After seeing the posts on helix construction I have been wondering what percent grade you build your helixes. Also, what do you consider the maximum grade you should build in an N Scale layout? I know that Woodland Scenics offers foam in 2%, 3%, and 4% grade. But I read an article in which an HO modeler mentioned he had a 5% grade.
2% 2% is the generally accepted "best practice". You can increase it but the steeper it gets the more problems or limits you will have. If you are willing to run shorter trains then 4% might be ok. Steam locos without traction tires may not be able to go up a 4% grade.
2%-3% is the most advantageous. For the sake of comparison, if you are allowing 2.5" between levels, here are the required radii for each of the grades: 2% = 16" radius 3% = 11" radius 4% = 9.5" radius 5% = 8" radius The 4%-5% grades, when coupled with the small radii will severely limit you pulling power, as well as contribute to other problems.
When considering grades and tight radii, be sure to calculate in the additional resistance of pulling a train around a curve. While your physical grade may be 3% or 4% on an 11 or 9.5 inch radius curve, the resistance will make the grade seem steeper. Longer trains will have greater resistance than shorter trains, in addition to the added weight of the extra cars. I had locos that could move 20 cars without problem on level and straight track. They could only pull 6 or 7 cars up a 16+ inch radius stacked helix with about a 3.5% grade. Tweaking car weights helped a little (many cars had been over-weighted), as did temporarily adding weight to the locos, but even then they still could only pull 7 or 8 cars and, with those particular locos, there was no space to put the weights permanently inside the shell. So I went with Plan B on my current layout: bowl-shaped spiral helixes instead of cylindrically-shaped stacked helixes. My blog is linked below. Look at some of the entries on helixes for additional comments about stacked helixes and construction of spiral helixes. It might be helpful if you can post a track plan or floor plan of the train space.
The "other" problems can be: Clotheslining - where the cars flip over toward the inside of the curve Coupler breaking - Mostly with "Accumates" Uncoupling - The drag on an incline can make this worse Derailments - In general happen more on steeper grades There are probably other issues as well.
Thanks everyone. I don't have a permanent layout plan. I have a 4'x8' table that I change layouts on frequently (Unitrack is a wonderful thing). I am planning on doing a small 24"x66" permanent holiday layout that I can store in the garage and pull out in late November. I wanted to incorporate a mountain with a small stacked helix. I was glad to see an experienced modeler say I can do 3% in 22". That will put the sides of the mountain very close to the edge of my board though, so I may go with a 4% grade using Kato's 9 3/4" curves. On this layout the locos won't be pulling more than 5 or 6 cars.
One of the things to look at is NMRA RP-11, Curvature and Rolling Stock. It rates cars and locos on length, and number of axles in the trucks. Since I have a fleet of steamers the rigid wheelbase measurements become an important factor in just how tight a curve can be negotiated without putting the wheels on the ties and ballast. The scales also apply to those big six axle diesels. So in short the radius of the curves in a Helix can be a factor when running the bigger stuff along with the percent grade. I'm currently toying with the idea of using two Helixs to reach the staging lower level, one at each end of the layout, connected by a ramp from the upper Helix to the lower Helix. I'm also toying with having both of the Helixs in a rectangular, or oblong format, and with the increased trackage being able to possibly get my grade down to about 1.5% maybe a little less. With over 25 feet of lower level space under the current trackplan I should be able to fit in both Helixs, thier connecting ramp, and about 15 to 16 feet of multiple yard and staging tracks. My biggest rigid wheelbase steamers, the Bmann J and the Concor S-2 Northern, will operate on a minimum of 14.5 inch radius, and the 2-8-8-2 will also operate on that radius due to the smaller driver size and the rigid wheelbase of each driver set being slightly less than the big Northerns. The standard Bmann 4-8-4 is doubtfull on that radius, where my small fleet of 2-8-0s will be very comfortable. My E-7units should also get by on the 14.5 inch radius along with the 70 foot passenger cars with diaphragms.
Just talking off the top of my head; could you make one double track helix instead of two? This might allow you to make the straights longer and reduce the grade.
