Im planning to build a double track helix on my N scale layout, and I need some tips and info on building them. What is the best recommended curve radius and height difference between each curve [I will be running long trains, with quiet a few long 89’ cars and some heavy cars] I am thinking of using Kato Unitrack in place of flex track to ensure an even smooth curve for the climb, with 12-3/8" for the inside curve and 13-3/4" for the outside. Is this going to be too tight of a radius for a helix? Has anyone else used Fixed track for a helix, is it a good idea and dose it work? Any help, info or tips will be appreciated.
Thanks,
Anthony.
hi Anthony
It seems pretty tight to me. A 1:3 ratio (length of your longest car versus the minimum radius) leads to a 20" minimum radius. Especially when using a longer incline and long trains you will be happy with a large radius and a moderate grade (just under 2% in stead of 2,5% with the 13" radius. A 2,5" separation will be sufficient.
Paul
That seems to be pretty tight - I would look at 19-20" radius for a minimum. You will need a minimum of 2" of clearance between the layers(this is to allow for roadbed/track thickness and those TOFC/stack cars. You have to allow for 'compensation' of the curve itself. A 20" radius curve will give you a 1.6% grade with 2:" separation - add another 1% for compensation(degree of curve times .05) and you have a 2.6% grade. Our HO club has a 30" radius helix that has 4.5" separation - this is about 2% with a 25 degree curve(1.25% compensation)for 3.25% grade for 4 1/2 turns - long trains needs very careful handling. Going down the helix is where the most problems arise as a heavy train 'pushes' on the engines. If there is any 'slop' in the gears, the engines can start 'hunting' and a derailment can happen. We make sure that the interlocking at the bottom that leads into staging is aligned before starting down the helix, and that the throttle settings are not changed mid-helix.
As far as sectional track - Kato Unitrack is good, but it still has lots of 'joints' - I would use flex track with soldered joints and electrical feeders every 3 feet to prevent voltage loss. Remember, this has to be 'bullet-proof' - Once it is built, it WILL be very hard to work on later!
Jim
Modeling BNSF and Milwaukee Road in SW Wisconsin
Take a look at Guide to helix and staging design (Vol. 1). For starters, the cover picture is an N Scale helix (also on page 5), and; The Silver Gate Northern, on pages 18-21, incorporates serial-staging into its helix under one dog-bone end of the layout.
Guide to helix and staging design (Vol. 2) has a helix (with serial-staging) under one side of an HO Scale 4'x8' layout, the Union Terminal Railway, with radius-curves of 19" and 22" which is tight for "HO" and better with "N".
Conemaugh Road & Traction circa 1956
RE Jim,
Do you think there will be sufficient space between tracks if I use 19" for the inside, and 20 1/2" to 21" for the outside track? Also, I have checked the heights, and I would need at least 2 1/2" between levels to allow clearance of Double stack cars. I am thinking this may make it a bit steeper. Could you also please explain the formula on working out the radius/grades in detail so I can write it down for planning?
A lot will depend on the total elevation between the top and the bottom. I've got a comparatively steep helix, but it only goes around 2.5 times to pick up about 6" of elevation. I'm getting away with 16" radius on the outer turn because I limit train lengths to about 20-25 cars, and have made provision for a helper on those rare occasions when I exceed that. I also use a lot of body mounted couplers and at least two diesels on the point.
It's true that once you overcome gravity going up, the trickiest part of a helix is going down... Heavy trains will want to buckle on even a modest grade and curvature, especially if you rely on truck mounted talgo couplers. Micro Trains couplers with their infamous "slinky" action can also ruin your day on a train going down.
I kept my vertical clearance at 2-1/8", allowing some air for cork and code 55 track.
Lee
Route of the Alpha Jets www.wmrywesternlines.net
Jim and Anthony,
some extra explanation. A curve is adding extra resistance, hence the compensation. The larger the radius the less compensation is needed. The difference between N-scale and HO is important.
(virtual) grade = compensation + clearance / length of 1 loop
grade in HO in perc. = 40/R + 16*clearance/R = ( 16 * Cl + 40) / R
grade in N in perc. = (16 * Cl + 20) / R.
With a 20 inch radius in N scale and 2,5 inch clearance (R = 20 and Cl = 2,5) the virtual grade (ViGr)will be 3%. ( 16 times 2,5 is 40; 40 + 20 = 60 and ViGr = 60 / 20 = 3)
With a 13 inch radius and 2,5 clearance in N it will be 4,6%. ViGr = (16 * 2,5 + 20) / 13 = 60 / 13 = 4,6.
A 19" radius with 2,5" clearance has in N-scale a ViGr of 60 / 19 = 3,16 %.
In HO a 30" inch radius with 4,5" clearance results in a 3,7% grade. ViGr = (16 * 4,5 + 40 ) / 30 = 112 / 30 = 3,7 (2,4% real grade and 1,3% compensation.)
The equations above have rounded values. On real railroads the degree of curvature is: 5700 divided by the radius in feet. Radii of several hundreds or thousands of feet are used. Compensate for the scale and inches, multiply by 0,05 and you will find the figures above.
For N scale the other way around: radius = (16 * Cl + 20 ) / ViGr . If you want 2,5 inch clearance with a 2% virtual grade the resulting radius will be 30" ; yes in N-scale.
In his book Track Planning for Realistic Operation (third edition) John Armstrong states on page 82 and 83: "if the ruling grade is to be an operating attraction in itself, calling for helper service, heavy motive power and short trains, a figure of about 4% is right. With a 2% grade the pulling power of your engines is about 40% of what it is on level track."
Finding the right grade and radius versus train-length and kind of equipment ain't easy.
Keep smiling
Paul, thanks for that dissertation. As much as I love math and lengthy equations (not at all), I prefer trial and error. My givens tell me what I have room for, and my druthers tell me what train length I like. A 20-25 car train in N scale is plenty on most home layout applications, and a couple of good diesels on the front will take that train pretty much anywhere you decide to send it.
A lot of guys over engineer things with the idea that one day they'll haul a 100 car train. If that's what your shortest passing siding lets you get away with, then you're in like Flynn. If you're like the rest of us, odds are you're working with some space limitations, which in turn limits your potential train length. I found that trying to pull 30 cars up the helix caused a string line situation as it neared the top. At 25 the problem went away. So 25 it is. Turns out 25 cars (40' and 50' cars) fit neatly in the A/D tracks in my yard, so I know right away if the train is oversize or not.
Paulus Jas Jim and Anthony, some extra explanation. A curve is adding extra resistance, hence the compensation. The larger the radius the less compensation is needed. The difference between N-scale and HO is important. (virtual) grade = compensation + clearance / length of 1 loop grade in HO in perc. = 40/R + 16*clearance/R = ( 16 * Cl + 40) / R grade in N in perc. = (16 * Cl + 20) / R. With a 20 inch radius in N scale and 2,5 inch clearance (R = 20 and Cl = 2,5) the virtual grade (ViGr)will be 3%. ( 16 times 2,5 is 40; 40 + 20 = 60 and ViGr = 60 / 20 = 3) With a 13 inch radius and 2,5 clearance in N it will be 4,6%. ViGr = (16 * 2,5 + 20) / 13 = 60 / 13 = 4,6. A 19" radius with 2,5" clearance has in N-scale a ViGr of 60 / 19 = 3,16 %. In HO a 30" inch radius with 4,5" clearance results in a 3,7% grade. ViGr = (16 * 4,5 + 40 ) / 30 = 112 / 30 = 3,7 (2,4% real grade and 1,3% compensation.) The equations above have rounded values. On real railroads the degree of curvature is: 5700 divided by the radius in feet. Radii of several hundreds or thousands of feet are used. Compensate for the scale and inches, multiply by 0,05 and you will find the figures above. For N scale the other way around: radius = (16 * Cl + 20 ) / ViGr . If you want 2,5 inch clearance with a 2% virtual grade the resulting radius will be 30" ; yes in N-scale. In his book Track Planning for Realistic Operation (third edition) John Armstrong states on page 82 and 83: "if the ruling grade is to be an operating attraction in itself, calling for helper service, heavy motive power and short trains, a figure of about 4% is right. With a 2% grade the pulling power of your engines is about 40% of what it is on level track." Finding the right grade and radius versus train-length and kind of equipment ain't easy. Keep smiling Paul
Paul,
I took my .05% for each degree of curvature directly from my ARA engineering book(prototype). It is interesting that your calcs also mention 0.05)This assumes standard profile steel/iron wheels on steel rail. On our models, the soft and oversize n/s wheels on n/s rail will make matter even worse. With an entire train on a hill with a constant curve(like with a model helix), the drag is quite severe. The compensation does not 'scale down' very good when going to 1:87 or 1:160, but it has worked out quite similar on tests I have run at our club layout. We use metal wheels on all freight cars, and most have had the 'truck tuner' applied to the journals. In our tests, the same 3 engine set can pull 4-5 cars more up the outside track(33" radius) than the inside(30" radius) track on our 4 1/2 lap helix.
The interesting thing is that going 'down' the helix is where folks have problems! Constant speed(hands off the throttle) is important to keep the 'surging' form dumping cars on the inside the the curve. Also, worm gears with 'slop' at the top of the gear tower will cause this 'surging' as well as the worm tries to climb over the spur gear. 'Thrust' washers on the worm gear shaft reduce this issue. Older BB Athearns usually have a lot of 'slop' in the worm. The newer 'RTR' and Genesis line are quite good, as is Kato and Atlas engines.
Thanks to all for your help on this topic,
Reading all your feedback has kind of crushed my plans of having a helix and running long trains. Seeing as I am not limited to a small space [a 40 by 9 foot portable office] I was planning for long trains, with a limit set at 15 foot. At first this sounds long, and I'll admit it is, but running long trains is something I love, and I find it reasonable at 42 cars with 3 locos for a coal train. A second idea, [which now looks like is my only option] is to run a hidden return loop from my staging along the lower level, up to the top level and have a return loop into a tunnel. I can imagine some of you would cringe at this idea straight up, but its an idea I am toying with. From my staging yard to the top level [with only the lower level in between] I am working on 2.5 foot difference in height. This will allow me to have a mountain climb, and run the long trains, but I still see some issues with descending trains. My layout is still only in the ideas stage [I’m still looking for a portable office] but please give me your thoughts on this idea. I know it means nearly double the amount of track work, but with the ideas that I have, I think it will be worth it.
Cheers all,
hi Anthony,
i can't believe you. Probably you should be more specific about what your wishes are. A 2,5% virtual grade in combination with a 24" minimum radius in the helix seems possible.
I always make drawings, doing more then just dreaming.
Paul.
Hi Paul,
I should of mentioned all the details at the start, but it slipped my mind. The helix will run from the stagin to the top level about 2.5 foot. If I use 24" on the inside, and say 25 1/2" for the outside track, with 2.5% grade, it should work fine? I am trying to pencil ideas down, but I keep changing my mind so often that I never get it down on paper. Ill come up with a rough design and Ill put it up or send it thru to you and you can let me know what you think.
Well I guess maybe I shoud have looked a little harder and I would have found some of the answers I was looking for. I'm not really sure if piggy backing a question onto someone elses post is acceptable. Again being new here I still need to learn the ok things to do on these fourms.
I have a question about a helix though. I need to build a helix for n-scale as well and I need to go up 6.5". My plan is to build it with the outside curve being about 32" since I have 36" to play with and go up 2½ levels. I dont plan on hauling long trains maybe 9 or 10 cars max. Is this going to work for me or will I need to ad another level to the helix? I figure I am pushing my limits for space between the levels if I need to add one. But from what I have read here it seems to me over that wide of a curve and height differnce I should be ok but I would like some opinions on it.
just an adition to that I have 36" total to work with not a radisu of 36"
Mike,
That's exactly what I've got on my layout... just about the same elevation change, radius, the whole bag o toys.
That's it under construction. First I built the supporting benchwork, then added the helix. I used sanded 1/2" plywood, and cut spacers allowing 2-1/8" vertical clearance (2-5/8" from top surface to top surface
Where the helix is snug to the wall, I used a piece of 1/8" masonite paneling for the spacer, and drove a 3" drywall screw down between the tracks to keep it secure.
My installation is in the attic, so I could add some distance by putting the first turn out about 6" under the sloped ceiling. This created the need for a little bit of acrobatics with the spacers back there.
There it is ready to install. 2-1/2 turns, 6 1/2" vertical rise, 32" radius on the outside track. Operationally, the inside rail takes trains down, while the slightly longer slightly larger radius outside track carries trains up.
Here it is in position, ready for the benchwork to be constructed around it. I did this to allow me to make minor adjustments to the approach grades as needed. I think I needed to tweak about a quarter inch on the approach from the left.
And with the approaches installed top and bottom.
A couple of construction notes:
Solder all of the track joints in the helix, and make sure there are no kinks or imperfections as you go. If you don't, the joint that will give you the most trouble will be the one that's the least accessible. Mr. Murphy was a model railroader, you know.
Check the vertical clearance with the tallest piece of rolling stock you own, or intend to run. For me it was a Micro Trains three deck auto rack with cars loaded on the top rack. I don't operate an era where double stacks run, so I don't know if they'd fit... I suspect they won't.
Before you install the helix, staple some flexible fiberglass screen strips around the inside and outside of the plywood to create guard rails. This material is strong enough to prevent derailed cars from plunging to the floor, but flexible enough to get out of the way when you have to reach in to clear a wreck. (Which I assure you, WILL happen.)
If you can, make a provision for a helper pocket in your staging yard. If you're running DCC, it's easy to give a heavier train a shove to help it make the grade. It takes a soft touch, but if you practice a bit, it can be done. The secret is to have an engine available that has a broken knuckle on the front, so you can let go of the moving train on the fly.
And finally, make sure you provide adequate barriers so this doesn't happen:
Him Kitteh Likey the electric mouses... This will never end well!
Thanks, I thought it would work and seeing it defantly helps. now to just build it.......right
Why don't you ask your club mates Anthony?
http://tropicalnscale.blogspot.com.au/