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Author Topic: Warped Foam Wing Fix?  (Read 859 times)

Online Motorman

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Warped Foam Wing Fix?
« on: December 22, 2019, 05:39:40 PM »
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« Last Edit: August 27, 2021, 11:45:59 AM by Motorman »
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Offline phil c

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Re: Warped Foam Wing Fix?
« Reply #1 on: December 22, 2019, 06:05:46 PM »
About the only way I can think of is to use a very sharp, thin knife to break the sheeting free, or just break it off in bits.  Foam usually doesn't take a set, so once enough sheeting is off you can see it the wing core can be straightened out to match the other side.  Then figure out a way to resheet it.

It's probably easier to build a new wing.
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Offline pmackenzie

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Re: Warped Foam Wing Fix?
« Reply #2 on: December 22, 2019, 06:25:20 PM »
Before you run a lawn mower over it, try cutting some spanwise slits through the sheeting.
Then twist it flat and re-glue the slits with foam safe CA.
Removing the TE might also let it move enough to get it straight.
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Offline Avaiojet

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Re: Warped Foam Wing Fix?
« Reply #3 on: December 22, 2019, 06:43:32 PM »
Quote from: pmackenzie on December 22, 2019, 06:25:20 PM
Before you run a lawn mower over it, try cutting some spanwise slits through the sheeting.
Then twist it flat and re-glue the slits with foam safe CA.
Removing the TE might also let it move enough to get it straight.

I believe the "cut" is to be diagonal for the fix, like from the LE to the TE the span of the half wing. Examination is important so the cut is made in the correct place.

You have two, are they both "twisted?" If they are R/C cores, possibly washout?

Guessing? 
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Online Brett Buck

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Re: Warped Foam Wing Fix?
« Reply #4 on: December 22, 2019, 07:46:14 PM »
Quote from: Motorman on December 22, 2019, 05:39:40 PM
I bought a set of Robins View balsa sheeted foam core wings 2nd hand and I think I know why the guy sold them. Didn't notice it until I started lining them up to glue the two halfs together. The out board wing trailing edge is up a good bit at the tip. Didn't know this kind of wing could get that way or maybe it got by QC but I'm really bummed about this whole project now.

Anyway, is there a way to get the wing straight again? It looks like someone has already sanded the sheeting as far as it will go and it's still going to have an effect on trim.

Was thinking to just sand it all the way into the foam then Zpoxy some fiberglass over the area. Or maybe glue some 1/16" balsa sheet on the other side and feather it in?

Also thinking about running it over with the mower so any advise would be welcome.

      Take a long, thin blade (like the Exacto carving blade), and cut all the way through the TE, horizontally, and the foam, up to the first hollow part, from root to tip. "Horizontally" meaning just like you were cutting slots for hinges, except much deeper and all the way from root to tip. This will leave the top and bottom of the monocoque shell separate at the TE. Figure out how to use the cradles to hold it straight, and test-fit it for the correct TE depth, and if necessary, cut a balsa shim to take up the space. Then take a thin metal ruler or something like it to put epoxy in the slot you cut, both sides and the "shim", if needed.  Then put it in your cradles, weight it down enough to make it straight, but not so much as to distort it over the hollows. Let cure, then square up the TE with a plane and sanding blocks. If you need to take a lot of material, add a cap on the TE to make up the lost wood.

   It won't be perfect, but you can get it very close, and you don't have to cut into the wood on the surface where it shows.

     Brett
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Offline Dan McEntee

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Re: Warped Foam Wing Fix?
« Reply #5 on: December 22, 2019, 09:48:32 PM »
  Lots of things can make an unfinished skinned core twist or warp, like how it is stored and temps involved, and add in humidity. It needs to be clarified by what exactly "warped" is. If it is more like a twist, the wing can be shimmed straight. I learned this back in my R/C sail plain days. You make diagonal cuts through the balsa sheet, then force in 1/64" ply shims. The severity of the twist determines how many shims you have to apply and how many cuts to make and where. This can work with a twisted fuselage also. Once you are satisfied, tack glue the shims in place, rough trim them, run a little foam safe glue over the shimmed area, and when dry, finish sand to final shape. the guy that taught me this trick learned from some guys that flew R/C pattern models with foam wings. Foam wings cores are not fool proof, and if not stored correctly can and will twist or warp.
  Type at you later,
   Dan McEntee
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