An airfoil deflects oncoming air downward (downwash), and by Newton's third law the air pushes back up on the wing — lift. Thin-airfoil theory gives lift coefficient roughly proportional to angle of attack until the flow separates (stall).
C_L ≈ 2π·(α + α_flap) [rad, pre-stall]
L = ½ρV²S·C_L
C_D = C_D0 + k·C_L²
D = ½ρV²S·C_D
- Angle of attack — pitch of the wing relative to the oncoming flow; more angle means more lift until stall (~16-18°).
- Airspeed — lift and drag both scale with velocity squared.
- Air density (altitude) — thinner air at altitude means less lift and drag for the same speed.
- Flap deflection — effectively adds camber, boosting lift coefficient at any angle of attack (used for takeoff/landing).
Real-world application: aircraft designers use exactly this lift/drag/stall relationship to size wings, set takeoff/landing flap settings, and define the safe angle-of-attack envelope pilots must stay within.