Re: > I dont feel that plywood is a good choice. Hi everyone... from Mattoon, IL. I am a newbee to the KRNet as of a couple of days ago. This will be my first post.
I would really be afraid to use sandwiched foam for plywood. If you think about it, when you hang 150+ lbs on the firewall, the fuselage sides between the engine and the landing gear take a lot of stress. The top longerons are being stretched (tension), and the bottom ones are trying to buckle (compression). The plywood is crucial in sharing this load. It serves as a shear web for the trussed fuselage and insures that the sides maintain their shape in load. The outer skin of a sandwich would do very little in sharing that shear load because it is only attached to the fuselage by the core foam. Sandwiched structure is great for other types of loads, but I think that the outer skin of the sandwich in that application would only keep the wind out like Mark said. I agree with Mark in that you cannot beat plywood. Ive been filling and sanding my wings for a few weeks now and will finally just give up and take defeat from some of the inperfections. That all said, I think it IS neat to brainstorm ideas and the what ifs. Im not hanging my life on a plywood structure substitute, but IF I were on a desert island that had plenty of spruce, foam, glass and epoxy but no plywood, I think I would sandwich the spruce members between fiberglass layers on the fuselage. In other words, I would put foam between the spruce members sand it to the thickness of the side frames, and then glass both sides (inside and out & biased to the longerons) with a couple of layers of glass, being sure to bond the glass to the spruce everywhere. I think that would make a much better structure than gluing sandwiched foam to the outside of the fuselage. You would need to glass AFTER the fuselage is assembled because I doubt that you could bend the sides after the glass was applied to both sides of the side frames. Even if you could, the inside skin would go into compression and do less good. You would also have lots of fun trying to sand the foam on the inside surfaces and would need to sand perpendicular to the longerons on the outside to maintain the fuselage curvature. After the boat stage were finished, I think I would probably get homesick and try using the structure to float home rather than spending 20 more years on the island building something airworthy! (Ive been building mine since 81). Good luck in whatever you decide, but just remember that neat ideas may get you into some real trouble some day if you arent careful! Im sure I will get a flashback of every deviation from plans that I have made when I get that dude up to 500 feet for the first time! Take care, Kerwyn Stoll Mattoon, IL KR2 N40102 (60%)
