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Old Oct 08, 2012, 06:01 PM
sewing machine thumb
United States, CA, Palo Alto
Joined Jul 2001
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Originally Posted by Frank S View Post
I'm pretty sure I found it! Hairline crack in the fuse ahead of the wing saddle. Needed the light to be just right to see it. Should be an easy fix.
Fixed with carbon uni. Just went out and threw it as hard as I could. No awful noise!
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Old Oct 08, 2012, 06:27 PM
usaf3kteam
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Joined Sep 2005
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Quote:
Originally Posted by Frank S View Post
Fixed with carbon uni. Just went out and threw it as hard as I could. No awful noise!
Cool Frank
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Old Oct 09, 2012, 08:13 PM
De Chelonian Mobile!
leipold's Avatar
Wilmington, Delaware, USA
Joined Jul 2006
199 Posts
Repair advice?

My CX2 had a midair (thanks, Reto!) in the flyoffs at Wilson last weekend. I took a quick look, didn't see any damage, and threw it again. And again. (Dumb move.) After the round, I noticed the damage.

There's a 6-cm-long split in the leading edge about halfway out the right wing. In that region, from the leading edge back to the spar, the top skin depresses and makes 'crunchy' noises when pressed. There are some wrinkles and delams in the top skin from the spar back to the hingeline. A 'bubble' of delam is centered over the spar.

When I flex the wingtip upward, the wing actually bends (a little), and the top skin over the spar visibly moves as it does When I try to flex the wing downward (putting the top skin in tension), it doesn't bend. If I grab the wing at the spar on either side of the damaged area and try to bend it, it doesn't feel like the spar itself has any flexibility, so I don't *think* I broke it.

What's the best way to repair my baby? Am I going to have to cut the wing open?

-- Walt
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Old Oct 09, 2012, 10:29 PM
Sink? Circling now to confirm.
JONBOYLEMON's Avatar
United States, UT, American Fork
Joined May 2002
16,661 Posts
Quote:
Originally Posted by Frank S View Post
Fixed with carbon uni. Just went out and threw it as hard as I could. No awful noise!
What are you launching to now Frank? 200'?
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Old Oct 09, 2012, 10:48 PM
sewing machine thumb
United States, CA, Palo Alto
Joined Jul 2001
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Originally Posted by JONBOYLEMON View Post
What are you launching to now Frank? 200'?
Maybe with a 30 mph headwind.

In dead air about 150'

We're going to need that "fix Frank's launch" party at BSoAZ
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Old Oct 10, 2012, 12:16 AM
usaf3kteam
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Joined Sep 2005
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Originally Posted by leipold View Post
My CX2 had a midair (thanks, Reto!) in the flyoffs at Wilson last weekend. I took a quick look, didn't see any damage, and threw it again. And again. (Dumb move.) After the round, I noticed the damage.

There's a 6-cm-long split in the leading edge about halfway out the right wing. In that region, from the leading edge back to the spar, the top skin depresses and makes 'crunchy' noises when pressed. There are some wrinkles and delams in the top skin from the spar back to the hingeline. A 'bubble' of delam is centered over the spar.

When I flex the wingtip upward, the wing actually bends (a little), and the top skin over the spar visibly moves as it does When I try to flex the wing downward (putting the top skin in tension), it doesn't bend. If I grab the wing at the spar on either side of the damaged area and try to bend it, it doesn't feel like the spar itself has any flexibility, so I don't *think* I broke it.

What's the best way to repair my baby? Am I going to have to cut the wing open?

-- Walt
Try Charlie he is pretty good at that cptsnoopy
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Old Oct 10, 2012, 03:05 AM
Where is the lift?
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USA, AZ, Phoenix
Joined Nov 2005
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Quote:
Originally Posted by leipold View Post
My CX2 had a midair (thanks, Reto!) in the flyoffs at Wilson last weekend. I took a quick look, didn't see any damage, and threw it again. And again. (Dumb move.) After the round, I noticed the damage.

There's a 6-cm-long split in the leading edge about halfway out the right wing. In that region, from the leading edge back to the spar, the top skin depresses and makes 'crunchy' noises when pressed. There are some wrinkles and delams in the top skin from the spar back to the hingeline. A 'bubble' of delam is centered over the spar.

When I flex the wingtip upward, the wing actually bends (a little), and the top skin over the spar visibly moves as it does When I try to flex the wing downward (putting the top skin in tension), it doesn't bend. If I grab the wing at the spar on either side of the damaged area and try to bend it, it doesn't feel like the spar itself has any flexibility, so I don't *think* I broke it.

What's the best way to repair my baby? Am I going to have to cut the wing open?

-- Walt
Hi Walt,
Sorry about the damage to your Concept. (I'm sure Reto feels bad about it too...)
I have repaired two wings that had the top skin delam from the spar cap. Both times I cut the approximately 1" square of spread tow on the bottom of the wing ahead of the spar where the delam has occurred. Once the square piece of skin is removed you can inspect the damage. If the spar appears to be intact and the Carbon spar caps are ok then you can puncture little holes in the upper skin foam working through the access hole. The idea is to allow thin epoxy to soak a bit into the foam to help stiffen it up. Then I carefully flex the wing to slightly open up the space between the upper skin and the spar where it has separated. I use 400 grit to rough up the surface of the skin and the spar so the epoxy will have something to grip when it dries. Then I set up a bed of magazines or something similar that will conform to the curve of the top of the wing. then I have large books or for this last repair I did, reams of printer paper that were fairly heavy to press the wing down into magazines while the epoxy setup. I used Carbon cloth to reinforce the first repair I did and lightweight fiberglass for the second repair. The fiberglass was much easier to work with. I cut a small patch that I could lay up against the top skin and the spar covering the area of delam. Once everything is ready I mix up some super thin epoxy and apply it carefully between the spar and the top skin plus the adjacent skin that I poked little holes into. Then the fiberglass goes in over the wet epoxy and a little more epoxy is used to ensure a thorough wetting of the glass. Once you are satisfied that everything is done inside the wing, then lay it on the magazines (or whatever sort of "bed" you have come up with) and stack books or the like on top of the wing to keep pressure on the upper skin so it will lay back down flat and contact the spar. After the epoxy has thoroughly dried you can pull the wing out of the "bed" and inspect the repairs. If all looks ok, you can glue little strips along the edges of the access hole that provided a "shelf" for the approx 1" square to sit on. I glued them back on the wings and then used taped to cover the small gaps. My repairs do not look new again but they are strong and they seem to be working out ok.

Good Luck,
Charlie
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Old Oct 10, 2012, 05:20 PM
sewing machine thumb
United States, CA, Palo Alto
Joined Jul 2001
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Quote:
Originally Posted by leipold View Post
There's a 6-cm-long split in the leading edge about halfway out the right wing. In that region, from the leading edge back to the spar, the top skin depresses and makes 'crunchy' noises when pressed.
What about this part of Walt's question? I have a Concept wing which had a split in its leading edge and makes similar crunchy noises and feels a little bit soft forward of the spar. I CAed the split shut and I've tried to wick CA through the skin but with minimal success.
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Old Oct 10, 2012, 05:25 PM
Aussie F3K Pilot
Melbourne, Australia
Joined Jun 2008
488 Posts
I also had a Concept damaged in a transportation accident and it delaminated the top skin in 4 different places (see photo). I did a similar thing to Charlie but cut access holes in the bottom skin, behind the D Box Carbon (and the spar, see photo) and between the Disser Carbon strands to avoid weakening the structure. I wicked in some thin CA to bond the skin back to the spar and then in the areas near the root (that needed a bit more strength/insurance) I layed in a Carbon tow wet with Epoxy and pushed it against the skin and the spar/web. I then put my skin pieces back in place and CA'd them. All done!

I have flown in some big winds and so far it is all holding up fine.

To fix the crunchy bits I use a medical syringe needle on my CA bottle, then put a pieces of clear packing tape over the wing (to stop CA running all over it) and jab the needle through the Carbon skin multiple times (about 10-20mm apart) and squeeze in some CA. It takes a while to get the pressure and needle angles right and also to stop CA running out while you jab the wing (support the wing vertically), but the CA wicks into the Rohacell nicely and forms a hard surface. Also, the quality of the packing tape is important ( I don't have a brand) as some break apart after you are done.

Good luck with your fix.

Marcus
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Last edited by Machineman; Oct 11, 2012 at 07:22 AM.
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Old Oct 11, 2012, 01:33 PM
Zeus
Wild East
Joined May 2008
259 Posts
crunchy noises

Quote:
Originally Posted by Frank S View Post
What about this part of Walt's question? I have a Concept wing which had a split in its leading edge and makes similar crunchy noises and feels a little bit soft forward of the spar. I CAed the split shut and I've tried to wick CA through the skin but with minimal success.
As sorry as I can be for the damage, perhaps I can give some input for help...

Especially, if the leading edge parting line was split open due to impact, most likely the inner shear web has separated from the Rohacell around the impact area which would be typically a source for the crunchy noises.
Needless to say, that here any attempt to fix this problem from the out side would rather fail, since the inner shear web can't be reattached this way.
Here I would recommend the method, so nicely described by Charlie, as the only possible way to go.
The only difference might be the fact that the leading edge is split open.
You can try to open up the split even a bit wider and hold the two shells apart by inserting some Balsa- or other wood pieces of suitable size, to provide a kind of "access hole", big enough that the fix after Charlie's method can be carried out, without cutting any access hole directly into the shell, as long as the damage is in front of the main spar.
After the fix is done, it should be easy to close the leading edge by a few droplets of CA.

Good luck, Roland
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Old Oct 11, 2012, 02:00 PM
usaf3kteam
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Roland what are you doing up?
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Old Oct 11, 2012, 04:20 PM
De Chelonian Mobile!
leipold's Avatar
Wilmington, Delaware, USA
Joined Jul 2006
199 Posts
Thanks to all of you for the detailed repair advice. It sounds like I have no choice but to cut the patient open -- I don't think the leading edge crack is quite long enough to work through. Since the season is over, there's no hurry, so I probably won't start the repair until mid-November. (Gotta clean off the workbench first.) If I find any surprises inside the wing, I'll be back with more questions.

Oh, yeah, and since I didn't say it before, the CX2 is an *awesome* airplane. Thanks, Roland!

-- Walt
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Old Oct 14, 2012, 08:52 PM
usaf3kteam
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How is Roland and Mong? It was 100F here today but 56F this morning talk about a change in temp in one day. Cheers
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Old Oct 15, 2012, 02:15 AM
Zeus
Wild East
Joined May 2008
259 Posts
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Originally Posted by rcgeorge View Post
How is Roland and Mong? It was 100F here today but 56F this morning talk about a change in temp in one day. Cheers
That's perfect conditions..... In the night the beers get cold for free and the next morning you can start drinking ice cold Coronas....
On Thursday we are going to the south and take our day off in Saichia paradise with some heavy flying and enough beers afterwards. Also trying FPV for the first time to find some lost planes in the jungle....

Cheers,

Roland
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Old Oct 22, 2012, 07:50 PM
usaf3kteam
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http://www.rcgroups.com/forums/showa...0773326Another great contest for the Concept-X2 1st and 2nd at sage much fun cheers
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