I have used this foam plenty of times in my planes. I started by wanting to secure some weights in the very tail of my first plane. After it was done, I realized that the tail end of the fuse while normally flexible if you squeeze on it, was now firm. I then started using it on stabs that you had to just slide through a hole in the fusealge on ARFs. I never really trusted using epoxy on the small amounts of area it was being epoxied to, so I spray some foam back in there and it is solid. The main thing you do need to look out for is that its in an open part of the fuselage and it has room to expand, if not you start popping holes all over.