Epoxy adhesive, yes or no?

No new blog posts don’t mean nothing’s happening behind the scenes – quite the opposite. At the moment, though, we’re facing a few challenges that are noticeably slowing down progress on the build. One of the main issues is proving a suitable epoxy adhesive for constructing the wing. But let’s take it step by step:

After assembling the upper and lower spar caps, the next step is the side sheeting of the spars with plywood. The bonding area is very large and also geometrically complex. The adhesive we’ve been using up to now, Aerodux, is no longer suitable here, as the required working times fall well outside its specifications. A modern epoxy-based adhesive seemed like the ideal alternative. At the same time, we’ve been working on the structural strength calculations for the wing, as required by the BAZL. For that, however, reliable strength values for the bonded joints are essential.

And that’s exactly where the problem lies: for epoxy resins used as adhesives in timber construction, there are no sufficiently well-supported strength values available. While there are various products that are regulator-approved, no manufacturer worldwide provides solid, verifiable data for this specific application. In the end, that means every aircraft builder has to prove the suitability of their chosen adhesive through extensive testing – and that’s exactly what we’re doing.

The past few months have therefore mainly been taken up with discussions with other aircraft builders and producing test specimens for shear testing. This was followed by some disappointment over unexpected results, root cause analysis, and then building new samples. At least 40 at a time to ensure the results are reliable. At present, another batch of shear samples is waiting to be bonded and tested under controlled lab conditions.

With a bit of luck, we should have some usable results in about a week – and can then get back to the real goal of this project: building the aircraft.