HI FLYINBLIND! The individual wings of a bipe only have to be half as strong as those on a monoplane, by the time you are done cantilevering the 2 wings together, there won't be much unsupported span. The thickness of the individual airfoils needs to be somewhat thinner than a single wing fun fly. A bipe doesn't make full use of the lift provided by the individual wings because there is aerodynamic interference between the wings, the more distance there is between the 2 wings, the less interference, BUT I'm sure that there are practical limits to how far apart to set them. The thrust line should be centered between the 2 wings. I have built the GOLDBERG bipe in various sizes down to a 12 oz, .061 powered and they have all been lots of fun. No matter how lightly I tried building them, I have never had a structural failure, which leads me to believe that it's difficult to build one that's too light. If you are building a large profile, try to get a look at how the MORRIS HOBBIES 1.20 size job is put together, there is a build up thread in the profile forum. It would be pretty hard to improve on their design!