On Sunday, we began to apply fiberglass on the outline of the primary ribs we routed on Saturday. In the blog posts about the wing design process and rib testing, we covered how we first used 3/32” aerospace-grade plywood cap strips on the top and bottom of the ribs. Unfortunately, it didn’t work that well – the plywood had difficulty adhering to the ribs and the ribs failed at 100lbs, half the weight we were anticipating it to be able to carry. The plywood’s overall lack of strength and difficulty to adhere to the foam led us to switch to using fiberglass cap strips instead. We also decided to incorporate glass micro-bubbles into the epoxy mixture for better adhesion to the foam.
To create the epoxy mixture used to adhere the fiberglass cloth to the ribs, we combined one pump West Systems 105 epoxy, one pump West Systems 105 hardener, then twice that volume of glass bubbles. This was only possible with the use of the West Systems pump kit which cost an additional $20 but it’s worth every penny. The process of measuring out the glass bubbles was tedious and occasionally inaccurate, so we had to sacrifice a few cups of epoxy because they were either too runny or thick. We would recommend creating a system with an actual measuring cup and process of extracting the power to limit the amount of glass bubble exposure. Please also note that the glass bubbles are unsafe to inhale and you should follow the SDS (ours is linked) recommended guidelines for your specific product.