Aerodynamic fan blade

In a multi-blade fan assembly for effecting flow of air in heat exchange relationship with a contained fluid responsive to a driving assembly for effecting rotation, and including:

• a. a central hub having means for being attached to the driving assembly;
• and
• b. a plurality of fan blades connected with said central hub and extending radially therefrom;
• the improvement comprising:
• c. having said fan blades manufactured in accordance with modified subcritical aerodynamic airfoil criteria so as to be efficient for moving ambient air at low relative speeds between said fan blade assembly and air and for minimum power consumption at high relative said speeds;
• each said fan blade having a length to width ratio L/W within the range of 1-], where L is the length of the blade from its base to its tip and W is the width of the blade at its widest point;
• each said fan blade having a length L within the range of 6-18 inches;
• having thin airfoil leading and trailing edges;
• said leading edge being sufficiently thin that said blade does not stall due to the high degree of separation of said air stream encountering the leading edge of said blade;
• and having a chord that is totally contained within a planar cross section of the blade at said chord, each said cross section being substantially symmetrical with respect to its chord with minimum camber and lift on said blade and having its maximum thickness t to its length l ratio t/l within the range of 0.03-0.12;
• each said fan blade having a center of mass located at a position in the range of (0.2-0.3) X (length of the chord at the respective location), as measured from the forward end of the chord;
• each said fan blade having a chord taper throughout the range of taper in the range of 0.25-0.75;
• and having a twist within the range of 10.degree.-20.degree. for obtaining a substantially uniform flow of air throughout the length of said blade;
• each said fan blade having a positive angle of attack throughout said length of said blade and having a pitch angle with respect to the central plane of said hub within the range of 25.degree.-45.degree. at the end adjacent said hub and within the range of 10.degree.-30.degree. at the outer radial end farthest from said hub.