Fiberglass Methods

[TJay 1041]

Wondering about some fiberglass methods, about ready to extend  my cowl or at least try, I ordered some aero-poxy from spruce along with some woven mat and some glass fiber mat. It said on the glass mat that it is not recommended for epoxy resins? I got some anyway because it was only 2 bucks a yard. Does anybody know why you shouldn't use it?

[marksires 484]

You won't get much strength with the woven mat.  It's possible that the sizing on the mat may not be compatible with epoxy, but I doubt it.  BID isn't terribly expensive, and would be better for making a new cowl.  If you are just doing one of the 'bubbles' to get around a muffler or intake, the mat would work fine.  If you are extending the cowl such that the new part will be taking some of the load of keeping the cowling in place, I wouldn't use mat.

 

Mark

 

[TJay 1041]

I also got some cloth, when I look at my cowl with a light shining through it you can see both a layer of the cloth and strands of mat, thought I would use both, have no clue since I have never done fiberglass work before but It sure doesn't look to hard, and does look like a fun way to create things.

[EDMO 1078]

Fun until you start cutting and grinding!  There are some good books on doing fg - I may have a composite book from school, if you want it.  Hint, put a layer of epoxy on the mold before starting to lay cloth - Sometimes, you want a layer of Dacron fabric (pealply) first, which wont stick to the epoxy - just depends on what you are doing.  Hardest thing without vacuum bagging is to get enough epoxy to wet out the fabric without putting on too much.  EdMO

Edited 1 Jun 2016 by EDMO

[wypaul 448]

The mat does not work well with the epoxy because of the sizing as Mark mentioned, the polyester releases the fibers and that allows them to move and to be shaped.  The epoxy will not do that so the mat cannot be shaped to go around compound curves.  Bite the bullet and buy the good bidirectional Rutan cloth and save yourself a lot of misery IMHO.

[marksires 484]

All good advice Ed.  The cutting and grinding isn't so bad - if you need to trim it, do it before it fully cures - when it will hold shape, but is still plastic, like stiff putty.  If you are picky about your finish, you can plan to spend most of the rest of your natural life sanding.  And if you weren't eligible for the northern regions of the afterlife, plan on spending eternity doing it also   You'll want some microballoons to mix some micro to fill with.  Bondo is way too heavy, and will peel off after a while.  You mix the micro balloons into epoxy until it is about the consistency of peanut butter.

Oh - and don't mix too much epoxy at once.  An exotherm will get your attention real quick!

Mark

 

[C5Engineer 1170]

I recently went down this road myself. I filled in the big square hole in my cowl where I took off the side scoop for the B model side radiator. A couple friends helped me out with some materials and some basic techniques and Youtube did the rest. Gobs of info from the Marine guys on a variety of jobs and techniques. I used Rutan Bid cloth and West Systems Epoxy. The west cans and the calibrated pumps were a bit spendy but they go a long ways and the one to one pump set up makes it super simple to mix up a batch. My first attempt at making a paste with the glass ballons and resin went pretty well but I had it a bit thick and some air bubbles showed themselves after I did the final sanding. One more coat and it will be good to go. My next project is to build a bubble over the water bypass hose and clean up where my plugs poke thru the bottom of my B model cowling. It's going to be a little more complex. Like everyone told me though the best part about fiberglass is if you screw it up, cut it off and start over. As far as finishing goes....sand, fill, sand, fill, repeat. I have a whole new respect for the guys who have built a composite airplane now.

Edited 1 Jun 2016 by C5Engineer

[EDMO 1078]

All good advice Ed.  The cutting and grinding isn't so bad - if you need to trim it, do it before it fully cures - when it will hold shape, but is still plastic, like stiff putty.  If you are picky about your finish, you can plan to spend most of the rest of your natural life sanding.  And if you weren't eligible for the northern regions of the afterlife, plan on spending eternity doing it also   You'll want some microballoons to mix some micro to fill with.  Bondo is way too heavy, and will peel off after a while.  You mix the micro balloons into epoxy until it is about the consistency of peanut butter.

Oh - and don't mix too much epoxy at once.  An exotherm will get your attention real quick!

Mark

 

Yeh - I cant remember how many quart cans I had to drop quickly before getting ? degree burns!  Not only in the can, but if you put epoxy on too thick it will start to warm, get hot, turn brown, GIVE OFF TOXIC FUMES, and warp whatever it is put on, (and maybe start a fire, although I have not experienced that!)   If you are just putting on a few layers, like 3 or 4, and just wet out the fabric, you probably wont have those problems.   EDMO

Edited 1 Jun 2016 by EDMO

[TJay 1041]

Well I bought a small practice kit from Arnold motor, Last night I covered a Tupperware bowl and made a flat piece, I think I will be alright,

 

[marksires 484]

Looks good to me, I only see a couple of air bubbles.  I was going to suggest this kit:

http://www.aircraftspruce.com/catalog/cmpages/practicekit.php?clickkey=339852

but it looks like you have a handle on it.

 

Mark

 

[Geoffrey Thorpe 31]

If you are not fussy about the surface finish on the mold side, duct tape and packing tape work well as a "mold release".  If the surface has too much curve, rip the duct tape into strips.

[Fly-n-Low 181]

The mat does not work well with the epoxy because of the sizing as Mark mentioned, the polyester releases the fibers and that allows them to move and to be shaped.  The epoxy will not do that so the mat cannot be shaped to go around compound curves.  Bite the bullet and buy the good bidirectional Rutan cloth and save yourself a lot of misery IMHO.

Exactly. The ester resins release the binders in the mat. I have a little experience with epoxies, and a lot with ester resins. Nothing wrong with mat as far as strength goes using the proper resins. I use to work for a guy building record holding race boats. Most of the glass used was mat.

BTW mold release is nothing more than a wax. I have used automotive wax in a pinch. Just make sure you apply several coats.

[EDMO 1078]

The mat does not work well with the epoxy because of the sizing as Mark mentioned, the polyester releases the fibers and that allows them to move and to be shaped.  The epoxy will not do that so the mat cannot be shaped to go around compound curves.  Bite the bullet and buy the good bidirectional Rutan cloth and save yourself a lot of misery IMHO.

Exactly. The ester resins release the binders in the mat. I have a little experience with epoxies, and a lot with ester resins. Nothing wrong with mat as far as strength goes using the proper resins. I use to work for a guy building record holding race boats. Most of the glass used was mat.

BTW mold release is nothing more than a wax. I have used automotive wax in a pinch. Just make sure you apply several coats.

We used Johnson's Paste Floor wax a lot - Not saying it is the best to use - Several coats work best.  Don't use anything with Silicone in it if you ever want to paint the mold side (or maybe either side) of your part - Paint just wont stick to silicone.   EDMO

Edited 6 Jun 2016 by EDMO

[TJay 1041]

My resin and cloth showed up today so hopefully I can play with it this week.