When the air encounters an aerofoil almost all of it flows either over its top surface or beneath its lower surface following the the upper and lower contours of the aerofoil. The upward flow of air before the leading edge is known as "Upwash" and the downward flowing air leaving the trailing edge is called "Downwash". A very small proportion hits the aerofoil head-on and is brought to a complete standstill.

The position of the leading edge stagnation point changes. As the angle of attack increases, it moves down onto the lower surface. This means that some of the air approaching the lower surface has to change direction and flow backwards before it eventually flows over the leading edge. The upwash and downwash become much more pronounced as the aerofoil's angle of attack increases.

The pressure distribution over a symmetrical aerofoil at 0° angle of attack is equal, so there is no lift production.

When a positive angle of attack is applied, an unequal pressure distribution takes place, with the least pressure on the upper surface, due to the increasing airflow velocity and a relatively higher pressure on the lower surface, due to the decreasing airflow velocity.