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[quote]QUOTE: Originally posted by nfmisso Let's say you need 2" rail top to rail top. With a 2% grade, you need 100" of run. DIvide 100 by 2(pi) and you get:16" radius. You may need to construct an oval helix instead of a round one. [/quote] It should be pointed out that the overall total thickness of the roadbed you choose to construct is of prime importance when calculating effective helix grades, and therefore effective radius you'll need. I believe conventional N scale vertical clearance is about 1 5/8". Therefore, if you use N scale cork roadbed ( 3/16" thick )over ,let's say, 1/2" plywood...you get 11/16" of extra rise required to achieve your clearance. This is now 2 5/16"...so on a 100" run, the grade is 2.3 %. If you use the cork + 3/4" plywood instead of 1/2", the grade for that same 100" run becomes 2.6%. Clearance side-to-side : Do you use long modern freight cars [ 80 ft.], or full length passenger cars ? This may also be a factor, if you might ever have a train parked on one track of the helix while another one is passing it. regards Mike
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