A pilot steers a plane by moving parts on its wings and tail. The elevators control pitch, the rudder controls yaw, and the ailerons control roll. Yaw is the nose of a plane swinging from side to side. Control surfaces work by changing the force on part of the plane. That force acts some distance from the center of gravity, so it makes a turning effect that rotates the plane.

The tail has a fixed part and a hinged part. The hinged part on the upright fin is the rudder, and the hinged part on the flat tail wing is the elevator. Raising the elevators makes the plane climb. The rudder turns a plane's nose left or right, and a pilot uses the rudder together with the ailerons to turn the plane. The ailerons, elevator and rudder are the primary control system and are needed to control an aircraft safely.

To roll a plane, the pilot raises the aileron on one wing and lowers it on the other, and the wing with the lowered aileron rises. Most airliners can also roll using spoilers. Spoilers are small plates that disrupt the airflow over the wing and decrease the lift when raised.

Wing flaps and slats let a plane keep enough lift while flying slowly at takeoff and landing. A slat is a movable part on the front edge of a wing, and a flap is a movable part on the back edge. They extend to add wing area and tilt down to add camber, the curve of the wing, which raises lift. They slide along metal tracks built into the wings.

On takeoff the flaps are set down a moderate amount for high lift with low drag. On landing the flaps and slats are fully out for high lift and high drag. Flaps also add drag, and that helps a plane slow down for landing. Spoilers are put up right after touchdown to dump lift, which moves the plane's weight from its wings onto its wheels so the brakes work better.

In steady, level flight at a constant speed, thrust equals drag and lift equals weight. Lift is 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. The atmosphere gets thinner with height: air pressure and air density both go down as altitude goes up.

The thrust of a jet engine depends on how much air goes through it and how fast the gas leaves. After the turbine takes some energy out of the hot exhaust, enough is left to speed the gas through the nozzle. Because the gas leaves faster than the air came in, the engine gets thrust. A jet engine gets its oxygen from the air around it, unlike a rocket engine, which carries its own oxygen. 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. A turboprop engine drives a propeller through a reduction gear. 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.

Wilbur Wright had the idea of controlling a plane by twisting the wing tips in opposite directions, after watching how birds steady themselves in flight. NASA says the first aircraft to achieve complete active control was the Wright brothers' 1902 glider. The Wright brothers based the size of their first glider and the curve of its wings on Otto Lilienthal's calculations about lifting power.

Words to know

• camber: wing's curve
• spoilers: lift-dumping plates
• slats: front wing parts
• nozzle: exhaust opening
• turboprop: propeller turbine engine