Patent Publication Number: US-2005123404-A1

Title: Fan blade

Description:
RELATED APPLICATIONS  
      This is a continuation-in-part of U.S. patent application Ser. No. 10/141,623 filed on May 8, 2002, which is a continuation-in-part of U.S. patent application Ser. No. 09/558,745 filed on Apr. 21, 2000, the entire disclosures of which are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION  
      The present invention relates generally to an apparatus and a method for moving fluids, and more particularly to a fan blade and a method of moving fluids with a fan blade.  
     BACKGROUND OF THE INVENTION  
      A typical fan assembly consists of a hub, a multi-wing spider, and two or more blades, although in some assemblies the hub and spider can be an integral unit, or the spider and blades can be an integral unit. In some cases, it is even possible to employ a fan assembly in which the hub, multi-wing spider, and blades are a single integral unit. In those fan assemblies in which fan blades are attached to a spider wing, each spider wing is often attached with a blade through riveting, spot welding, screws, bolts and nuts, other conventional fasteners, and the like.  
      Fan assemblies are employed in a large number of applications and in a variety of industries. However, there exist a number of common design criteria for fans in many of such applications: fan efficiency, noise, and the like. For example, it is desirable for a fan assembly of a residential or commercial air conditioning system to be as efficient and quiet as possible, resulting in energy savings and a better operating system.  
      With continued reference to air conditioning system applications by way of example only, the fans in such systems are typically directly driven by a motor to draw airflow through condenser coils to achieve a cooling effect. Existing condenser fan assemblies employ rectangular blade shapes. Although these fans will generate sufficient airflow to meet varied cooling needs when the fan blades are pitched properly, such fans also radiate high levels of noise during operation and can be relatively inefficient.  
      In many applications, the upstream airflow of a rotating fan is partially blocked by a motor or other driving unit, frame or other structural members, and other elements. For example, in a typical condenser cooling application, the upstream airflow of a rotating fan is often partially distorted due to the blockage of a compressor, controlling panels, etc. As a result, tonal and broadband noise is often generated by the leading edges of the rotating fan blades as they cut through the flow distortion (i.e. turbulence). In addition, each segment of the fan blade leading edge along the radial direction can act as a noise radiator.  
      In light of the above shortcomings of conventional fans, there are increasing market demands for fans that can generate sufficient air for cooling at reduced noise levels. In addition, fan assemblies and fan blades that are durable, easy to manufacture, easy to assemble, and are inexpensive are highly desirable for obvious reasons.  
     SUMMARY OF THE INVENTION  
      The present invention employs improved fan blade shapes to generate improved fan blade performance in one or more manners (i.e., increased fan efficiency, lower fan noise, greater fluid moving capability, and the like). In some embodiments, the fan blade is shaped to reduce noise during operation thereof.  
      The fan blade of the present invention can be formed from a flat blank bent to a desired shape to form the fan blade. Alternatively, the fan blade can be cast, molded, or produced in any other manner desired.  
      In some embodiments of the present invention, the fan blade has a front side, a rear side, an inner attachment portion, an outer edge, a curved leading edge and a curved trailing edge. The outer edge can define an arc between a forward position and a rearward position of the fan blade. In some embodiments, the leading edge extends outward and intercepts the arc of the outer edge at the forward position, and the trailing edge extends outward to the rearward position.  
      The shapes of the blades of the various embodiments of the present invention can be defined at least in part by one or more angles or lengths, including the radius of the fan assembly at different locations on the blade (e.g., the radius of the fan assembly R L  at a leading edge of the fan blade and/or the radius of the fan assembly R T  at a trailing edge thereof), a radius of a circle that coincides or substantially coincides with a majority or all of the length of a trailing edge of the blade, an angle at which a leading edge of the fan blade is swept forward, an angle at which a trailing edge of the fan blade is swept forward, the chamber-to-chord ratio of the leading edge of the fan blade, the chamber-to-chord ratio of the trailing edge of the fan blade, the chamber-to-chord ratio of a cross-section of the blade at various radial distances of the blade (from the rotational axis thereof), and an angle of the outer radial portion of the blade with respect to a plane passing perpendicularly through the rotational axis of the blade. Blades falling within the spirit and scope of the present invention can be at least partially defined by the size of any one or more of these blade parameters.  
      In some embodiments, the angle at which the leading edge of the fan blade is swept forward is formed by a straight line having a length equal to R L  extending from a given axis coinciding with the axis of the fan to the forward position of the fan blade (mentioned above) and a line extending from the axis to a first position on the leading edge and having a length equal to about 0.5R L  wherein the angle ∝ L  is equal to at least 35 degrees. In other embodiments, this angle is formed by a straight line extending from the axis to the forward position of the fan blade and a line extending from the axis to a first position on the leading edge and having a length equal to about 0.65R, wherein R is the radius of the fan assembly and ∝ L  is between 15 and 45 degrees, 20 to 35 degrees, or 25 to 30 degrees (in different embodiments of the present invention). In other embodiments, this angle is formed by a straight line extending from the axis to the forward position of the fan blade and a line extending from the axis to a first position on the leading edge and having a length equal to about 0.75R, wherein R is the radius of the fan assembly and ∝ L  is between 15 and 35 degrees, 18 to 30 degrees, or 20 to 28 degrees (in different embodiments of the present invention).  
      In another aspect, the chamber-to-chord ratio of the leading edge of the fan blade in some embodiments is larger than about 0.10 but less than about 0.20, wherein L L  is the length of a straight line from the first position to the forward position and H L  is the maximum distance from L L  to the leading edge as measured from a straight line perpendicular to L L  and extending to the leading edge. In other embodiments, the chamber-to-chord ratio of the leading edge of the fan blade is between 0 and 0.22, 0.05 and 0.17, or 0.08 and 0.13 (in different embodiments of the present invention). In still other embodiments, the chamber-to-chord ratio of the leading edge of the fan blade is between 0.05 and 0.30, 0.10 and 0.25, or 0.15 and 0.20 (in different embodiments of the present invention).  
      In a further aspect, the angle at which a trailing edge of the fan blade is swept forward is formed by a straight line having a length equal to R T  extending from the axis of rotation of the fan assembly to the rearward position (mentioned above) and a line extending from the axis to a second position on the trailing edge of the blade and having a length equal to about 0.5R T , wherein ∝ T  is at least 30 degrees but less than 40 degrees. In other embodiments, this angle is formed by a straight line extending from the axis to the rearward position of the fan blade and a line extending from the axis to a second position on the trailing edge and having a length equal to about 0.65R, wherein R is the radius of the fan assembly and ∝ T  is between 10 and 35 degrees, 15 to 30 degrees, or 20 to 25 degrees (in different embodiments of the present invention). In still other embodiments, this angle is formed by a straight line extending from the axis to the rearward position of the fan blade and a line extending from the axis to a second position on the trailing edge and having a length equal to about 0.75R, wherein R is the radius of the fan assembly and ∝ T  is between 5 and 20 degrees, 5 to 15 degrees, or 8 to 12 degrees (in different embodiments of the present invention).  
      In another aspect, the chamber-to-chord ratio of the trailing edge of the fan blade in some embodiments is larger than about 0.10 but less than about 0.20, wherein L T  is the length of a straight line from the second position to the rearward position and H T  is the maximum distance from L T  to the trailing edge as measured from a straight line perpendicular to L T  and extending to the trailing edge. In other embodiments, the chamber-to-chord ratio of the trailing edge of the fan blade is between 0 and 0.20, 0.05 and 0.17, or 0.07 and 0.12 (in different embodiments of the present invention). In still other embodiments, the chamber-to-chord ratio of the trailing edge of the fan blade is between 0.05 and 0.20, 0.05 and 0.17, or 0.07 and 0.12 (in different embodiments of the present invention).  
      With regard to the chamber-to-chord ratios of cross-sections of the blade at various radial distances of the blade (from the rotational axis thereof), in some embodiments this camber-to-chord ratio falls between 2.0% and 7.5%, and can be constant or vary with increasing distance from the rotational axis of the fan assembly. In other embodiments, this camber-to-chord ratio falls between 4.0% and 13.5% and can be constant or vary with increasing distance from the rotational axis of the fan assembly. With regard to the angle of the outer radial portion of the blade (with respect to a plane passing perpendicularly through the rotational axis of the blade), this angle is between 4 and 15 degrees, 6 and 13 degrees, or 8 and 11 degrees (in different embodiments of the present invention). In other embodiments, this angle is between 5 and 18 degrees, 8 and 15 degrees, or 10 and 15 degrees (in different embodiments of the present invention).  
      Other features and advantages of the invention along with the organization and manner of operation thereof will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings, wherein like elements have like numerals throughout.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention is further described with reference to the accompanying drawings, which show a preferred embodiment of the present invention. However, it should be noted that the invention as disclosed in the accompanying drawings is illustrated by way of example only. The various elements and combinations of elements described below and illustrated in the drawings can be arranged and organized differently to result in embodiments which are still within the spirit and scope of the present invention.  
      In the drawings, wherein like reference numerals indicate like parts:  
       FIG. 1  is a perspective view of a fan assembly according to an embodiment of the present invention, shown attached to a shaft of a motor;  
       FIG. 2  is rear plan view of the fan assembly illustrated in  FIG. 1 , shown with the fan blades having no pitch;  
       FIG. 3  is a front plan view of the fan assembly illustrated in  FIGS. 1 and 2 , shown with the fan blades having no pitch;  
       FIG. 4  is a rear plan view of one of the blades of the fan assembly illustrated in  FIGS. 1-3 ;  
       FIG. 5  is a cross-sectional view of the fan blade illustrated in  FIG. 4 , taken along lines A-A of  FIG. 4 ;  
       FIG. 6  is a cross-sectional view of the fan blade illustrated in  FIG. 4 , taken along lines B-B of  FIG. 4 ;  
       FIG. 7  is a cross-sectional view of the fan blade illustrated in  FIG. 4 , taken along lines C-C of  FIG. 4 ;  
       FIG. 8  is a cross-sectional view of the fan blade illustrated in  FIG. 4 , taken along lines D-D of  FIG. 4 ;  
       FIG. 9  is a cross-sectional view of the fan blade illustrated in  FIG. 4 , taken along lines E-E of  FIG. 4 ;  
       FIG. 10  is a cross-sectional view of the fan blade illustrated in  FIG. 4 , taken along lines F-F of  FIG. 4 ;  
       FIG. 11  is an end view of one of the fan blades illustrated in  FIGS. 1-3 , shown mounted upon a motor shaft;  
       FIG. 12  is a side view of the fan assembly illustrated in  FIGS. 1-3 ;  
       FIG. 13  is a front plan view of one of the blades of the fan assembly illustrated in  FIGS. 1-3 , shown attached to a spider having no pitch;  
       FIG. 14  is a cross-sectional view of the fan blade illustrated in  FIG. 13 , taken along lines M-M of  FIG. 13 ;  
       FIG. 15  is a rear plan view of a fan blade according to a second embodiment of the present invention;  
       FIG. 16  is cross-sectional view of the fan blade illustrated in  FIG. 15 , taken along lines N-N of  FIG. 15 ;  
       FIG. 17  is a front plan view of a fan blade according to a third embodiment of the present invention, shown attached to a spider having no pitch;  
       FIG. 18  is a front plan view of the fan blade illustrated in  FIG. 17 ;  
       FIG. 19  is a cross-sectional view of the fan blade illustrated in  FIGS. 17 and 18 , taken along lines A-A of  FIG. 19 ;  
       FIG. 20  is a cross-sectional view of the fan blade illustrated in  FIGS. 17 and 18 , taken along lines B-B of  FIG. 19 ;  
       FIG. 21  is a cross-sectional view of the fan blade illustrated in  FIGS. 17 and 18 , taken along lines C-C of  FIG. 19 ;  
       FIG. 22  is a cross-sectional view of the fan blade illustrated in  FIGS. 17 and 18 , taken along lines D-D of  FIG. 19 ;  
       FIG. 23  is a cross-sectional view of the fan blade illustrated in  FIGS. 17 and 18 , taken along lines E-E of  FIG. 19 ;  
       FIG. 24  is a cross-sectional view of the fan blade illustrated in  FIGS. 17 and 18 , taken along lines F-F of  FIG. 19 ;  
       FIG. 25  is a cross-sectional view of the fan blade illustrated in  FIGS. 17 and 18 , taken along lines G-G of  FIG. 19 ;  
       FIG. 26  is a cross-sectional view of the fan blade illustrated in  FIGS. 17 and 18 , taken along lines H-H of  FIG. 19 ;  
       FIG. 27  is a front plan view of a fan blade according to a fourth embodiment of the present invention, shown attached to a spider having no pitch;  
       FIG. 28  is a front plan view of the fan blade illustrated in  FIG. 27 ;  
       FIG. 29  is a cross-sectional view of the fan blade illustrated in  FIGS. 27 and 28 , taken along lines A-A of  FIG. 28 ;  
       FIG. 30  is a cross-sectional view of the fan blade illustrated in  FIGS. 27 and 28 , taken along lines B-B of  FIG. 28 ;  
       FIG. 31  is a cross-sectional view of the fan blade illustrated in  FIGS. 27 and 28 , taken along lines C-C of  FIG. 28 ;  
       FIG. 32  is a cross-sectional view of the fan blade illustrated in  FIGS. 27 and 28 , taken along lines D-D of  FIG. 28 ;  
       FIG. 33  is a cross-sectional view of the fan blade illustrated in  FIGS. 27 and 28 , taken along lines E-E of  FIG. 28 ;  
       FIG. 34  is a cross-sectional view of the fan blade illustrated in  FIGS. 27 and 28 , taken along lines F-F of  FIG. 28 ;  
       FIG. 35  is a cross-sectional view of the fan blade illustrated in  FIGS. 27 and 28 , taken along lines G-G of  FIG. 28 ; and  
       FIG. 36  is a cross-sectional view of the fan blade illustrated in  FIGS. 27 and 28 , taken along lines H-H of  FIG. 28 . 
    
    
     DETAILED DESCRIPTION  
      Referring now to  FIGS. 1-3 , one embodiment of the fan blade according to the present invention is identified at  31 . In this illustrated embodiment, three of the blades  31  are shown attached to an attachment device or spider  51  which is attached to a hollow cylindrical member  53  which forms a fan assembly  55 . The member  53  is fitted around and attached to the shaft  57  of an electric motor  59  by way of a threaded member  61 . The fan assembly  55  can be used for cooling a condenser, for moving air within, into, or out of a room, for cooling equipment in an enclosure, or for any other application where it is necessary or desirable to move air or other fluid. The fan assembly  55  illustrated in  FIGS. 1-3  has three identical blades  31 . However, it should be noted that the fan blades  31  according to the various embodiments of the present invention can be employed in fan assemblies having any number of fan blades  31 , such as two, four, or more identical fan blades  31 . Furthermore, although the fan blades in the various embodiments of the present invention produce excellent results in fan assemblies having a diameter of 10-24 inches, and also in fan assemblies having a diameter of 24-36 inches, it should be noted that the fan blades of the present invention can have any size desired (e.g., for fan assemblies having diameters greater than 36 inches, smaller than 10 inches, or having any diameter therebetween).  
      Each of the blades  31  can be formed from a flat metal blank. For example, the blades  31  can be stamped, pressed, or machined from such a blank. In other embodiments however, the blades  31  can be cast, molded, or manufactured in any other manner desired. The blades  31  can be made of metal, and in some embodiments are made of aluminum. Other blade materials include steel, plastic, composites, fiberglass, and the like.  
      In some embodiments, the blades  31  are bent or are otherwise shaped to have a generally concave rear side and a convex front side. Referring to  FIG. 13 , the blade  31  of the first embodiment illustrated in  FIGS. 1-3  (as well as  FIGS. 4-12  and  14 ) has an inner attachment portion  77 , an outer edge  79 , a curved leading edge  81  and a curved trailing edge  83 . Other embodiments falling within the spirit and scope of the present invention can have less than all of these features (e.g., a leading edge  81  that is not curved, a trailing edge  83  that is not curved, and the like). The attachment portion  77  of the blade  31  can be attached to an arm  51 A of a spider  51 , which is attached to a hub  53 , cylinder, or other element adapted to be mounted upon a motor shaft or other driving unit. Alternatively, the attachment portion  77  can be shaped to connect directly to the hub  53 , if desired (in which case no identifiable spider  51  need exist). In this regard, the fan assembly  55  of the various embodiments of the present invention can be defined at least in part by one or more fan blades  31  that are integral with respect to the spider  51 , or that are integral with respect to the spider  51  and hub  53 . In such embodiments, the blades  31  and spider  51  (or the blades  31 , spider  51 , and hub  53 ) can be manufactured as an integral unit in any conventional manner, such as by pressing, stamping, molding, casting, and the like. Also, in some embodiments the blades  31  can be integral with respect to the hub  53  (in which case no identifiable spider  51  need exist). The fan assembly  55  can be connected to a driving unit in any conventional manner, such as by a splined shaft connection, a clearance, press, or interference fit upon a motor shaft, by being bolted or otherwise attached to a mounting plate driven in any conventional manner, and the like. In the illustrated embodiment of  FIGS. 1-3  for example, the hub  53  has a central aperture  53 A with a centerpoint  53 C at an axis of rotation  63  of the fan assembly  55  (see  FIGS. 11 and 12 ).  
      The shapes of the blades  31 ,  231  of the various embodiments of the present invention can be defined at least in part by one or more angles or lengths. Some of these angles or lengths include the radius of the fan assembly  55 ,  255 ,  455  at different locations on the blade (R L  and R T  described in greater detail below), a radius R of a circle that coincides or substantially coincides with a majority or all of the length of a trailing edge of the blade, an angle ∝ L , ∝ l , ∝ l , at which a leading edge of the fan blade is swept forward, an angle ∝ T , ∝t, ∝t at which a trailing edge of the fan blade is swept forward, the chamber-to-chord ratio H L /L L , H l /L l , H l′ /L l′  of the leading edge of the fan blade, the chamber-to-chord ratio H T /L T , H t /L t , H t′ /L t′  of the trailing edge of the fan blade, the chamber-to-chord ratio H/L of a cross-section of the blade at various radial distances of the blade (from the rotational axis thereof), and an angle β, β′, β″ of the outer radial portion of the blade with respect to a plane passing perpendicularly through the rotational axis of the blade. Blades  31 ,  231 ,  431  falling within the spirit and scope of the present invention can be at least partially defined by the size of any one or more of these blade parameters. These blade parameters according to the present invention will be described in greater detail below.  
      The blade shapes and blade shape parameters hereinafter described with reference to the embodiments of the present invention illustrated in  FIGS. 1-26  can be employed in blades having any size. However, superior performance is obtained by using these blade shapes and blade shape parameters in blade assemblies that are approximately 10-24 inches in diameter.  
      With reference again to the blade embodiment illustrated in  FIG. 13 , the arcs of the blade edges  79  and  81  join at a forward position at juncture  85 , while the arcs of the blade edges  79  and  83  join at a rearward position at juncture  87 . Accordingly, the outer edge  79  of the blade  31  defines an arc from point  85  to juncture  87 , although other shapes for the outer edge  79  can be employed in alternative embodiments of the present invention. The leading edge  81  of the blade illustrated in  FIG. 13  is forward swept in a region between point  91  and point  85 . Point  91  is defined as the location where the leading edge  81  of the blade  31  intersects an imaginary circle centered about the rotational axis  63  of the blade  31  and having a radius that is one-half of the radius of the fan assembly  255  at the tip  233  of the blade  31  (0.5R L ). Point  85  is defined as the location where the leading edge  81  and the outer edge  79  would intersect if their respective arcs were extended (in those embodiments such as the illustrated embodiment of  FIGS. 1-14  in which point  85  is located off of the blade  31 .  
      The trailing edge  83  of the blade illustrated in  FIG. 13  is a forward swept region between point  93  and point  87 . Point  93  is defined as the location where the trailing edge  83  of the blade  31  intersects an imaginary circle centered about the rotational axis  63  of the blade  31  and having a radius that is one-half of the radius of the fan assembly  55  at point  93  (0.5R T ). Point  87  is defined as the location where the outer edge  79  meets the trailing edge  83 , and in some embodiments is the rearmost location of the blade  31  that has a radius substantially the same as the radius of the fan assembly  55 . In some embodiments (such as the embodiment illustrated in  FIGS. 17-26  described in greater detail below), the trailing edge  83  is defined in either manner just described or in another manner dependent at least partially upon the shape of the trailing edge  83 . With regard to this third manner, some blades  31  employ a trailing edge  83  that has a substantially constant radius over at least a majority (and in many cases, a large majority or all) of the trailing edge  83 . In some embodiments, the arc defined by this portion of the trailing edge  83  intersects or can be extended to intersect an imaginary circle having the radius R of the fan assembly  55 . This point of intersection  87  can be on or off of the blade  31 , and represents another manner of defining point  87  according to the present invention.  
      The leading edge  81  of the blade  31  in the embodiment of  FIGS. 1-14  has a swept angle ∝ L  formed by and between lines  95  and  97 . Line  95  has a length equal to R L  and is an imaginary straight line passing from the axis of rotation  63  of the fan assembly  55  to point  85 , while line  97  is an imaginary straight line passing from the axis of rotation  63  to point  91 . In some embodiments of the present invention (including the blade embodiment illustrated in  FIGS. 1-14 ), ∝ L  is at least about 35 degrees.  
      The fan blade leading edge  81  in the region between points  91  and  85  can be concave as illustrated in  FIGS. 1-14 , and can have a camber ratio defined by the largest depth H L  of the fan blade leading edge  81  between points  91  and  85  divided by the length of a straight line L L  extending between points  91  and  85  (H L  being measured perpendicular to L L ). In some embodiments of the present invention, the camber-to-chord ratio H L /L L  is larger than 0.10 but less than 0.20.  
      As mentioned above, the trailing edge  83  of the fan blade  31  illustrated in  FIGS. 1-14  is forwardly swept in the region between points  93  and  87 . More specifically, the fan blade  31  in the embodiment of  FIGS. 1-14  has a swept angle ∝ T  formed by and between lines  99  and  101 . Line  99  is an imaginary straight line passing from the axis of rotation  63  of the fan assembly  55  to point  93 , while line  101  has a length equal to the radius of the fan assembly  55  at point  87 , R T , and is an imaginary straight line passing from the axis of rotation  63  to point  87 . In some embodiments of the present invention, ∝ T  is at least about 30 degrees but less than about 40 degrees. The radius of the fan assembly R T  (at point  87 ) can be the same or different than the radius of the fan assembly R L  (at point  85 ).  
      The fan blade trailing edge  83  can be convex, and can have a camber ratio defined by the largest height of the fan blade trailing edge  83  between points  87  and  93  divided by the length of a straight line L T  extending between points  87  and  93  (H T  measured perpendicular to L T ). In some embodiments of the present invention, the camber-to-chord ratio H T /L T  is larger than 0.10 but less than 0.20. With particular reference to  FIG. 13 , line  88  is an imaginary straight line extending radially from the axis of rotation  63  of the fan assembly  55  along the middle of the wing  51 A of the spider.  
      The blade  31  can have any cross-sectional shape desired (i.e., any shape into and out of the plane of  FIGS. 2-4  and  13 ). However, in some embodiments, the blade  31  is shaped such that the surface of the front side is concave and the surface of the rear side is convex as shown in  FIGS. 5-14 . With reference to  FIG. 14 , this shape can be measured with reference to an imaginary line  103  extending radially inward from point  87  at the outer edge  79  of the blade  31  to intersect the axis of rotation  63  of the fan assembly  55  in a perpendicular manner. In some embodiments of the present invention, the angle β (the angle between line  103  and the blade in the radially outer region of the blade  31 ) is at least 10 degrees. In this regard, the radially outer third to half of the blade  31  at line  103  can be flat or substantially flat as best shown in  FIG. 14 . Accordingly, in such embodiments, the angle β is defined between this portion of the blade  31  and line  103 .  
      The spider  51  in the illustrated preferred embodiment of  FIGS. 1, 2 ,  3 ,  12 , and  13  has three arms or wings,  51 A,  51 B, and  51 C, each of which extend outward from the axis of rotation  63 . The spider arms  51 A,  51 B,  51 C can extend from the axis of rotation  63  at a pitch angle as best shown in  FIG. 11 . Any pitch angle of the blades  31  can be selected. In some embodiments, the spider arms  51 A,  51 B,  51 C extend at no pitch angle.  
      Each of the blades  31  is attached to one of the spider arms  51 A,  51 B,  51 C in any conventional manner, such as by bolts  65 , rivets, screws, or other conventional fasteners, welding or brazing, adhesive or cohesive bonding material, and the like. With continued reference to the embodiment illustrated in  FIGS. 1, 2 ,  3 ,  12 , and  13 , and with particular reference to  FIG. 13 , the spider arms  51 A,  51 B,  51 C (only one of which is shown completely in  FIG. 13 ) are spaced apart from one another, such as by 120 degrees between arms as illustrated, or by any other regular or non-regular spacing. Accordingly, adjacent blades can be angularly separated corresponding to the separation of the spider arms, such as by 120 degrees in the embodiment of  FIGS. 1, 2 ,  3 ,  12 , and  13 .  
      As shown in  FIG. 12 , the trailing edge  83  of each blade  31  in the illustrated embodiment of  FIGS. 1-14  is forward of a plane  103  perpendicular to the axis  63  and passing through the spider  51 , while the leading edge  81  of each of the blades is rearward of the plane  103 . This arrangement of the blades  31  is dependent at least in part upon the shape of the blades  31  and the spider arms  51 A,  51 B,  51 C (e.g., the pitch of the spider arms  51 A,  51 B,  51 C).  
      Another embodiment of the fan blade  31  according to present invention is illustrated in  FIGS. 15 and 16 . In this embodiment, the fan blade  31  shares the same features as the blade illustrated in  FIGS. 1-14 , but has a substantially flat mounting portion or pad  111  by which the spider  51  can be attached to the fan blade  31 . In this regard, it should be noted that the spider  51  can be attached on the front side, rear side, or on both sides of the fan blade  31  at this mounting portion or pad  111 .  
      Yet another embodiment of the fan blade according to the present invention is illustrated in  FIGS. 17-26 . With the exception of differences evident from a comparison of  FIGS. 1-16  and  17 - 26  and the differences indicated below, the fan blade (indicated generally at  231 ) has the same features as those described above with reference to the blade embodiments shown in  FIGS. 1-16 . Accordingly, features of the fan blade  231  corresponding to those of the embodiments of  FIGS. 1-16  are assigned the same numbers increased by  200 .  
      The blade  231  illustrated in  FIGS. 17-26  has an extended trailing edge  283  as best shown in  FIGS. 17 and 18 . In addition, the outer edge  279  of the blade  231  has a substantially constant radius along a majority of (and in the illustrated embodiment of  FIGS. 17-26 , almost all of) the outer edge  279  of the blade  231  between points  285  and  287 . However, the blade  231  in the illustrated embodiment of  FIGS. 17-26  has a slightly smaller radial dimension near point  287  as shown in  FIGS. 17 and 18 , where it can be seen that a circle having a constant radius R extends past the edge of the blade  231  at point  287 . In addition, point  291  in the embodiment of  FIGS. 17-26  is defined as the location where the leading edge  281  of the blade  231  intersects an imaginary circle centered about the rotational axis  263  of the blade  231  and having a radius that is 0.65 times the length of the radius of the blade assembly (0.65R). Similarly, point  293  is defined as the location where the trailing edge  283  of the blade  231  intersects an imaginary circle centered about the rotational axis  263  of the blade  231  and having a radius that is 0.65 times the length of the radius of the blade assembly (0.65R).  
      As described above, the shape of the blade  231  according to the present invention can be defined by any one or more parameters. In this regard, any combination of such parameters can be employed to define a blade  231  according to the present invention. With continued reference to  FIGS. 17-26 , the angle ∝ l  (at which the leading edge  281  of the fan blade  231  is swept forward) falls between 15 and 45 degrees in some applications to produce good fan performance. In other applications, a leading edge angle ∝ l  falling between 20 and 35 degrees is employed for good fan performance. In still other applications, a leading edge angle ∝ l  falling between 25 and 30 degrees is employed for good fan performance.  
      With reference now to the trailing angle ∝ t  (at which the trailing edge  283  of the fan blade  231  is swept forward), the trailing angle ∝ t  falls between 10 and 35 degrees in some applications to produce good fan performance. In other applications, a trailing edge angle ∝ t  falling between 15 and 30 degrees is employed for good fan performance. In still other applications, a trailing edge angle ∝ t  falling between 20 and 25 degrees is employed for good fan performance.  
      As described above, the blade  231  can have a concave leading edge  281  having a chamber-to-chord ratio H l /L l . This chamber-to-chord ratio H l /L l  is between 0 and 0.22 in some applications to produce good fan performance. In other applications, a leading edge chamber-to-chord ratio H l /L l  falling between 0.05 and 0.17 is employed for good fan performance. In still other applications, a leading edge chamber-to-chord ratio H l /L l  falling between 0.08 and 0.13 is employed for good fan performance.  
      With reference now to the chamber-to-chord ratio H t /L t  of the trailing edge  283 , the chamber-to-chord ratio H t /L t  of the trailing edge  283  falls between 0 and 0.20 in some applications to produce good fan performance. In other applications, a trailing edge chamber-to-chord ratio H t /L t  falling between 0.05 and 0.17 is employed for good fan performance. In still other applications, a trailing edge chamber-to-chord ratio H t /L t  falling between 0.07 and 0.12 is employed for good fan performance.  
      As also described above, the blade  231  can have a concave front side and can have a cross-sectional shape taken along line  203  that is flat or substantially flat along the outer radial portion of the blade  231 . This flat or substantially flat portion of cross-section can be along the radially-outermost 25% of the blade  231  or along a larger radially-outermost portion of the blade  231  (such as the radially outermost half of the blade  231  in the embodiment of  FIGS. 17-26 ) as desired, and can be at an angle β′ with respect to a plane orthogonal to the rotational axis  63 . This angle β′ falls between 4 and 15 degrees in some applications to produce good fan performance. In other applications, this angle β′ falls between 6 and 13 degrees for good fan performance. In still other applications, this angle β′ falls between 8 and 11 degrees for good fan performance.  
      With reference again to  FIGS. 17 and 18 , cross-sections of the fan blade  231  can be taken at different radial distances from the rotational axis  263  of the fan assembly  255 . In some embodiments of the present invention, the cross-sectional shapes of the blade  231  at such cross-sections changes with increasing distance from the rotational axis  263  of the fan assembly  255 . In the illustrated embodiment of  FIGS. 17-26  (and in still other embodiments of the present invention), these cross-sectional shapes are bowed, and define a camber-to-chord ratio H/L. In some embodiments, this camber-to-chord ratio H/L decreases with increasing distance from the rotational axis  263 . For example, the camber-to-chord ratio H/L can decrease from 0.65R to the outer edge  79  of the blade  231  for good fan performance.  
      With reference now to  FIGS. 17-22 , the cross-sectional shape of the blade  231  at different radial locations of the blade  231  can be quantified in terms of camber to chord ratios H/L. In some applications, this camber-to-chord ratio H/L of the blade  231  at a radial distance of 0.95R falls between 2.0% and 5.5% for good fan performance. In other applications, this camber-to-chord ratio H/L falls between 2.5% and 4.5% for good fan performance. In still other applications, this camber-to-chord ratio H/L falls between 3.0% and 4.0% for good fan performance.  
      At a radial distance of 0.85R, the camber-to-chord ratio H/L of the blade  231  in some embodiments falls between 3.0% and 6.5% for good fan performance. In other applications, this camber-to-chord ratio H/L falls between 3.0% and 5.0% for good fan performance. In still other applications, this camber-to-chord ratio H/L falls between 3.5% and 4.5% for good fan performance.  
      At a radial distance of 0.75R, the camber-to-chord ratio H/L of the blade  231  in some embodiments falls between 3.5% and 7.0% for good fan performance. In other applications, this camber-to-chord ratio H/L falls between 4.0% and 6.0% for good fan performance. In still other applications, this camber-to-chord ratio H/L falls between 4.5% and 5.5% for good fan performance.  
      At a radial distance of 0.65R, the camber-to-chord ratio H/L of the blade  231  in some embodiments falls between 4.0% and 7.5% for good fan performance. In other applications, this camber-to-chord ratio H/L falls between 4.5% and 6.5% for good fan performance. In still other applications, this camber-to-chord ratio H/L falls between 5.0% and 6.0% for good fan performance.  
      In some embodiments of the present invention, additional strength and desirable airflow characteristics are obtained by employing a blade tip section  235  that is not flat. Specifically, and with particular reference to  FIGS. 18 and 24 - 26 , the portion of the blade  231  that is adjacent to the tip  233  (such as the forwardmost 10-30% of the blade  231  with respect to the rotation of the blade  231 ) can be shaped to have a concave or convex cross-sectional shape, and in this regard can have a curved or angled cross-sectional shape formed in any manner desired. For example, the tip section  235  of the blade  231  can be stamped, embossed, machined, molded, pressed, or formed in any other manner to produce a curved or angled cross-sectional shape. The curved or angled cross-sectional shape can be constant or substantially constant across the tip section  235  of the blade  231  (i.e., in a direction away from the tip  233  and between the outer and leading edges  279 ,  281  of the blade  231 ), or can instead have a varying cross-sectional shape from the tip  233 . In the illustrated preferred embodiment of  FIGS. 17-26 , the tip section  235  of the blade  231  has a concave cross-sectional shape on the front side of the blade  231  (also presenting a convex shape on the rear side of the blade  231 ).  
      As noted above, although the shapes of the fan blades  31 ,  231  described above with reference to the embodiments of  FIGS. 1-26  can be employed in blades having any size, superior results of these fan blade shapes have been obtained in fan assemblies having a diameter of between approximately 10 and 24 inches.  
      Another embodiment of the fan blade according to the present invention is illustrated in  FIGS. 27-36 . With the exception of differences evident from a comparison of  FIGS. 1-16 ,  17 - 26 , and the differences indicated below, the fan blade (indicated generally at  431 ) has the same features as those described above with reference to the blade embodiments shown in  FIGS. 1-16  and  FIGS. 17-26 . Accordingly, features of the fan blade  431  corresponding to those of the embodiments of  FIGS. 17-26  are assigned the same numbers as those in the embodiment illustrated in  FIGS. 17-26 , increased by  200 .  
      The blade shapes and blade shape parameters hereinafter described with reference to the embodiment of the present invention illustrated in  FIGS. 17-36  can be employed in blades having any size. However, superior performance is obtained by using these blade shapes and blade shape parameters in blade assemblies that are approximately 24-36 inches in diameter.  
      The blade  431  illustrated in  FIGS. 27-36  has an extended trailing edge  483  as best shown in  FIGS. 27 and 28 . In addition, the outer edge  479  of the blade  431  has a substantially constant radius along a majority of (and in the illustrated embodiment of  FIGS. 27-36 , almost all of) the outer edge  479  of the blade  431  between points  485  and  487 . However, the blade  431  in the illustrated embodiment of  FIGS. 27-36  has a slightly smaller radial dimension near point  487  as shown in  FIGS. 27 and 28 , where it can be seen that a circle having a constant radius R extends past the edge of the blade  431  at point  487 .  
      In some embodiments (such as the embodiment illustrated in  FIGS. 27-36  described in greater detail below), the trailing edge  483  is defined in a manner dependent at least partially upon the shape of the trailing edge  483 . With regard to this manner, some blades  431  employ a trailing edge  483  that has a substantially constant radius over at least a majority (and in many cases, a large majority or all) of the trailing edge  483 . In some embodiments, the arc defined by this portion of the trailing edge  483  intersects or can be extended to intersect the imaginary circle having the constant radius R of the fan assembly  455 . This point of intersection  487  can be on or off of the blade  31 , and represents one manner of defining point  487  according to the present invention.  
      In other embodiments, point  487  is located at the intersection of the imaginary circle having the constant radius R substantially defined by the outer edge  479 , and a line  501  extending from the rotational axis  463  swept counter-clockwise between about 62 and 78 degrees from line  495 . In other cases, line  501  is swept counter-clockwise between about 65 and 75 degrees from line  495 . In still other cases, line  501  is swept counter-clockwise between about 67 and 72 degrees from line  495 .  
      In addition, point  491  in the embodiment of  FIGS. 27-36  is defined as the location where the leading edge  481  of the blade  431  intersects an imaginary circle centered about the rotational axis  463  of the blade  431  and having a radius that is 0.75 times the length of the radius of the blade assembly (0.75R). Similarly, point  493  is defined as the location where the trailing edge  483  of the blade  431  intersects an imaginary circle centered about the rotational axis  463  of the blade  431  and having a radius that is 0.75 times the length of the radius of the blade assembly (0.75R).  
      As described above, the shape of the blade  431  according to the present invention can be defined by any one or more parameters. In this regard, any combination of such parameters can be employed to define a blade  431  according to the present invention. With continued reference to  FIGS. 27-36 , the angle ∝ l′  (at which the leading edge  481  of the fan blade  431  is swept forward) falls between 15 and 35 degrees in some applications to produce good fan performance. In other applications, a leading edge angle ∝ l′  falling between 18 and 30 degrees is employed for good fan performance. In still other applications, a leading edge angle ∝ l′  falling between 20 and 28 degrees is employed for good fan performance.  
      With reference now to the trailing angle ∝ l′  (at which the trailing edge  483  of the fan blade  431  is swept forward), the trailing angle ∝ l′  falls between 5 and 20 degrees in some applications to produce good fan performance. In other applications, a trailing edge angle ∝ t′  falling between 5 and 15 degrees is employed for good fan performance. In still other applications, a trailing edge angle ∝ t′  falling between 8 and 12 degrees is employed for good fan performance.  
      As described above, the blade  431  can have a concave leading edge  481  having a chamber-to-chord ratio H l′ /L l ′. This chamber-to-chord ratio H l′ /L l′  is between 0.05 and 0.30 in some applications to produce good fan performance. In other applications, a leading edge chamber-to-chord ratio H l′ /L l′  falling between 0.10 and 0.25 is employed for good fan performance. In still other applications, a leading edge chamber-to-chord ratio H l′ /L l′  falling between 0.15 and 0.20 is employed for good fan performance.  
      With reference now to the chamber-to-chord ratio H t′ /L t′  of the trailing edge  483 , the chamber-to-chord ratio H t′ /L t′  of the trailing edge  483  falls between 0.05 and 0.20 in some applications to produce good fan performance. In other applications, a trailing edge chamber-to-chord ratio H t′ /L t′  falling between 0.05 and 0.17 is employed for good fan performance. In still other applications, a trailing edge chamber-to-chord ratio H t′ /L t′  falling between 0.07 and 0.12 is employed for good fan performance.  
      As also described above, the blade  431  can have a concave front side and can have a cross-sectional shape taken along line  403  that is flat or substantially flat along the outer radial portion of the blade  431 . This flat or substantially flat portion of cross-section can be along the radially-outermost 25% of the blade  431  or along a larger radially-outermost portion of the blade  431  (such as the radially outermost half of the blade  431  in the embodiment of  FIGS. 27-36 ) as desired, and can be at an angle β″ with respect to a plane orthogonal to the rotational axis  463 . This angle β″ falls between 5 and 18 degrees in some applications to produce good fan performance. In other applications, this angle β″ falls between 8 and 15 degrees for good fan performance. In still other applications, this angle β″ falls between 10 and 15 degrees for good fan performance.  
      With reference again to  FIGS. 27 and 28 , cross-sections of the fan blade  431  can be taken at different radial distances from the rotational axis  463  of the fan assembly  455 . In some embodiments of the present invention, the cross-sectional shapes of the blade  431  at such cross-sections changes with increasing distance from the rotational axis  463  of the fan assembly  455 . In the illustrated embodiment of  FIGS. 27-36  (and in still other embodiments of the present invention), these cross-sectional shapes are bowed, and define a camber-to-chord ratio H/L. In some embodiments, this camber-to-chord ratio H/L decreases with increasing distance from the rotational axis  463 . For example, the camber-to-chord ratio H/L can decrease from 0.65R to the outer edge  479  of the blade  431  for good fan performance.  
      With reference now to  FIGS. 27-32 , the cross-sectional shape of the blade  431  at different radial locations of the blade  431  can be quantified in terms of camber to chord ratios H/L. In some applications, this camber-to-chord ratio H/L of the blade  431  at a radial distance of 0.95R falls between 4.0% and 9.5% for good fan performance. In other applications, this camber-to-chord ratio H/L falls between 5.5% and 8.5% for good fan performance. In still other applications, this camber-to-chord ratio H/L falls between 6.5% and 7.5% for good fan performance.  
      At a radial distance of 0.85R, the camber-to-chord ratio H/L of the blade  431  in some embodiments falls between 6.5% and 11.5% for good fan performance. In other applications, this camber-to-chord ratio H/L falls between 8.0% and 10.0% for good fan performance. In still other applications, this camber-to-chord ratio H/L falls between 8.5% and 9.5% for good fan performance.  
      At a radial distance of 0.75R, the camber-to-chord ratio H/L of the blade  431  in some embodiments falls between 8.5% and 13.5% for good fan performance. In other applications, this camber-to-chord ratio H/L falls between 9.0% and 12.0% for good fan performance. In still other applications, this camber-to-chord ratio H/L falls between 10.5% and 11.5% for good fan performance.  
      At a radial distance of 0.65R, the camber-to-chord ratio H/L of the blade  431  in some embodiments falls between 7.5% and 12.5% for good fan performance. In other applications, this camber-to-chord ratio H/L falls between 8.5% and 11.0% for good fan performance. In still other applications, this camber-to-chord ratio H/L falls between 9.5% and 10.5% for good fan performance.  
      As described in the embodiment of  FIGS. 17-26  above, in some embodiments, additional strength and desirable airflow characteristics are obtained by employing a blade tip section  435  that is not flat. Specifically, and with particular reference to  FIGS. 28 and 34 - 36 , the portion of the blade  431  that is adjacent to the tip  433  (such as the forwardmost 30% of the blade  431  with respect to the rotation of the blade  431 ) can be shaped to have a concave or convex cross-sectional shape, and in this regard can have a curved or angled cross-sectional shape formed in any manner desired. For example, the tip section  435  of the blade  431  can be stamped, embossed, machined, molded, pressed, or formed in any other manner to produce a curved or angled cross-sectional shape. The curved or angled cross-sectional shape can be constant or substantially constant across the tip section  435  of the blade  431  (i.e., in a direction away from the tip  433  and between the outer and leading edges  479 ,  481  of the blade  431 ), or can instead have a varying cross-sectional shape from the tip  433 . In the illustrated preferred embodiment of  FIGS. 27-36 , the tip section  435  of the blade  431  has a concave cross-sectional shape on the front side of the blade  431  (also presenting a convex shape on the rear side of the blade  431 ).  
      As noted above, although the shapes of the fan blades  431  described above with reference to the embodiments of  FIGS. 27-36  can be employed in blades having any size, superior results of these fan blade shapes have been obtained in fan assemblies having a diameter of between approximately 24 and 36 inches.  
      By virtue of the blade shape of the blade  31 ,  231 ,  431  according to the embodiments illustrated in  FIGS. 1-36  above, the swept leading edge  81 ,  281 ,  481  can vary the timing of leading edge segments in order to cut through fixed-position turbulence generated during operation of the fan assembly  55 ,  255 ,  455  thereby changing the phase of the noise radiated by the fan blades  31 ,  231 ,  431 . This leading edge shape and arrangement can therefore help to at least partially cancel acoustic energy as a result of phase differences (as compared to straight leading edges or other fan blade designs).  
      During operation of the fan blades according to some embodiments of the present invention (including those illustrated in  FIGS. 1-36 ), boundary layers are formed along the suction face of the rotating fan blade  31 ,  231 ,  431  (i.e., the convex rear surface of the fan blades  31 ,  231 ,  431  in  FIGS. 1-36 ) and become turbulent near the trailing edge  81 ,  281 ,  481  of the fan blade  31 ,  231 ,  431  due to a positive pressure gradient. This turbulence often significantly contributes to fan noise, and can be reduced by a well-swept trailing edge as employed in the fan blades  31 ,  231 ,  431  illustrated in  FIGS. 1-36  and in other embodiments of the present invention. The natural path of air past the fan blades  31 ,  231 ,  431  (along which a boundary layer can be created) can be formed from the leading edge  81 ,  281 ,  481  to the trailing edge  83 ,  283 ,  483  and is moved slightly outward toward the tip of the fan blade  31 ,  231 ,  431  due to centrifugal effects. The shape of the trailing edge  83 ,  283 ,  483  of the fan blade  31 ,  231 ,  431  as described above can generate a relatively short air path, thereby reducing boundary layer separation, or turbulence, to reduce fan noise while maintaining a sufficient blade chord length to achieve air performance and efficiency. The curvature in the blade chord as described above with reference to some of the embodiments of the present invention (including those illustrated in  FIGS. 1-36 ) can enable the blade to suck air from the blade tip to increase air flow, to reduce turbulence in the tip region, and to thereby reduce fan noise.  
      Although the blades  31 ,  231 ,  431  of the present invention can be any size as mentioned above and can have dimensions (e.g., angles and lengths) that fall within ranges or otherwise can vary, dimensions (in inches) for example blades are provided on  FIGS. 4-11 ,  13 ,  15 ,  16 , and  17 .  
      The embodiments described above and illustrated in the figures are presented by way of example only and are not intended as a limitation upon the concepts and principles of the present invention. As such, it will be appreciated by one having ordinary skill in the art that various changes in the elements and their configuration and arrangement are possible without departing from the spirit and scope of the present invention as set forth in the appended claims.