Hi all!
I have a noob question. I have a return loop that is double main lines. The inside is about 21 inch radius.
I want to hide at least half of it in a tunnel. My problem is I can’t afford to buy some of the locos that I will have down the road. So the tunnel I build now may not work when I add an SD-40 or a steam locomotive.
Are steam locos any higher than say a GP40? I worry about swing out hitting the walls or something hitting the top.
If I had a NMRA track gauge would this be a: “if it fits anything will” kind of thing?
Thanks
21" is a bit sharp but never mind.
The real RR have standard Loading Gauges and Standard Structure Gauges. Anything that fits within the first will go through the second.
The NMRA does bot a loading gauge tool and a page or two of guides as to what will fit where. (search for NMRA and gauges). They also give a guide on track centres that will enable things to miss each other… you don’t just have to miss the tunnel but stock on the other track.
What you have to look out for is overhang/outswing at the ends and undercut in the middle.
The “cheap and nasty” system I use is qan 89’ boxcar with pencils strapped to each corner and the middle. Roll the car gently round the curve and it should give you a clearance line inside and outside the track. I don’t think that there is anything much more awkward than an 89’ car.
Then again… how much does the tunnel need to have walls each side right through the tunnel length? From an appearance point of view you do want tunnel lining as far as normal viewing allows sight into the tunnel but beyound that it isn’t needed. I hope your tunnel will have access for maintenance…
Hope this helps.
[:P]
Quick and dirty clearance checkers:
Get a scale drawing of your favorite ‘long-nose’ locomotive, and notice just how long the ‘swinging arm’ is. For an honestly-modeled semi-articulated, the answer is from the smokebox door to the center of the rear engine. Now, take a short flat car and mount something on it as wide as the locomotive’s boiler over walkways, with the overhang adjusted so the swing arm length falls 1/2 the wheelbase of the locomotive’s rear drivers toward the center of the flat car from the truck pivot. Roll the flat car around the curve, and note where the outer front corner of the overhanging item tracks - probably well beyond the ends of the ties.
For inside clearance, if you don’t own a humongubox or long passenger car, simulate them by screwing a pair of trucks to a common wooden ruler. When you roll that around your curve it will give you a good idea of the inside clearance needed.
The tallest steam locomotive I found in Steam Locomotives is 16 feet 3 inches from rails to the top of the stack. In HO, that’s a tad under 2 1/4 inches. The NMRA gauge gives 3 inches of rail-to obstruction clearance.
Note that, if your curve is superelevated, that will shift the inner clearance line inward.
I performed similar tests with my own rolling stock (not simulations, since I already own the neessary items) to establish my clearances. Since I model a different set of prototypes in a different scale, my numbers wouldn’t be very helpful.
Chuck (Modeling Central Japan in September, 1964 - in HOj, aka 1:80 scale)