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SuperCub Wing Shear Repair (With pics)

Old 12-26-2008, 09:59 PM
  #1  
bullrich
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Default SuperCub Wing Shear Repair (With pics)

This is a follow-up from my "First Flight, First Repair" post (http://www.wattflyer.com/forums/show...d=1#post531427).

Since I tore the entire right wing off at the root, I was immediately thrown into the world of "Fix It If You Wanna Fly It" that some many of you know so well. So...this morning I trekked over to my LHS and got some advice, some parts, and headed home. Here's the result:

Synopsis: I needed to repair a cleanly sheared foam wing. I was concerned about the strength of the repair because the shear was at the wing root, which bears a fair amount of wing-loading, and this wing lacks a traditional wing spar. Planning to use foam-safe glue and tape, I decided to re-inforce the repair using carbon fiber rods embedded in the wing foam.

Material:
  • 1 stick of Carbon-Fiber Rod (Midwest Products, Part number #5709)
  • 1 bottle of foam-safe Cyanoacralate (CA, or "Super Glue for Modelers", easily found at any hobby store)
  • 6-8" of blue painters masking tape
  • 14" of hockey stick tape
  • 1 small piece of 120 grit sandpaper
Tools:
  • small hobby saw (to cut carbon-fiber rod)
  • Black Sharpie pen

Process:
  1. Ensure wing pieces fit together cleanly.
  2. Using hobby saw, cut carbon fiber rod to length (for me, about 5.5" did the trick)
  3. Using the sandpaper, sand each end of the rods to a point, to aid in inserting into the foam.
  4. Dry-fit the wing together, and tape along the underside using the painters masking tape (I use this because it peels off easily, but still holds well enough to perform the measuring and marking)
  5. On top of the wing, place the first cut-carbon-fiber rod perpendicular to the shear, near the leading edge of the wing.
  6. Using the Sharpie, mark a line indicating the placement of the rod in the wing.
  7. Repeat steps 5 and 6 near the trailing eadge, ansuring that there is enough wing chord to work with. Remove painters masking tape.
  8. On the larger wing piece, line up the rod with mark on the top of the wing, exactly halfway through the wing chord (this is tricky; I measured it, and still had to adjust about 2mm to get it right due the vagaries of the jaggedness of the shear. Experiment carefully), and mark the spot with the Sharpie.
  9. Slowly insert the carbon fiber rod, turning the rod back and forth with your fingers as you apply downward pressure, until it is about halfway in.
  10. Line up the second wing part with the mark on the top of the wing and the embedded carbon fiber rod. Using the same method from above, mark a spot with the Sharpie.
  11. Line up the wing pieces, then slowly push the second wing piece on the rod, ensuring each piece lines up perfectly (again, this might take a couple of tries, but foam is a forgiving medium).
  12. Once the first rod is settled, remove it, then repeat process steps 8 though 11 for the second rod.
  13. Re-insert the first rod, and dry-dit the wing together again for a final time, checking fit and alignment.
  14. Once you are satisfied, pour CA into the holes on the second wing piece for the rods.
  15. Apply CA liberally along the edges of the shear, and along the interior areas.
  16. Immediately fit wing pieces togther, and apply pressure for approximately 2 minutes, or until glue takes hold.
  17. Apply additional glue to any separation along the shear line, and again apply pressure until glue sets.
  18. Place wing in natural position on work area, root section down, supporting the wings dihedral (upward tilt) with any item that does not artificially increase the dihedral (I used 2 rolls of masking tape, 1 for each wing-tip). Then place something heavy on the root section to hold the wing in place. Let glue cure for an hour or so.
  19. Using hockey tape, wrap along shear line once or twice, starting rearward from leading edge, applying pressure to ensure adhesiveness (I used hockey tape instead of packing tape or other nylon/plastic reinforced tape because it is highly adheasive, is cloth beased and highly re-inforced, and is fairly lightweight).
  20. Re-attach wing.
  21. Fly airplane.
  22. Repeat as necessary :-)
Happy fixing, and even happier flying!

Brian
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Old 12-26-2008, 10:02 PM
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birdDog
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Generaly, we all become excellent mechanics/body repair persons before we ever become good pilots. Sounds like you are on the right track.

P.s. the clear packing tape has about zero stretch.
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Old 12-26-2008, 10:06 PM
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xuzme720
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This is a super post on a sometimes difficult type of repair! Fantastic info, but you mentioned pictures in the title.:o
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Old 12-26-2008, 10:20 PM
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Rolling Thunder
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its nice to know that even the pros will dork em' into the ground like the rest of us.Nice explanation of the fix.You might want to try using gorilla glue next time.It expands as it drys to fill in little voids
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Old 12-26-2008, 10:39 PM
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cbatters
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Nice report on repair.

Note: I have had much better luck with 5 minute Epoxy for structural repairs. I apply epoxy, press parts together then then apply clear tape over seam and rub flat. Excess epoxy flattens out under tape and creates extremely strong repair.)


Clint

Last edited by cbatters; 12-27-2008 at 12:32 AM.
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Old 12-26-2008, 11:40 PM
  #6  
bullrich
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Good info, all. Clearly, there is more than one way to skin a cat, and most everyone has thier favorite glues and tape selections. In retrospect, I did not consider the "void" issue with the glue, although I pretty much slathered a sh!tload of CA on the broken side of the wing, so maybe it was more implcit in my mind than explicit. OK, enough psycho-babble.

I love the info on the 5-minute epoxy with the tape taking the excess as well. I took that approach myself with the CA, although I didn't explicitly mention it. Thanks for bringing that up, Clint. :-)

Clear packing tape is indeed HIGHLY stretch resistant, and is light. It's tensile strength is what gave me pause, mostly because of the location of the shear, and that is what led me to my son's hockey bag. Hockey tape is pretty dang stretch-resistant in it's own right, and it's tensile strength is off the charts (any parent who's tried to take taped-on hockey equipment off of their child can attest to this).

And the photos will be coming soon... :-) I just need some time to get them uploaded is all.

My main focus with the DIY was to illustrate how fairly catostrophic damage could be repaired, even in the field, without the need for major replacement parts.

Now, that being said, I am indeed a realist. I did purchase a replacement wing, just in case my repair wouldn't hold...wind. Besides, I don't know how many bad landings this wing will withstand, and with my 9-y.o. son on the throttle also, it's bound to need replacing at some point.

I just hope to get some good air under her before I put several hundred dollars in replacement parts into a $160 airplane! :-)

I sure am glad I found this group. Y'all rock!

Brian
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Old 12-27-2008, 01:48 AM
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cbatters
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You can almost always repair and make the part stronger than the original. The problem is that each repair adds weight and eventually performance suffers. (I have a delta wing that I have shattered into multiple pieces several times and it is still flying strong.)



Clint
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Old 01-03-2009, 04:44 AM
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Airhead
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Clint is absolutely correct. great report on your repair. sounds like a good solid repair. Were there pictures that I missed? I do forget things you know..
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Old 01-08-2009, 11:39 PM
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Wrench66
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I have also used the 'ol epoxy under the tape trick
Another little tid bit trick specially for a wing or other stressed area is to insert bamboo sticks or small dowels (toothpicks also work here) in to one piece and as you apply your glue of choice mate the two pieces...inserting the opposite ends of the sticks into the other damaged piece to act as an internal brace of sorts. I did this with a 40" foamy FW190 that I dumb thumbed while making a low pass at near WOT . The wing (along with all the other carnage) was cleanly split very near the root, I repaired it using this same method mentioned above using gorilla glue and 1/16th wood dowels. Worked great, super strong no worries ALTHOUGH the first big loop I did I was squinting 'cause I wasn't sure she'd come out of it ok.........it was fine

Good luck!

--Ray
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