Bonding Carbon Fiber Airfoil Halves 1

[Mr168]

I have a small extruded airfoil I am looking to duplicate in carbon fiber (amateur garage setup). It is 6 feet in length, but with only a chord length of about 2 inches. I am looking at duplicating using a two part mold and wet layup with vacuum bagging (for the sake of this discussion, I am not looking at using a foam core).

My question is in joining the mold halves. Due to the very small leading edge, I don't feel that I can reliably use a lap/joggle joint. I can flange the two halves and bond before trimming/sanding to the finished shape, but am worried whether or not this will provide adequate peel strength at the leading edge. My worst case scenario is to flange/bond/shape, and then wrap the whole assembly with a final layer of carbon and vacuum bag, but this will make the element slightly larger than the one I'm trying to duplicate, which is not preferred. Is there a preferred method here I may be overlooking?

Any feedback/practical thoughts would be much appreciated.

 

[berkshire]

Mr 168
One method is to build a small flange inside the leading and trailing edges to increase the bond width, depending on whether, or not, you need to save weight, materials can be epoxy resin or whatever resin you used for the original layup, filled with shopped strand material, phenolic Micro balloons, Glass microspheres. or cellulose filler like milled cotton fiber. Other methods you did not want to get into, are secondary molding of a lap joint that curves up the inside of the part, this will require minimal cleanup of the leading edge.
B.E.

You are judged not by what you know, but by what you can do.

 

[Mr168]

Thanks, berkshire. I had not given any consideration to forming an interior flange after the fact with CSM or similar. I had initially dismissed it on the basis that I couldn't form an interior flange with the initial layup due to geometry limitations with the vacuum bag. And as you noted, it wouldn't be too difficult to make a third mold of just the leading edge to form a "backing bar" insert to increase surface area for bonding. Great suggestions!

 

[blakmax]

I have heard of rumours of such attempts to make split aerial sections before ending badly. The two halves end up unbalanced and unsymmetric laminates. You end up with two cork-screw panels that you have to force together, with consequent residual stress and fitment issues.

Good luck.

Blakmax