coloradoz

My Feedback: (38)

Hello all, I think I'm needing some help in the repair of a fiberglass fuse. I am wanting to relocate the engine from a top mount to side mount - as such I need to rebuild the fuse and cut my new holes. I used some foam sealant to build a 'plug' in-place. I sanded it and got i looking - more or less - like the original. I know it will take some work to get the finish right, but I used some finishing resin and glass cloth from my LHS. I wrapped it onto the foam plug. But alas, this thing never cured. It was spongy and was hardly stiff enough. Also, when this cured - it shrunk to the point of melting the top part of my plug. Soooo, I ripped it off and here I am.

I think I'm needing very specifc information on exactly what kind of epoxy resin to get, cloth, etc. In this application I know there will be heat generated that could deform the plug - how do I deal with that???


...AJS

ps2727

AJS,
You didn't say what kind of resin you used, but a couple of things come to mind. First you must know if the original fuse is polyester or epoxy. Both types are used in model parts although nowadays most are epoxy. You should use the same resin for your repair. Some epoxies don't cure properly over polyester and vice versa.
Also the foam you are using might also be interfering with the cure. I suggest making a few test samples of resin alone and then resin over your foam to see if you get a good cure.
You mentioned that the resin melted the plug. Polyester will attack the kind of foam normally used for modeling but I'm not sure about the foam sealant you mentioned.
If the foam is the problem you might try tack glueing thin balsa to the inside of your fuse. Then do your fiberglass layup over the balsa to "fill the hole". After it cures you can sand away the balsa and shape the repair. You may need to add more glass and resin to build up to your desired contour. Once to hole is filled simply add and remove until you get what you want.
Hope this helps.
Paul

coloradoz

My Feedback: (38)

Thanks Paul - Firstly, I'm not sure what kind of resin it is - the plane is a Bridi UFO - maybe you can tell me, but I thought it was epoxy resin. I did try - after the fact - a test piece, and it didn't harden very well either. I think part of my problem is the resin itself - I just don't know what to use and where to go get it. The LHS has SIG polyester resin - but that won't work on Epoxy (maybe a bad assumption in 2 dimensions?). I can't say the the foam was really 'attacked' - like i've seen before in my deep dark past - it was gradually eroded over a period of 3 days - but like I said - it appeared that my patch was shrinking too.

ps2727

AJS
If your test didn't harden then it's gotta be the resin. Hobby shop epoxy will work but don't get the 5 minute stuff, go for at least 30 minute or even more. You want a slow cure to allow time to get it just right and its a stronger bond.
I don't know if Bridi used epoxy or not but polyester parts are rather stiff and brittle and if you lightly sand the inside somewhere there is no mistaking the smell of polyester. If you decide it really is epoxy proceed with your repair as before (making sure the stuff will cure before putting it on the plane).
One other thing I would do is to scuff up the repair area with some 60 or 80 grit to allow the resin to adhere to the fuse. Don't want your nice job cracking when you fire up the engine.
This stuff is not rocket science, mostly sanding once you get your compatiblilty issue solved.
Good luck
Paul

ps2727

AJS
I re-read your original post and can add a couple other points.
Heat from curing will not be a problem in this small a layer. It will not get hot enough to melt a foam plug.
I don't know of any fiberglass cloth that will not work. The weight of cloth is not terribly important for this either. I'd probably go for a 2 oz cloth or thereabout but if you go lighter it will take more layers and fewer with a heavier cloth, but don't worry because it will all get sanded down after the cure.
The main thing about the resin when doing this kind of work is you want the resin to cure hard. If it's hard it will sand, if it cures sort of soft sanding it will be nearly impossible.

coloradoz

My Feedback: (38)

Thanks again - but I need to ask a question out of ignorance - what does sanded polyester smell like - This maybe my problem. This fuse is pretty stiff - not like my GP Tiporare, unfortunately I can't tell what its made of - it looks orange-ish - just like my Tipo, so I just assumed it was epoxy.