A while back, I built some skin samples using 3 oz/yd2 fiberglass face sheets and 1/4" thick 3 lb/ft3 divinycel. The parts came out very stiff and smooth. The part was about 50% heavier than the combination of skin, core and epoxy individual weights. I vacuum bagged the part, but the core absorbed a lot of epoxy that didn't add to the strength. The skins were easy to puncture and probably not damage tolerant enough.

The 1/32" birch ply core is pretty resistant to punctures and the 1.45 oz/yd2 face sheets will take all of the torsion loads.

The 2 ply carbon (282 style) samples were pretty brittle and easy to puncture.

Nomex core is difficult as you note. The skin is easy to puncture between the cell walls, it requires a mold and probably an oven and film adhesive to get good bonds. For my experiments, I have been keeping to relatively simple technologies. Since the glass plys are adequate for the loads, the core could be something like dense balsa or cedar. The core has to take out of plane compressive loads without denting easily. The samples I made with balsa cores dented too easily. The core was about 6-8 lb/ft3 balsa. 12 lb/ft3 balsa might work, but I haven't tried it. The core wouldn't have to be plywood since the face sheets are adequate for the shear loads. If you have ever seen a cedar strip kayak, this would make some beautiful gliders. Northern white cedar can be found with density of about 19 lb/ft3. A .05" or .06" thick core would allow around 5" rib spacing in the d-tube.

These notes are from some work I was doing in the late 1990's, but are probably still possibilities.

Dan


DAn,
A Very good topic! Yeah, the real problem is that the graphite is too strong for what is needed, In fact my buddy did a wing with two plies of glass ans said it was VERY robust. Using the thinner fiberglass with some type of core would likely be a good choice. The stickler is the core, NOMEX is expensive, and some times the foam has adhesion issues. Too bad they don't make some balsa wood plywood, or do they? You get lighter weight, and still get the separation of plies. Of course NOMEX would be deluxe, and I think Hexcel has a new prepreg for going directly onto the core without a layer of adhesive (which adds weight), but I'm not sure if the home-builder, sans the autoclave etc., would get the kind of product that is theoretically possible...


Some testing is obviously in order, but I think you are on to something; plus, if the carbon pultrusions in the spar caps the overall wing deflection should still be low even without the carbon leading edge.