carbon kevlar LE D-box repair

[balsabozo]

real bummer, landing approach mishap on my Organic 2m:
plane disappeared on downwind leg. the wing center section LE got a serious ding as i swung it around to re-establish visual and it hit the tree that camo'ed it.

d-box + carbonkevlar = pain in the a** repair.
any suggestions? (or better yet - spare center section for sale?)
Pat M responded to my "wanted" post - what do you think Pat? can you do it justice?

1. the spar is intact
2. the main ding is between 2 bays
3. on 1 side of the bay, the LE of the rib is crushed, on the other, no damage
4. on the side that is crushed, the next rib over has delam'ed from the carbon kevlar

club folks discussed whether the carbon kevlar was actually providing some torsional stiffness. hence, there will be a need to span at least 3 bays to make up for the weakness. i dunno i am a dumb thumb newbie (see the crashed easy? doh!).

[pmccleave]

This would be a rather simple repair to make strong enough to be functional. It would be a little harder to make it real pretty again. If you decide not to repair this wing, I would be willing to purchase it from you for a fair agreed upon price or would be willing to repair it for you for a fair agreed up on price. I have recently done a much more extensive repair on an AVA Tip Panel that even required some work to the spar. On this repair I would use a patch of bi-directional carbon on a 45 DEG Bias and would extend 3-4 inches either side of the damage area. Let me know if you would like my help on the repair.

See Ya,

Pat McCleave
Wichita, KS

[balsabozo]

so would the carbon obviate the need for some sort of a former underneath to reshape the airfoil? i was thinking of shaping a piece of balsa and blocking it in underneath and then covering with wetted fiberglass. but you think th carbon might have enough strength in and of itself?
can you pm wiht cost estimate?

[pmccleave]

I would probably try to get in throught the small hole in the LE to repair the broken rib first. I would then drill small holes through the broken areas of the D-tube and then stick a bent wire through the hole to pull up on the skin and reshape everything the best I could and use CA wicked into the carbon and kevlar to retain. Where the D-tube delaminated from the good rib, I would drill 1/64th or smaller holes along where the rib is and wick CA in to re-attach the skin to the rib. Once all of that work has ben done, I would overlay the carbon patch, feather the edges of the patch and call it good. The carbon patch should be one piece that wraps from the spar - around the LE - back to the spar. It will not look like new when you are done but it will strong and functional and a whole lot cheaper than buying a new center section.

See Ya,

Pat

[Matt_at_CST]

You can fix this fairly easily if you have the right materials. You can use a undamaged portion of the wing leading edge as a form to mold a patch to go over the damaged area of the wing. You need a bit of bias cut fabric in the 5 to 6 oz range. Carbon will work well or a Carbon Kevlar hybrid is cheaper but harder to work with. Use a high performace laminating epoxy system like Pro-Set which is much stronger and stiffer than hobby shop epoxy. Cut the patch on the bias and a little oversize, I normally outline the patch with masking tape and cut down the center of the tape. Bias fabric distortes easily and this will help stabilize the fabric. I use yellow vac-bag film to wet out the fabric. Cut two pieces of film much larger than the fabric. Lay one down on the bench and lay out fabric in the middle and pour out epoxy in the middle of the fabric. Then lay the second layer of film on top of the fabric. Spread out the epoxy useing a squeege on the top of the top film. Work all the air bubbles off to the edges of the fabric. Continue to squeege all the resin you can off to the edges of the fabric. I press very hard on the fabric and push all the resin I can out of the fabric. The two layers of plastic film will not let you push too much resin out of the fabric. Push the excess epoxy out away from the fabric about an inch so you can use sisors to cut around the fabric and cut away the excess epoxy and excess plastic film. The fabric should be larger than the patch you will need on your model.

On your wing protect the area you are going to use as a mold with some plastic film. Again larger than the fabric batch you are molding. Epoxy will migrate and you want to protect your wing. Form the film and fabric sandwich you have wet out over the leading edge and put a layer of thick soft material over the top. 1/4 inch foam will work well or a couple layers of vac-bag breather. Apply some pressure over the molded fabric, while making sure that it stays in place. An ACE bandage or several layers of a steachy plastic wrap will work. Let your patch cure overnight.

The next day unwrap the patch and remove the vac-bag film from both sides of the part.

Now for the broken part of the wing. Cut away all the broken leading edge shell and repair or replace the broken ribs inside. If there is a rib in the area where you removered the shell you will need to replace that rib with one that is slightly larger. Block sand these ribs to the outside contour of the shell.

Cut the patch you have molded to extend about 1/2 inch beyond damaged part of the original shell inboard and outboard along the wing and back to the back edge of the spar on the top and bottom.

Epoxy the new shell over the broken protion of the leading edge. I always use DP 460 epoxy for these repairs. It is the strongest epoxy for bonding cured composite parts. Of course sand all the surfaces before you bond them and apply some light pressure while the epoxy cures.

After the epoxy has cured sand the edges to fair them in and recover the wing. You should have gained very little weight and the strength and stiffness should be just like befor your wing was damaged.





real bummer, landing approach mishap on my Organic 2m:
plane disappeared on downwind leg. the wing center section LE got a serious ding as i swung it around to re-establish visual and it hit the tree that camo'ed it.

d-box + carbonkevlar = pain in the a** repair.
any suggestions? (or better yet - spare center section for sale?)
Pat M responded to my "wanted" post - what do you think Pat? can you do it justice?

1. the spar is intact
2. the main ding is between 2 bays
3. on 1 side of the bay, the LE of the rib is crushed, on the other, no damage
4. on the side that is crushed, the next rib over has delam'ed from the carbon kevlar

club folks discussed whether the carbon kevlar was actually providing some torsional stiffness. hence, there will be a need to span at least 3 bays to make up for the weakness. i dunno i am a dumb thumb newbie (see the crashed easy? doh!).

[Robglover]

Matt -

About time you showed up and 'splained this sticky goopy plane building stuff to us heathens. ;)

[nuevo]

balsabozo,

yes the carbon/kevlar cloth provides all the torsional stiffness. I completely took apart an Ava wing once. Under the cloth is nothing but balsa ribs and the spar.

Also the cloth has no stiffness of it's own until it's glued on the ribs. One more note, the cloth was not molded into the shape of the airfoil. The cloth was cured on a "V" shaped mold, with the bend of the "V" at the LE of the wing. The cured cloth conforms to the airfoil shape when it is glued to the ribs.

My method is similar to Matt_at_CST's, but maybe a bit simpler.

To me a repair should be straightforward.

Cut out the damaged area of cloth. Not much more is required.
Rebuild & glue in any LE ribs as required. If needed, cut out the damaged area larger, so you can trace the outline of an adjacent rib.
purchase some carbon/kevlar cloth (2 oz / ft^2) or just carbon cloth (say 3 oz / ft^2).
Wet out a patch of the cloth, and cure over your own mold. You can make the mold out of a block of wood and waxed paper. make the "V" angle about 45 degrees. Make sure the cloth is on a 45-degree bias, just like is already on your wing. let cure.
apply patch to the plane. The ribs and the surrounding area will ensure that the cloth exactly conforms to the existing airfoil. Unlike pmccleave, I believe a 1" overlap to any adjacent area is sufficient. But a 3-4" overlap is not going to do any harm.
enjoy


Like Matt_at_CST said, you should use laminating epoxy, not 5/30 minute structural epoxy. It's too thick to properly wet out the cloth, and you'll end up with too much epoxy (weight) in the cloth. Z-poxy at your local hobby store will suffice for this skin repair.

If you don't want to do the repair yourself, I have some friends who've had pmccleave do repair work for them. They were very satisfied with his work.

[nuevo]

I take that back, the cloth weights used by the Ava are certainly heavier than 2 or 3 oz/ft^2. Go with the weights Matt_at_CST mentioned.

[tonyestep]

[QUOTE=nuevo]...the cloth was not molded into the shape of the airfoil. The cloth was cured on a "V" shaped mold, with the bend of the "V" at the LE of the wing. The cured cloth conforms to the airfoil shape when it is glued to the ribs....
=================
Ya know, Jon, that's really interesting info! It's nuggets like that that keep me reading these forums.

Anyway, balsabozo, what everybody has said is true: it ain't so hard. Here's another tip to make it even easier: instead of balsa ribs, make the necessary rib or ribs out of blue foam about 3/8" thick. Cut away the damaged stuff, but leave enough so you can wedge the ribs inside the skin. The wide foam surface provides excellent support and gluing surface for your repair. Pat and Jon didn't mention it, but when I make such a repair I cover the whole repaired area, plus about 1/2" all around, with 1/2 oz. glass cloth. If you don't get any epoxy runs or globs anywhere, you can sand with 600 grit and feather the repair so that it's pretty inconspicuous. After it's all done, get a friend with a vinyl cutter to make you a nice graphic and stick over it.

[balsabozo]

thanks folks for the tips. i am going to let the repair sit for a while, sometimes better to let such things age. besides, slope season is dawning and the flat field will soon be marshes here. thanks also for the offers for repair, i may come a knockin if that center section starts nagging me before Im ready.