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plywood properties 12 Dec 2013 01:21 #742

One other thing to consider is ground handling abuse resistance. After handling my 1mm birch plywood Mitchell Wing D-tubes for years I notice that I have to be extra aware of pokey things that can go right through the leading edge. The Carbon/Kevlar/foam/Carbon/Kevlar leading edges on my Millennium are much more resistant to pokey protuberances.
Think of "The Pencil Test".

Billj3cub

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On 7/5/2011 8:32 AM, Kenny Andersen wrote:

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...

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