Turning air downwards
A wing produces lift by deflecting air downwards. By Newton's third law, the reaction pushes the wing upwards. Angle of attack — the angle between the wing chord and the oncoming air — is the main control the pilot has over how much air is deflected.
Pressure difference
The same flow field can be described with pressure: air accelerating over the curved upper surface has lower static pressure than the slower air beneath. Both descriptions are correct; they are two views of the same physics.
The stall
Increasing angle of attack increases lift only up to the critical angle, typically around 15–16 degrees. Beyond it the flow separates and lift collapses. A stall depends on angle of attack, not on airspeed — you can stall at any speed.
Key points
- Lift comes from deflecting air downwards; pressure difference is the same effect described differently.
- Lift is proportional to air density, wing area and the square of airspeed.
- Stalls are caused by exceeding the critical angle of attack, not by low speed alone.
Knowledge check