"SPAD" refers to Simple Plastic Aircraft Design, which originated as about the simlest, cheapest thing you could possibly build. The SPAD designs have developed quite a bit in the past appx 3 years... to include some very nice looking stand-off scale aircraft which can be built for just a few dollars. (almost any SPAD can be built for under $30, not counting radio and engine.)

Visit www.spad.org Lots of neat stuff to look at.

Yo can build a mock-up of almost anything using styrofoam, gutter downspout PVC and coroplast, especially if the mock-up doesn't have to actually fly. A double layer of 4 mil coro for the wings, and single layer for the tailplanes, with a gutter downspout plastic main fuselage does fairly well simulate the weight distribution of most .40 size aircraft made from balsa or lite ply. (The finished weight is fairly well simulated too) For larger models... you'd need thicker materials to get a good simulation and to come close to the correct finished weight.