NB: I am asking specifically about aircraft made with foam-fiberglass sandwich construction, not carbon, wood composite, or other.
I first became aware of composite aircraft when I read an article in the July 1980 issue of Omni magazine, which had an article on Burt Rutan’s aircraft. In the early-'80s I visited the Rutan Aircraft Factory at MHV. (There’s a possibility I still have the video I bought there. Rutan really liked Don’t Dry For Me, Argentina. Incidentally, I saw Burt Rutan and his girlfriend flying a kite in a park in Lancaster, CA once.) One of the things I remember from the presentation was that the aircraft must be painted white because dar colours would damage the structure in the heat – or something like that.
How are composite aircraft built in the '70s and '80s holding up? I see a lot of fiberglass boats, and the older ones look pretty rough. Granted, they’re outside and aircraft are commonly stored inside. What percentage of these homebuilt aircraft are still airworthy after 40 years? If there were an internal problem, how would one know?
I started (but never finsihed) a Q2. (gave away the kit).
It seems to me the question is - how well does fibreglass hold its strength? I’m not aware that boats (different construction) or Corvettes are experiencing deterioration of the resin composite.
Part of the warning about paint colours was, IIRC, that long exposure to excess heat would possibly “melt” the foam under the fibreglas skin, this removing a lot of the stiffness of the minimal parts of the skin; without the extra stiffness the foam provided, buckling was possible. As anyone whose car has a dark interior can attest, the sun can make dark things very very hot.
The body, for example, was simply foam about 3/4" with 1 or 2 layers of fibreglas on each side. remove the foam and there is very little stiffness.
Properly painted and maintained, and kept in a hangar while not in use then a plane won’t end up looking an old boat. I remember reading about painting aircraft white in Kitplanes, musta been back in the 80s. Noticeable effects of temperature softening glue and allowing composite parts to warp were seen with some colorful paintjobs. I think it needs a high level of opacity though, ultraviolet is great at breaking down the matrix of epoxy or polyester, and the foam cores. Other issues could arise. Carbon fiber were found to cause corrosion in metal parts because the carbon is electrically conductive. Later designs placed a layer of glass or plastic between the materials to prevent that.
Some of the issues with warping were attributed to poor curing. Building a composite in a cool environment over witner, then flying to Florida in the spring - the fiberglass in the wings apparently sagged badly since it never fully cured.
It may be worth noting that glass-fiber composite sailplane designs first came to market in the 1960s. Of these a decent number are still airworthy and actively flown today.
I don’t have any information about numbers, but have heard of 1960’s sailplanes that were stored outside that became no longer airworthy due to UV. Old unpainted/uncompleted kits sometimes come up for sale and the usual question is how much sunlight has it seen, with even exposure to a window being enough to destroy it over time.
Stored inside and with the paint being renewed as needed they do seem to hold up.