Repairing a hollow molded sailplane wing

[lenb]

This past week in Cumberland MD was an epic week of soaring and also a first for me. During a slope frenzy one afternoon, A friend of mine ( or at least used to be) and I tried to claim the same airspace and the DG800 won over the Stingray, but not before suffering a severe laceration to the wing.

Here are some photos of the damage and the rerepair process.

[lenb]

Once the damage is cut away, I sanded back the carbon skin on a decent angle to expose the layers of carbon and provide a bonding area.

[stevekremer]

any spar damage that you can see?

Steve K

[lenb]

No spar damage, not even scratched.

[Xroadie]

Len,
Last week, when I saw Stephane's photo on Facebook of the damaged model....I commented "If that's a CARF DG800 there is nothing left of the other model!"
Being able to go 180mph takes some very strong wings! That added strength meant for speed may have added to your ability to survive the mid air. How thick is that carbon skin?
Pete

[lenb]

Hi Pete,
The skin is pretty thick. I'll post a picture later today with a close up.

Moving on with the repair,
I went to the local craft store and bought a stiff foam used for sticking fake flowers into, its crisp and sands/cuts nice. Plus it wont suck up the resin and weighs nothing,.



The foam I put in will need to be installed in two pieces since I want to slide it under the skin on each side. Trace the airfoil on the foam and cut on the bandsaw.















Test fit the pieces and adjust the shape if needed.





Next step is to get all the carbon pieces ready, here is the tow which will be installed along the leading edge inside the wing.

[lenb]

Carbon fiber layups complete,
I left the LE recessed a bit so I can install more carbon tow on the exterior to form a sharp LE to match the rest. ( also to help cut through other planes )






Onto the carbon tow and fill/sand

[Xroadie]

I have fixed TD ships like this, but used white foam....never thought about the green foam...it would be easier to shape than the white foam, but I thought the green foam would absorb liquids! I have a second repair to make and will try green foam!!

[lenb]

Pete,
This foam is very stiff and crispy, its not the liquid absorbing one they have. This feels like Rice Crispies

[hello82]

looking good....nice idea on the foam inserts! Are you scraping the epoxy off the carbon fiber top with a card once applied , or just brush on, and it's good?

errrr...Don't forget to do the other wing too so it balances out!

Matt

[ARUP]

Excellent repair tutorial!

[Steve P]

Please forgive this one post thread hijack, but this seems a good place to post a carbon repair. A tow plane rolled out of the pits onto the field as I was landing at Cumberland. I overreacted in correcting, caught a wingtip and whipped the tail. This broke the horizontal stab out of the top of the fin.

My repair sequence...
- Get all of the fin top pieces so that they cleanly go back together. In this design, the nuts are encased in a fg/carbon layup so they just popped back in place in the voids. All cracks were clean and any dust or dirt was removed
- Lube both wing bolts with white lithium grease, run them through the nuts so the nuts will not get clogged with epoxy.
- Inject Hysol 120HP epoxy into everything
- Clamp overnight then remove bolts in the morning, corse sand the entire top of the fin with the Proxon belt sander to smooth, remove all white gelcote
- Mark up the top of the fin with a razor saw blade for more surface grip for the next step
- Two layers of fiberglass/carbon weave cloth with each laid on the bias to the other. Wet out with West System epoxy
- Scooch the carbon tows to the side of each bolt hole
- Cover the bottom center of the horizontal stab bottom with Gorilla tape. Wax the tape. Add extra blue tape to protect in case of spills
- Lube the blots again, attach the stabilizer tight as if you were about to fly the plane. This will mold the cloth and repair to the exact shape of the stab.
- Let everything fully cure. Remover stab. Trim excess cloth. Paint new edge white.

[lenb]

Nice Steve

I had to do that same sequence a few times in the past, plus it makes for a nice looking saddle if you leave it carbon. Great information, thanks for the tutorial.

[lenb]

Pete,
The skin is pretty thick as indicated.



Next up was adding more tow to the leading edge to get the shape I wanted



Fill, Sand , repeat

The first two filler applications were done with West Systems epoxy and 410 lightweight filler. I mix it very thick so its really light and sands like chalk, then the last bit is done with "Split Second" filler. The final coat is super thin.






While I'm at it I'm touching up a chip on the tail section of the Shark.




There's a couple tiny pinholes I need to address on the LE, but overall its a near perfect. I'll wet sand this down and add the color coat this week.

[Stew2]

What paint will you use for the color coat Len?

[lenb]

I have some of the paint used by the factory, when the plane arrived it had a few issues and they sent some paint. Hopefully its still good.

[Mosquito]

Looking good. All great information!