What grade are those figure 8 trains sets?

Since I am considering a folded dogbone on my next layout (possibily a double folded dogbone, if I have room), I will need to incorporate a few inclines/declines on the the ends of the layout. Kind of like the sets you would buy that are an elevated figure 8.

Since the reasonable reach for a layout is about 30", and I want a double folded dogbone, I guess the minimum radius I can use is 15" and outer radius should be 16" (Is this spacing enough for N scale?), I guess my depth will be about 34". I should be okay with this since the back part is more scenery, right? I could go with a tighter radius, but I would limit my car selection. If need be, I can. I was thinking 15" minimum on a single folded dogbone originally.

And if I need to go up at minimum 2" from the top of the rail head to the bottom most part of the tunnel, I would say 2.25" might need to be the minimum rise over the course of roughly 9 feet. Am I correct in thinking this will probably be a round a 2.5% grade? So, if I am running a 10 car train as a roundy round while I am doing my operations, this should be comfortable for the locos, or it might be a problem?

I will try and get a rough schematic up as soon as I can. I am still just a bit tired from celebrating a World Series victory the past couple of days. 8-D

 

Just off hand 2.25% should be in the ballpark (but not the ballpark you've been thinking about!) But use the longest grade you can fit in. In laying track I always start with the outer loop, using as large a radius as seems reasonable. You might not want to put it too close to the the layout edges where derailments could result in stuff hitting the floor. A one inch radius between tracks may be too small. Long cars and engines on curves can hit each other in passing if the tracks aren't far enough apart to allow for overhang. I test with the longest cars I have (89' flats, 80' passenger cars, whatever I can find). The end of a long car on the inside track can hit the middle of a long car on the outside track. This is why I began laying track on the outside.