We've all been said that airplanes fly because of the shape of the airfoil- forget the engines, airplanes can glide-, the upper camber being longer
than the lower one, thus, creating a low pressure area above the
wing and a high pressure area below, which makes the airplane fly.
I was told once by an aeronautical engineering professor that the shape
of the wing created a suction force on the upper surface. But, I've been
asking myself for a long time that if this is so, why airplanes can fly
inverted or at a 90 degree bank angle.