(Please note ... we are not in disagreement, but I wanted to address this) Asking how 'planes fly upside-down and putting one's theory to the test in this thou

(Please note ... we are not in disagreement, but I wanted to address this) Asking how 'planes fly upside-down and putting one's theory to the test in this thought experiment is useful, but it doesn't refute the "downwash" theory. If you have a wing at an appropriate angle of attack, even if upside-down, then provided the flow remains attached, it (the flow) can still be deflected downwards. If the wing is reasonably asymmetrical then the angle of attack needs to be large, which makes it more likely that the flow will become detached, so we deduce that a 'plane designed to fly upside-down needs to have symmetrical, or near symmetrical, aerofoil profiles ... which they do. So the downwash theory is not refuted by the "upside-down" question. (Please note: All that notwithstanding, the unadorned downwash theory is not the complete explanation of how lift is generated)