Axial flow fan and fan blade

A fan blade for an axial flow fan, comprising:

• a hollow airfoil section comprising a sheet of alloy bent to form a leading edge and having a trailing edge formed from the joining of two long edges of the sheet, each of the long edges having a substantially continuously changing curvature, the sheet possessing a bend of a first direction adjacent one of the two long edges and a bend of a second direction adjacent the other of the two long edges, whereby the airfoil section possesses a twist;
• and
• a transition piece having first and second airfoil bearing surfaces, substantially all of the bearing surfaces being in contact with an interior surface of the airfoil section, and wherein each of the bearing surfaces after joining to the airfoil section possesses a twist complementary to the twist of the airfoil section.

A fan blade for an axial flow fan, comprising:

• a hollow airfoil section comprising a flat sheet of airfoil material shaped to form a leading edge and having a trailing edge formed from the joining of two long edges of the sheet, each of the long edges having a substantially continuously changing curvature, the sheet possessing a bend of a first direction adjacent one of the two long edges and a bend of a second direction adjacent the other of the two long edges, whereby the airfoil section possesses a twist;
• and
• a transition piece having first and second airfoil bearing surfaces, substantially all of the bearing surfaces being in contact with an interior surface of the airfoil section, and wherein each of the bearing surfaces after joining to the airfoil section possesses a twist complementary to the twist of the airfoil section.