It is a shame that there is no way of searching within the discussion group. I'm certain this must have been addressed many time before.
My HO scale layout, on which I run a fair number of 85' cars, has minimum mainline radii of 36". But I'm building a hidden section of track and it would help to gain some inches on a helix. So the question is: How tight can curves be before derailments (or other problems) begin to appear?
Thanks,
The GN Goatkid
Cheers, the Bear.
"One difference between pessimists and optimists is that while pessimists are more often right, optimists have far more fun."
The curve radius rule of thumb - link posted by cuyama in the thread linked by jabear is probably as good a guideline as you will find.
http://www.ldsig.org/ldsigwiki/hints-tips/curve_radius_rule-of-thumb
You need reliable operation on hidden track. Reliability is often harder to achieve on a helix because of the combination of long grade and curvature.
Based on the rule of thumb 36" (your current main line radius) is probably as sharp as you want to go.
cuyama is a professional layout designer with many sucessful projects. His web site http://www.layoutvision.com/ has a lot of useful information as do his many posts on these Forums.
I tried to sell my two cents worth, but no one would give me a plug nickel for it.
I don't have a leg to stand on.
There is a search box about 1/2 down on the right side of the page. It lacks the ability to search title vs body of the post or date range so it works well only for very recent threads or very unique threads.
The title of your thread is exactly what it should be so it attracts people who know the answer and is searchable later. Helix problem, passenger car question or what do I do? are not helpful titles.
Welcome to the forum.
Henry
COB Potomac & Northern
Shenandoah Valley
GN goat kid My HO scale layout, on which I run a fair number of 85' cars, has minimum mainline radii of 36". But I'm building a hidden section of track and it would help to gain some inches on a helix. So the question is: How tight can curves be before derailments (or other problems) begin to appear?
For the hidden section of track, in my experience, a 30" radius curve would suffice. When I run 85' passenger cars on my double mainline, consisting of 30" and 32" radius curves, I have no problems with derailments or uncouplings.
Rich
Alton Junction
If the hidden track is going to be in a helix, the grade (and additional effective grade caused by friction through the curve) is higher the tighter the radius. For this reason, many experienced modelers would opt to stay with the 36” minimum in the helix for full-length passenger cars.
A recent HO custom project of mine dropped to 30” in the helix and the resulting effective grade is pretty stout. If there had been room, I would have preferred 32” or broader in the helix.
If the effective grade in the helix is much steeper than anywhere else on the layout, it can create operational challenges.
Good luck with your layout.
Byron
Layout Design GalleryLayout Design Special Interest Group
There is no 'best' minimum radius for hidden track. There are too many variables. All of the below refers to my 1:80 scale layout, but the trackwork conforms to NMRA HO standards.
350mm (14">) radius - including a 470 degree (1+ turn) helix on a 3.51% uncompensated grade. Short or extremely flexible rolling stock, very short trains, low (15 scale mph) speed. Anything bigger than a 40 foot AAR boxcar is embargoed from the Tomikawa Tani Tetsudo (Literally Wealth River Valley Iron Road) unless it's articulated and can bend in the middle. The standard gauge version of the Mantua Logger 2-6-6-2T can handle it. The other locos are teakettle tanks.
550mm (21.65") radius. Low speed back-in radius only used in Down local train staging. Have to avoid something very short coupled to something long to avoid the latter being forced over the rails due to coupler swing limits. Most of my rolling stock can handle this, but a few of my stiffest juice jacks can't. Neither can my 'blue train' passenger cars - but they'll never have reason to be there.
610mm (24") radius. My 'standard' minimum. Rolling stock maximum length 250mm (9.8") over sills - only a few passenger cars and even fewer freight cars. All of my locomotives have been adjusted as necessary to handle this radius. Hidden track includes back-in staging and hidden track backup over a 'hump' with 2% grades in both directions.
Note that all of my curves have spiral easements, and all grade changes incorporate vertical hyperbolic easements as well. Translation - no sudden lurch where curve meets tangent, no vertical kink where the grade changes.
Also note that the geometry is driven by the rolling stock. To get the same results with North American prototypes in HO I would have to add at least 25% to each radius stated above. There are advantages to modeling small locomotives and short cars.
Chuck (Modeling Central Japan in September, 1964 - with tight radii)
GN goat kidMy HO scale layout, on which I run a fair number of 85' cars, has minimum mainline radii of 36". But I'm building a hidden section of track and it would help to gain some inches on a helix. So the question is: How tight can curves be before derailments (or other problems) begin to appear?
Jan 2009 MRH has an article on this exact topic, along with photos. In summary, if you have a solid train of 85' cars, you can probably get away with 2.5x the length in inches as your minimum. About 29.25" radius ((85/87.1)x12x2.5). Throw in 50' cars and you may have issues with the long cars staying on the tracks.
Edit:
The article I referenced tested the LDSIG's recommendations listed above. They added in 2.5x for more mechanical reliability. You can trick an 80' car around a 23" radius (sometimes), I had issues with Walthers heavyweights going around 24" radius.
GN goat kidIt is a shame that there is no way of searching within the discussion group. I'm certain this must have been addressed many time before.
Google came up with 3 or 4 discussions on this and other forums. Also on the right hand side of the page, above the box that says users on line there is a search box called "search the community" (already covered by Henry). I have found it to be not the best, google works better.
Feeble as the MR search engine is, newbies have no trouble at all finding threads that are 10 years old. :-o
Derailments may not be the only issue with the radius of a helix. If you are running steam passenger trains (without a helper district), the bigger issue may be the grades. The tighter helix is shorter so the actual grade is higher (unless you make it an oval shape) and the effective grade is higher due to the empirical 32/R factor. [e.g. a 32 inch radius curve adds 1% to the grade.] Many passenger cars (especially Walthers) don't roll well and need a lot of work in order to get a 10-15 car passenger train to be able to climb a 2% helix. It's not just the cars, will you ever run big brass steam, some of mine need 32" radius curves? I have a 32" radius helix on a 2.2% grade, but it is a helper district.
Grinnell
Thanks Henry,
Great answers.
GN gk
Grinnell,
Excellent points. I'm running 7 brass steam locos, the biggest being a Q1 Santa Fe (2-10-2) or Mikado or Northern. My helicies all a "oval" rather than round to keep the incline as low as possible.
GN Goat Kid
BMMECNYC.... Jan 2009 MRH has an article on this exact topic, along with photos. In summary, if you have a solid train of 85' cars, you can probably get away with 2.5x the length in inches as your minimum. About 29.25" radius ((85/87.1)x12x2.5). Throw in 50' cars and you may have issues with the long cars staying on the tra The article I referenced tested the LDSIG's recommendations listed above. They added in 2.5x for more mechanical reliability. You can trick an 80' car around a 23" radius (sometimes), I had issues with Walthers heavyweights going around 24" radius. [
Jan 2009 MRH has an article on this exact topic, along with photos. In summary, if you have a solid train of 85' cars, you can probably get away with 2.5x the length in inches as your minimum. About 29.25" radius ((85/87.1)x12x2.5). Throw in 50' cars and you may have issues with the long cars staying on the tra
The article I referenced tested the LDSIG's recommendations listed above. They added in 2.5x for more mechanical reliability. You can trick an 80' car around a 23" radius (sometimes), I had issues with Walthers heavyweights going around 24" radius. [
These 2 items caught my attention since I am intending to use 24' mainline radius, and 30" helix.
Brian
My Layout Plan
Interesting new Plan Consideration
I bought a bunch of Kato Unitrack in various radiusses (sp?) and ran experiments. To my pleasent surprise nearly all my equipment runs flawlessly on 22 inch radius curves. My Rivarossi Heavyweights pulled by a pair of Athearn PAs run fine on 28 inch curves.
.
These will be my hidden minimums.
-Kevin
Living the dream.