Min. Radius Hidden Turnback Loops?

Min. Radius Hidden Turnback Loops?

Postby ConnRiver » Fri Sep 06, 2013 10:33 am

Considering an E-unit consist and 89-foot cars, off the top of your head can anyone here state a "reasonable" radius for a hidden turn back loop -- that is, efficient operation (no derailments) without caring about appearance? Just doing a bit of off-the-cuff planning. Will look closely at it when planning gets serious.

Thanks much,

Brian Chapman
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Re: Min. Radius Hidden Turnback Loops?

Postby areibel » Fri Sep 06, 2013 4:16 pm

Hi Brian,
When I finally do build a permanent layout, I was planning a minimum 18" radius in TT, with 15" being an absolute last resort if 18" just wasn't possible. TT tries to claim some fame for being able to run 12" (roughly 300MM), but even with some of the more modern existing equipment I think there are just too many chances for wonky operation. The old TT stuff would do it (and it looks pretty comical doing it), but I think that's just because the way the trucks were built- they had enough slop that allowed a side to side shift of the axles and it eases the transition.
My 2 cents worth!
Al
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Re: Min. Radius Hidden Turnback Loops?

Postby Arseny » Fri Sep 06, 2013 4:40 pm

European 2-axle TT-cars and locomotives can take very sharp radiuses.

00413.jpg
02807.jpg


Tillig's minimum radius (R0) is 267 mm.

A lot of european locomotives can take 310-mm radius easily (for example, Roco's BR44 steam locomotive, 2-10-0 - !!!).

So, I think, you must test your cars...
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Re: Min. Radius Hidden Turnback Loops?

Postby AstroGoat760 » Fri Sep 06, 2013 4:54 pm

I agree with Al, I would recommend 18" for E-units and full length passenger cars, less of a chance of derailment that way. 20-24" would be better, though.
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Re: Min. Radius Hidden Turnback Loops?

Postby ConducTTor » Fri Sep 06, 2013 8:37 pm

14" minimum.
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Re: Min. Radius Hidden Turnback Loops?

Postby AstroGoat760 » Fri Sep 06, 2013 10:41 pm

The thing to keep in mind, especially with passenger cars and longer locomotives (such as E-Units, and PAs/PBs), is that the couplers and draft gear have to have plenty of room to avoid binding. This brings in the entire problem of balancing prototypical looks with operational concerns.

That said, I have a few HP passenger cars that can run 310mm (12.2407") curves, with the couplers/draft gear adjusted to allow the cars to negotiate the curves, and they look ridiculous making those curves, almost like looking at a scaled down Lionel train.

The big thing to keep in mind is that it is a good idea to look ahead when you plan your layout, and see if there is anything that you might want later to run on the layout that may need a wider curve (such as a larger steam engine, or a DDA40X), as it is easier to build larger radii curves than it is to rebuild a layout to accommodate said larger curves.
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Re: Min. Radius Hidden Turnback Loops?

Postby sd80mac » Sat Sep 07, 2013 2:59 am

Here's a quick radius equivalency reference:

HO__TT
18" = 13"
22" = 16"
24" = 17.5"
26" = 18.85"
28" = 20.3"
30" = 21.75"

Also, an 85' passenger car is 8.5" long.

Given these numbers, a 4' x 8' TT- scale layout would be awesome! The layout would easily be long enough to employ #6 and #8 turnouts, and would contain moderate to broad curves. Man, this really is the "ideal" scale!

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Re: Min. Radius Hidden Turnback Loops?

Postby ConnRiver » Sun Sep 08, 2013 9:46 am

Thanks for the help, guys.

The visible section of the layout will use broad curves, the minimum I asked about is for hidden turn back loops -- to save space yet preserve reliability. Right now I'm planning 18" radii (HO 24"+) but will look at 22" radii (HO 30"+).

And, I should have posted my question in the Layout/Track section. Sorry.

I am going to build a Sipping & Switching Society "honeycomb" module to test weight savings over the modules I have already built -- mine are heavy and cumbersome, I'd like to do better. I'll post about this in the Layout/Track section.

Brian C.
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Re: Min. Radius Hidden Turnback Loops?

Postby railtwister » Sun Sep 08, 2013 3:03 pm

I seem to recall a rule of thumb formula concerning reliable coupling on a curve that the radius should equal the car or loco length times five. As stated this was for coupling on a curve, not just how sharp of a radius a piece of equipment could squeek around.

For the most part, curve radii are like checking accounts, bigger is better!

Bill in FtL
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