The air pressure on a wing changes from place to place as the air speed changes. Adding up the pressure times the area all around the wing gives the aerodynamic force. Lift is the part of that force at right angles to the flow, and drag is the part along the flow. Weight is a different kind of force from lift and drag: lift and drag need the plane to touch the air, but gravity is a field force that acts without touching.
The FAA says that in steady, straight flight there can be no unbalanced forces, which follows Newton's third law, but it adds that this does not mean the four forces are equal to one another. An airplane rotates about its center of gravity, the average location of its mass. Roll, pitch and yaw are all turns about that point. Even in level flight, the wings push air down onto the tail, and the faster the plane flies, the stronger this downwash and the greater the downward push on the horizontal stabilizer.
The Wright brothers based the size of their first glider and the curve of its wings on Otto Lilienthal's calculations about lifting power. Lilienthal, of Germany, designed a glider that could fly a person, and he wrote a book on aerodynamics, published in 1889, that the Wrights used as the basis for their designs. Octave Chanute's 1894 book Progress in Flying Machines gathered and analyzed the technical knowledge of the world's aviation pioneers, and the Wrights used it as a basis for much of their experiments.
The Wright brothers took turns piloting four flights on December 17, 1903. The first flight reached a top speed of only 6.8 miles per hour, and the longest flight that day went 852 feet in 59 seconds. Few people noticed the first flights. The Wrights did not become famous until August 8, 1908, when Wilbur flew two circles over a racetrack in Le Mans, France, at about 60 mph.
A turbofan makes more thrust than its core alone but burns nearly the same fuel, because adding the fan changes the core's fuel flow only a little. The air that bypasses a turbofan's core adds thrust, cools the engine, and helps muffle the sound of the exhaust. Turboprop engines are most efficient at speeds between 250 and 400 mph and at altitudes between 18,000 and 30,000 feet.
The Boeing 307 Stratoliner was the world's first pressurized airliner. Jet passenger service began in the United States in the late 1950s with the Boeing 707 and the Douglas DC-8. Air France and British Airways together began Concorde service in 1976. The Concorde flew from New York to London in under three hours, compared with about seven hours on a regular airliner as of November 2026.
Whenever a wing is making lift, induced drag occurs and wingtip vortices, swirls of air at the wing tips, are created. Engineers measure a wing's lift in a wind tunnel at a known speed, air density and wing area. That gives a number called the lift coefficient, which lets them predict the lift at other speeds, altitudes and wing areas. In a wind tunnel, engineers can measure the lift and drag on a model with special instruments.
Wind tunnels come in many sizes, from a few inches wide to large enough to test a full-size airplane. Some are best for testing at less than 200 miles per hour, and others move air at more than five times the speed of sound, about 4,000 mph. In a closed-loop wind tunnel, the air is brought back to the fan and recirculated continuously, which allows long test times. Other tunnels release pressurized air at very high speed for short tests.
In some wind tunnels, models are held in place by magnetic fields, so they do not have to be mounted on stands that would disturb the airflow. As of November 2026, the world's largest wind tunnel is at NASA's Ames Research Center in Moffett Field, California. Engineers use wind tunnels to test new aircraft designs, new materials, new shapes for airplane parts, and even how to keep ice from forming on wings.
Words to know
- vortices: swirls of air
- downwash: air pushed down
- coefficient: a measured number
- turbofan: engine with fan
