So, I'm just starting to get down to the nuts and bolts though I've been a CD fan for a long time. I thought that the wings were covered with dacon or something and that the plywood LE (leading edge) was just there for structure (i.e. not the actual aero surface)? If that were the case, you could just cover the carbon with the rest of the wing, and it would be pretty smooth, or maybe fill it with the micro ballon stuff and then cover with the fabric? Does the wing covering fabric only go from the D tube to the TE (trainling edge)?

Molds would be the way to go for sure (but that's a big time investment, no?), but I was thinking of adding a bit more root and tip to increase the payload to around 200 (maybe some extensions?), which would allow me to wear clothes! LOL Actually, I could probably drop to 170, but with clothes and gear, that sill puts me a maybe 180-185 which seems a little heavy for the CD? I was hoping to keep the wing loading somewhere near the original target. I assume you laid the fabric up at 45 degrees?

Adding the extra ribs like you did was exactly the way to go, I was thinking of either changing the spacing from one intemediate rib to 2, or just adding a rib between the the existing ribs based on the LE (leading edge) skin buckling (which would give 3 intermediate ribs). So, did you go to 2 intermediate ribs, or 3? Since they are just there for skin stability they should be fine -- not much load there, and you're right -- not much weight.

Speaking of ribs: has anyone been swaping out foam ribs for the built-up trusses? That seems like another area that might yeild some small weight-savings, or would at least perhaps simplify the construction a bit.

Do you have a blog or anything that shows your build?

Thanks, Kenny

--- On Tue, 7/5/11, Rick Mullins <This email address is being protected from spambots. You need JavaScript enabled to view it.> wrote:

From: Rick Mullins <This email address is being protected from spambots. You need JavaScript enabled to view it.>
Subject: Re: [Carbondragonbuildersandpilots] plywood properties
To: "This email address is being protected from spambots. You need JavaScript enabled to view it." <This email address is being protected from spambots. You need JavaScript enabled to view it.>
Date: Tuesday, July 5, 2011, 11:14 AM



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.
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...