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Old Oct 31, 2011, 09:36 PM
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Idea
Molded Wing Repair

Happy Halloween, meet F.S. Trugly (FrankenStein ugly FS3). This comes from the ashes and down under, actually way down under, like China where I crashed it.

You don't let a Freestyler die so I had to come up with some idea how to fix it. The damage was limited to the leading edge of both wings and since I have another FS3 the original idea was making a mold using the good wing.

Had done that in the past for a friend pulling a mold off my Aspire tip. At that time I wrapped the top and bottom of the airfoil to make a single mold which does work but then it is very hard to pull a good skin replacement out of such mold, the LE doesn't like to stay attached to the mold.

First I'll show pictures of the Aspire wing mold since I didn't take any pictures of the FS3 during the mold process.
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Old Oct 31, 2011, 09:36 PM
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And here it is, the lovely and repaired FS3. I wouldn't post any repair ideas without testing so I tried to break this wing on launch without success. Must say it wasn't windy enough for a full test but I tried with all sorts of line thickness, drum diameters and ballast and so far so good.

So here is the repair idea. I build the molds for the FS3 in two separate sections, top and bottom. This way I could easily bag a new skin replacement, sort of like the way it is done by the manufacturer. Done that for one wing and then came the idea, why build a skin then glue the skin to a piece of foam them cover all with some glass if I could do all at once.

So here is the sequence. Build a mold form another set of wings, good to have friends with the same model. Clear the damaged LE. Cut a piece of foam with the airfoil shape, you can sand the foam if needed. Roll bias carbon fabric or glass to the foam and roll some epoxy on it. Install this in the wing, the foam is longer than the damage so you have to slide it inside the wing. Get some 1mm Rohacell or balsa, roll some epoxy and put on top and bottom of the damaged area. Now put an outside layer of bias carbon, you can use glass above everything for a better finish. And last, put your wing mold above all this, yes it is a Taco.
I know you are confused so just follow through the pictures.
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Old Oct 31, 2011, 10:15 PM
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So, if you build your mold thick enough and all goes well, your repair is done, just sand a bit of the edges and paint. Or you can paint the mold and be done on a single step.

I can say this part of the wing is much more ding and crush resistant then the rest so I probably overbuilt as usual.

As weight goes, no biggie on a B plane but I think it added close to one ounce per side.

If I would do it again, I would probably build a single piece mold.

Glauco
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Old Nov 01, 2011, 01:42 AM
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Great thread Glauco! Thanks!

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Old Nov 01, 2011, 02:36 AM
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Great tips Glauco. Thanks for your efforts.

I had planned on doing this to repair a Furio a while back only thing is the donor Furio had exactly the same damage so I couldn't take a mold ;0(

I guess I need another pristine Furio ;0)
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Old Nov 01, 2011, 04:27 AM
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Are you leaving the white foam fractionally over-size so it's compressed by the mould? Or put another way, are you using the compressability of the white foam to ensure a good contact between the carbon and the mould surface?

Thanks for sharing.
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Old Nov 01, 2011, 04:47 AM
flo
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Hi,
great idea.
I do it slightly different. saves the "hazzle of sanding foam... in your otherwise great repair.
Just a variation for those intrested:

First of course cut your break clean and campfer the flanges, same as above.

1. I produce 2 single mouldet pices, one made of cf one of glass. (reason later)
-the carbon one is taken from further out of the wing , as it goes inside
the wing.
- the glass one may be build either side, i usually build it from further
inwards as so i do both pices in one go.

2. no need to wax and pray, just pull kitchen-cling wrap around your wing.
Pull it wrinkle free with tape. Tape off rest of wing to keep clean.

3. After laminating the cf putt a layer of peel ply on top as a last
layer.
This will ensure good bonding without the hazzle of sanding.
Pull thight with kitchen cling wrap again.

Note:
the cf will be glued inside and will thake the loads so i usually about double the amount of cf that is in the wing outer layers.

4. before "laminating" the glass putt a layer of peel ply as a first
layer
for same reason as in 3.(just other way round) cling wrap agian...

5. Once cured glue in your cf layer/part whatever you may call it now
overlapping your damaged area as much as you can. I often do cut open
the LE for a few cm to pry open. Use "Endfest 300" (sorry i am german) or
likewise for a strong bond. reglue LE in the same go.

6. slide glass part over your damaged area and trace outline (this is the
reason to use glass - you can see through) cut and campfer to fit.

7. cover your glass part with wide office/packaging tape on the outside.cut
around cleanly.

8. Now fill your damaged area with a dry, not runny mix of micoballon and resin (quite lightweight), push your glass part over it and squize using long wooden blocks to keep things straight. The office tape will push your part about 1/10 of a mm below your wing and thus there is a tiny recess to fill and sand. (better than standing proud and beeing sanded off again.)

sounds like a lot of work but it is easy and fast, reliable and quite lightweight. I have repaird many wings for my buddyies this way. Done right a few of this planes still DS like before.

greets from munich

flo
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Old Nov 01, 2011, 09:45 AM
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Quote:
Originally Posted by Shedofdread View Post
Are you leaving the white foam fractionally over-size so it's compressed by the mould? Or put another way, are you using the compressability of the white foam to ensure a good contact between the carbon and the mould surface?

Thanks for sharing.
Correct, I even thought about using EPP for this reason. Actually, I tried to cut the foam as close as possible to the airfoil but knew the added layer of carbon would give the oversize dimension.

Glauco
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Old Nov 01, 2011, 11:02 AM
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repair

Hi Glauco
Missed you this summer but I know you had a good time.
You have seen some of my repairs so I thought I would tell you how I would have done it. I piece in wing skins from wreck wings that have undamged aeras. I have done this on serveral planes with zero failures and on repairs larger than yours and the wings are hollow when I am done. I know some are going to say its a different airfoil but once the patch is cut out of the doner wing it is only skin and you can form it to match your wing. this is how I do it.

Cut a patch from the doner wing for the top surface, I cut the sides at angles, don't have to be 45 degree what ever looks right. Use the patch to trim the damaged aera so the patch is as close to perfect fit as you can get. CA it in very carefully aligning the surfaces. Done right there will be very little fill. I then glass the inside of the top surface with 1 1/4 glass, use a little light cabon if you think it needs it maybe up around the spar but remember on most planes it was two layers of glass with foam in the middle.
On the bottom you can't glass the inside to join the skins so I will put in a ledge made of 1/32 balsa to join them together. 1/2inch wide med balsa cut across the grain, 1/4 inch CA under old wing 1/4 inch exposed to lay patch on. Put a good layer of epoxe and micro balloons on the inside LE so you can match it. I then sand top and bottom fill as needed, wont be much if you did it right and glass top an bottom with 1/2 oz cloth

I repaired two planes this summer for Norm Poti this way using skin from Mark's Tragi. One a Image with damage as big as your right wing. That wing wieghed 17 grams more than the wing I did not fix and I painted 2/3 of that top wing.
The other was a Perfect that he flew at Fall Roundup and placed 2nd or 3rd with on Sun and it will launch just as hard as when Chris had the plane.

As I said at the begining you have seen my repairs and know the are sound
Hope I explained it well enough

See you next summer .
Jerry
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Old Nov 01, 2011, 12:45 PM
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Jerry,

No one that has seen your repairs will question you are one of the best. From all the repairs I've seen, you and Mark Miller are the masters.

Have repaired a few wings like you described and have a stash of broken wings to serve as a donor, I agree it is a lighter and simpler way to do it.

The reason I did this more complicated version were two. First it was a serious crash where I bent some steel tubing so don't know the extent of the damage. Since this is a F3B plane it has to take serious abuse on launch no other type of plane sees it.
Second reason was airfoil integrity since flying fast requires a bit more precision in the airfoil.

Don't really know if it is worth the effort repairing this way but wanted to pass the experience.

Glauco
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Old Nov 01, 2011, 02:33 PM
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I have no way do judge airfoil integrity but have had people not no which side I fixed so I think I am pretty close. Is it close enough or stong enough for F3B? I think it is but may be wrong, haven't had any experince with that.The one thing I wondered about was the foam in the wings.Is that a good thing? I like the tips as light as I can. One other thing, if motivated enough I could have had it repaired and painted in three evenings. I do like all the work you went to, it seems to be the only modeling we get to do these days. By the way, not looking for any jobs. So little time to get anything done these days.
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Old Nov 02, 2011, 02:16 PM
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Was a laboratory, an elevated table, and lightning involved?!?!
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Old Nov 02, 2011, 08:23 PM
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Wait until you see Brendan's Tragi repair....Just finished the fuselage. Broken into three pieces. Back together. Paint matching. It weighs 1/10th ounce lighter than my unprepared one.
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Old Nov 04, 2011, 06:21 PM
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I just happen to be repairing a skin delam myself. I have the damaged portion of the wing protected with tape, then tape on some breather. I make two holes in the surface skin at opposite ends of the delam. One is to inject resin into, the other is to use vacuum to pull the resin through the delam. I then cover the area with bag and chromate tape, pull vacuum. Peirce a small hole in the bag where I want to inject resin between the skins and inject the resin, seal the hole with tape. The vacuum will pull the resin through the delam and pull the skins back together.
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Old Nov 04, 2011, 07:12 PM
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Let me see if I understood your delam repair method.

The hole you poke in the skin to inject the epoxy goes through only the outside shell and stop at the Rohacell, otherwise the epoxy would flow inside the hollow part of the wing, correct?

Is the vacuum efficient pulling epoxy through Rohacell?
How far can you make the exit hole from the place you inject the epoxy?
Heated epoxy to help lower the viscosity?


Thanks,

G
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