Fan blade assembly for electric fan

Abstract

Fan blade assemblies are provided for quiet and efficient operation in portable electric axial flow fans intended for home or office use. The blades of the fan blade assemblies include a forward sweep to provide relatively quiet operation. The camber lines of the blades are curved to provide generally concave pressure surfaces and generally convex suction surfaces.

1 . A fan blade assembly for an electric axial flow fan comprising: 
 a hub, and    a plurality of fan blades mounted to the hub for providing axial air flow as the hub is rotated in a direction about an axis of rotation, each blade including:    a blade body having an airfoil portion of substantially uniform thickness and including radially inner, outer and mid-span portions,    a leading edge,    a trailing edge,    an outer edge connecting the leading and trailing edges and having a length that is shorter than the lengths of the leading and trailing edges,    a pressure surface,    a suction surface,    a curved mean camber line wherein the pressure surface is generally concave and the suction surface is generally convex between the leading and trailing edges,    the leading and trailing edges being curved such that the airfoil radially inner portion is rearward swept with respect to the direction of rotation of the hub and the radially outer portion is forward swept with respect to the direction of rotation of the hub about the axis,    the pressure surface being generally concave and the suction surface being generally convex between the hub and the outer edge.    
   
   
       2 . A fan blade assembly as described in  claim 1  wherein the blade body includes a mean camber angle exceeding twent-two degrees.  
   
   
       3 . A fan blade assembly as described in  claim 2  wherein the leading edge defines a forward swept angle greater than sixty degrees.  
   
   
       4 . A fan blade assembly is described in  claim 3  wherein the ratio of blade chord to pitch is about 0.4 or greater.  
   
   
       5 . A fan blade assembly as described in  claim 4  wherein the ratio of blade chord to pitch is about 0.4.  
   
   
       6 . A fan blade assembly as described in  claim 4  wherein the hub includes a plurality of radially outwardly extending arms, a fan blade being secured to each arm.  
   
   
       7 . A fan blade assembly as described in  claim 1  wherein the mean camber line has a maximum curvature near the trailing edge.  
   
   
       8 . A fan blade assembly as described in  claim 7  wherein the blade body has a mean camber angle of the airfoil portion greater than twenty-two degrees.  
   
   
       9 . A fan blade assembly as described in  claim 7  wherein the ratio of blade chord to pitch is about 0.4 or greater.  
   
   
       10 . A fan blade assembly as described in  claim 7  wherein the leading edge defines a forward swept angle greater than sixty degrees.  
   
   
       11 . A fan blade assembly as described in  claim 7  wherein the blades are arranged on the hub and configured such that, when rotated about the axis of rotation, peak loading on the blade occurs near the leading edge of the outer and mid-span portions and away from the leading edge near the hub.  
   
   
       12 . A portable fan comprising: 
 a support;    an electric motor mounted to the support;    a fan blade assembly operatively associated with the electric motor;    a grill at least partially enclosing the fan blade assembly; and    the fan blade assembly including a hub and a plurality of fan blades mounted to the hub, each blade including:    a blade body having an airfoil portion of substantially uniform thickness and including radially inner, outer and mid-span portions,    a leading edge,    a trailing edge,    an outer edge connecting the leading and trailing edges,    a pressure surface,    a suction surface,    a curved mean camber line wherein the pressure surface is generally concave and the suction surface is generally convex between the leading and trailing edges,    the leading and trailing edges being curved such that the airfoil radially inner portion is rearward swept with respect to the direction of rotation of the hub and the radially outer portion is forward swept with respect to the direction of rotation of the hub about the axis,    the pressure surface being generally concave and the suction surface being generally convex between the hub and the outer edge.    
   
   
       13 . A portable fan as described in  claim 12  wherein the leading edge of each blade defines a forward swept angle greater than sixty degrees.  
   
   
       14 . A portable fan as described in  claim 12  wherein the ratio of blade chord to pitch is about 0.4 or greater.  
   
   
       15 . A portable fan as described in  claim 12  wherein the mean camber line has a maximum curvature near the trailing edge.  
   
   
       16 . A portable fan as described in  claim 15  wherein the blade body has a mean camber angle which exceeds twenty two degrees.  
   
   
       17 . A portable fan as described in  claim 15  wherein the hub includes four radially outward extending arms, a fan blade being secured to each arm.  
   
   
       18 . A portable fan as described in  claim 12  wherein the blades are arranged on the hub and configured such that, when rotated about the axis of rotation, peak loading on the blade occurs near the leading edge of the outer and mid-span portions and away from the leading edge at the inner portion near the hub.  
   
   
       19 . A fan blade assembly for an axial flow electric fan, comprising: 
 a hub,    a plurality of fan blades mounted to the hub for providing axial air flow as the hub is rotated in a direction about an axis of rotation, each blade including:    a blade body having an airfoil portion,    a leading edge,    a trailing edge,    a pressure surface,    a suction surface,    a curved mean camber line wherein the pressure surface is generally concave and the suction surface is generally convex between the leading and trailing edges,    the leading edge and trailing edge being curved such that the airfoil portion includes a radially inner portion that is rearward swept and a radially outer portion that is forward swept with respect to the direction of rotation of the hub, and the ratio of blade chord to pitch being about 0.6 or greater.    
   
   
       20 . A fan blade assembly as described in  claim 19  wherein the airfoil portion of each blade has a substantially uniform thickness.  
   
   
       21 . A fan blade assembly as described in  claim 20  wherein five blades are mounted to the hub, each blade overlapping an adjoining blade near the hub.  
   
   
       22 . A fan blade assembly as described in  claim 21  wherein the hub includes a circular edge, each blade including a root portion adjoining the airfoil portion and an arcuate boundary separating the root and airfoil portions, the root portion being secured to the hub, the arcuate boundary adjoining the circular edge of the hub.  
   
   
       23 . A fan blade assembly as described in  claim 21  wherein each blade has a mean camber angle of about 13.65 to 13.7 degrees and the solidity is about 0.68.  
   
   
       24 . A fan blade assembly as described in  claim 20  wherein the camber line has a maximum curvature near the leading edge.