minimum radius for helix

I am designing a new layout for n-gague (never done n-gauge before).What should I use as a minimum radius for: 1) curve on the flat?
2) Helix up? 3) Helix down?
Cheers
Phlil
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fghdf wrote:

Length of one turn of helix T = 2*pi*radiusR, or T=6.28*R
Grade is: vertical separation H / T*100, or G0*H/6.28*R
Min. recommmended H is 1.5 inches, and max recommened grade is 3%. Do the arithmetic. :-)
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On Tue, 18 Jan 2005 11:36:14 -0500, Wolf Kirchmeir

I'd also say it depends on what you're going to run up it. A good old fashioned Grafar 0-6-0 with a rake of coaches won't come close to the pulling power of my Jap outline Kato electrics.
Pete
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Wolf Kirchmeir wrote:

Try http://www.fortunecity.com/westwood/beautiful/819/HeliCal.htm there is a useful tool to do the maths mentioned above. Used it to help plan a 'OO' helix.
Chris
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Thanks for that. As it happens I have a PhD in mathematics, so I can do the sums myself. I was rather hoping to benefit from your expertise, not so much on the steepness, but the effect for the curve in a loco's ability to pull up the helix, and also on the incidents of derailments. I was also hoping for some comment on going up and down the helix, as well as what minimum radius I should use in my design on the flat.
Cheers
Phill

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Standard rule, use the largest radius that will fit in your space, it can never be to large only to small. Keith
Make friends in the hobby. Visit <http://www.grovenor.dsl.pipex.com/ Garratt photos for the big steam lovers.
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Well in that case you can also work out what superelevation (cant, banking) to use on the curves to make it easier for your stock to go up (or down) without falling off the track because of the lack of suspension. As you are no doubt aware, you will only ever have a maximum of three wheels of a 4-wheel wagon or bogie in contact with the track at any one time.
I built a "rectangular helix" on my OO layout. The curves are 4 feet radius, and there is an 8 foot straight between the two semi-circles at the ends. More details on my web pages (URL in sig, and select "helix" in the navigation list). The incline works out at about 1 in 75, which means I should be able to pull rather a lot of coaches/wagons up it behind my favourite locomotives (Bachmann 56XX 0-6-2T, since you ask).

Derailments should only happen because of your bad tracklaying. Since you will be taking extra care over laying the track on your helix, you shouldn't have any bad track. So you shouldn't have any derailments.

You don't say how much space you have. I suggest you use the largest radius possible that fits in with the rest of your layout. Let us assume that you are going to use "my" radius (4 ft), but since you are building it in N, you halve that to 2 ft. Then you are going to build the incline at 1 in 50 (2%) which is not too steep so you should be able to get a reasonable train up it. The circumference (on the flat) will be 150 inches, which means the rise for one turn will be 3 inches. The height from the track on one level to the underside of the support of the next level will obviously be less than that, say 2.5 inches. Now you have to consider the future, and maintenance. Is 2.5 inches going to be enough room for you to get whatever tools you need in there to keep your helix going whenever things go wrong (as they undoubtedly will sooner or later). On my helix, the levels are 6 inches apart, and that is too little sometimes, especially when you want to insert a few more trackpins, or you want to solder another wire on the wrong (i.e. inaccessible) side of the track.

--
John Sullivan
OO in the garden http://www.yddraiggoch.demon.co.uk/railway/railway.html
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John Sullivan wrote:

Superelevation becomes a vertical curve on sharp radii curves. I've never decided if there is any real advantage or disadvantage to it for models.

On trials on my helix, a train of rather expensive rolling stock let go from the loco right at the top. I listened to the train circulating and gathering more and more speed down the helix and at the last moment removed my hand from the bottom exit (guaranteed destruction) and let it go! The train ran the length of the track along the baseboard, rounded the 180 degree bend at the end, negotiated the half dozen turnout throat and rolled to a halt in the staging yard. I wandered off for a stiff drink and wrote myself a mental note that time spent carefully laying track is time well spent!
Regards. Greg.P.
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I read on a website that a mere 2% incline will halve the pulling power of some locomotives while the weight of cars on the descent will increase the speed and likelihood of a derailment on the curve.
http://www.naisp.net/users/mfischer/m_train5.htm
(kim)
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...

Can't work in percentages but on my first effort I had a 1:30 incline running down to a set-track 3rd radius curve, very careful driving was required to prevent a derailment. In the end I re-built the curve, had to maintain the radius but I super elevated it to around 5 degrees. That cured he problem, didn't look at all life like though.
--

All the best,

Chris Wilson
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"Chris Wilson"

And I can't work on 1st, 2nd or 3rd radius curves either as they are completely nonsensical. What the hell is a 3rd radius curve, why not just state the diameter?
At least percentage of grade can be worked out. Just divide the percentage into the 100. 2 in to 100 goes 50 times, grade in UK terms = 1 in 50. Easy.
Now, how do I do that for 3rd radius curve?
As for the minimum radius of a helix? Use the largest one you can fit in but I'd suggest nothing much under 30" radius.
-- Cheers Roger T.
Home of the Great Eastern Railway http://www.highspeedplus.com/~rogertra /
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On Tue, 18 Jan 2005 15:35:34 -0800, "Roger T."

It's a setrack measure. If someone has a circle of track using 2nd radius curves they know they can double the circle by adding either first on the inside or third on the outside. In that instance, as a measurment device it does its job perfectly.
Pete
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Yes, but how do you know what size board it will fit on? Do the Brits sell boards in the local shops labelled 1st board, 2nd board, 3rd board to match?
VBG...
John Dennis
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:-)
The set track thing comes from the train set side of the hobby and to that extent train sets do have instructions and guides inside with regards to base sizes yes. As it happens board sold by timber merchants in the UK are 8'x4' (or nearest metric equivalent nowadays) which surprisingly enough are just the right size to accommodate the plans available to build using set track components. What a co-incidence. ;-)
--

All the best,

Chris Wilson
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FWIW my old train set with oval of track and 2nd radius curves has the minimum space required printed on the front of the box and they are 37"x57" although I would recommend at least 39"x60".
(kim)
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"Boards"? People in the UK still build model railways on "boards"? :-)
Yes, just making mock but seriously, do people still build their model railways on a flat board?
The only place you'll find a "flat board" is under one of my yards. Even then, the "flat board", 3/4" Good One Side plywood was cut so that the outside edges flowed with the planned shape of the yard.
-- Cheers Roger T.
Home of the Great Eastern Railway http://www.highspeedplus.com/~rogertra /
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"Roger T." wrote:

If you're going to build a decent helix then build it properly on a rigid base! That would be a flat base with solid framing so that it will not bend or flex.
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Gregory Procter wrote: [...]

The helix track base is supported by posts (on the inside, usually), which are supported by the layout substructure. That's rigid enough, and then some.
It's a question of cost, convenenience, and available skills. For large layouts, flat table tops are an unnecessary waste of good lumber. For very small layouts on the order of a couple feet square, such as the micro-layouts built by some NG freaks, er, sorry, modellers :-), a corresponding chunk of 3/4" or even 1/2" plywood may be rigid enough as is. Hollow core doors are very light and rigid, and have been used successfully as bases for smallish layouts.
See Linn Westcott's book on building benchwork, which introduced the "L-girder" method. He found (as bridge engineers discovered before him) that it's not the amount of material but its shape that determines rigidity and strength.
HTH&HF
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Wolf Kirchmeir wrote:

I guess we each develop our own favourite methods of building baseboards. I always seem to move before I complete a layout so I build mine to be rigid enough to be transportable and each section small enough so that I can just move it by myself. The third factor is that I tend to build from whatever timber is available - I gather "offcuts" from other jobs and store them long enough for then to be good and dry. :-) I'll stand by my call for a rigid board with framing under a helix - mine uses threaded rods both inside and outside of the circular track bed to allow for precise height setting and they have to screw into something. The flat board also allowed me to cut out the center for access. That wouldn't have been possible with framing/substructure. My skill at wood-working is about a step above "abysmal" so I plan around achieving what I need within that skill level and in assuring that dimensional errors cancel each other out rather than adding together.
Regards, Greg.P.
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"Gregory Procter"

All the N.A. articles I've read have the inside of the helix open for access, I've yet to read about one with a "solid" base. Mind you, all the ones I've read about have a radius of something like 30 plus inches or more to achieve a minimum 2%, or 1 in 50, grade on the helix itself, so there is more than enough room to stand inside the helix structure.
-- Cheers Roger T.
Home of the Great Eastern Railway http://www.highspeedplus.com/~rogertra /.
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