Large Scale Central

Curved tunnel Side Clearance for larger engines

Track and Trestles
#1

I’m in process of building a tunnel with an increasing radius curve. there is one 6" strretch that the side clearance from outside rail to side wall drops to 2.7125".

While I don’t have plans to run heavyweights or modern length freight cars I would like to be able to run some of the larger steam profile engines like the 3 truck shay, a J3 Hudson, or Unitah mallet.

I have not found a difinitive resource that outlines curve overhangs and limitations. Any sources? or experience?

thanks in advance for input…

mark

#2

Not really. It’s always been trial and error…with a fair amount of error…:confused: The thing to do is set up a mockup of the curve and run the locomotive through the curve to see what the clearance is. On steam locomotives watch the cab. That is what usually gets me for clearance on curves. Straight aways is usually the cylinders that like to clear things out like bridge abutments.

Unless your curve is a really wide radius I would say that no American outline road steam locomotive would clear that tight of a measurement.

#3

From empirical data:

3.5 inches from track centerline will give clearance on the outside of the curve for a mallet, aristo hw passengers, USAT streamliners, and the USAT container cars.

The trick is the inside of the curve, you need about 4.5 inches.

This is on 10 foot diameter curves.

I would mock it up on your curves and measure as Warren recommended.

Regards, Greg

#4

Thanks for the input—

Greg – Given the centerline discussion I believe the clearance to outside wall with 332 rail is going to be over 3.5 inches. The 2.7125 from the out side of the rail plus an inch more or less to center.

Warren – Inside clearances are all above 3.5 inches from center, but if I need more, again given the discussion above how much more?

Mark

#5

The easiest way to figure this all out is to take a board the size of the piece of equipment that you are questioning, place some trucks on it as close to where they are on the desired equipment and run it through the curve and see what happens. With steam locomotives, the thing to watch on the outside is the cab roof overhang. That can swing out quite a ways and clip a lot of things that get in it’s way. On the inside it’s the middle of the car that rubs. Because of the way they ride the rails, locomotives are not as prone to inside problems like passenger cars. Again the board with trucks is the most sure fire way to figure it out.

#6

If you’re really keen, check out http://www.geocities.com/budb3/arts/tech/curv.html. The examples use HO, not G, but the mathematics will work with both.

That said, empirical data is always preferable to theory. Warren and Greg are giving you good advice.

#7

Warren / Dave – thanks for the input. I’ll try the website and the more practical board on the track approach.

mark

#8

If you ever plan to own, in the future, any Accucraft K’s–make that board 6.5" wide.
I don’t own any “F” scale stuff right now (waiting on a rich uncle or Lottery). But I am building my layout: curves, bridges, etc to accommodate such locos. Or maybe a friend would like to run theirs on the layout.
Something to think about…:slight_smile: :slight_smile:
jb

Dave,
Link doesn’t work.
jb