that those minimums are either impossible or leave us with a loop of track and little else.
Many of us would do well with talgo trucks and deep flanges. That’s how Lionel O27 trains get around a 13" radius curve.
Paul
I bought John Armstrongs book back in the 1980’s and it has been a major help in my designing and building 3 layouts so far. But keep in mind, not only was John Armstong dealing with smaller spaces and “givens and druthers”, he was also a product of times when standards were simply oriented around sharper curves.
For example, in his book he refers to 3 major classes of curves by the folloing terms (from memory):
18" Radius - Sharp
24" Radius - Conventional
30" Radius - Broad
Just my observations but since the mid-late 1980’s and after, I have noticed the majority of moderate sized layouts in MR magazine articles have minimum radius curves of 30". Noting that trend, it might be appropriate to update the terms:
18" Radius - very sharp
24" Radius - moderately sharp
30" Radius - conventional
42" Radius - broad
Of course many modelers still have to contend with limited space and use old style sectional track curves such as 18" and 22" radius, but it does limit the rolling stock being run and beyond that, appearances of rolling stock can be impacted as well. There is a great article written by Joe Fugate on that subject in the January 2009 MRH issue.
http://model-railroad-hobbyist.com/mrh2009-01/curve_insights
Some rules of thumb are discussed in the article which point out that the curve ratio is a factor of the length of rolling stock. By
Yeah, maybe if your observations were correct. This is like the situation we have today with cable news - people seek out the news that agrees with their point of view. If you look at the track plan database and do the math like I did, you’ll find the median minimum radius for modest layouts is 24".
I do agree that the work done by the Layout Design SIG that Byron mentioned earlier and was the source for the MRH article you quoted is the best advice available today.
Using transition curves you can get away with a tighter radius.
My observations were correct for me and not meant to contradict any “databases”; I gravitated to articles I found the most inspirational to me personally (e.g. Eric Broomans Utah Belt, David Barrows CM&SF), and many other articles of that caliber) and noticed remarkably consistant pattern of 30 inch minimum radius listed in the layout information tables. It bespoke that quite a few trend setters in the hobby appeared to also be setting some standards in minimums, at least in that class of layout.
Personally I think there are some major advantages to pushing the boundaries if layout design and making curve radii a priority as much as possible. Joe’s article mentioned above gives “legs” to it.
A big part of that change in radius classification is the trend to bigger equipment by the prototype. In the 50’s even the real railroads didn’t have 89 foot articulated auto racks. The trends didn;t follow exactly liek today, but in the 50’s there were a lot more people modeling the 1920’s and earlier, which had even SMALLER equipment than the then-contemporary 50’s railroads. Modern stuff is just HUGE. An RS3 looks small next to an SD70ACE or AC4400CW. Just like a 1910 Consolidation looks small next to a late steam era 4-8-4’s.
Since I model the 50’s with predominantly 40’ box cars (and shorter hoppers), 30" radius curves will be just fine - that’s the 5x car length figure. There’s a guy posting in the LDSIG and Layout Construction groups on Yahoo who seems to think he needs 48" radius minimum for N SCALE which is just insane - although the style of his postings makes it hard to understand what he’s trying to say. Pushing the limits is great but in the end I want to have a workable raillroad and I only have so much space. If I had a hanger to build in? Sure I’d go 60" minimum radius and no turnouts smaller than a #10. I haven’t seen a model made yet that REQUIRES those sort of dimensions (in HO). Sure it would look nice, but can I build a practical layout in my basement if I used 60" radius curves? If all I wanted was a giant version of your basic oval, I could do it.
–Randy
And awsome looking if he can get away with it! =p
Hence why John Armstrong always did a “givens and druthers”. Context is the key here; no air craft hanger? It’s common sense that model railroading is all about compromises, although some might be able to kick up the radius a couple of inches without a major change to a track plan.
It is interesting to note that curve radius is probably the one item where the selective compression between model railroads and the prototype is most pronounced. In the prototype, curves below a radius of 870 ft are very rare; that would amount to 10 ft in HO. Taking it to the extreme, the standard curve radius on new high-speed tracks is 4000 m for 300 km/h (186 mph), and up to 7000 m for higher speeds. 4000 m equals around 13,000 ft; in HO, this would give you about 150 ft (feet, not inches).
They have the unfair advantage of not having to turn before hitting a wall.
The question is not having to turn before you hit the wall, the question is how close do you get to the wall before you start turning…
Seriously, if one wants to run modern equipment, or if one wants to run passenger cars, something above 30" radius, and preferably above 36" radius, should be considered the minimum for the mainline. And they should be minimums, with any curves that can be larger, being larger for the visual effect.
All curves should have sprial easements, changes in direction less than 45 degrees parabolic curves (two easements back to back, no fixed radius), just like the prototype.
Just my views…
Sheldon