Considerations...

Nick--

There are several plans within the MR data base that might be used as ideas on what can be or has been done.  Some are portions of larger RRs.  However, one thing caught my eye with your general thoughts on this.  The turn-back curves at each end will take a lot more space than you think.  Even at 24 in radii, you will need to devote 5 feet or so of width to each one.  For a shelf RR it will mean the end blobs will have to bulge out from the wall, or the entire RR will have to be offset from the wall. 

Charles

Shelf layout along one wall

One layout that immediately popped into my head when I read your post was Andreas Keller's CN Fergus Subdivision. It's a three deck shelf layout along one wall, with a hidden helix connecting the different levels. Although with a different theme than yours, maybe you can get some ideas?

Svein

Thanks for the comments.  The

Thanks for the comments.  The Fergus Subdivision looks like a good example to reference.

As far as the curves/helix, I realize that this will take up a lot of space.  The size of the room is 30ft by 10-20ft depending on the spot, so it is large enough to accommodate that.  Just don't want the layout to get unmanageably large and interfere with other things taking place in the room.

I've heard a lot of different opinions on radii in HO Scale, particularly with regards to helixes.

Ideally, I'd like to get the curves/helix into a 4x4ish square, which would mean 22inch outer and 20inch inner radius curves - is this too tight?  I don't have much of an interest in running steam, but I will be running large locos such as the GTEL Turbines.  I have the Athearn Turbine models, and they seem to be articulated enough to take a fairly tight turn, so the question really is how will the cars handle it?  The area where the turns are made will likely be hidden, so looks isn't an issue but reliability certainly is.

Appreciate the input and look forward to sharing more with you all as this progresses.

No Way

Way too tight. Ask Joe F. about his experience with a 24" radius helix. The story does not have a happy ending. Keep in mind the trains are climbing a steep hill while negotiating the turn. This become especially problematic with smaller radii.

Min recommend Helix radius is 30 inches for HO

I done the math on this a few time and 30" really is the best minimum radius.  30" give you a track length of 188.5" (circumference)  per turn.  A 188.5" run per 4" of climb is about a 2.12% grade.  Although a 2.12% grade does not sound too bad once you compensate for the drag of the curve, it will be like going up a 3.2% grade. 

The compensation factor for the curve has been researched by John Allen years ago and works out to about:   Grade Compensation Factor = 32 divided by Radius in inches.  Therefore a 30" radius is comparable to a 1.067% grade.

If you wanted to add an second track inside the radius of 30" the math would work out to be a 27.5" radius with a track length of 172.8".  This would give you a grade of 2.32% to make a 4" climb per turn and the radius would give you a comparable grade of 1.16% for a total grade of 3.48%.  For me this would be pushing the limit for too steep.

Hope this helps  

Art
 

Okay. So would a 6' square

20" radius helix climbing 4" per turn would equal a 4.78% grade

I did the math on a 20" radius helix. The run would be 125.66" per turn. To climb 4" per turn would require a grade of 3.18%.  The compensation factor for the curve would be 32/20 = 1.6% grade.  Your total grade equivalent would be 4.78%.

r/

Art

MRH Radius Answers

Refer to this article in MRH for everything you need to know about track radius:  http://model-railroad-hobbyist.com/mrh2009-01/curve_insights

There is no hard and fast rule for helix radius. Larger radius = greater reliability and longer trains. Make your radius as large as space permits. Accept the fact that whatever radius you end up with will have a maximum train length that a single locomotive can pull up the hill. There are too many variables to give exact answers. Some locos pull better than others, some cars roll easier than others, etc. Most people shoot for 30" radius or larger.

MRH Radius Answers - great article

Alan hit the nail on the head in the above comment, especially concerning the number of variables involved.  The article referenced really provides detailed example of radius effects.  In reference to the article, I personally lean towards a ration of 4, meaning a 40 foot box car would require a min of 22" to look right.

One comment I would like to add is concerning your helix.  Your comments indicate that you plan to use 2" spacing between your tracks on the helix. I recommend using 2.5" spacing on the helix (which is why my example above is 30" and 27.5").  If you want to go less than 2.5" space I recommend you mock it up and do some testing before committing to construction.

Also visit Alan's website.  IMHO he has set the standard for layout planning.

r/

Art   

" is 22" and 20" radii okay for a flat turnabout "

    If you don't need to pull long trains around the curve you can get by with pretty sharp curves.When I was a kid I had an HO layout with 18 inch radius and it worked but now it would look kinda funny to me. I'm using 24 inch curves on my new N scale layout and they still look sharp ........DaveBranum

" is 22" and 20" radii okay for a flat turnabout "

yes, in N Scale

Curves

15 and 18 inch radius curves come with train sets in HO scale. They would be suitable for industrial track where only a few cars will be moved. 22 and 24 inch curves are about as tight as you can get short trains of 50 to 60 foot cars to run around reliably. 30 to 36 inch curves will let most locomotives and full length cars run reliably. If your rolling stock is good and your throttle hand as well it is possible to easily run 50 car trains both forward and backward through these radius curves at speed and up and down grades. Modern locos of good quality can handle grades up to 4% provided you have done a good job on wheels, couplers, weight, and your track. If you limit your grades to about 2% you will be happier. In addition to your train where one track passes over another you may find the need to put your hand inside to handle a problem with rolling stock or maintenance. 4 inches rail head to rail head will be tight but I think the minimum I would use. Many folks choose radius even broader than this, Bill Darnby of the Maume Route fame uses 42 inch minimums on his layout and runs 8 coupled steam.

An all diesel layout could likely get by with 30 inch curves on the mainline however if you could make them bigger you would be happy with the result. I am looking at a couple of different designs for different spaces I have in my future for a layout and would go no smaller than 30 inches on the main.

To give you an idea of a 4% grade in the real world there is one that I believe is 4% and that is Saluda Grade in the  Carolinas. It requires special operations and is a real headache for the prototype. You may actually be able to find videos on the net of trains running on the grade I have seen some.

Hope this helps.

Rob

Floorplan

Here is a floorplan of the basement for reference.  I'll be doing some designs later this week hopefully and will post them.

/sites/model-railroad-hobbyist.com/files/users/Nick Royerfiles/RoyerBasement.jpg