HP-24 Project

Last night I cracked open the test coupons that I laid up and vacuum bagged on Tuesday this week. These are some random notes, in no particular order:

• I learned that 17" hg of vacuum is too much for 1 lb beaded polystyrene foam cores. It's not a big issue for me, since my plug cores will all be 2 lb foam. But just for reference, when you apply that much vacuum to 1 lb foam it gets sorta wrinkly. I think I'll stick with 10" hg for future coupons, even with the denser 2 lb foam.

• The materials properties you get from vacuum bagging is incredible! With just two ply of 7 oz. fiberglass on cheap styrofoam, I still got great stiffness. Not necessarily strength, but strength always isn't what you're looking for. The bond between the core and the fiberglass is just fabulous; way better than I was expecting, and way better than I've ever gotten using wet ambient layups.

• Vacuum bagging also yields an incredibly uniform laminate thickness. There are no puddles or thin spots - it's the same all the way across, and even down in the wrinkles where the foam crushed from too much pressure. That's the real reason why I'm vac bagging my non-structural plugs - it offers greater fidelity in matching the reference surface of the CNC-hotwired foam cores.

• Peel ply is slightly mis-named - "pry-ply" might better reflect the experience of getting it off. I used cheap 100% polyester cloth intended for shears (that is, those thin frilly curtains). And cheap polyester quilt batting for the breather ply. And it all worked great. But getting it all off was an experience and a half. I eventually worried up a corner of it, which I could grab with pliers and start to peel away. What worked well was to notch it so that I could tear away 1" strips. The amazing thing was that, for all the force I was applying to the peel ply, there was not a single spot where I delaminated the laminate from the foam core.

• I still need to develop a vacuum bagging technique that avoids wrinkles along the leading edge. With the stiff bag material I was using, the extra material would bunch up along the leading edge, and form wrinkles that would reflect in the laminate. My next coupons will test a technique that uses stretchy material for the bag. With that stuff, I can stretch it over the leading edge so that when the vacuum draws it tight against the layup, it doesn't wrinkle - it just returns a bit closer to its original dimension. We'll see if that works in next week's tests.

• For saturating multiple layers of glass, thick resins like the West 105 take a lot more time and work. Next test will use a thinner resin that hopefully will be easier to wet out.

• Even though epoxy doesn't have the nasty smell of many industrial chemicals, it is still good to avoid breathing its fumes. I'm still a bit congested after doing the test layup, and that's likely a lingering cold but it also might be an allergic reaction. From now on, I'll use a mask.

Return to HP-24 page