I'm planning an HO helix but math isn't my strong point. I need some help here. I know I'll need 4" from railhead to rail head. I have an 18" radius. Can anyone tell me what grade % that works out to be? I'm guessing just over 3%. Will that work with steam locos? I'm hoping to be able to pull a min of 6 cars.
The way I have it pictured in my head, most of the helix will be hidden inside a mountain with 2 sides accessable from the back. It'll have 2 revolutions giving me about 8 inches of height, then a gradual decline throughout the rest of the layout.
Lorne
With that spacing, and with that drastically tight turn that almost nobody would urge you to go ahead and try, and assuming your sub-roadbed won't be more than about 1/2" thick, your compenstated grade will be much higher, closer to 4.5%.
Your proposed curve will have a diameter of 36" at the centerline. The formula for the circumference of a circle, which is effectively what you are using, except as a ramp, is P X D, or 3.14159 times the diameter. The simple math says you intend to rise 4" in 113". It works out to 3.5%, but wrapping all those flanges around the inside rails of the entire helix will add about a full percent to the grade figure. Very tough sledding.
My helix has only one turn, and it rises about 4", a bit more. The twinned mains running parallel up the ramp have 33 and 36" at their centerlines. The grade works out to just over 2% for the outer track.
Crandell
If you are talking HO scale, I would not go less that 30" radius. You are looking at a 3.5% grade, plus another 2.25% for compensation(based on my engineering tables) - a 5.75% compensated grade. Our club has 33"/36" curves on the helix, which rises 5: with every turn. This is a 2.4% grade, with another 1.2% for compensation - 3.6%. Two heavy diesels(12-16 oz each) will lift a 30 car train out of staging and up the 5 turns of the helix.
BTW, I am using an old CB&Q engineering booklet to get the compensation information. It adds .05% for each degree of radius. 18" radius is 45 degrees, and 33" radius is 24 degrees. I have seen other engineering books that list the compensation at about .03% for each degree of radius with steel rail. Our n/s rail is a lot softer and may affect the actual compensation. I tend to calculate on the safe side...
Jim
Modeling BNSF and Milwaukee Road in SW Wisconsin
Sorry Crandell, but something you mentioned didn't make sence to me. Like I said, math isn't my thing. You mentioned that my 36" at the centerline will give me more than a 3.5% grade, but you also mentioned that you have a 36" rising 4" for a 2% grade. I don't understand the difference. Is it because of the additional level in my helix?
If I decide to elongate my mountain, making the helix more oval than round by addind a couple straight peices, would that help lower my grade %?
Jim, when you say your club's helix has 33"/36" curves, are those the measurments from center rail to center rail? Or total radius? If it's total radius, then the actual size of the helix must be almost 5' across. Way too big for my available space. If I understand this right, and I hope I do, then I might want to scrap the whole HO idea and go N. This leads to another problem which comes to mind immediately. Is N scale too small for kids to play on? The ages of these kids are 7, 8, and 12.
Curves are generally described by the radius. Mavryk, you have an 18" radius curve planned, 36" diameter. They are referring to helixes with a 36" RADIUS, 72" diameter. I'd recommend using a 24" raduis helix with 4" railhead to railhead with no roadbed to maximize clearance. The grade for that works out to 2.7%, and therefore you could get about 8 to 10 cars behind a 2-8-2 or comparable loco.
Modeling the Pennsy and loving it!
Lorne, you have a good question and a critical mind. I forgot to mention that I had switched back to radius when I mentioned my 36", so in my case the D, diameter, is 72". Sorry for not making that clear.
Bottom line, you'll have to fight with this. Your grades will be so severe that this important part of your layout plan will be a nightmare for you unless you are willing to run short trains or multiple engines on longer ones. It's not such a big deal when you recollect that the real railroads do that anyway...shorten trains or double up the head-end power when they simply have to move the moichandice. But, your world is one you have to enjoy in the end, and you must consider the consequences of decisions you make today.
Is there any way at all you can eke out another six inches in radius? Believe me when I tell you that you'll be very happy you went with 2.7% grade with 24" radius and not what you are contemplating at the moment. And that's 2.7% uncompensated for the curvature, remember. Jim's tables will probably add another 1.5%.
As to your question of ovalizing the helix, yes, it will lower the grade for every unit of longitudinal axis you add over the rise at the end of the ramp. The curves will still be tight at about 18" if I understand you, but if you can get two 'sides' of an oval adding another 4" each, it adds up and will help....some...a little.
N would probably be OK for your 12 year old (it was when I was 12), but N and a 7 year old may be asking for trouble. Those models are so darn fragile, a wrong touch could break something. Stick with HO, the larger size will be worth it when it comes to detailing and weathering. A 24" radius helix would come out to about 52" across with the subroadbed. You might want to consider an around-the-walls climb at 2% or so (1 inch rise in 50 inches along the track. 1 divides by 50 equals 0.02 0.02 times 100%/1 equals 2%) An around-the-walls climb will also eliminate the time operators will spend waiting for their train to reappear.
Another possibility that takes up less space is a train elevator. The length of the elevator will determine the maximum train length, but if a helix that is 5' across is too big, then a 6 to 8 foot long elevator should be plenty big.
Mavryk you'll want to consider your transitions into and out of the helix also. The steeper grade will require longer transitions so your knuckles don't uncouple. If your running steam this can be a real critical part of a successful operation.
Nick
Very good point Nick.
I was looking at a few youtube videos on building a helix. Looks like the easiest method would be to use allthread rods with bolts holding up the supports which in turn hold the track bed. This will allow me to make adjustments as I go. Also, watched a video on layout flex track on a helix with offset joints. This eliminates kinks. I thought that was a great idea.
My situation is a little tricky here. I want to build a small layout, roughly 4'x8' or even 5'x9'. Can't really go bigger because I need to keep it mobile. I don't own my house and I'll eventually need to move. The layout right now is planned in my head. It's the Royal Hudson trip from West Vancouver to Squamish which is a trip my wife and I took as part of our honeymoon. There will be a mountainous side, a hidden side (which is the helix), and the sea to sky side. For those that don't know this run, sea to sky is up the coast of BC, Canada. On the west side you have nothing but water, and on the east side, high mountains, hence the name, sea to sky. Absolutely beautiful country, high mountains, tall trees...amazing. The track plan is for continuous running. The helix provides a break in the action and represents the train entering a different area of the route. Very vital.
After thinking it over and reading what you all recommended, I decided to go N scale on this. This will allow me a helix that fits on the layout and still have some layout left over. I can see my oldest son getting into this layout, but my other 2 have a cheap HO scale they can fart around with. Trains are hit and miss with them anyways.
Thank you for all your helpful tips guys. Much appreciated.
Great choice in protoypes, Mavryk; that is one seriously beautiful run up the Sea to Sky (it was one of three I had shortlisted when planning my own layout). Just think, you and the wife could always swing through on the Rocky Mountaineer for some 'research'!
A thought: have you considered making your helix detachable from your layout? As in standalone next to it? It would mean a heck of an easier move when the time came, and wouldn't be too tough to pull off. More room on the layout as well.
Stu
Streamlined steam, oh, what a dream!!
Funny how you mention that Stu. I just received a message from Nick about a type of "module" setup. He uses 2'x8' tables with 3'x3' corners. When he needs to move the layout, it's just a matter of cutting a bit of track and scenery, and away it goes. I love that idea. Going N scale, I can get a decent size layout in my puny basement. The helix can sit on a corner table on it's own. By doing it this way, I might be able to have an "L" shaped layout with the helix in the corner. I'll have to work out the table sizes still.
Really good ideas guys, thank you.