Steve didn't make molds for his leading edges. He made plugs by filling in the spaces between ribs with foam and then laid his leading edges up on them. Because that leaves a rough surface he did two layers of carbon and a lighter fiberglass layer on top that was largely sanded away to make it all smooth.
I have made molds (contact me if you are interested in using them) so I have made my leading edges of just two layers of 284 carbon, and also because of advise from Steve and Mick Roberts, I added and extra foam rib to each of the first 8 bays so there is less unsupported space between them. The ribs are only 1/2 foam with holes cut in them so it didn't add much weight.
Rick
From: Kenny Andersen <This email address is being protected from spambots. You need JavaScript enabled to view it.>
To: This email address is being protected from spambots. You need JavaScript enabled to view it.
Sent: Tuesday, July 5, 2011 11:32 AM
Subject: [Carbondragonbuildersandpilots] plywood properties
So, what I've done is taken the properties from birch (assuming it's birch plywood) and made a composite based on 3 layers of birch oriented in the 0, 90, 0 directions (its' the same way (tool) that we use to model composite layups. I had to assume some of the orthotropic properties, since they only publish the axial ones, but it will probably get close. One interesting thing I've figured out so far is that 2 plies of graphite fabric weigh just slightly more than the 1/32 (.8 mm) plywood -- a bit more than a pound per airplane more, but it will be more stable than the plywood.
It makes me wonder how many plies Steve used on his magic dragon leading edge? Interestingly enough, even though the 2-ply composite is 1/2 the thickness, the shear buckling is the same (actually slightly higher)due to being able to orient the composite fabric in the 45 degree direction, and the carbon being much stiffer than the wood. I haven't had a chance to run the in-plane buckling, which I assume the composite will buckle at a lower load for the same reason. However, since the function is to carry primarily shear, it might be OK -- I'll probably have to get around to making a non-linear FE model to smoke that out. I will say 2 plies isn't very thick...
