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How flying works

Why Do Planes Fly? How Wings Make Lift, and Why They Stall

Short answer

A plane flies because its wings turn the air they move through downward. Pushing air down creates an equal upward push, called lift. The same flow leaves lower pressure above the wing and higher pressure below.

By Elvis Li and Jay Yang

Lift: one flow of air, two descriptions

Lift is the force that holds an aircraft up against its weight. A wing makes it by turning the air that flows past it, and both of its surfaces help bend the flow downward. Pushing air down pushes the wing up: action and reaction, as in Newton's third law.

The same flow has lower pressure above the wing and higher pressure below, which Bernoulli's principle links to the speed of the air. These are not rival theories. NASA calls both descriptions correct, and the FAA says both are at work whenever a wing makes lift.

Try it yourself

Move the angle-of-attack slider and watch lift grow along the curve until the critical angle, where the airflow separates and lift drops.

Angle of attack and lift

Oncoming air6.0°LiftA curve that rises steadily with angle of attack, peaks at the critical angle and then drops.0°8°16°24°Lift (illustrative)Critical angle

Normal flight: lift grows smoothly as the angle increases.

An illustration with a generic wing, not data for any aircraft. Real wings stall at about 16 to 20 degrees, depending on the wing, the flaps and the conditions.

Two myths about lift

The equal transit time idea says air over the longer top of the wing must speed up to meet the air from below at the back edge. It is wrong: the air over the top moves even faster and reaches the back edge first. It also cannot explain flat paper-airplane wings or flying upside down.

Another myth says science cannot explain flight. The details are complex, and short explanations often oversimplify them, but the equations of air flow describe lift, and engineers use them to work out the force on a wing.

Angle of attack and the stall

The angle of attack is the angle between the wing and the oncoming air. It is the pilot's main way to change lift, using the control wheel or stick. More angle gives more lift, up to the critical angle of attack, about 16° to 20° depending on the design. Past it, the air separates from the top of the wing and lift drops sharply: a stall. The wing still makes some lift, but not enough to hold the aircraft up.

Why speed and weight matter

Lift also grows quickly with speed: at twice the airspeed, the same wing at the same angle makes four times the lift. So a slow aircraft needs a larger angle of attack to stay level, and a fast one needs a smaller angle. Weight matters too, because lift must match it.

Common mistakes and myths

  • Thinking Newton and Bernoulli are rival explanations. Both describe the same flow.
  • Thinking a stalled wing makes no lift. It still makes some, just not enough.
  • Thinking only the curved top of the wing matters. Its angle to the air matters just as much.

Questions people ask

How can a plane fly upside down?

Lift does not need a curved top surface. Symmetrical and even flat paper-airplane wings make lift because they meet the air at an angle. Upside down, the pilot holds the wing at an angle that still turns the air toward the ground, so the push stays upward.

Why does a heavier plane need more speed?

A heavier aircraft needs more lift. The pilot can raise the angle of attack, but only up to the critical angle, which does not change with weight. Beyond that, only more speed gives more lift, so a heavier aircraft stalls at a higher airspeed.

Can I see this in a flight simulator?

Yes. AeroFox's free lessons let you raise and lower the nose of a light trainer and watch the speed change, then fly slowly near the stall warning at a safe height. It is a learning tool, not certified training, and does not count toward a licence.

Practise it in the simulator

The free Slow flight lesson lets you fly a light trainer just above the stall warning, hold your height, then raise the nose until the horn sounds and recover at once.

Start this lesson: Slow flight

Another lesson on this topic: Controls and trim

Sources

  1. What is lift? (NASA Glenn Research Center, Beginner's Guide to Aeronautics)
  2. Bernoulli and Newton (NASA Glenn Research Center, Beginner's Guide to Aeronautics)
  3. Equal transit theory (an incorrect theory of lift) (NASA Glenn Research Center, Beginner's Guide to Aeronautics)
  4. Effects of inclination on lift (NASA Glenn Research Center, Beginner's Guide to Aeronautics)
  5. Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), chapters 4 and 5 (FAA)
  6. Airplane Flying Handbook (FAA-H-8083-3C), chapter 5: slow flight and stalls (FAA)

About these explainers

AeroFox is a free, public-interest project with no paid features. The explainers are written by the AeroFox team from public sources such as FAA handbooks, NASA and regulators, and, for the lessons from the news, from the news reports we link to. Each page lists its sources, and pages are updated when the facts or the lessons change. They explain ideas. They are not flight instruction, medical advice or legal advice, and they do not count toward any licence.