How does Bernoulli's principle explain how planes can lift off the ground?

Answer 1

For a thorough but deep description look at the link in the Related links section below.

The basis principle states that for an object in motion in a fluid (or a stationary object in a moving fluid), the pressure of the fluid on the body decreases as the speed of the fluid over the body increases. Air is considered a fluid for aerodynamic purposes.

The basic cross section of an aircraft wing is a bottom surface that is essentially flat or slightly curved (the term is "camber", for the purists) while the upper surface is much more curved. For the sake of demonstration (and ignoring a lot of variables and factors), assume that the wing is 5 meters from the front or leading edge to the back or trailing edge (a distance called the "chord" of the wing), including flaps, and the plane is traveling at 100 meters per second (m/s), or 224 miles per hour for the US readers.

When moving through air at 100 m/s, the air flows over the 5 meters of flat bottom surface at roughly 100 m/s. However, the curved upper surface means that the distance that air moves over it from front to back is more then 5 meters. If the curve adds 1 meter to the distance, air must travel over 6 meters of surface to go the 5 meters from front to back. The only way that can be done is for the speed of the airflow to increase to 120 m/s over the curved contour of the wing.

By Bernoulli's Principle, this results in lower pressure on the curved surface than on the flat lower surface. ergo lift is generated. The formulas for calculating the lift are beyond the scope of this post, but are included in the Wiki article.

An aside: helicopters aka rotary wing aircrafts typically use a symetrical blade cross-section. The rotor has no inherent lift, to avoid instability when the rotor is spinning while on the ground. Its lift is created by rotating the blade on its long axis so that it moves at an angle (pitch) to the plane of rotation.

Class dismissed :-)