Lift pushes a plane up. Weight pulls it down. Thrust pushes it forward. Drag pulls it back. These are the four forces of flight. A plane needs enough lift from its wings to beat its weight. It needs enough thrust from its engines to beat its drag. Weight is the pull of gravity that tries to bring the plane down toward the ground.

Airplane wings are shaped so that a wing meeting the air pushes the air down. The air pushes the wing up. In a wind tunnel, the model sits still and fans blow air past it. Engineers can measure the lift and drag on a model with special instruments.

A plane has to move for its wings to make lift. A plane that is not moving through the air makes no lift. Lift only works where there is air. The higher a plane goes, the thinner the air gets. Airplanes cannot switch gravity off. They make forces that oppose gravity but do not remove it.

Thrust comes from pushing gas backward. The engine pushes gas to the rear, and the gas pushes the engine forward. A jet engine pulls in air through its front opening, called the inlet. A turbofan has a big fan at the front. Some of the air goes through the engine's core. Some goes around it. Both streams add thrust.

A pilot steers a plane by moving parts on its wings and tail. The tail helps keep the plane's nose pointing straight ahead. The elevators control pitch, the rudder controls yaw, and the ailerons control roll. To roll a plane, the pilot raises the aileron on one wing and lowers it on the other. The wing with the lowered aileron rises.

The Wright brothers picked Kitty Hawk, North Carolina, for their tests. It had steady winds, tall sand dunes for launching and soft sand for landing. They tested gliders there for three years before they tried a plane with an engine. Wilbur Wright had the idea of controlling a plane by twisting the wing tips in opposite directions. He thought of it after watching how birds steady themselves in flight.

Wilbur and Orville Wright built their own engine for the Flyer. It made almost 12 horsepower. The Wright brothers made the first flight of a powered airplane in 1903. On December 17, 1903, Orville was the pilot on the first flight, and Wilbur ran beside the wing. The brothers took turns flying that day, and made four flights. The first flight lasted only 12 seconds. It went 120 feet.

Words to know

• thrust: forward push
• drag: air pushing back
• inlet: front opening
• turbofan: engine with fan
• ailerons: hinged wing parts
• rudder: tail turning part

The short version

Wings make lift, the force that holds a plane up in the air. Engines make thrust, a push that moves the plane forward through the air. Airplane wings are shaped so that a wing meeting the air pushes the air down, and the air pushes the wing up.

Quick facts

• An airplane's wings make lift, the force that holds the plane up in the air.
• A plane's engines make thrust, a push that moves the plane forward through the air.
• Lift pushes a plane up, weight pulls it down, thrust pushes it forward and drag pulls it back: these are the four forces of flight.
• A plane has to move for its wings to make lift.
• The Wright brothers' first flight, on December 17, 1903, lasted only 12 seconds.