nght...@bellsouth.net wrote: > To put the engineering in perspective, the foam controls two very > specific and important structural concerns - first, the pure moment > of inertia of the structure; the larger the moment of inertia, the > easier it becomes to make a structure stiff for the amount of > material needed- here in lies the secret to building superior > composite structures. Second, the foam nearly eliminates the > composite lamina critical local buckling stress (the critical local > buckling stress is primarily in reference to the side of > fiberglass/carbon/kevlar that is in compression, which in most cases, > is a composite structure's failure mode). To complete Steve's > reasoning (below), a cored composite maintains its structural > integrity so long as the skins *stay* apart.
Back to this, now that I'm home from getting the an annual on the 150 (622 nm at 80 knots is no fun). What type of forces are on the core material? I'm thinking it's mainly compression with shear increasing as the core gets thicker. If someone had more money than they knew what to do with, how about using nomex honeycomb for a core? It's not as easy to work with since you really need to use prepreg skins and autoclave them, but there are a couple of ways to do it with normal materials. I'm planning on filling the open areas in the fuselage with EPS foam and glassing it inside and out, then hotwiring the wings in 3 sections (leading edge to the spar, then upper and lower spar to trailing edge sections), glassing the outside surfaces, hollowing out the cores so there's .5" of foam, and glassing the inside. Then I'll cut inch or so thick slices from the chunks I cut out when hollowing, glass both sides, and bond those into the LE every foot or so. Same thing between the spars. Haven't decided whether or not to hollow out the ailerons yet, right now I'm leaning towards just making them solid foam with precured carbon at the trailing edge to keep them straight and a continuous layer of glass wrapped and bagged. Note that when I say "glass" I really mean kevlar with a thin outer skin of glass to keep sandpaper away from the yellow stuff. -- Steve 33...@swbell.net N3343V- '75 C150M N205FT- KR1 #6170 He who seeks will find, and he who knocks will be let in.
