How long is a Class 31, an OBA barrier wagon, a nuclear flask on a Welltrol/Flatrol, another barrier wagon and a brake van?
This will be the "train unit" of the layout.
So this is what the layout has to be designed around.
This is the length of train that needs to be visible on the layout.
This is the length of train that the visible section of the passing loop must take. OK so the visible section of the loop ideally need only to fit the wagons.
It's a pretty important question to answer.
It's no point having a loop with a capacity of 24" when the train is 25" long.
Why a class 31? They are my favourites. I suppose I could allow for a larger loco like a Class 37 or a 47. A class 47 passes 11" long I think. Besides I don't like them as much as 31's. I like 37's and 20's though a 20 is shorter than a 31 and a 37 is pretty similar so I'm OK there I think.
A Class 31 scales out at 9" long. An OBA 6" the Weltrol/Flatrol probably 8" and the brake van another 3" All in all about 32". That's what I have to plan the layout around.