Minimum Radius

[jward]

i think you are wrong about the minimum radius of an f7 or gp35. western maryland ran them on curves of up to 30 degrees on the line to webster springs, wva. i have personally seen f7s on these curves, and know gp40s were run down there after the gp7s and gp9s were retired.

how sharp is a 30 degree curve? well, in engineering terms, degrees of curvature is calculated by taking a 100 foot long chord off the curve, then measuring the resultant angle between lines drawn from the end of the chord to the center of the curve.

thus , these locomotives ran on curves of less than 200 foot radius. the approximate figure i calculated was 190 feet, which scales out to about 26" radius..... that's alot closer to the 18" radius curves often used in HO. the 45" radius works out to approximately a 17.5 degree curve. that is getting pretty near the minimum curvature for an sd45......

[rogertra]

some model railroads are exceptions, I consider mine exceptional

Now that little quote I like.   

[Atlantic Central]

Jeffery,

You are correct and I made a mistake that lead to a series of calulation errors.

The correct minimum radius for an EMD F unit or GP is 225', not 325', or 23 degrees

Sorry for my error, but that is still not as sharp as you indicated and I have verified the 23 degree figure from several sources.

That is still about 30" radius in HO and would be a very restricted speed curve, not a mainline curve.

And, to deminstrate how quickly this increases with larger locos I also have specs from an EMD E8, right from its operation manual. Minimum radius 274', 21 degrees, or 38" in HO scale.

So even people with curves like mine are just into the range of what the loco will crawl around and we use those as high speed mainline curves.

Point remains, most of our curves are VERY compressed. I understand those who feel they have no other choice, but why do they feel "offended" by those who choose differently or suggest to others that sharp curves should be avoided if possible?

Sheldon

[jward]

keep in mind that the figures you are using are from the builder in all probability. railroads could, and did, run them on sharper curves than the builders recommended. operation on 30 degree curves required the removal of footboards from the units involved. to see what a 4 unit set looked like on a 30 degree curve, look up the book "the western maryland railway in the diesel era" by stephen j salomon and william e hopkins. on page 123 is a photo of a 4 unit set of f7s descending the curve in 1971. my dad and i hiked into this same curve to catch another train in about 1980. note that curves this sharp had guardrails on the inner rail.

[Atlantic Central]

Jeffery,

I understand and agree, also most prototype curves are actually eliptical or parabolic and are only at their sharpest "degree" for a very short distance.

This too has a large effect in allowing equipment to negotiate curves "sharper" than the manufacturers rating.

I actually use such eliptical curves on my model curves where I can and all my curves have easments as well.

Popular OPINION still remains, anything 70-80 scale feet long looks silly on a 18" radius curve, or even a 22" radius curve for that matter. And it does not start to look like a "model" until 30" or larger.

Sheldon

[jward]

you are correct there. i wouldn't recommend cars longer than 50' on 18" curves, for operational reasons as much as aesthetic. if i had the room i'd probably go with 24" curves and up, and limit my use of 85' cars. 30" and above are a pipe dream for me.

the photo of the f7s i mentioned has them pulling 40' and 34' hoppers. i've never seen anything longer than a 50' gondola on this line. but they do look alot like they are on an 18" radius curve.....

[RAM]

 I bet that the Western Maryland ran about 10 mph on those 30 degrees curves. Not like the modeler who want to ran 85 mph.

[jward]

you are correct about 10mph. and the flange squeal even with 40 foot cars was deafening.