A fellow in the local EAA chapter has a BD-4 that he has replaced the original wing with a new one from Bede that is uses bonded aluminum. The thing is it looks like the wing is bonded using something like Proseal (grey and sort of elastic). The wing skin is made up of several sheets of aluminum that wrap from rear spar up around and back again to the rear spar, so there are several spanwise joints. There are a few rivets by the rear spar, but otherwise it is clean except for the gaps at the butt joints between sheets (you can see the gray Proseal along the joints). Now the owner reports he is very happy with the new wing. It went together quickly and he flew it to Oshkosh and back this last summer. But the Proseal kind of worries me. I know from my background that bonding aluminum has traditionally been difficult at best (for a homebuilder) and I couldn't find much info regarding actual strength properties of polysulfides (Proseal). So anybody have any good info on this type of adhesive, used in this way? I was thinking of setting up a small test using a sheet of aluminum over a closed box that I could then cyclically vary the pressure inside to simulate loading and unloading a wing skin to see if the Proseal would actually last that many cycles. Don't know the guy well, but I would still hate to see him kill himself.