24 vs 26-inch minimum radius

[jlsmith7017]

Would anybody care to share their opinion about the benefits of using a 26-inch minimum radius over a 24-inch? I'm trying to develop a track plan based on the Tehachapi region to fit in an 11X21-foot room (double-decked) with no duckunders (if I can figure out how to post it for viewing, I will). I can get it to work (I think) using a 24-inch minimum radius and maintain 24-inch minimum aisleways. Going to a 26-inch mimimum radius narrows the aisles to about 21-inches and compreses the space for scenery somewhat. I mostly run F7s, GP7s, PAs with Athern (shortened) passenger cars. However, I have my eye on BLI's cab-forward. So, is it worth going to a 26-inch minimum radius?
Thanks,
- Jeff

[selector]

You don't have to, but the visual appeal, if realism is a fairly high priority for you, will be enhanced as you raise the radius. It is just a general rule, but you have to make concessions to your OVERALL plan. If I really thought I would be squeezed for structure and topographical features due to 26", I'd go with the 24".

Just so you get my drift, I am currently stuck with 22". Everything works very well on those curves, but the tender on my BLI Hudson is markedly turned away from the loco as it rounds those 22" radii. It just doesn't look very good, I have to admit. Next time, my minimum will be 26", and I will take a very hard look at using 30" on the main.

[rrinker]

I would pick the 24" curves over the 21" aisles. Even a 24" aisle is kind of tight. Of course, that doesn't mean you can't use bigger curves anywhere it would not squeeze the aisleway or scenery.
If you decide you want to start running full length 80' and 85' passenger cars, 24" won't cut it. But 26" won't be much better.

--Randy

[Adelie]

Go with the larger aisle in this case. Randy's right, even a 24" aisle is going to be snug.

For performance, consider using an easement on the 24" curve rather than going to 26". Easing the 24" curves will cost you about an inch of extra width for both sides, rather than 2" for each side.

[IRONROOSTER]

Here's the NMRA's page on recommended radii for different types of equipment http://www.nmra.org/standards/rp-11.html
BLI says their cab forward will run on 22" radius. Probably with quite an overhang and appearance will suffer but the 2" won't change either of those. Since you'll mostly run 40-50' diesels I'd go with the 24" radius and keep the aisles wider.
Enjoy
Paul

[Anonymous]

24 is the lowest I would go. 26 is better. I run big stuff. But have some small trains that are good for 22" radius.

Try to find room to "reach" into that area of the aisles from a different direction.

[GMTRacing]

With a small room (12x12) are you better off using the shortened passanger cars, since by my calculations you end up with virtually no straight, or is there a way to bodge a decent look ? At least one turn can be hidden in a tunnel, but with full size cars, what radius looks prototypical?

[nfmisso]

Jeff;

Spend some more time in the design phase, and try to get to 30" minimum radius. You will not regret it.

[nobullchitbids]

I suspect that there are other, more complex solutions:

1) Does the larger radius require that the ENTIRE aisle be reduced to 21 inches? I would suspect not, and if we are talking about just a bottleneck, I have seen such areas compressed to 18 inches (enough to get by). But keep such areas short.

2) I have seen Tehachapi, and at least a portion of the helix above the bridge is hidden by a tunnel. One way to get larger radii outside the tunnel is to install shorter radii inside it. Just make certain your "mountain" is sufficiently hollow to allow for clearance.

3) Sometimes, longer equipment can be run through a compound curve called a cycloid. In effect, the idea here is to create one giant easement through the curve, so that the sharpest radius is in the part of the curve where the curve naturally will be viewed from the inside. The bad looks come primarily in those areas where the curve is viewed from the outside; by cycloiding the curve, it is possible to get some larger radii in the outside-viewing areas in exchange for some sharper radii in the inside-viewing areas. The math for laying out a cycloid is a little hairy, and a modeler would not be able to use commercially curved track (but flex track is fine). The results well could be worth it, depending on exactly what you will have when done, and what you may find as an added bonus is that the longer equipment actually performs better -- it is the sudden jerk into a curve which tends to be the troublemaker here.

Formulas for laying out cycloids may be found in any railroad engineering book.

[Anonymous]

I have a similar problem, I am also endeavouring to build the Tehachapi, (out of a book and photos, not been to USA never mind Tehachapi. But would have to agree with nfmisso, a go for further planning and try to achieve 30" rads.
I decided to slightly modify the approaches from both sides using slightly tighter rads down to 26 & 28" and the loop 32".
I trialed by just lying track on a flat area with radii’s in place and run some of my rolling stock around to get the visual effect. I have Cab Forwards also get around. The loop is probably going to be the main focal point, and sharp curves will spoil your effect and may also possibly give you no end of trouble in running.
Suggestion spend a little more time try and get the larger curves where ever possible, I have minimum aisle width in some areas down to 20" just enough to get through to the main cab areas, I also use DDC.

[joebraun]

Just as a general rule, I feel that the larger the radius, the better -- assuming all other important factors are considered. Long ago I opted away from a winding peninsula design that would have required 30" radii to an open quasi-spaghetti bowl with 48" to 110" radii. What I have sacrificed in visual complexity has been more than compensated for by the increased realism of seeing trains flow through almost prototypical curves. Go for the 26"!

[jlsmith7017]

Thanks for all your thoughts. Seems like the consensus is to go bigger yet (been trying to get to 30" but would have to sacrifice Bakersfield) or, if not, 26" doesn't get much over 24" (given my late '50s era equipment). No, the entire aisle would not be 24" (or 21"), just the pinch points. The main aisle should be about 30" (still not great, but better). And, yes, I'm planning to use easements.

[Anonymous]

I ran into similar discusions in my head when designing my layout. Some suggestions that'll help reduce the migranes down the road.

1. Simplify the design. If you have to squeeze the design to make it work on paper, it won't work. When the work hits the table it seems to always take more room thatn shown on paper to get it done.

2. Remember, an inclined curve is harder to pull up than a straight incline, and it's dependant on the curve radius. If you're going to climb on a curve, straighten it out and level it off some.

3. Ease the curves. It'll cost you 1" in curve radius, but it'll be MUCH easier on the equipment when it runs into the curve, and it'll look better. You can actually run tighter curves that are eased than you could otherwise.

4. Leave room for scenery in your plans.

5. Leave room for an expanding waist line!

Good luck!!!

Mark in Utah

[nobullchitbids]

For those building Tehachapi from photos, do remember that the portion of the line through much of the helix is double-tracked -- if the outside portion modeled is only 30-inch radius, the inside radius probably would have to be no more than 27.667-inch radius. To the extent modelers can opt for larger radii, the inner track gets closer to a two-inch separation from the outer, which allows for use of commercial products provided the option of cyclic curves is not used.

Do keep clearances in mind.

The complete loop, itself, is very complicated: It is approached from below via a snaking "S" curve itself needed to gain elevation to the loop; the top of the loop is not too complex (most modelers "end" the loop in the tunnel and free-base it from there, but if you do the whole thing, there is another "S" curve to get the line over the top of the mountain).

The prototype uses special rail through this section -- it is softer steel designed to allow locomotives to increase their grip going up what I recall was 2.8 per cent -- not as steep as the top of Cajon but still pretty steep for any Class-1 railroad. This rail wears out quickly; therefore, proper modeling will have stocks of replacement rail positioned along the right-of-way.

The warning about lifting weight through a helix should be heeded: Model cars are far more topheavy than their prototypical counterparts, and pulling them up a helix has a tendency to tip them into the center. This phenomenon is accentuated by tighter radii, making for the worst of situations for the modeler with a small space. Do NOT super-elevate your curves! You would simply have to rip out the helix and rebuild it.

[dinwitty]

running a South Shore little Joe its minimum radius is 26".
Easements keep the cars from overhanging the couplers too much going into the curve, easing into an 18" radius can work, its the snap track sudden curve thats a problem with large cars and equipment.
No, I don't reccomend 18" for large equipment, for most standard HO stuff 24" is a reccomended radius for anything to run with exceptions.
But of course compromise, do a 25 inch radius....

I am currently planning a layout and I have freight switching going down to 15", but the mainline always larger, 22" in I can keep it, I have not much room either but where I may run larger engines the radius is going to be designed best for the loco's equipment that will run on it.
I wont be doing tehachapi, but theres going to be plenty of looping tracks going over and under.
(Trying to stay away from spaghetti bowl and look right)

But I really like 36" radius..but cannot do it :mad:

[Tilden]

And some would say sacrificing Bakersfield is a Good idea. [:D]

[dinwitty]

QUOTE: Originally posted by Tilden

And some would say sacrificing Bakersfield is a Good idea. [:D]

lots of Model RR's used the Tehachapi trick, its a space saver, it just wasn't Tehachapi... :rimshot:

[bogp40]

QUOTE: Originally posted by GMTRacing

With a small room (12x12) are you better off using the shortened passanger cars, since by my calculations you end up with virtually no straight, or is there a way to bodge a decent look ? At least one turn can be hidden in a tunnel, but with full size cars, what radius looks prototypical?

Starts to look good at 36", but what would look prototypical, You would need to knock out all the walls in your house. Real scaled radius, maybe min of 15'. But really, 24" is the bare min for 85' pass 30" works good but equipment always looks better the largest you can use.
Bob K.