How Airplanes Fly

How airplanes fly seems to be a question that many people have in the back of their minds when they go to board a flight. The author of this article has over 20 years of experience as an airline pilot and has served as a flight and ground intructor as well as FAA designated examiner for a major U.S. airline.

Aerodynamics you ask? The wing is the thing, or so we like to say. In essence, the wing is what generates the lift that keeps the airplane in the air. Ever looked at a birds' wing? If you take a close look you will see the wing of a bird is arched when looked at from a cross section. The same is true of an airplane wing, it too has a cross section that is arched. Take a look at the drawing above and you will see the five basic components that comprise the wing of a conventional airplane. In this diagram there are two cambered surfaces. One labled "upper cambered surface" and the other labled "lower camber surface"? In between these two cambered surfaces is the "Chord line".

The chord line divides the wings center cross section. If you measure the distance from the center of the chord line, between the leading and trailing edges of the wing, to the upper cambered surface and compare that with the distance to the lowered cambered surface from the same point, you will note that there is a greater distance to the upper cambered surface than to the lower cambered surface.

In the diagram to the right right, labled "Airflow Above and Below The wing" please take note of the shape of the wing. The airflow above the wing is bent/curved with a great amount of precision as it follows the upper cambered surface. A rather straight surface on the bottom of the wing leaves the airflow underneath the wing relatively unbent.

Bending/curving the airlfow above the wing forces air to travel a GREATER distance than the straighter airflow below the wing. If the airflow above the wing is to reach the trailing edge of the wing at the same time as the airflow traveling accross the bottom of the wing, it needs to speed up to cover the greater distance in the same amount of time.

Something remarkable happens when air, flowing over a surface, increases its speed. A physicist named Bernoulli determined that the faster air flows over a surface, the less pressure it exerts on that surface. High velocity airflow over the wing causes a slight decrease in pressure on the wing's upper surface. In other words, the pressure on the top of the wing is now less than the pressure on the bottom of the wing. The scientific term for this is Translational Kinetic Energy, better known as, Bernoulli's principal and is what keeps airplanes of all sizes flying.