Composite wing repair...

[Sparky Paul]

Flying my CR Renegade today, taking advantage of the 35 gust 50 winds.... hear a noise, and the right wind bent up a bit, then straightened out during a high-speed pass and turn.
After landing, no visible damage, but it bends up when the plane is held solidly, and the tip lifted.
The upper wing skin pooches out, about 1 foot out from the root.
I presume this means the bond between the skin and the foam has vanished, and the foam is compressed into uselessness.
How to fix this problem, other than don't fly fast anymore? :(

[Ollie]

It might be possible to reattach the skin to the foam by drilling a few small holes in the skin, bending the wing up to get the skin to bulge away from the foam and injecting a mixture of epoxy and micro balloons through the small holes with a syringe. If you put small pinholes every inch or so around the edge of the delamination you can check to see that the excess epoxy comes out of each pinhole. This would verify that the epoxy has spread over the entire delamination. If some pin holes are dry the bulging and injection can be repeated before the epoxy starts to cure. After every pinhole oozes the wing can be aligned and the excess epoxy wiped off. i think it is important to use very slow cure epoxy so that the exotherm doesn't cause more bulge from heated air bubbles in the epoxy and so that the exotherm doesn't melt any foam. This repair will add some weight and the other wing will have to be weighted but that may be better than ordering or building a new wing.

The kind of bulging and delamination that you describe usually starts at the aileron hinge line where the top and bottom skins aren't tied together with fiberglass. If that is the case, then you may want to close the foam gap between the top and bottom skins after the delamination is repaired. You could do this by removing the aileron and sanding away about 1/16 of the foam where it is exposed. This will expose a 1/16 inch wide strip of skin on the inside of the top and bottom skins. Then you could epoxy a strip or two of bias cut 3/4 ounce cloth over the foam and the exposed strips of inside skin. A little masking tape will keep stray epoxy off of the outside surfaces of the wing. Then just trim off the excess light cloth and rehinge the aileron.

[Ledbetter]

Oh ascended one,

I love Palmdale. You must have lots of space to fly.

How about a couple of carbon fiber rods running the length of the wing, glued into a groove under the skin with Gorilla glue?

Regards.

[Sparky Paul]

The damage was a bit more than it was at first, after flexing the wing.
Actually made getting epoxy into the area a lot easier! :)
The leading edge doesn't wrap around from top to bottom, but is two seperate sheets, the top one lifted off the foam.
By flexing the wing to get the opening nice an large, it was simple to pour in the epoxy from the front and rear and spread it around the delaminated area.
Now it's curing..

[Ollie]

I never imagined that the wing skins were not glassed together at the leading edge. Are you going to do that with light glass cloth next? If not, perhaps a strip of mylar packing tape around the L.E. would be enough to give the structure a bit more integrity.

[Sparky Paul]

I saw the same situation on the other side, but not yet to seperation. Soaked the gap in CA.
Gonna add mylar tape to the leading edges, about a 1/2" overlap top and bottom.

[davidfee]

Paul,
I don't know about the CR wings specifically, but I think it's pretty common to have a weakness at the LE of a bagged wing. I've seen it on my home-made wings and it's easy to understand. You start out with glass wrapped around the LE, but then you sand it to make it smooth after the bagging process... so you've reduced the thickness and strength somewhat. It's the nature of the beast, I guess. I've used glass over Kevlar on the LE's of bagged wings for this very reason. I can sand through the glass and still have the Kevlar intact. Definitely overkill, but... ;)

I think mylar tape would be a perfect idea. Maybe even use the sparkly stuff to make it easier to see while you're at it.

-David

[Ollie]

David,
When i bag wings i use three or four strips of 1.5 ounce glass cloth of varying width on the leading edge. I use brown paper towels as air bleeders and the brown paper is incorporated into the flash at the leading edge. When removing the flash I stop sanding and scraping when the brown color disappears and I don't thin the glass around the leading edge. Yet, I get a very smooth leading edge contour.

[davidfee]

Ollie, that's a good tip! I think I'd read about that somewhere (probably from something you posted). I make bagged wings infrequently enough that, inevitably, I forget one or more of the great tips I've read.

Next time I'll try that, for sure! ;)

-David