How do planes fly?

Aerospace engineers (like Mary Golda Ross) design air and space vehicles, like air planes or space shuttles. If you've ever watched a big, heavy plane take off and soar through thin air, you might have wondered: "How does that even work??"

There are four forces that affect a plane: thrust, drag, gravity, and lift. Each of these forces act on the airplane in different directions.

Cartoon of an airplane experiencing the four forces: lift, thrust, gravity, and drag

Thrust is the force that drives a plane forward through the air and is produced by propellors or a jet turbine. Drag slows a plane down due to friction between the air molecules and the surface of the plane. Gravity pulls the plane toward Earth, just like gravity keeps our feet on the ground. Lift is the most mysterious force, and it keeps the plane suspended in the sky.

Lift is possible because of the Coanda effect. When a stream of fluid (such as air or water) encounters an object it tends to stick to the surface. This is called the Coanda effect, and the result is that the fluid stream follows the shape of a surface even if it's curved.

Cartoon of an airplane wing cross section with air streams flowing along the top and bottom

You can observe the Coanda effect by placing a round glass or jar under a stream of water. The water will stick to the surface and wrap around the curves rather than flowing off.

As air travels along the wing of a plane, the airstream is suctioned to the surface of the wing. The shape of the wing creates a downward force on the airstream, meaning the air particles are pushed down as they travel along the wing. But Newton's second law (every action has an equal and opposite reaction) means that the air particles are also pushing back on the wing in the opposite direction: up! That upward force of the air particles on the wing is lift.

Cartoon demonstrating that the airplane wing exerts a down force on the airstream, and the airstream exerts an equal and opposite force on the wing in the up direction.

Explore how wing shape and the plane's speed affect the lift and drag of a plane's wings using the FoilSim from NASA.

Example of air flowing around a wing in the FoilSim simulator