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Old Mar 10, 2012, 03:58 PM
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Wing repair suggestions for my Akcent

Hello all,

I've had an incident with my Akcent II.

I've repaired a fair number of models in the past, but this is my first problem with a foam-core disser wing, and I would like your suggestions.

You'll see in the pics that the top of the right wing has suffered some damage. The is a crease that extends from the leading edge to the aileron hinge line, directly over the hollowed out portion for the top drive pushrod. The carbon cap has buckled slightly under, and the wing (obviously) flexes on this crease. And as I'm right-handed, this is the throwing side of the wing.

Not surprisingly, I want my repair to be strong, not disrupt the airfoil, and light.

I have the following materials available to me:

West systems finishing resin
.5oz fiberglass cloth
1.5 oz fiberglass cloth
a small portion of fairly light CF cloth
yards of fairly thick and heavy CF cloth
plenty of carbon tow
plenty of kevlar tow
cured carbon skins from broken heli blades that could be used as shear webs

A buddy has some vacuum equipment, but I think using that here is a long shot.

As this is a moldy, I don't have original wing beds for it, but I do have wing beds from my Arrow that are pretty close, and could be used if needed.

I don't care about looks -- I just want it strong, light, and clean.

Advice, please!

Thanks in advance, Mark
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Old Mar 10, 2012, 06:17 PM
Jim C
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Is the spar broken? Are the skins Rohacell? That will be good to know first.
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Old Mar 10, 2012, 06:53 PM
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It's solid core, something other than Rohacell, can't use regular CA. That spar looks to be damaged, you'll likely have to insert a few CF rods along the spar stiffen the area. You can fill the crease with lightweight spackle and glass patch it. Steam makes a blister pretty fast on those wings, I'd just avoid doing that.
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Old Mar 10, 2012, 06:56 PM
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Spars are intact. The wing is solid machined foam (orange in color, I have no idea of what type ), covered with carbon disser and light fiberglass.
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Old Mar 10, 2012, 08:14 PM
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I forgot to mention that I also have some small diameter carbon tubing available, as well as some carbon flat stock.


Thinking about placing some spanwise reinforcements below the skin, there are some obstacles -- specifically the aileron servo and the pushrod. I think that rules out using the flat stock or the carbon skins from heli blades as shear web reinforcement.

However, the tubing is a possibility.

My current thought is to place carbon tubing reinforcement about 1/8" in front of the servo, another just behind the spar, and a third in between the spar and the pushrod exit. Each of these could be buried below the surface of the wing.

Then maybe some 1.5 oz fiberglass cloth over the whole thing. Finally, spackle to smooth out the airfoil and perhaps .5 oz cloth over that.

Comments, thoughts, advice, or critique?

With this plan, how long should the reinforcing carbon tubes be?

-- Mark
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Old Mar 10, 2012, 08:44 PM
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Mark:

I'm looking at the pictures, and I need to understand. You can't use the sear webs, because the servo push rod has to go through, right?

If you do go the carbon tubes (or rods?), be sure the each is a different length. I'd put the longest one closest to the spar.

Yours, Greg
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Old Mar 10, 2012, 08:50 PM
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Greg,

you've got it sussed.

Aft of the servo, the aileron pushrod would have to go through any reinforcement that protrudes too far below the top of the wing. So a full-depth shear web is out. And of course, the further one goes back, the less depth one has to place the reinforcement.

I'm not too sure how far back I could place a tube reinforcement, but I believe that I could sand a recess in for the flat stock fairly far back, and then maybe place CF tubes just behind the spar and just forward of the servo.

Suggestions on the length of each reinforcing piece?

-- Mark
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Old Mar 10, 2012, 10:48 PM
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Mark:

How about this: use the carbon shear webs anyway, one each side of the spar and full wing depth. Use tapers at each end to avoid stress risers. I'd slit the skins from the top, use thin epoxy. You'll have to remove (temporarily) the push rod.

You've got the tunnel for the push rod as a guide. Use it to bore a new hole, small, in the new web for reinstalling the push rod.

For rods or tubes, I don't have any direct experience or expertise. I would use maybe six inches at the spar, and four inches in front and rear. That way, there would not be any stress risers from all of them ending at the same span-wise location.

I admit to a personal interest in your success, seeing as how I caused the problem. Good luck!

Yours, Greg
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