# How do airplanes fly 4

Fluid mechanics follows its own laws. As we know today, a so-called circulation flow forms in the aircraft wing. This circulates around the wing, where it flows faster on the wing surface than below - according to Bernoulli's formula, lift is generated again and the aircraft flies.

Why is the circulation flow formed? If the wing moves slowly, it does not yet exist. The air that lies directly on the wing is slowed down by friction. If the aircraft gets faster and faster, this air can no longer follow the movement at some point. It therefore separates from the surface at the trailing edge of the wing. However, the air lying further out is not slowed down, it is not subject to friction with the wing surface and therefore follows the movement around the trailing edge of the wing. This creates a vortex, the so-called approach vortex. It causes the formation of a counter-vortex, therefore a vortex is formed around the entire wing.

The approach vortex creates a flow around the wing - lift is created.

This model can also be used to explain the difference in speed above and below the wing. One can imagine that both currents add up. On the one hand there is the already presented flow (see section pressure differences / Bernoulli),

on the other hand the circulation flow. Both together ensure that the air flows faster above the wing and the speed drops below the wing. And according to Bernoulli, the different speeds create a pressure difference, which in turn causes the lift.

A detailed representation of the circulation flow around the aircraft wing can be found in the script: "How do you explain flying in school? An attempt to analyze various explanatory patterns" by Rita Wodzinski, professor for didactics of physics at the University of Kassel.