Answer is - as big as you can fit. Even if the loco says on the box it can handle an 11" radius, odds are that's the loco alone, with nothing coupled to it, AND it will only run on curves that sharp if run very slowly. The cynic in me says take the manufacturer spec and double it, but that may be overkill - adding 50% is probably more reasonable. So if out of all of them, the largest minimum radius you cna find specified is say 12", I'd make the loop 18" radius. Big locos need big space. 15" might work, but you shoudl test before fastening anything down.
Not sure why this is in this section? DC or DCC, reverse loop or just a turnback curve, makes no difference. It's a question of loco size and what curve radius the manufacturer designed it to handle.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
The manufacturer/importer will have that information in the details and literature for the model, and it should be found by clicking on images where they are sold.
When you learn that, and if you do acquire the model, make tight track curves temporarily tacked to plywood and test to see what the REAL minimum is. Then, add some rolling stock behind the locomotive and REPEAT. Finally, place those same items in front of the locomotive and shove them around those tight loops. You'll be sure to learn something, particularly passenger cars with diaphragms.
Hey guys I have a question for you, I'm going to run Nscale modern era loco's six axle, SD90MAC, SD70Ace etc. I would like to know what is the tighest loop radii I can do, without any problems, its going to be just a hidden staging loop, I will be using the Digitrax AR1. Take Care ALL