I’m working on my new track plan and I like the idea of putting a helix hidden in a mountain in one corner of layout to raise the track level up to a good tressel hieght. I would like to use 18" radius to keep the size of the mountain size to a minimum. The longest loco I’m going to run is probably a AC 4400 or a 4-6-4 Hudson.(HO scale). I know these don’t “look” right on 18", but the helix will be hidden. Any problem with this radius? What grade % should I stiick to?
Grade percent and radius are not independent of each other. The other factor in helix design is “headspace”, the height of the train itself. If we use 4" as the vertical spacing from rail head to rail head, and 18" radius for the helix, the resulting grade is rather steep.
2% is comfortable, 4% is possible, but not recommended.
36" x pi = ~113"
4" rise in 113" run is just under 4%.
How many cars do you want to pull up that grade, and how many engines do you want to use?
I want to pull about 40 or 50 cars and I realize that I wiil have to consist 2 or 3 locos to do this. My tallest car sitting on a track with no road bed is 2.5" from the table to the top of the car. Do I need to have 4" of head space or can I get by with 3" or 3.5" to keep the grade down? Also, what about not using road bed on the helix to cut down on height? I know I have to keep the back of the mountain open for maintanance.
Reducing the headspace will bring the grade down. I just grabbed 4" because it was convenient, figuring you were in HO. Just don’t forget the subroadbed and any other roadbed thickness in your height per turn calculations.
40 to 50 cars is a lot, and if you could get out to 22" that would help reduce the grade even more. If possible, put some straight track on a couple of boards, and raise them up to test grade performance with a load. Keep in mind that pulling on a curve is more difficult than on a straight.
Here is a photo of my helix. 10’ diameter O gauge, 2% grade.
I do not think that you will get a train of 40 to 50 cars (20+ feet long…) up a 4% grade around a 18" radius curve, even with 2-3 extra “helpers”… The train will stretch around more than one complete turn of the helix!
If you want to have a dramatic trestle, you should probably raise the overall height of the layotu a bit, and drop a section (possibly to the floor) to install your bridge.
Andrew
I have a section of 4% on my layout (a mining branch), and even my heaviest engines are hard-put to get six cars up it. Lightening the cars is unfortunately not a real solution, because the tendency on a curve as train weight increases is for the outer wheel to lift, and the cars to spill inward.
The decrease in pulling power for each percentage point of grade looks a lot more exponential than arithmetic, so I would agree that you want to keep it to 2%; the big advantage with a helix (since it will be covered up) is that you can make quite a few circuits. The curve resistance isn’t as much of a concern, but manufacturers are making even medium-sized engines like USRA 2-8-2s for a minimum radius of 22" these days. My suggestion: use 24" radius curves. They’ll accomodate anything short of a very large (i.e., 2-8-8-2) brass model. And you really only add a foot to your helix diameter. I went through a similra process with my layout: I had originally intended to put 18" curves on my main line, since much of it will eventually be urban trackage anyway. But I found that even my moderately-sized engines ran better on the 24" radius curves - fewer shorts from trailing trucks hitting overhanging details, for example.
Another thought: the locomotives that are small enough to run well on an 18" radius curve generally won’t be heavy enough to pull well, Shays excepted.
I’m thinking of twice around with 3.5" head space to give me a total rise of about 7" and then making a resest river bed/canyon to make the modest tressel look more dramatic.
That’s a good idea about a test track. I have a temp 4 by 8 with 18" curves right now. I could just jack one side of the table up to test grade performance. I guess I’ll just have to get my basic bench work set up to see if I can go to 22"
Can a DCC throttle and decoder be set to help compensate for the change in speed when going up and down grades?
That will not be a good test. Your engine pulling up hill will be offset by the cars trailing downhill.
Better to use a straight or pull the track off the plywood and raise it without the downhill.
Also, I’ve planned on putting my helix inside a mountain. But after watching the helix at my club for a while, well too many things go wrong. Unless you can see what’s going on with your train, you won’t know to increase power or fix a derailed wheel.
Lothar
Keep in mind that curvature adds drag to the train, and increases the effective grade.
For example, my first helix on my Siskiyou Line was 2.5% and 24" radius curve. The drag effect on that tight a curve adds about 1.4% to the actual grade, making 2.5% on a 24" radius curve being equivalent to a 3.9% grade on straight track! Yikes!
I pulled out the 24" helix and replaced it with a 40" radius helix at a 1.75% grade. Fortunately I had the room for the larger helix, so it all worked out.
But beware of what tight radius curves on a grade do to train drag. It’s BAD and can cause no end of operating grief since a helix is also typically hidden trackage.
Your 18" radius curve will probably add about 2.5% extra drag to the existing helix grade, which means the train drag will be 5%+ equivalent … not GOOD. Your loco pulling power will be reduced to zilch, and if you add power to the train to get up the helix you’ll probably start stringlining cars to the inside of the curve because of all that drag.
And having the ruling grade on the railroad be in hidden trackage is just asking for operating problems – which is why my 24" radius helix went bye-bye real fast … [B)]
Most helixes are double-tracked to avoid the bottleneck of having a single-track line many feet long within the helix. This creates more space requirements because the radius becomes larger to accommodate the extra track. You will also have to have significant spacing (perhaps 2.5 to 3 inches) between tracks to allow clearance for large locomotives and any full-length passenger equipment you may run. If you have 24" minimum radius curves and double track, you need a width of at least 58" - almost six feet! (24" plus 2.5" plus 2.5", times 2) to accomodate the trains.
In my current trackplan fitting into a bedroom, I through out the idea of a helix as it is a huge space eater. Instead, I had the track spiral twice around the room with 30" radius curves to access to the 22" higher upper deck which covers two walls (creating a deck-and-a-half layout).
For a 10 by 12 foot room, John Armstrong has a neat plan in 20 Custom Designed Track Plan (published by Kalmbach) starting on page 24 – the Compact Atlantic & White Mountains Railroad. But it has 20" minimum radius curves, a single-track helix, is designed for shortline operations, and has narrow aisle space (20") which would allow for limited 2-person operations.
What are your space availability and operation/equipment preferences? Almost all of us want more than is practical.
I have to agree with Joe due to experience. I had one with 4 levels at 24" radius and worked out to about 3.25% grade. I fine tuned the track to the Nth degree and used 4 units to pull the hill with 50 cars. It would actually pull it without a hitch…sometimes! And when Murphy’s gremlins wanted to play there was no end of grief. I just couldn’t rely on it enough to enclose it in a mountain. 32" to 36" radius is good, 42" to 48" radius is much better! You want it ro run flawlessly. That means making sure the track is in guage and level across the centerline all the way up, and every joint is fine filed smooth. Enjoy!
P.S. - I forgot to add… while you are at it add a full length passing track or two and you can use the helix for staging. Just keep the grade to a minimum and you do your stops/starts very gradually.
Some ideas to help with the "climb up the mountain:
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Start the climb before you get to the mountain. Lets face it, everyone does it, the RR’s, the highways, etc. The more you stretch it out the better off you are. Starting the climb 5’ or even 10’ away will add to the realism. Remember the first couple of feet of the climb are spent in the transition from horizontal to sloped. A 1% slope change per foot of run is good, otherwise you may decouple the cars at the junction.
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The first climb around the mountain can be exposed, and should be. It’ll provide some extra visibility to the train, and help access WHEN you have problems.
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Make sure you have space between the levels on the helix for your fingers to handle the locomotives and cars. It’s no good if you have to build a special “spatula” to get a derailed car out of the helix.
If you go for a 3% grade for exposed track with broad curves, the climb will roughly work out to 1/2" in the first 3’, and then 1" per 3’ thereafter.
Mark in Utah
WHEN I have problems.(don’t like the sound of that.) Don’t like the sound of 24" radius problems either. Maybe I gotta rethink this idea. Thanx for all the tips guys! Just thought it’d be neat to see the end of the train disappear into the mountain and the locos not imediattly come out the exit. (and not because of derailment)
just a thought
if you are only raising the track for a helix, masonjar’s response may be the better way to go
i had originally planned a helix for my layout, but i found that its requirements were too big since i wanted a 30in rad
since then i have completely scrapped that plan in favor of nolix designs
There is another issue that has been overlooked. Pulling 40 to 50 cars up even a 2% rulling grade would probably dictate that the three locomotives be six axle units rather than the 4 axle types. If you review the test reports on these larger locomotives, they usually state that while the engines may be able to negotiate an 18" radius curve, the ovehang is so great that they cannot be coupled to most of your rolling stock without pushing them off the track, even with a transition curve. Better to use a much wider radius. If you want to hide the helix, leave openings in the mountain so you can monitor the train’s progress. Watch the end of “Von Ryon"s Express” to see how a train can go in and out of a mountain.
I went out and did some looking at things after all this advise and realized 40 or 50 cars is just insane. (what was I thinking???) After REALLY looking at the prospect, I think maybe 20 cars would still look good. (reallity check Duhhhhh!!!). Does anyone have any revised advise for a 22" helix that would raise the height maybe 7 to 10"???( I like the idea of half of it being exposed in the front, kind of like a double tunnel portal) That might cure some of the access issues.
Thanx guys!!!
Well, I would say you’re heading in the right direction, toward reality. Your numbers are improving. At 22" radius, and 3.5" per turn, your grade is now around 2.5%.
Access shouldn’t be that big an issue, since the inside of a helix is virtually unusable. Just crawl inside.
Some additional ideas for you…
Have you though about building a “variable radius” helix?
That is, by incorporating the front of the helix into a mountain the lower levels hand out further (exposed mountain climb) but on the back side all line up? If you make the top level with a 22" radius (44" diameter), and kick it out 3" for each turn, you’d have it exposed as it winds itself around the mountain, with only the back side hidden inside the helix. You could also alternate levels that are exposed so that the mopuntain’s not one monotonous spiral of track!
You could also “oval out” the mountain, where it’s not round but more ovaled, which would give you more frontal exposure. Just 6-12" wpould make a big difference for realism. It wouldn’t have to be consistent either from one level to the next, as mountains are ALMOST never perfectly symetrical.
This would also allow the lower levels to acomplish more of a climb than the higher elevation.
Assuming 2.5% elevation, and assuming that you build 5 turns in the helix, and that every other tun is exposed, and that you build a 8" offest oval…
Level 1 (top): 22" radius, 152" track, 3.85" climb.
Level 2: Same as level 1 - 152" track, 3.85" climb.
Level 3: 4" kick out (24" radius), oval expands to 16", 182" track, 4.57" climb.
Level 4: Same as Level 3 - 182" track, 4.57" climb.
Level 5: 4" kick out (26" radius), oval expands to 24", 211" track, 5.28" climb.
You’ve just climbed a total of 22" by using hiding a helix in a mountain using three exposed loops around the mountain. It took 879" of track, which represents 1.2 scale miles to make the transition, which should take something on the order of 1 1/2 to 2 minutes to properly make the climb (slow train).
The total footprint of the mountain would be something on the order of 76" wide X 52" deep. You could reduce the width 8" by eliminating the oval in the top level, which woul
Mark, don’t you mean… Choo, choo choo… ?
Sorry, couldn’t resist.[:o)][swg]