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Darren_O

Stark wing repair

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Darren_O

Spar, skin and servo pocket needs doing.

Spar will be done with carbon tow, several layers like a leaf spring to try to avoid creating a break/stress line.

Servo pocket will have some carbon cloth layed into it.

Rest of wing I'll cut some blue foam OR has anyone tried expanding foam for this this type of job? Would create a perfect fitting foam base for a carbon/glass skin and save a bit of time.

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Darren_O

No answer on the expanding foam so I'll leave that for another day. I've put some tow on the opposite wing to set, then I'll use it to make a frame for the new wing skin to sit on. Cling film over wing and a ziplock bag with water in to hold it flat.
Servo pockets have had the carbon laid in. I only had 200g cloth so it's a bit heavy for the job. Should have used glass really thinking on it.
 

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oipigface

I've used expanding foam (Gorilla Glue) to replace foam melted by mistake in a foam wing, but not for any hollow moulded structure. Give it a try. I can't see that much damage can be done, and you'll be able to entertain us with your experience.

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satinet

It's not a hollow moulded wing John, it's a foam core DLG wing.

Personally I don't think expanding foam has the required density for the job.  I would glue in foam blocks to the shape of the aerofoil and glass over.

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Darren_O

I was thinking builders foam rather than gorilla glue.  

Going with a carbon tow frame now....

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Peter G

Don't use builders foam :no:

Unless you can acurately calculate the amount of expansion and the volume dispensed (which you can't). I know of a hollow moulded wing repair that resulted in a significantly 'modified' wing section after squirting in builders foam. Its quite powerful stuff when trapped in an enclosed wing structure.

It went from a nice RG15 modified to something resembling a Clark Y! Total disaster.

Gorilla glue is a different kettle of fish as its expansion is more controlled but still quite tricky to predict. Tom's suggestion of foam blocks and sanding would work well.

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Darren_O

The actual part that needs foam is open topped bit behind the LE and in front of the spar, I figured the open top would allow expansion without distortion.
Been experimenting with lightweight filler and epoxy mixed,anyone used it before to fill gaps that need a bit of strength? Want to use it to push into gaps by the spar.
Having studied the wing I've realised it's effectively the same design as the spar. The foam keeps the two skins apart creating a lot of stiffness. Because the bottom skin is partially missing along the entire chord I don't think a simple butt jointed new skin will be strong enough.

 

IMG_20170420_183008.jpg

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Eryk

Trim some XPS or similar foam to the size of space, make sure it's standing out of the wing a little so that in later stage you can sand it down.

Glue it in with satisfactory amount of epoxy & aerosil/microballon.

Sand the excessive amount of foam to section shape (frog tape around the hole to avoid damaging the healthy part).

If it's a carbon wing use some Carboline/textreme/Vlad etc. to cover up the patch and add some glass for top layer, if glass, use a layer or 2 of 25-50g/m2. Make sure it's overlapping on the edge of the healthy part of the wing.

Wet the fabric on the side on a piece of PET/mylar etc. cut to the shape of that section of the wing.

Stick it on, press from top and bottom with some foam, the kind you find in furniture etc. and let it set.

With enough luck you'd end up with a not-so-heavy need-no-putty patch.

All you've got to do afterwards is to sand it with some 1000-1500 wet sanding paper and paint spray lightly.

 

That's at least how I'd do it. Tried in past with hollow mouldies with good success.

 

PS. Instead of making tow 'structure', mould a piece that would cover the whole patch on the other side of the wing. Then use some XPS to fill the gap and glue in using Epoxy & filler.

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Darren_O

I don't think paint is an option, I can't get the RAL number off the manufacturers for a paint match. Although I may add a black stripe over it.

My thinking with the filler/epoxy mix is that is would add strength, if you look the foam is cut through the entire wing, the damage, the servo pocket and then the tunnel that the pushrod travels through means there is no strength at along the chord. 

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Eryk

A black stripe would do, brings more colour 😂

Whole strength of the wing is in spar and wing skin. As long as the foam doesn't have space to move it'll do it's job. 

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Darren_O

Foam in, spar done and 2x layers of carbon cloth laid on opposite wing to mould using freezer bag filled with water to weigh it down,conforms to curve and leaves a decent finish (hopefully).

I'll be making a skin to go over both sides where the pushrod is routed as well, only thing structural left is top wing skin so it's a weak spot. 

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Darren_O

Patch #1 in place overlapping damaged area. Two layers of light carbon weave.

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