Fixing a plug mistake

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#1

I am making a plug of a wing. It is 60" long and 12" wide. I am currently sanding, and sanding, and sanding, and sanding to get it perfect. The trailing edge wasn’t straight, so I was using my 15" sanding block to get it even. For whatever reason, perhaps the combination of Bondo fumes and Budweiser, when I got to the end I wasn’t seeing straight. I basically sliced back the end 5 inches a small amount. At the very end, it is about 3/8" cut back, and it tapers in a straight line inward 5 inches where it is correct.

I was about to mix up some microbubbles and try to somehow form the correct shape. It would involve putting the putty in, letting it set up for 24 hours, and sanding the crap out of it hoping I don’t mess up and have to start over. I was about to get the epoxy out when I smashed my elbow on my block of clay. That gave me another idea.

Since this is a plug, maybe I could install the parting boards and then use the clay to make the shape. The worry is that it would not be perfect, and I’d have to fix the mold itself if it were way off. But it’s only a sliver of defect.

What would you guys do if you were me? Any advice would be greatly appreciated. Thanks!

#2

I am not sure if I get a good picture of what the defect is, but if it is so shallow, can you build it up using fast curing primer/filler? (polyester based)

#3

I can’t use polyester based anything because it will eat the foam core. Needs to be epoxy based or some sort of foam safe something or other.

Let me try to better describe the problem. Imagine your part is a wing. The back of the wing is the sharp edge. Now imaging giving your wing to an idiot (me) and I sanded that back edge on one end so it isn’t sharp anymore. That’s pretty much what happened. Further, I dropped the wing when I was spraying primer on it and took out a 3/4" chunk of the back edge about a half hour ago…

Somebody said I should use Gorrilla glue (the foam stuff) and “grow” the edge back. Then glass and sand. I may try that.

#4

Have you glassed the wing core yet?

#5

Yes. It was glassed last week, then bondo’d, sanded, bondo’d again, sanded, sanded, bondo’d, sanded…

But where I sanded the end, the glass is sanded away and the foam is exposed.

#6

I would take some glass and some foam safe CA and quickly build it back up and then sand/fill. The CA will saturate the glass and cure in 2 seconds. Perfect for quick repairs.

Did you use the mylar transfer method to apply the glass to the core?

I’ve made most of my wing plugs by vacuum bagging 1/64" plywood and 3/4 ounce glass onto the core via the mylar transfer method.

BTW, the back edge of a wing is called the “trailing edge”.

#7

Thanks. Yes, I am aware of what the back of the wing is called (15 year pilot, aerospace engineering degree, etc. lol). :slight_smile: I was trying to use layman terms.

I’m not familiar with the mylar transfer method. I will look it up. Thanks!

#8

I had a couple of places on the plug where I sanded too much the glass skin and had to do major surgery. First microbaloons with epoxy and then a precise poliurethane filler alexis bladerepair.

#9

I think I understand the problem now.:smiley:

I’ve done things similar to what you are trying to accomplish on foam plugs before. If you are good with the clay, you can get a fairly good result but it will be an artistic endeavor and you may end up touching up the mold anyway. I’ve had good success coating the foam with epoxy and then using a poly or vinyl ester filler. From your description, I don’t know if a filler will have enough bonding strength to withstand sanding it back to shape but it’s worth a shot.

Maybe an alternative would be to install the parting boards as you suggested and then use a filler. If what I imagine is the problem the board could act as a backing for the filler or at least create another attachment point.

#10

That’s a good idea.

I tried the microbubbles bit and it fell off… lol (noob alert). So I just put a layer of microbubbles/epoxy over everything that got screwed up so I can use whatever I need to to fix it. I’ll try the bondo filler (I think it’s polyester). Thanks!