Thanks Bob, that is most interesting! My .15 powered gyro has simple balsa blades and no stiffening leading edge of harder wood. I have now fitted a new hub with stronger hinges, but the same blades. I will fly it carefully. I only noticed (heard!) the flutter when the plane was not far off, if it had happened at some distance a blade could fly off without it being known that flutter was the cause.
Originially I was using the hub design ( non- delta) design of the plane you mention, I had a failure of a glued join in a blade mounting and lost a blade. Now I always have small nuts & bolts to clamp the parts of my plywood hubs together (as well as glue).
Regards, Colin
ps - made a new hub yesterday- realised today I got the delta angles the wrong way around!!! Now fixing that.