A jet engine runs in stages: the compressor passes air to the combustion chamber, where fuel is added and lit. The expanding gas drives a turbine, and a shaft from the turbine turns the compressor, which keeps the engine running. The turbine works like a windmill, because the hot exhaust spins its blades. The compressor squeezes the air to a much higher pressure before fuel is added and lit. A jet engine gets its oxygen from the air around it, unlike a rocket engine, which carries its own oxygen.

A jet engine takes in a lot of air and adds only a little fuel. In a typical jet engine, 100 pounds of air per second is mixed with only 2 pounds of fuel per second, so most of the hot exhaust comes from the surrounding air. After the turbine takes some energy out of the hot exhaust, enough is left to speed the gas through the nozzle. The thrust depends on how much air goes through the engine and how fast the gas leaves. A jet engine will not work in outer space because there is no surrounding air.

There are four types of aircraft turbine engine: turbojet, turboprop, turbofan and turboshaft. Most modern airliners use turbofan engines because of their high thrust and good fuel efficiency. Because the fan of a turbofan is enclosed by the engine inlet and has many blades, it can work efficiently at higher speeds than a simple propeller. Jet engines have far fewer moving parts than piston engines, so they are more reliable, safer and less costly to operate. The air that bypasses a turbofan's core adds thrust, cools the engine, and helps muffle the sound of the exhaust.

A wing's angle of attack, the tilt of the wing to the oncoming air, makes lift by turning the flow of air. If a wing is tilted up too much, the smooth airflow pulls away from the top surface and turns turbulent, and the wing suddenly loses lift. This is called a stall, and tilting the wing back to a more level position brings smooth flow back. Lift is also proportional to the square of an aircraft's velocity, so doubling the speed, with everything else the same, gives four times the lift. Lift and drag both vary directly with the density of the air, so thinner air means less of each. Flaps change a wing's curvature and increase lift, so an airplane can keep lift at lower speeds, which allows a slower, shorter landing, and the extra drag from flaps helps slow the plane.

The higher a plane goes, the thinner the air gets: air pressure and air density both go down as altitude goes up, while aerodynamic forces depend directly on the density of the air. Because air gets thinner as a plane climbs, a plane must fly faster at high altitude to keep the same lift. Thin air at high altitude means less drag, but a plane needs enough air to make lift. Above its flight ceiling a plane cannot make the lift it needs to stay airborne. The Boeing 307 Stratoliner could cruise at 7,500 meters, or 25,000 feet, while other airliners of its day flew no higher than about 3,000 meters. Flying above the weather let it fly faster and more efficiently, with a smoother, quieter ride.

The Wright brothers designed and used a wind tunnel to test the shapes of the wings and tails of their gliders. The heart of a wind tunnel is the test section, where a scale model is held in a carefully controlled airstream that duplicates the flow of air around the full-size aircraft. In a wind tunnel, engineers can measure the lift and drag on a model with special instruments. Engineers also inject smoke or dye into the tunnel and photograph how the air moves around the object, and NASA uses wind tunnel tests to make sure a new airplane will fly the way it should before it flies.

The Boeing 247 of 1933, the world's first modern airliner, carried 10 passengers and flew 50 percent faster than the Ford Tri-Motor, and it had a sleek low-wing, all-metal body and retractable landing gear. Jet passenger service began in the United States in the late 1950s with the Boeing 707 and the Douglas DC-8. The Boeing 747 entered service in 1970 and carried more than twice as many passengers as the 189-seat 707, with about 400 seats and much lower seat-mile costs.

Wide-body airliners followed the 747, which was powered by four high-bypass turbofan engines. Its success led Airbus, Lockheed, McDonnell Douglas and later Boeing to build wide-body jets. The Concorde cruised between 55,000 and 60,000 feet, so high that passengers could see the curve of the Earth, and it carried only 92 to 128 passengers, in a four-across seating arrangement. As of November 2026, the Airbus A380 is the largest passenger plane ever built, about 73 meters long with a wingspan of nearly 80 meters, and it can carry over 850 passengers in an all-economy layout.

Words to know

• combustion: burning
• stall: sudden lift loss
• turbulent: rough, swirling
• turbine: windmill-like part
• altitude: height