Our club is currently building two permanent multilayer layouts. Both will feature at least one helix to allow trains to transverse between the levels and a couple of reversing loops. I have a couple questions with regards to the helix: 1. The standard seperation between two main line tracks in HO is 2-1/2 inches between track centers (I'm not sure what it is in N scale). Can we maintain this spacing through the helix or must it be widened? We will be running rolling stock of up to 85 foot cars and double stack container cars. We will also be running Big Boys, DD40AX Centenials, SD90Macs and various other locomotives and rolling stock. What is a good double track mainline sepration through the helix for both HO and N scale? 2. What is the best grade percentage or the worst for each scale? We have a couple Bachman HO GS4 Daylights (they do not pull too great) that may need to transverse the loop in HO). I realize that the lower the percent grade the better, but we only have room for one HO helix with one 36 inch radius and one smaller radius to be determined by the answer to question #1 above. The other HO helix (other end of the layout) has room for a 34-34.5 inch radius outer track and one inner track to be determined by the answer to question #1. In N scale, we have room for between a 24-26 radius for the outer most track on it's helix. I also realize that I can decrease the grade percentage by making the helixes slightly oval shaped in stead of completely circular. We have room on each layout to add a couple feet of straight track into the loops to make them oval, we just cannot make the radius of the curves wider than I listed without cutting down the walkway spaces in the clubhouse. 3. What is a good loop to loop elevation change (IE 3.5 or 4.5 inches between the top of the rails of the track on one loop level to the top of the rails on the next loop level)? 4. What are the recommend minimum radius curves that can be used in a helix (HO and N scale) without having problems.? I realize that the grade percentage is affected by the radius of the curves. Many of the answers to these questions problably can be found in some magazine, somewhere, but I'm not sure where. I also have found that the experience of other model railroaders is often very valuable in allowing a person to get the BEST results. We would appreciate any help any of you folks could give us. I also have viewed the helix photos on the forum site from one of the members' layouts, including photos of his staging tracks. Very impressive. I was able to learn some things form just viewing the pictiures. Our entire layout will utilize the radio equipped Digitrax Super Chief System with boosters and several PM42's for power district control and reversing loop control. The layout will also feature block detection. Later, down the road, wewill install stationary decoders for all the tortoise operated turnouts (main line) to allow train operators to operate the turnouts from their radio throttles. thanks 3.