Radius for Allen Mogul?

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doublereefed
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Radius for Allen Mogul?

Post by doublereefed » Tue Oct 22, 2019 10:24 pm

What's a good minimum radius to use for planning a backyard railroad? Allen Moguls, LE Pacifics? Backyard railroad vs. a club railroad, I'm presuming I could use tighter radii if not trying to accommodate bigger, fancier engines. Not so much physically the minimum, but a good working minimum.

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Harlock
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Re: Radius for Allen Mogul?

Post by Harlock » Tue Oct 22, 2019 10:47 pm

The minimum radius listed on our site for the Allen Mogul is 32 feet. However I wouldn't recommend that for continual mainline use as you'll subject the rail and or the wheels to excess wear depending on the material of track used, not to mention a reduced pulling capacity and more wear on the valve gear due to working harder because of flange binding. For a home railroad with a conventional road engine, 45 ft radius is decent. 35 is very tight. 32 is minimal for a conventional engine like that.

For tight radius railroads we have four smaller wheelbase engines, the Harpur 2-4-0, the yard engine, the Chloe and the Fitchburg Northern.

The Chloe will do very tight curves (20ft) with an adjustment to the rear truck. (mine is modified this way.) The 0-4-0 Yard Engine will handle 25ft with its comparatively bigger drivers, and the 2-4-0 has a 30ft min radius. The Fitch can do 25 ft.

The two important factors are wheel diameter and rigid wheelbase. A larger wheel diameter will result in more contact area for the flange and thus more binding on tighter curves. A long rigid wheelbase can be overcome with generous side to side play, which has to be baked into the build from the get-go. A lot of model locomotives are set up to run curve radii that the prototype scaled down could never do, but you have to build it that way.

In terms of the Allen Engines, the Fitch and the Chloe both have a smaller diameter driver than the others, which gives them better ability out of the gate, combined with their overall smaller size.

Another thing to consider is doing 1.5" scale narrow gauge for 4 3/4" gauge. This is one of the reasons Jim Sabin chose this size for his home railroad, which runs a tight loop around his house plus a point to point spur down a wash area. You can use much tighter track with a fairly comfortable engine size.



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-Mike
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cbrew
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Re: Radius for Allen Mogul?

Post by cbrew » Tue Oct 22, 2019 11:03 pm

my Allen American and Ten Wheeler both would go around a 25 foot radius with not issue. i would suggest steel rail and steel tires to keep wear in check. a blind center driver will help a lot.
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Pontiacguy1
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Re: Radius for Allen Mogul?

Post by Pontiacguy1 » Wed Oct 23, 2019 7:56 am

If you can: Keep everything to 45 foot radius or larger. That's pretty good for a home layout. That way, you should be able to handle MOST 6-coupled steamers, and all diesels including 6-axle versions. You probably won't be able to run most pacifics or hudsons there, but some might can if they've been modified so that the trucks swing more. Also a small Consolidation won't have problems. This way, a lot more people might be able to visit and run on your railroad, and it also saves wear on your own stuff. Once you get down near 30 feet or less, you are really limiting what can reasonably run there, and anything larger and longer will have problems. Once you get down below 25 feet, you are completely restricted to 4-coupled steamers, 4 axle or 2 axle diesels, and geared locomotives. I have run my 0-4-0 at a place with just under 20 foot minimum radius. It was fun, but there were definitely limits, and most people's stuff wouldn't run there. Only the equipment I described above would work, and excessively long cars also wouldn't work on that railroad. I think that a 5' car was about the longest I saw running there, but I'm sure a 6' would have been OK. Once curves get tighter, you have to start worrying about the side-pull for your couplers.

doublereefed
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Re: Radius for Allen Mogul?

Post by doublereefed » Wed Oct 23, 2019 4:47 pm

Many thanks for the input. There's room for 45' so I think I will go with that consensus. When the time comes...

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Harlock
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Re: Radius for Allen Mogul?

Post by Harlock » Wed Oct 23, 2019 5:00 pm

doublereefed wrote:
Wed Oct 23, 2019 4:47 pm
Many thanks for the input. There's room for 45' so I think I will go with that consensus. When the time comes...
That's great. We just built a private railroad for someone with 45 degree radius curvature throughout. He has a very large electric locomotive and it has no issues. Anything up to a consolidation in 1 1/2" scale should be easily fine, bigger and it pays to check to see if it will make it first.
San Lorezo Flume & Lumber Co. #2 - "Felton"
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Harold_V
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Re: Radius for Allen Mogul?

Post by Harold_V » Thu Oct 24, 2019 1:28 am

Harlock wrote:
Wed Oct 23, 2019 5:00 pm
That's great. We just built a private railroad for someone with 45 degree radius curvature throughout.
??
Is that what you really meant to say? Did you mean 45' radii instead?

H
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Glenn Brooks
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Re: Radius for Allen Mogul?

Post by Glenn Brooks » Thu Oct 24, 2019 12:56 pm

Somewhere there is a fairly simple formula to determine minimum radius curvature for locomotives. It involves measuring the fixed distance between centers of first and last drivers and then computing the chord length from those points (and maybe gauge] to determine minimum radius. I found the formula “somewhere” on line whilst researching my backyard layout. Of course now, don’t remember the formula, or where I found it.

Anybody recall the formula? Might be a handy thing to post into our reference area.

Glenn
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rkcarguy
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Re: Radius for Allen Mogul?

Post by rkcarguy » Thu Oct 24, 2019 6:32 pm

I sort of cheated on my calculations. Figure an HO scale model as an example (6 axle diesels needed 22" minimum radius and even then sometimes would lift a wheel on a solder joint). The following math roughly applies.

1/87 scale to 1/8 scale is 10-7/8X.
22" min radius x 10-7/8 = 239-1/4", or 19.93'. So in THEORY, if you simply blew up an HO scale model DIESEL to 1/8th scale, say an SD9, it should barely traverse a 20' radius curve.
The problems show up when we start looking at steam, models would navigate 26"-28" radii, but because the models have fake linkage and tons of side-to-side play in the drivers we can't really compare. I'd say to be safe you'd have to at least double the min radius to 40' and to be able to accommodate the X-8-X steamers the 45' radius is probably a wise choice.

Another interesting fact is that minimum radii are almost half what they are in full scale, in model sizes. A general rule of a 410' min radius on the a full size RR, would be 51' in 1/8th scale. And that is a general minimum for spurs and such, not mainline which is typically over 700'.

Cary Stewart
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Re: Radius for Allen Mogul?

Post by Cary Stewart » Fri Oct 25, 2019 6:21 pm

Long ago at LALS we had a trash siding the came off the track between the Webb yard and the drive way. It also had a air operated experimental switch operation. RRSC brought over their company CP 173 to test if it would navigate that sharp a curve. It did with one small problem. The corners of the tender and cab would interfere. The answer was to lengthen the draw bar a bit and all was well.
Cary

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