Bernauli Theorem

The aerofils are so designed that

so that the aerofils get a lifting force in upward direction. According to Bernoullis theorem, where the pressure is large, the velocity will be minimum or vice-versa.
Thus,

According to Bernoullis theorem, in case of steady flow of incompressible and non-viscous liquid through a tube of non-uniform cross-section, the sum of the pressure, the potential energy per unit volume and the kinetic energy per unit volume is same at every point in the tube, i.e.,

Dividing this expression by
we have
In this expression
is called the pressure head,
the velocity head and the gravitational head.