Fan blade tips

Abstract

Fans having blade tips with downwardly extending airfoil surfaces are disclosed herein. In one embodiment, for example, a high volume low speed ceiling fan includes a plurality of blades, each having an anhedral or downward sloping tip portion. The blade tips can also include an aft swept portion that extends between the main airfoil portion of the fan blade and the anhedral tip portion.

1 . A ceiling fan comprising:
 a central hub configured to be suspended from a ceiling of a building; and   a plurality of blades extending outwardly from the central hub, wherein each blade includes:
 a main airfoil having an inboard end portion fixedly attached to the central hub and an outboard end portion spaced apart from the central hub; and 
 a tip portion attached toward the outboard end portion of the main airfoil and extending downwardly relative to the main airfoil portion. 
   
     
     
         2 . The ceiling fan of  claim 1  wherein the plurality of blades define a fan outer diameter of from about 6 feet to about 24 feet. 
     
     
         3 . The ceiling fan of  claim 1  wherein the main airfoils extend horizontally outward from the hub. 
     
     
         4 . The ceiling fan of  claim 1  wherein each blade further includes an aft swept portion attached to the outboard end portion of the main airfoil between the outboard end portion and the tip portion, and wherein the tip portion extends downwardly relative to the aft swept portion. 
     
     
         5 . The ceiling fan of  claim 1  wherein each blade further includes an aft swept portion attached to the outboard end portion of the main airfoil between the outboard end portion and the tip portion, wherein the main airfoil and the aft swept portion of each blade lie in a horizontal plane, and wherein the tip portion extends downwardly relative to the aft swept portion. 
     
     
         6 . A fan comprising:
 a motor driven central hub; and   a plurality of blades extending outwardly from the central hub fan, wherein the plurality of blades are configured to move air in a direction D when rotating in a direction R during normal operation, wherein each blade includes:
 a main airfoil having an inboard end portion fixedly attached to the central hub and an outboard end portion spaced apart from the central hub; and 
 a tip having:
 an aft swept portion; and 
 an anhedral portion, wherein the aft swept portion has an inboard chord attached to the outboard end portion of the main airfoil and an outboard chord attached to anhedral portion, and wherein the anhedral portion extends away from the main airfoil in direction D. 
 
   
     
     
         7 . The fan of  claim 6  wherein the inboard end portion and the outboard end portion of the main airfoil lie in a common plane, and wherein the anhedral portion is positioned at an angle relative to the plane. 
     
     
         8 . The fan of  claim 6  wherein the main airfoil and the aft swept portion lie in a common plane, and wherein the anhedral portion is positioned at an angle relative to the plane. 
     
     
         9 . The fan of  claim 6  wherein the aft swept portion extends away from the main airfoil opposite to the direction R. 
     
     
         10 . The fan of  claim 6  wherein the anhedral portion extends away from the aft swept portion opposite to the direction R. 
     
     
         11 . The fan of  claim 6  wherein the main airfoil and the aft swept portion lie in a common plane, wherein the anhedral portion is positioned at an angle relative to the plane, wherein the aft swept portion extends away from the main airfoil opposite to the direction R, and wherein the anhedral portion extends away from the aft swept portion opposite to the direction R. 
     
     
         12 . The ceiling fan of  claim 6  wherein the main airfoil and the aft swept portion have complimentary airfoil cross sections and lie in a common horizontal plane, and wherein the anhedral portion has a first chord thickness where it attaches to the aft swept portion and a second chord thickness a distal tip, and wherein the first chord thickness is greater than the second chord thickness. 
     
     
         13 . The ceiling fan of  claim 6  wherein the main airfoil has a rectangular planform and the aft swept portion and the anhedral portion taper outwardly. 
     
     
         14 . The ceiling fan of  claim 6  wherein the anhedral has a curved leading edge and a curved trailing edge. 
     
     
         15 . The ceiling fan of  claim 6  wherein the anhedral portion has a curved leading edge that forms a convex parabolic curve and a curved trailing edge that forms a concave parabolic curve. 
     
     
         16 . A fan comprising:
 a central hub;   means for rotating the central hub;   means for coupling the means for rotating to a ceiling or other elevated structure in a building; and   a plurality of blades extending outwardly from the central hub, wherein each blade includes:
 a main airfoil having an inboard end portion fixedly attached to the central hub and an outboard end portion spaced apart from the central hub; and 
 a tip portion attached toward the outboard end portion of the main airfoil and extending downwardly relative to the main airfoil portion. 
   
     
     
         17 . The fan of  claim 16  wherein the plurality of blades define a fan outer diameter of from about 6 feet to about 24 feet. 
     
     
         18 . The fan of  claim 18  wherein each blade further includes an aft swept portion attached to the outboard end portion of the main airfoil between the outboard end portion and the tip portion, and wherein the tip portion extends downwardly relative to the aft swept portion. 
     
     
         19 . The fan of  claim 18  wherein each blade further includes an aft swept portion attached to the outboard end portion of the main airfoil between the outboard end portion and the tip portion, wherein the main airfoil and the aft swept portion of each blade lie in a horizontal plane, and wherein the tip portion extends downwardly relative to the aft swept portion.