"Axial Fan" takes its name from the fluid inflow and outflow from the axial impeller in the axial direction. Its working principle is based on leaf airfoil theory: gas by an angle of attack. When entering the impeller, a lift generating wing back, while generating an equal and opposite force on the wing of the abdomen, the force to remove the gas spiral impeller to move axially forwardly. At the same time, due to the fan inlet pressure of the gas continue to be inhaled. For variable pitch "Axial Fan", the greater the angle of attack, the greater the perimeter wing back, then lift the greater the pressure, the greater the fan, and the air flow decreases. When the angle of attack reaches a critical value, the gas will leave the back of the wing profile and eddy occurred "Axial Fan" a significant decline in pressure generated stalling.