When I put my -12 in the sun, 80+ degrees the wing skins wrinkle almost as though the aluminum was loosely pulled fabric. I understand aluminum has a high coefficient of expansion so I am guessing this is normal? I don't remember seeing other metal planes doing this but I really haven't looked closely. The horizontal stabilizer, vertical, and fuse do not seem to do this. Once the plane is back in the hangar for 30 minutes it looks all normal. Is this typical?