Okay, this is for those who love trivial matters in N scale. The rest of you can go to sleep. I am re-reading for about the fifteenth time Armstrong's track planning book. In the latest edition (p.76), he talks about radii that define broad, convential and sharp curves. Most of us are familiar with HO. 30 inches is defined as a broad curve, 24" conventional, and 18" sharp. But when I do the math for N scale, converting his recommendations it doesn't quite come out the same. In N Armstrong recommends, 17" as a broad curve. If you do the math, 17" converts to 31.48 in HO, whereas 16 inches converts to 29.62 in HO. It would seem to me 16 inches would also qualify as a broad curve. Again doing the math, his recommendation of 14" as conventional converts to 25.925 - or 26" in HO. and 11" converts to 20.37. Does N scale need this wide a divergence from HO or is Armstrong guilty of bad math.
Maybe neither. As I remember, the radii were based on performance and appearance. Broad radius (and I'll probably get corrected a number of times here) is based on C-C diesels, large steam (ie, 4-8-4 and up) and 85' cars. I suspect that there isn't a formula involved, or a mathematical conversion, perhaps just trial and error. Course, this is just a guess, so let the corrections begin....
You have to remember that N -Scale is 1 to 160 ratio, and HO is 1 to 87 ratio. so N-Scale is not quite 1/2 size HO. If it was 1/2 size it would be 1 to 174 ratio. This is where the difference in math comes in. You can take 1/2 HO size to get a "in the ballpark" measurement , for converting HO to N. Don't get too hung up on the minimum radius stuff, use the largest radius curve that you can, always put an easement between an tangent (straight) track and a curve.
I did the math based on the fact that N is 54% of HO. If you take 17 and just double it, it comes out to 34.
I guess it's all a matter of semantics. Back in the days when Armstrong came up with his book, the cars were 40-50 feet. Now we have 62-foot to 89-foot freight cars, which require larger radii to operate (you could use a smoewhat smaller radius, with using transition curves). To quote Bugs Bunny, "I don't ask questions- I just have fun!"
I try to stay above 22" radius in my N scale layout which is 290' ((22/12) * 160) radius in real life. It looks real nice with the 89' flats and SD-90's
As I understand it, with n-scale today you would be better-off building directly off of an HO plan using n-sacle track-work and no change in the deminions (except track centers).
Who said we rivet count here on TB? Precisely! My experience with HO over the years and the extreme tight curves that 15", 18" and even 22" radius curves brings to HO, was disappointing, to say the least. I was disastisfied with the performance of my trains and the appearance as the trains negotiated the curves. It looked like they were wedging themselves around the curves. When I tried to push the curves out... I simply didn't have the room. Then N Scale came along and it was easy to make the transition. Useing HO's dimensions I could build the layout I always wanted. Wow! To this day the concept works. It was now possible to have the wide curves and the potential for, "Twice the Layout". My first experiment with N Scale taught me much. Atlas flex track came along and I found I could custom make curves and suddenly Armstrong's advice of 17" radius curves made perfect sense. Anything larger was a bonus and made even better sense. It's true N scale is not 1/2 HO. However, it comes close and a basic rule of thumb would be correct to say 1/2 HO. You'd have to be nit picking to make a bigger issue out of it. Awww heck it wouldn't be any fun if we didn't picker-nick! Rivet count, bolt pluck, count chain links or dime and nickel ourselves to death. Grin! Still.... keep the math in mind and have fun!.
I suspect John Armstrong knew the math wasn't precise, and picked his numbers after some consideration of usage. I use 18 inch minimums, with some curves far broader. If I ever start anew, I will definitely go with at least 24 inches, and probably 30.
The difference is the same as why an ant can pick up and carry several times it's body weight. At 15", trains are very limited in length. Long trains tip over, you need a lot of power on a hill and every single irregularity causes a derailment. Physics, which in the old days was bought at the drug store and taken internally to make you regular!
Looks like I'll be suffering much of this... Well... since I'm relegated to relatively narrow curves due to spatial limitations... 15" will be the largest radii on my mainline. Sure... I'll use some 19" easements... but most areas on the layout just won't accomodate any more than 15" radii. Most of what Armstrong seems to be alluding to is 'running' reliability... as Tony B has mentioned. Appearance wise... the broader the curves... the more realistic the train will seem as it goes through the scenes where curves are present. Unfortunately (in my case)... since I'm using Kato Unitrack... there are some design limitations in addition to my space limitations. IFFF Kato made some 17" radii... I could have made my layout 4" wider to accomodate that radius and operational and aesthetics would have been better. Using two 19" 15 deg piece easement in each of the semi-circular loops, that will give an 'effective' 15.66" radius. If I use four 19" 15 deg pieces in the curve it will give an effective 16.33" radius. The later would be better but will put trains dangerously to close to the edge. Fortunately, I'm still early into the trackwork to make some changes to 'squeeze-in' that effective 16.33" radius.
One has to remember that one chooses N scale partly because it gives you more space to have more prototypical curves. I would assume that Armstrong felt that with N scale he had a little latitude to increase the radii. 17" doesn't strike me as a broad curve in N scale. (I agree that it's all semantics anyway.). If I were building a new layout, 17" would be about my minimum in areas off the mainline. Prototypical mainline curves, generally over 400', wouldn't be less than 30" in N scale. There's no way I would use the supposed N scale minimum of 9 3/4", which is about the equivalent of the "sharp" curve in HO.
curves I just finished my main line in "N" scale right on my old "HO" table top,the HO had 18" curves on it,I used the center line from the HO to put down the N scale track!So now I'am running 18" curves in N scale and like it so doe's my test engine An Bachmann 4-8-4 that gives me 36" for N-scale curves,It works and looks great!! JIM
Even though I have, and will again on my new layout, have a fleet of primarily 40' cars, I plan to have no less than 18" radius, and prefer 22-24" inches. Boxcab E50
Building over... a HO Layout in N Scale. Now we are talking. I do believe a 17" radius curve is a broad-based curve. Allow me to explain: In other words the 17" radius curve as stated by Armstrong, is the minimum radius he used to illustrate the point at which you can consider the curve to be a broad based curve. My finest broad based curve on my layout is a 22" radius curve or the HO equivalent of (just under) a 44" radius curve. Starting at 17"=HO Equiv., 34" radius curve is the point we move from toy train curves to something more authentic and prototypical. I do agree with Armstrong, as I respect his work. He was one of our pioneers and helped to lay the way for the success's we are having today. My two cents...of course by now you have my four or six cents. I happily take change. Rule #1: Have fun and enjoy. In BigPine's example; He has moved from a tight HO curve of 18"s, installing N scale right over his previous HO layout, to an approximated 36" radius curve HO equivalent.
Depending on your exact definition of "broad', the NMRA recommends either 17 3/8" or 21.5": http://www.nmra.org/standards/rp-11.html Recommended minimum is a surprising 2 3/4"...for streetcars, of course!
I have a minimum 18 inch radius and mostly use 20-22 inches. I used 89 foot flat cars, but I am now removing them as any car over 50 feet begins to appear unrealistic. So, I basically agree with all this, especially building the N scale layout on an HO track plan.
'Broad' curves vs. minimum radius When I was responsible for traffic and industrial development for a short line, I had a copy of the "Manual for Constructing Sidetracks Connecting with CSXT Lines". It specified that CSXT would not operate over sidetracks with a radius of less than 350 feet. In N scale, that's a 26.25 inch radius curve. So, considering that a major Class I wouldn't operate a switch engine over the real equivalent of a 17 inch radius curve, it certainly cannot be considered a "broad curve". That said, 22 inches is the minimum I'm using on my new layout. :cat:
