Prototype Minimum Radius Equivalent in N Scale?

[highway70]

 From         http://trn.trains.com/en/Railroad%20Reference/ABCs%20of%20Railroading/2006/05/Grades%20and%20curves.aspx


"Curves of 1 or 2 degrees are the most common on mainline railroads; the sharpest curve a common four-axle diesel can take is about 20 degrees when coupled to other rolling stock, more than 40 degrees when by itself. Mountainous territory, however, generally dictates curves of 5 to 10 degrees, or even sharper. Branch lines and minor spurs may have an even greater number of sharper curves."

This link is to a chart that shows degree of curvature, prototype radius and equivalent  HO radius.  Multiply HO radius by 0.54 for approximate equivalent N scale radius.

http://www.trainweb.org/freemoslo/Modules/Tips-and-Techniques/degrees_of_curve_to_radius.htm

[robert3985]

Prototype Big Boys were designed to take a 20 deg. curve.  My mainline minimum radius is 24" with most being larger than that.  A 20 deg. curve in N-scale comes out to a 21.6" radius, which means that my curves, if scaled up, would allow a prototype Big Boy to negotiate them.

The UP loco that was the hardest on the rails was the "Union Pacific Type", the UP 4-12-2, which had the longest wheelbase of any steam engine in North America.  Even with "Lateral Motion Devices" on the 1st and 6th driver axles they were limited to 8 deg. curves minimum.  They wouldn't run on my layout since that translates to a 53.76" radius.

Just for $hits and giggles, here's a comparo of the real Echo Curve, and my echo curve.

Photo 1: The Real Deal, with the 3985 accelerating upgrade through Echo Canyon toward Evanston:


I won't be running any of Jason's 4-12-2's, but I hope to be running at least two of his TTT 2-10-2's on this very curve as rear train helpers.  This is my dream layout, built a module at a time...and a 24" minimum radius has worked out well, even though I always attempt to run bigger radii than the minimum and sometimes I actually succeed! 

Photo 2: My Model...just track and unfinished pink foam cliffs:

[learmoia]

Comment Removed.

[Baronjutter]

When I was measuring a bunch of curves in some industrial areas I found many that actually worked out to about 10-12" in N scale.

[randgust]

One of the more interesting minimum-radius quirks I ever got called in on was trying to determine why a certain (real) steam locomotive consistently derailed its trailing truck on one particular wye on one particular railroad.  It had effectively shut down three excursions, despite rebuilding the track, checking the gauge, etc.  It had derailed on three different legs of the wye at different times.

Some real vintage paperwork digging later - in ancient clearance diagrams dating to 1915 - the locomotive was designed to be OK on a 14-degree curve running FORWARD, but a 12-degree curve in REVERSE, right on the erecting shop clearance diagram, and sure enough, it was a 14-degree curve on the wye, so whatever curve they had derailed on in backing it worked just fine heading into it, but as soon as they went backwards, on the ground she went.   Apparently it was the angle of attack on the rear-truck flanges that allowed it to climb the railhead, as it sure did, only in reverse.  That's the only time I've ever seen prototype equipment with different minimum radius listed specific to direction.

[nkalanaga]

Many interurban and industrial lines use radius rather than degrees, often because they can lay the curve out with a center and "string", the way modelers do.  The mainline curves are far to big for that, and are plotted in sections, by "taking offsets" with a transit, so it's easier to define the curve by degrees.  Also, the mainline curves are seldom uniform, with the actual radius varying from point to point in the curve, and almost always include spiral easements at the ends.  The degree measurement is the sharpest section, similar to the "ruling grade", not necessarily the entire curve.

[Kisatchie]

This has been a very interesting thread. I'm glad I asked the question.


Hmm... Kiz asked a
question...?

[randgust]

The 'worst railroad' I've ever personally been on for both curves and grades in combination is the Webster Springs (WV) branch of the Western Maryland, from Elkins to Spruce is some of the worst of it.   This line is still operated as the tourist West Virginia Central.

When we started working with the state on it, the track chart just stunned me; my track guy brought to my attention the following:

"20 miles of track with 20 curves over 20 degrees; one curve that is shown as 33 degrees, and all on a prevailing 2% grade".....

Remember this entire line was built as a logging railroad and later purchased by the WM to get coal out.   It also features a curved tunnel with a 10-degree curve just east of Elkins.

That 33, or 30 (depends who you talk to) is High Falls Curve on the WM is so sharp we derailed a Chevy Suburban hirail truck on it, the hirail wheels stayed on the railhead and the tires fell down to the inside.   I think it works out to about 22" radius (11" in N) or so.   They actually manage to get 85' cars around it, with some modifications.

http://www.railpictures.net/photo/437627/

[trainforfun]

An old surveyor of Canadian National once gave me this old trick to find the degree of curvature on the real thing :

> you elongate in straight line ( chord ) a tape measure of 66 feet along the curve rail.
> measure the distance in "INCHES" at 33 feet between the tape and the rail

If it's 5 inches than the degree of curvature is close to 5 degrees .

It's not pin point acurate but good enough .