How a wing makes lift

Two truths make lift

Definition

A wing makes lift two ways at once — and they describe the same thing. Newton: the wing deflects air downward, and the equal-and-opposite reaction pushes the wing up. Bernoulli: air moves faster over the curved top than underneath, so pressure on top is lower than below, and that pressure difference is a net upward force.

Explanation

Both pictures are correct and grow with angle of attack and camber: more AOA (up to the critical angle) deflects more air and widens the pressure difference — more lift.

Figure 4-7. Pressure distribution on an airfoil and CP changes with AOA. — Figure 4-7 · FAA-H-8083-25C, Pilot's Handbook of Aeronautical Knowledge (p. 95)

Why it matters

This is the mechanism behind the angle-of-attack lesson: lift comes from the flow over the wing, and AOA is how you control it — until you exceed the critical angle and the flow separates.

From the Right Seat

Don't get stuck arguing Bernoulli vs. Newton — they're the same event described two ways. I teach both so a student can answer a DPE either way.

A DPE might ask

Give me two ways to explain how a wing makes lift.
What happens to lift as you increase angle of attack?

PHAK ch. 5 — Aerodynamics of flight

The myth to unlearn

Definition

You'll hear that the air splitting at the leading edge 'has to meet up' at the trailing edge, so the longer path over the top forces it to go faster. That's a myth.

Explanation

The air over the top actually reaches the back sooner — there is no rule that the two halves rejoin. The speed-up is real, but it comes from the flow curving around the top of the wing, not from a meet-up.

Common error

The 'equal transit time' explanation — air over the top travels farther so it must speed up to meet the bottom air — is wrong. The upper air arrives sooner, and the parcels never need to reunite. Explain lift with air deflected down (Newton) and the pressure difference from the curving flow (Bernoulli).

Why does the air move faster over the top of a wing?

A DPE might ask

What's wrong with the 'air has to meet at the back' explanation of lift?

PHAK ch. 5 — Aerodynamics of flight