Well, I have just completed my 1/4 scale N-scale helix mock-up. It is double tracked and contains no switches internally. The outside grade is 1.8% and the inside grade is 2%. This helix forms the heart of my eventual three level layout in my small train room (9' 8" X 10' 10").
I constructed the helix from thick paper of which I glued two pieces together to provide more rigidity and propped up with drinking straws. I essentially built this to see if my multiple levels would work out with clearances etc. I'm glad I did this as I was able to solve some problems that would have been expensive to fix in the wood and glue and screw stage!
The N-scale car in the picture shows the relative size to the model. Now all I have to do is make it 4 times bigger!
Here are some more pics:
I updated the thread for easier viewing.
Oops!
I forgot to ask... has anyone built a 12-turn sized helix before? If so, any tips on what to do/avoid as I build it? I anticipate the wood and track alone will cost upwards of $500 to make and I want to avoid any obvious pitfalls if I can. I plan on using Atlas code 55 flextrack.
Thanks a bunch!
Why not use code 80 in the helix? It's enough cheaper to add up in there. What are you planning to use for wood, and how are you building it? What's the loop to loop spacing?
Jeff But it's a dry heat!
I could use code 80 in the helix. There are several areas that are herniated out to become scenic "windows" to add visual interest to that corner of the room and I would want those areas to be code 55 for asthetics.
The loops are spaced 2.5" apart which is a rail to rail measurement. I basically made it such that once constructed I would have enough room for the tallest equipment plus roadbed and subroadbed.
What I plan to do for constructing the helix is to take 1/4" plywood and rip it into long thin pieces. The pieces will then be cut up into shorter pieces with an approx 4-6 degree cut on each end (I still have to work out the math). What I plan to do then is construct it so that each loop is built with two layers of these "wedges" of 1/4 inch ply that are overlapped 50%, glued together and screwed as well. This way I will have a 1/2" subroadbed that is one continuous piece from bottom to top without the need for splice plates that will compromise loop spacing.
I am essentially copying Bruce Chubb's idea that he posted on his BNSF Chilli Sub Webpage:
www.bnsfchillisub.com
Here are pictures from his site which shows the construction method:
I'm not sure if I will use threaded rod or not to seperate the layers... I may use notched external bracing as I've allowed extra width in the subroadbed and the radii are quite broad for N-scale and overhang shouldn't be too much of an issue.
The helix will be up off the ground enough and wide enough that I will be able to stand up in it quite comfortably when done. The top will remain open to let in some light.
Thanks for the help.
I wouldn't worry about code 80 showing the helix, but that's just me. If you are worried about that, then I don't think I'd switch back and forth inside the helix.
I like that construction method, make sure you leave room for supports, whatever you use.
Remember as you are building it up you need to lay the track and be happy with it has you go. Reaching in to fix anything is a bit of a pain (don't ask. please!)
Vail and Southwestern RR wrote: Remember as you are building it up you need to lay the track and be happy with it has you go. Reaching in to fix anything is a bit of a pain (don't ask. please!)
Thanks... it should be an adventure to be doing benchwork, track laying, wiring etc. and so on all at once!
I calculated that approx. 1/3 of my mainline run is in the helix... mind you, only 1/3 of that has to be traversed at any one time during the run (except at the very end or very beginning- then you have to traverse 100% of the helix). Perhaps I can raise my mainline speed up to 65 mph in the helix??
Nah 200.
Anyways have fun with the math and the power saw at nine pm. What pecent of grade are you going to have?
I just realized in ho scale to get three inches of clearnce(sp?) with a 3% grade the helix need's to be over a hundred inches in diameter. BIG curves no over hang.
cheese4432 wrote: What pecent of grade are you going to have?
What pecent of grade are you going to have?
My inside radius will have a 2.0% grade and my outside radius will have a 1.8% grade. The radii are approx. 22" and 24" respectively (N-scale).
cheese4432 wrote: I just realized in ho scale to get three inches of clearnce(sp?) with a 3% grade the helix need's to be over a hundred inches in diameter. BIG curves no over hang.
Not quite. You need a hundred inches of run. A circle of 32" diameter (16" radius) times pi (3.14) gives the 100" run.
Realistically, in HO the minimum distance between levels is 4" to allow for thickness of plywood, roadbed, ties, and rails plus the rolling stock. On a 3% grade, to achieve 4" separation requires a circle of 22" radius. Grade, radius, and separation are all directly related. Pick 2 of those, and the math determines the 3rd.
Operationally, you should generally use a helix radius bigger than your minimum radius, and a grade gentler than you maximum for the rest of the layout. Stringlining (where the cars tip inward on the curves) is most likely in a helix-type situation. The factors that control stringlining are 1) free rolling ability of ALL trucks in the train; 2) radius of curve; 3) uphill grade (if any); 4) length of train. Since the helix is often hidden, and pretty difficult to access in any case, giving yourself less susceptability to stringlining in the helix compared to the rest of your layout is recommended.
just my thoughts
Fred W
fwright wrote: Operationally, you should generally use a helix radius bigger than your minimum radius, and a grade gentler than you maximum for the rest of the layout. Stringlining (where the cars tip inward on the curves) is most likely in a helix-type situation. The factors that control stringlining are 1) free rolling ability of ALL trucks in the train; 2) radius of curve; 3) uphill grade (if any); 4) length of train. Since the helix is often hidden, and pretty difficult to access in any case, giving yourself less susceptability to stringlining in the helix compared to the rest of your layout is recommended.just my thoughtsFred W
Thanks for the advice Fred.
It turns out, interestingly enough, that my modelrailroading/computer guy/closet mathematician has calculated that in order to build the helix as posted above, we are going to need more than 700 of those wedges and they will only be 4 1/2" long! Thats a lot of gluing and screwing... (the wood that is ) not to mention all the cuts!
Looks like the chop saw is going to get plenty of use soon!
Hope that severe s-curve you seem to have as the approach at the lowest level is not actually what you have planned.
Jon
alco_fan wrote: Hope that severe s-curve you seem to have as the approach at the lowest level is not actually what you have planned.Jon
Actually the curve is a little exaggerated due to the way I cut the paper free-hand. When extrapolated, the curve is actually 28" in radius which is very generous for N-scale and it will taper out to a more flatter radius as it leaves the helix (it won't hug it so much). The model was mainly built to test the track-plan theory and clearances.
I also only plan on running 15 car trains as a maximum anyways, so the trains will be relatively small and not entirely within both halves of the S curves at any one time. With properly weighted cars, proper scale speed and well laid track... not to mention very broad radii, I don't forsee any major issues.
Dustin wrote:My inside radius will have a 2.0% grade and my outside radius will have a 1.8% grade. The radii are approx. 22" and 24" respectively (N-scale).
I'm puzzled... How can the inner track and outer track have different grades ??? Aren't they going to be built on the same helix ?
chateauricher wrote: Dustin wrote:My inside radius will have a 2.0% grade and my outside radius will have a 1.8% grade. The radii are approx. 22" and 24" respectively (N-scale).I'm puzzled... How can the inner track and outer track have different grades ??? Aren't they going to be built on the same helix ?
The inner track will have less of a run for the same amount of rise. On a helix, the run is Pi (3.14) times 2 times the radius. The rise is the vertical distance (rail to rail) between each level. Grade equals rise divided by run times 100 (to get grade as a percent).
Since run, rise, and grade are all related, with a helix you normally fix the rise to the minimum separation you are willing to live with. Then the radius is adjusted to get the desired grade, or a fixed radius determines the grade.
hope this makes sense
fwright wrote: chateauricher wrote: Dustin wrote:My inside radius will have a 2.0% grade and my outside radius will have a 1.8% grade. The radii are approx. 22" and 24" respectively (N-scale).I'm puzzled... How can the inner track and outer track have different grades ??? Aren't they going to be built on the same helix ? The inner track will have less of a run for the same amount of rise. On a helix, the run is Pi (3.14) times 2 times the radius. The rise is the vertical distance (rail to rail) between each level. Grade equals rise divided by run times 100 (to get grade as a percent).
Duh !!! I guess I should have slept a bit more... I should have known that. Thanks for reminding me.