What composite layup is required for a HLG Wing?

I have been making my hlg wings from carbon mat. I have tried various spars. My problem is folding during launch. I assume my technique is flawed(throwing and/or building). But it seems as if the mat does not adhere well to the blue foam. I do not wet out the mat, only the .75 oz. outer skin. Comments?

Also, I am beginning to question the cost effectiveness of the carbon mat material in general. What weight fiberglass do you use on a hlg assuming some type of carbon spar?

From : Don Stackhouse

Thomas,

Throwing technique has a very strong influence on the incidence of wing folding; a flawed technique can fold almost any wing, no matter how strong. The particularly tragic thing about most of those techniques is that they usually don't give you any more launch height than the good low-stress methods. Be particularly careful if you use a peg for throwing that you rest the "ball" of your fingertips on the back of the peg, and that you don't wrap your figertips around and over the top of the peg (that's a good way to exert a downward pull on the wing at release, causing very high wing stresses). Check Joe Hahn's article on "How to throw a Monarch" for more info on this issue.

If you are properly wetting out the .75 oz. skin only, your carbon mat is almost certainly very dry. This will result in increased delamination and skin buckling problems.

You could try making the outer skin overly wet, but then you will have a lot of trouble controlling the resin content of the total. You can try wetting out the carbon mat, but you will have to be very good with your technique to avoid messing up the fiber arrangement in the mat. There are other techniques, such as peel plies, notched squeegies, etc. that may help, but the bottom line is that mat is tricky to work with, and it is also usually very difficult to judge when opaque materials like carbon are properly wetted-out. It can be done, but expect some failures until you get the process developed.

Regarding your question about glass skin weight, if you're familiar with some of my other discussions on structures you will know that I definitely do NOT subscribe to the "one size fits all" school of engineering. No two designs are alike in their structural requirements, and the requirements vary in different areas of the wing. Your priorities in things like weight, dent resistance, etc. also play a part. Also, the weave of the fabric used, the fiber orientations, the number of layers and the resin system used all effect the characteristics of the finished skin. The differences are particularly significant in a thin laminate on a soft substrate such as a bagged-glass-over-foam wing skin. That said, a skin of about 1.5 oz. total is probably a good general starting point for an HLG, although you will probably have to make local adjustments. In any case, expect to test and discard a few before you arrive at your final design. Of course, you could skip all that hassle and just buy one of our kits, since we've already gone through all that trouble for you! :-)

Don Stackhouse @ DJ Aerotech