Gravity pulls aircraft down. Lift holds them up. The upward aerodynamic force comes from air moving over a wing, creating lower pressure on top and higher pressure below. Stop the airflow and the lift disappears, which is exactly what happens in a stall.

Lift depends on several factors. Wing area, air density, speed, and angle of attack all change how much force the wing produces. Double the speed and lift roughly quadruples, which is why takeoff and landing speeds are so carefully calculated.

Ways to increase lift

• Extend flaps to increase wing area and camber
• Deploy slats to smooth airflow at high angles
• Increase angle of attack up to the critical point
• Add power to accelerate airflow over the wing

Lift also has a cost. Generating it creates induced drag, which rises with the square of the lift coefficient. Designers balance the two, because a wing that makes lots of lift but also lots of drag burns more fuel.