Comment by rawgabbit
4 hours ago
That was what I was taught 30 years ago in university.
To be more precise, we defined or made a shorthand of this downward force W. Originally it stood for weight but we knew it was the downward force that must be counteracted by an upward force called L for lift. Lift by convention was always an upward force.
These are conventions taught and used.
I should also remark the laminar fluid boundary layer only is true for subsonic flight. When you go over Mach one, a permanent shock wave forms in front of the wing. This shock wave disrupts the laminar boundary layer. Lift is achieved by Newtonian breakdown of the air hitting the wings underside. This is why supersonic planes require fly by wire. As computers are constantly issuing commands to ailerons and rudder to prevent stall.