People who argue about lift usually fall into two camps. One says lift comes from a pressure difference across the wing, which is the Bernoulli position. The other says lift is the reaction force on a body that deflects a flow of gas, which is the Newton position. The two famous explanations of lift are both correct: in the Bernoulli view the wing makes a pressure difference, and in the Newton view the wing turns a flow of air and the air pushes back. Adding up either the pressure or the velocity around the wing gives the same aerodynamic force, and the two explanations describe the same force. Neither Isaac Newton nor Daniel Bernoulli ever attempted to explain the aerodynamic lift of an object.

The equal transit time idea says air going over the top of a wing must meet the air from underneath at the back edge, so the top air must go faster. NASA Glenn calls this the most popular incorrect theory of lift. The speed the idea predicts is too low, because the real speed on top of a lifting wing is much higher than the speed that would give an equal transit time. Wings that are the same shape on top and bottom still make plenty of lift, and their top and bottom surfaces are the same length. NASA Glenn warns that many explanations of lift in encyclopedias, on web sites, and even in some textbooks are incorrect and confuse students.

The Smithsonian's How Things Fly says the downwash behind a wing results from air pressure differences on the wing, so it is an effect of lift rather than the cause. The wing feels the pressure of air molecules against its surface, not the air leaving behind it. The Smithsonian also says Newton's third law of motion is often given as the explanation for thrust, but that it explains the effect of thrust, not the cause. Pressure is the basic source of thrust from a propeller, jet engine or rocket engine. Jet engines make thrust by raising the pressure inside the engine, and that pressure pushes harder on the front of the engine than on the rear, so the net force is forward.

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, and lift is the part of that force at right angles to the flow, while drag is the part along the flow. To truly work out lift you must keep track of the mass, the momentum and the energy of the air at the same time. Newton's laws are statements about momentum, and Bernoulli's equation comes from energy, so both are satisfied when a wing makes lift. Conserving mass makes lift harder to picture than the motion of solid things, because when air changes speed in one direction, its speed changes in the direction at right angles too.

The equations that describe airflow without friction, called the Euler equations, are named for Leonard Euler, Bernoulli's student, and adding air's friction, called viscosity, gives the Navier-Stokes equations. Engineers measure a wing's lift in a wind tunnel at a known speed, air density and wing area, which gives a number called the lift coefficient. That number lets them predict the lift at other speeds, altitudes and wing areas. The method works well below about 200 mph, where air's compressibility hardly matters, but at higher speeds engineers must match the Mach number between the test and the real flight.

Every airplane has six basic instruments: the airspeed indicator, attitude indicator, altimeter, turn coordinator, heading indicator and vertical speed indicator, and they let pilots fly safely even when they cannot see the ground or the horizon. The altimeter, airspeed indicator and vertical speed indicator work from air pressure measured by a Pitot-static tube, while the heading indicator, attitude indicator and turn coordinator work from gyroscopes. The two-axis autopilot in most small airplanes controls the aircraft's pitch and roll. An autopilot system is a set of servo actuators that move the controls, plus control circuits that make the servos move the right amount, and the flight director is the brain of the autopilot system.

The Concorde was the first turbojet-powered supersonic airliner to enter service flying passengers across the Atlantic at twice the speed of sound. It flew from New York to London in under three hours, compared with about seven hours on a regular airliner as of November 2026. Because of its speed, the Concorde's aluminum skin heated to over 120 degrees Celsius in flight, and the plane stretched about 8 inches in length. High operating costs meant very high fares that few could afford, and all Concordes were retired in 2003. The Concorde used an average of one ton of fuel per seat, and as parts became harder to get, its small market shrank.

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 designed a glider that could fly a person and 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. 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, and the brothers designed and used a wind tunnel to test the shapes of the wings and tails of their gliders.

Words to know

• downwash: air pushed down
• viscosity: air's friction
• servo: control mover
• gyroscopes: spinning direction sensors
• compressibility: air squeezability