Eli5 what bernoulli’s principles is and how it works for aviation.

Question

Eli5 what bernoulli’s principles is and how it works for aviation. Been watching videos about it and still cant wrap my head around it, thanks heaps for any help.

In: 847

Answer 1

A lot of partial answers here. Bernoulli’s law actually contributes very little to lift.

The purpose of a wing is to force a mass of air down while minimizing drag.

Most replies seem less clear about how wings accomplish this.

When an airfoil meets airflow, it splits the air in two, with some going under — and the rest going over.

If the airfoil meets airflow at a slightly positive angle (angle of attack) the bottom surface displaces air mass down, which exerts a force up.

However, air going over top of the wing follows a surface that begins to recede away from the airflow, which creates a partial vacuum. Ambient atmospheric pressure tries to fill this void from all directions. The wing inhibits air underneath from filling the void (but lifts the wing by trying) so air from above does it instead. Air held against the upper surface still moves down as it passes the wing’s trailing edge, so the net force of moving this air down implies an equal force that pushed the wing up.

The wing rides this constant pressure differential as it moves forward, which we call lift.

Now if the wing’s angle of attack is too steep, the airflow’s intertia overcomes atmospheric pressure holding it against the wing and it separates. Tendrils of atmospheric gas seep into the void from around the wing’s leading and trailing edges which create’s turbulence and drag.

So now, not only does does substantial portion of the passing air mass stop moving down, but drag substantially increases too, destroying the wing’s efficiency in a condition known as a “stall.”

A wing’s stall angle (the attack angle at which flow separates) is the same, regardless of speed. This occurs because even though slow moving air holds less inertia than fast moving air, this also means that less differential pressure is needed to draw air from around the leading and trailing edges to fill the pressure void above the wing and separate the boundary layer.