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Old Jul 08, 2012, 07:43 PM
Mike M.
like.2.fly's Avatar
United States, UT, Eden
Joined Jan 2010
5,071 Posts
Yes, this is the exact same place that Finch's wing broke, on both his CX2's. We have heard other reports of this same thing, and I for one felt some concern. Don't know if it's the summer heat softening the resin, or what.

Please understand that I still love the Concept and consider it at the very tip top of the pyramid in the DLG world. I don't own one personally, but wish I did. I do have some stick time on them and have nothing but good to say. And nobody can argue their performance record, nor the record of the great pilots that own and fly them. So please don't think I'm trying to trash the design, designer, or owners in any way. Discussing these things helps us make them better, right? Or educate us better on how to take care of them. I also don't know the history or details behind the incidents mentioned above, so please take my worthless opinion for what it's worth (zero, I guess ).
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Old Jul 08, 2012, 08:07 PM
Where is the lift?
cptsnoopy's Avatar
USA, AZ, Phoenix
Joined Nov 2005
6,404 Posts
Hi Matt,

When my wing looked like yours, I cut an access hole in the bottom of the wing along the outline of the spread tow square. I cut one in front of the spar and one behind the spar. The upper skin had separated from the spar cap allowing the spar to crush at the RDS openning. Fortunately like you my wing had not fully buckled. I used some sandpaper to scuff the upper skin and the spar and a needle to perferate the inner skin and allow epoxy to flow into the foam. Proppy John gave some German epoxy to use along with some carbon cloth. I applied the epoxy pretty generously to the upper skin that had been deformed and the spar. I layed some carbon cloth against the spar and upper skin to support the area where the RDS cutout was and over the buckled skin. I kept pressure on the skin from inside the wing to help reduce the waviness and let it all dry. Then I glued back in the little access hole squares and it's been fine since. John Finch may have a better technique as he has fixed much worse.

Charlie
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Old Jul 08, 2012, 08:23 PM
hot air rises...
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Pleasant Grove, UT
Joined Jul 2005
7,716 Posts
That looks like it's pretty creased, was yours creased that much Charlie? You're going to have to do what charlie did at the least. Not being able to see it with my own eyes, I could be overdoing it but, I filled the inner space of the wing with 40 psi foam before glueing the skin pieces back in. I've got pictures, but they're home and I'm sitting on a beach in Key Largo . But basically what I did was use a contour gauge to get the airfoil shape for the top skin in the area over the RDS. Then make a foam cutting templates and cut an extra thick wing core (bottom of the wing is flat... no lower template). Then hog out channels for the RDS and spar. Line the outside foam chuck with mylar (or plastic sheeting), back both the chuck and "core" with 3/8" plywood, then glue the top of the core to the upper skin (from the inside) and clamp the core and outside chucks together. this forces the outside skin to bond to the core and conforms to the upper airfoil shape. Then sand the foam at the bottom of the wing to be flush with the rest of the wing. Use a dremel to get the foam just below the skin thickness and glue the cutouts back in. I also put a patch of .75 oz glass over the outer skin on top and bottom. It's been very strong. Adds about .3 oz to the plane.
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Old Jul 08, 2012, 08:30 PM
usaf3kteam
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5,676 Posts
[op corn:
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Old Jul 08, 2012, 08:43 PM
usaf3kteam
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Joined Sep 2005
5,676 Posts
Common sense when 85 to 90 to 100 ,110 keep all your planes in the shade. As resin on all the planes will get soft. Carbon planes of all makes will get weaker if left in the direct sun. And delam as Mikes plane did from a hard landing will be very bad and hard to fix. Remember I also flew that contest as did Charlie with no problems. Donnie and Charlie were with out a Question the highest launchers by far. Any other Concepts at that contest with trouble wings? I saw lots planes sitting in the sun at that contest. Mike yours were in my trailer and in the shade. Hope your Polaris is back together and flying. Cheers Finch have fun in the sun brother see you soon.
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Old Jul 08, 2012, 09:12 PM
Where is the lift?
cptsnoopy's Avatar
USA, AZ, Phoenix
Joined Nov 2005
6,404 Posts
John,

Matt's looks a bit worse than mine did...
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Old Jul 08, 2012, 09:21 PM
hot air rises...
jfinch's Avatar
Pleasant Grove, UT
Joined Jul 2005
7,716 Posts
Looking forward to seeing/flying with all my Concept buddies this weekend. My planes will all be in shade from now on!
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Old Jul 08, 2012, 10:57 PM
C-c-c-custom!
United States, NM, Albuquerque
Joined Nov 2011
330 Posts
Thanks for the input, Finch and CMO in particular. Also, GMO the advice from BSOC was fantastic, launches are much improved with my R/E now tight as can be.

I'll cut open some access squares tomorrow and see what things look like before I decide to proceed. Depending on the state of things I'll decide if I'll go with the internal cloth or foam fill methods.



-Matt
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Old Jul 08, 2012, 11:18 PM
Zeus
Wild East
Joined May 2008
291 Posts
Damage due to ground contact

It is clearly indicated that the delam (disintegration) damage occurred is not caused by overheating, rather than being caused due to overstress during ground contact. Another words, a typical crash damage, which might have been overlooked during repair work.
Picture 2a shows the repair place at the fuselage which shows that the fuse was cracked due to a sideward overload on ground contact. Along with it goes the clear visible crack in the leading edge in an ~45 angle, which indicates the additional contact of the wing tip with the ground at the similar angle, causing this overstress damage due to a high impulse load, starting at the leading edge.
Picture 2b shows the angle of the crack which continues into the delam area at the same angle.
As a consequence, the Rohacell core has been either disintegrated or delamed from the outer- and perhaps also inner sandwich layers.

Some inspection holes in the D_box and behind the spar can reveal the total extend of the damaged area, which might be determined first before selecting the right measures for repair.
If I could have a close-up of such damaged area(s) it would be more easy to suggest the right method for the proper repair.

This type of damage IMO has nothing to do with a buckling caused by overheating and therefore reduced matrix (resin) strength, rather than a sandwich disintegration due to high impact forces.

Roland
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Old Jul 09, 2012, 10:30 AM
C-c-c-custom!
United States, NM, Albuquerque
Joined Nov 2011
330 Posts
Thanks for the sharp eye Roland. There does indeed seem to be a small crack there on the LE.

I have cut two access panels out (one in the D-box, one just behind the spar where the RDS passes) - I tried to take pictures but was not getting anything good. There is breakage of the top section of the spar in the middle of the RDS hole, but it is to one side and appears as a fracture (there are no parts missing, it all fits together tightly until I squeeze). I can spot no delamination or breakage of the inner skin or Rohacell. A small section (about the width of the RDS hole) is the only spar separation.

It looks to me like I fractured the spar, the foam bent inward and the outer skin delaminated. As such, the repair process I would use (I'm a newb so tell me where I'm wrong):

1. From the inside, apply pressure to reshape the LE within the D-box. Wick thin CA to rebond outer skin and force shape to be restored.
2. CA fractured spar back into one piece.
3. Use laminating epoxy with unicarbon to bolster the spar and it's connection to the foam. Potentially add carbon or FG cloth without bias onto inner skin of top wing surface (including recessed area and crack location).
4. Replace access hatches and cover their installation with light glass.
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Old Jul 09, 2012, 08:06 PM
Zeus
Wild East
Joined May 2008
291 Posts
Quote:
Originally Posted by closedloop View Post
Thanks for the sharp eye Roland. There does indeed seem to be a small crack there on the LE.

I have cut two access panels out (one in the D-box, one just behind the spar where the RDS passes) - I tried to take pictures but was not getting anything good. There is breakage of the top section of the spar in the middle of the RDS hole, but it is to one side and appears as a fracture (there are no parts missing, it all fits together tightly until I squeeze). I can spot no delamination or breakage of the inner skin or Rohacell. A small section (about the width of the RDS hole) is the only spar separation.

It looks to me like I fractured the spar, the foam bent inward and the outer skin delaminated. As such, the repair process I would use (I'm a newb so tell me where I'm wrong):

1. From the inside, apply pressure to reshape the LE within the D-box. Wick thin CA to rebond outer skin and force shape to be restored.
2. CA fractured spar back into one piece.
3. Use laminating epoxy with unicarbon to bolster the spar and it's connection to the foam. Potentially add carbon or FG cloth without bias onto inner skin of top wing surface (including recessed area and crack location).
4. Replace access hatches and cover their installation with light glass.
Hi Matt,

That would be pretty much it.....:-)

In addition, you should bridge the leading edge crack from the inside with some carbon strands and thin Epoxy.
From the inside, poke needle holes trough the inner glass layer and Rohacell core within the damaged area to allow Epoxy to seep-in, strengthening the most likely structurally damaged Rohacell, before you apply the inner reinforcement layer. Insert a prepaired rib made from blue foam or similar, to push the outer shell back in place.
Apply thin Epoxy to the outer visible crack and let it seep -in. wipe off the extend with tissue paper......
Return to your suggested procedure.....

Good luck, Roland
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Old Jul 09, 2012, 08:31 PM
C-c-c-custom!
United States, NM, Albuquerque
Joined Nov 2011
330 Posts
Thanks Roland, will do!



-Matt
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Old Jul 10, 2012, 03:30 PM
C-c-c-custom!
United States, NM, Albuquerque
Joined Nov 2011
330 Posts
Well, it worked!

Flew like new today. Best of all - after both repairs (fuse + wing) I'm at 9.75 ounces. Figured there would be a much higher toll with all the carbon and epoxy that has been added.

Thanks again for the help guys!
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Old Jul 11, 2012, 11:46 AM
Zeus
Wild East
Joined May 2008
291 Posts
Quote:
Originally Posted by closedloop View Post
Well, it worked!

Flew like new today. Best of all - after both repairs (fuse + wing) I'm at 9.75 ounces. Figured there would be a much higher toll with all the carbon and epoxy that has been added.

Thanks again for the help guys!
You are welcome Matt! And congratulations for the successful surgery...

Cheers, Roland
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Old Jul 12, 2012, 10:44 AM
Chuck 'Em and Chase 'Em
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United States, NY, Plainview
Joined Aug 2005
8,116 Posts
is there any need to stagger the height of the servos so the arms of the back servo do not hit the pull- pull cables of the front servo?

I was thinking of putting a bass or ply shim glued in place to raise one of them.
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