An advantage of N scale, it's said, is its potential to pack a lot of track into tight spaces. But what's an acceptable minimum radius? There are as many opinions on this matter as there are N scalers, I am sure, but I'm interested in running 85' passenger consists without them looking ridiculous. When I say "ridiculous," I have two things in mind: overhang and offset between the ends of lengthy passenger cars.
1. Overhang... the radius is so tight that the middle of the car hangs out past the width of the ties, to the point that an 85' passenger car looks toy-like. For me, a radius of 12.5 inches is going too far, because you can see the outside rail when you look straight down the side of the car:
https://picasaweb.google.com/lh/photo/Pf-xTR-XPL1LaiVyrHVHK6jRXJ57668QI4U306rwdio?feat=directlinkA minimum radius of 13.75" produces a lot of overhang, but at least you can't see the outside rail. So I'm going to assume that I might be able to go with a 13.75" minimum radius. I am of course aware that, to some, the overhang still looks ridiculous, and larger radii are needed. But hey, it's my railroad.
But there's another problem!
2. Lateral offset of car ends... this produces the "toy train" look when a consist enters a curve.
https://picasaweb.google.com/lh/photo/XRzCRWwEWZSlpGP2U-cwEqjRXJ57668QI4U306rwdio?feat=directlinkYou can eliminate Problem #2 with easements, we're told. An easement starts a curve gradually, increasing the radius until the radius of the curve is attained. To create an easement, your curve broadens as it joins with the straight track (tangent)... this is called the offset. In addition, the curved portion of the track will be somewhat lengthened at each end. Let's call this the length extension.
The following picture shows two curves leading to tangent (straight) track: A 12.5" curve without an easement, and a 13.75" curve with an easement. Note the offset and length extension in the curve with an easement:
https://picasaweb.google.com/lh/photo/xT4ts_0HBCcHugHg30lPrajRXJ57668QI4U306rwdio?feat=directlinkMy question is very simple: How much offset do I need, and how long must the length extension be, in order to avoid Problem #2 with 85' passenger cars?
As anyone who has studied this matter will no doubt attest, the model railroading literature concerning easements is full of formulae, intonations, incantations, quotations from Authorities, rules of thumb, and magical procedures.
But my inspiration comes from John Armstrong, who noted that ridiculously tight curves look good as long as you construct good easements.
My approach is empirical. To heck with theory. I just experimented until I got what I wanted -- a smooth transition from straight track to a 13.75" radius without ANY lateral offset between 2 85' passenger cars:
https://picasaweb.google.com/lh/photo/gYoVyhzWgQDm7u-YvcaV9KjRXJ57668QI4U306rwdio?feat=directlinkI found that I could not achieve my aim (eliminating Problem #2) without an offset of 1.25" for a 13.75" curve. In addition, I needed a length extension about as long as Kato passenger car: 6.75".
I also found that the offset between the two cars is EXTRAORDINARILY sensitive to seemingly minor irregularities in the gradual build-up of the easement curve. I learned that I'll need to test every easement to make sure I've got it right before gluing the track in place.
From this inquiry, I learned that -- in a pinch -- I can use a 13.75" radius without risk of what, to me, would look unacceptably toy-like, so long as the overhand isn't readily visible. I'll go with 15R as a minimum for highly visible areas, preferring broader radii if I've room.
--Bryan
The photographs in this post are the author's, and they are expressly released to the public domain for the benefit of other modelers.
