The view from an aircraft window is too narrow to see the curve. If you had unobstructed view, you could see it. People who have been high enough in a balloon testify to the curvature of the earth. I realise that does not fit in with your theory, so you are bound to find fault. You need to be around 35,000 feet with a 60 degree view. Concord passengers could see it easily as they flew at 70,000 ft.