Chapter 3 - Education and Practice Layups

Chapter 1 lays out administrivia of building a plans-built aircraft, and is largely obsolete nowadays anyway. Chapter 2 lists out the materials needed, both in total, and by chapter, which is very helpful. Chapter 3 involves actual work, as it details how to actually build the plane, and includes 3 practice layups.

I only did the flat layup and confidence layup before I proceeded onto chapter 4. I forgot to order the foam for the bookend project, so I skipped it.

Flat Layup

The flat layup is a very simple layup of 6 12.5” x 18” pieces of BID. The goal is to internalize how to apply epoxy and fiberglass, and how to apply the correct amounts. This piece is then cut down to a 10” x 16” rectangle that should weigh between 10.5 ounces, and 11.5 ounces, with 11 ounces being near ideal.

I ended up doing 2 of the flat layups. The first, I ended up running out of mixed epoxy as I finished it, and as a result, the layup was too light (~9.7 ounces). You can see this in the many light spaces in the fiberglass, indicating both the lack of epoxy and what looks like a bunch of trapped air bubbles?

Because the first layup was obviously bad, I decided to do a second flat layup to get it right. For the second version, I mixed just over 8 ounces of epoxy, which is way more than I needed. I left some in the cup to cure, so that I could verify that it was properly mixed in the first place. This one also turned out to be too light (10.2 ounces), though it had significantly less light spots. Still, there was enough errors that if it were a real part, I’d be either rejecting or spending effort to repair it.

For the third layup, I left an electric heater on in the area while it cured. I also utilized a sheet of 100% polyester as peel ply. Combined, this worked to produce a pretty good layup with very little noticeable defects. Downside, the polyester I used was a bit annoying to peel off, so I’ll find a different fabric to use for peel ply.

Confidence Layup

The confidence layup is a piece of urethane foam sandwiched between layers of BID and UNI. The goal is to learn how to shape urethane foam, learn how to apply fiberglass to foam, and overall gain confidence that the part, once cured, is incredibly strong. I used scrap foam that Aircraft Spruce included to be packing material.

I did two of these. In the first, I accidentally measured the BID incorrectly. You’re supposed to cut it at a 45° angle, with a width of 4 degrees. I instead measured as if I wasn’t cutting the fiberglass at a 45° angle - as if I was cutting straight into the roll of fiberglass - which resulted in the BID strips being too short, and part of the layer directly on top of the foam delaminated during curing.

I made sure not to repeat this mistake on the second one. I also utilized the polyester peel ply for this (I did this at the same time I did the third try on the flat layup). This resulted in another pretty good and strong layup.

Last updated: 2021-10-12 21:29:46 -0700