Patent Publication Number: US-2022226709-A1

Title: High loft, low center-of-gravity golf club heads

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 17/105,109, filed Nov. 25, 2020, which is a continuation of U.S. patent application Ser. No. 16/803,635, filed Feb. 27, 2020, now U.S. Pat. No. 10,888,753, issued Jan. 12, 2021, which is a continuation of U.S. patent application Ser. No. 16/192,311, filed Nov. 15, 2018, Now U.S. Pat. No. 10,596,432, issued Mar. 24, 2020, which is a continuation of U.S. patent application Ser. No. 15/830,920, filed Dec. 4, 2017, now U.S. Pat. No. 10,143,903, issued Dec. 4, 2018, which is a continuation U.S. patent application Ser. No. 15/146,581, filed May 4, 2016, now U.S. Pat. No. 9,844,708, issued Dec. 19, 2017, which is a continuation of U.S. patent application Ser. No. 13/339,933, filed Dec. 29, 2011, now U.S. Pat. No. 9,358,430, issued Jun. 7, 2016, which claims the benefit of U.S. Provisional Patent Application No. 61/429,013, filed Dec. 31, 2010, all of which are herein incorporated by reference in their entirety. 
    
    
     FIELD 
     The present application concerns golf club heads, and more particularly, golf club heads having high static loft angles, low centers of gravity, or both high static loft angles and low centers of gravity. 
     BACKGROUND 
     The center of gravity (CG) of a golf club head is a critical parameter of the club&#39;s performance. Upon impact, the position of the CG greatly affects launch angle and flight trajectory of a struck golf ball. Thus, much effort has been made over positioning the center of gravity of golf club heads. To that end, current driver and fairway wood golf club heads are typically formed of lightweight, yet durable material, such as steel or titanium alloys. These materials are typically used to form thin club head walls. Thinner walls are lighter, and thus result in greater discretionary weight, i.e., weight available for redistribution around a golf club head. Greater discretionary weight allows golf club manufacturers more leeway in assigning club mass to achieve desired golf club head mass distributions. 
     Golf swings vary among golfers. The mass properties (e.g., CG location, moment of inertia, etc.) and design geometry (e.g., static loft) of a given golf club may provide a high level of performance for a golfer having a relatively high swing speed, but not for a golfer having a relatively slower swing speed. 
     It should, therefore, be appreciated that there is a need for golf club heads and golf clubs having designs that perform over a wide range of club head swing speeds. The present application fulfills this need and others. 
     SUMMARY 
     The following describes golf club heads that include a body defining an interior cavity, a sole portion positioned at a bottom portion of the golf club head, a crown portion positioned at a top portion, and a skirt portion positioned around a periphery between the sole and crown. The golf club head body has a forward portion and a rearward portion, with a striking face positioned at the forward portion of the body. 
     In a first aspect, embodiments of the golf club head include a face having a static loft angle greater than or equal to 11 degrees. In some instances, the golf club head has a center of gravity that is 7 mm or more below the geometric center of the face of the golf club head as measured along a z-axis of the golf club head having an origin at the geometric center. 
     In a second aspect, embodiments of the golf club head include a ball striking face of the club head body having a geometric center, and a center of gravity whose projection onto the ball striking face of the club head body is located off-center from the geometric center in a direction toward the sole. 
     In some instances of the embodiments of the golf club heads of the second aspect, the club head body has a center of gravity that is between 7 mm and 40 mm below the geometric center of the ball striking face of the club head body as measured along the z-axis of the golf club head. In some other instances, the club head body has a static loft angle of between 11 degrees and 33 degrees. 
     The foregoing and other features and advantages of the golf club head will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front elevation view of an exemplary embodiment of a golf club head. 
         FIG. 2  is a top plan view of the golf club head of  FIG. 1 . 
         FIG. 3  is a side elevation view from a toe side of the golf club head of  FIG. 1 . 
         FIG. 4  is a front elevation view of the golf club of  FIG. 1  illustrating club head origin and center of gravity origin coordinate systems. 
         FIG. 5  is a top plan view of the golf club of  FIG. 1  illustrating the club head origin and center of gravity origin coordinate systems. 
         FIG. 6  is a side elevation view from a toe side of the golf club of  FIG. 1  illustrating the club head origin and center of gravity origin coordinate systems. 
         FIG. 7  is a side elevation view from a toe side of the golf club of  FIG. 1  illustrating the projection of the center of gravity (CG) onto the golf club head face. 
         FIG. 8  is a schematic elevation view of the trajectory of a golf ball hit with a driver having a CG z  aligned with the geometric center of the ball striking club face. 
         FIG. 9  is a schematic elevation view of the trajectory of a golf ball hit with a driver having a CG z  lower than the geometric center of the ball striking club face. 
         FIG. 10  is a first graph showing static loft and CG z  values for exemplary embodiments of the disclosed technology. 
         FIG. 11  is a second graph showing static loft and CG z  values for exemplary embodiments of the disclosed technology. 
         FIG. 12  is a graph showing the total yardage values and CG z  values for simulated golf shots taken by exemplary embodiments of the disclosed technology. 
         FIG. 13  is a graph showing the total yardage values and loft values for simulated golf shots taken by exemplary embodiments of the disclosed technology. 
         FIG. 14A  is a side elevation view from a toe side of an exemplary embodiment of a golf club head. 
         FIG. 14B  is a top plan view of the golf club head of  FIG. 14A . 
         FIG. 14C  is a perspective view from a front and toe side of the golf club head of  FIG. 14A . 
     
    
    
     DETAILED DESCRIPTION 
     I. General Considerations 
     The following disclosure describes embodiments of golf club heads for wood-type clubs (e.g., drivers) that incorporate higher loft angles, lower centers of gravity, or both higher loft angles and lower centers of gravity relative to conventional wood-type clubs. The disclosed embodiments should not be construed as limiting in any way. Instead, the present disclosure is directed toward all novel and nonobvious features and aspects of the various disclosed embodiments, alone and in various combinations and subcombinations with one another. Furthermore, any features or aspects of the disclosed embodiments can be used in various combinations and subcombinations with one another. The disclosed embodiments are not limited to any specific aspect or feature or combination thereof, nor do the disclosed embodiments require that any one or more specific advantages be present or problems be solved. 
     The present disclosure makes reference to the accompanying drawings which form a part hereof, wherein like numerals designate like parts throughout. The drawings illustrate specific embodiments, but other embodiments may be formed and structural changes may be made without departing from the intended scope of this disclosure. Directions and references may be used to facilitate discussion of the drawings but are not intended to be limiting. For example, certain terms may be used such as “up,” “down,” “upper,” “lower,” “horizontal,” “vertical,” “left,” “right,” and the like. These terms are used, where applicable, to provide some clarity of description when dealing with relative relationships, particularly with respect to the illustrated embodiments. Such terms are not, however, intended to imply absolute relationships, positions, and/or orientations. Accordingly, the following detailed description shall not to be construed in a limiting sense. 
     A. Normal Address Position 
     Club heads and many of their physical characteristics disclosed herein will be described using “normal address position” as the club head reference position, unless otherwise indicated.  FIGS. 1-3  illustrate one embodiment of a driving-wood-type golf club head at normal address position.  FIG. 1  illustrates a front elevation view of golf club head  100 ,  FIG. 2  illustrates a top plan view of the golf club head  100 , and  FIG. 3  illustrates a side elevation view of the golf club head  100  from the toe side. By way of preliminary description, the club head  100  includes a hosel  120  and a ball striking club face  118 . At normal address position, the club head  100  is positioned on a plane  125  above and parallel to a ground plane  117 . 
     As used herein, “normal address position” means the club head position wherein a vector normal to the club face  118  substantially lies in a first vertical plane (a vertical plane is perpendicular to the ground plane  117 ), the centerline axis  121  of the club shaft substantially lies in a second substantially vertical plane, and the first vertical plane and the second substantially vertical plane substantially perpendicularly intersect. 
     B. Club Head Features 
     A driving-wood-type golf club head, such as the golf club head  100  shown in  FIGS. 1-3 , includes a hollow body  110  defining a crown portion  112 , a sole portion  114 , a skirt portion  116 , and a ball striking club face  118 . The ball striking club face  118  can be integrally formed with the body  110  or attached to the body. The body  110  further includes a hosel  120 , which defines a hosel bore  124  adapted to receive a golf club shaft. The body  110  further includes a heel portion  126 , a toe portion  128 , a front portion  130 , and a rear portion  132 . 
     The club head  100  also has a volume, typically measured in cubic-centimeters (cm 3 ), equal to the volumetric displacement of the club head, assuming any apertures are sealed by a substantially planar surface. 
     As used herein, “crown” means an upper portion of the club head above a peripheral outline  134  of the club head as viewed from a top-down direction and rearward of the topmost portion of a ball striking surface  122  of the ball striking club face  118 . As used herein, “sole” means a lower portion of the club head  100  extending upwards from a lowest point of the club head when the club head is at the normal address position. In some implementations, the sole  114  extends approximately 50% to 60% of the distance from the lowest point of the club head to the crown  112 . In other implementations, the sole  114  extends upwardly from the lowest point of the golf club head  110  a shorter distance. Further, the sole  114  can define a substantially flat portion extending substantially horizontally relative to the ground  117  when in normal address position or can have an arced or convex shape as shown in  FIG. 1 . As used herein, “skirt” means a side portion of the club head  100  between the crown  112  and the sole  114  that extends across a periphery  134  of the club head, excluding the striking surface  122 , from the toe portion  128 , around the rear portion  132 , to the heel portion  126 . As used herein, “striking surface” means a front or external surface of the ball striking club face  118  configured to impact a golf ball. In some embodiments, the striking surface  122  can be a striking plate attached to the body  110  using known attachment techniques, such as welding. Further, the striking surface  122  can have a variable thickness. In certain embodiments, the striking surface  122  has a bulge and roll curvature (discussed more fully below). 
     The body  110 , or any parts thereof, can be made from a metal alloy (e.g., an alloy of titanium, an alloy of steel, an alloy of aluminum, and/or an alloy of magnesium), a composite material (e.g., a graphite or carbon fiber composite) a ceramic material, or any combination thereof. The crown  112 , sole  114 , skirt  116 , and ball striking club face  118  can be integrally formed using techniques such as molding, cold forming, casting, and/or forging. Alternatively, any one or more of the crown  112 , sole  114 , skirt  116 , or ball striking club face  118  can be attached to the other components by known means (e.g., adhesive bonding, welding, and the like). 
     In some embodiments, the striking face  118  is made of a composite material, while in other embodiments, the striking face  118  is made from a metal alloy (e.g., an alloy of titanium, steel, aluminum, and/or magnesium), ceramic material, or a combination of composite, metal alloy, and/or ceramic materials. 
     When at normal address position, the club head  100  is disposed at a lie angle  119  relative to the club shaft axis  121  (as shown in  FIG. 1 ) and the club face has a loft angle  115  (as shown in  FIG. 2 ). Referring to  FIG. 1 , the lie angle  119  refers to the angle between the centerline axis  121  of the club shaft and the ground plane  117  at normal address position. Referring to  FIG. 3 , loft angle  115  refers to the angle between a tangent line  127  to the club face  118  and a vector  129  normal to the ground plane at normal address position. 
       FIGS. 4-6  illustrate coordinate systems that can be used in describing features of the disclosed golf club head embodiments.  FIG. 4  illustrates a front elevation view of the golf club head  100 ,  FIG. 5  illustrates a top plan view of the golf club head  100 , and  FIG. 3  illustrates a side elevation view of the golf club head  100  from the toe side. As shown in  FIGS. 4-6 , a center  123  is disposed on the striking surface  122 . For purposes of this disclosure, the center  123  is defined as the intersection of the midpoints of a height (H ss ) and a width (W ss ) of the striking surface  122 . Both H ss  and W ss  are determined using the striking face curve (S ss ). The striking face curve is bounded on its periphery by all points where the face transitions from a substantially uniform bulge radius (face heel-to-toe radius of curvature) and a substantially uniform roll radius (face crown-to-sole radius of curvature) to the body. H ss  is the distance from the periphery proximate to the sole portion of S ss  (also referred to as the bottom radius of the club face) to the periphery proximate to the crown portion of S ss  (also referred to as the top radius of the club face) measured in a vertical plane (perpendicular to ground) that extends through the center  123  of the face (e.g., this plane is substantially normal to the x-axis). Similarly, W ss  is the distance from the periphery proximate to the heel portion of S ss  to the periphery proximate to the toe portion of S ss  measured in a horizontal plane (e.g., substantially parallel to ground) that extends through the center  123  of the face (e.g., this plane is substantially normal to the z-axis). In other words, the center  123  along the z-axis corresponds to a point that bisects into two equal parts a line drawn from a point just on the inside of the top radius of the striking surface (and centered along the x-axis of the striking surface) to a point just on the inside of the bottom radius of the face plate (and centered along the x-axis of the striking surface). For purposes of this disclosure, the center  123  is also be referred to as the “geometric center” of the golf club striking surface  122 . See also U.S.G.A. “Procedure for Measuring the Flexibility of a Golf Clubhead,” Revision 2.0 for the methodology to measure the geometric center of the striking face. 
     C. Golf Club Head Coordinates 
     Referring to  FIGS. 4-6 , a club head origin coordinate system can be defined such that the location of various features of the club head (including a club head center-of-gravity (CG)  150 ) can be determined. A club head origin  160  is illustrated on the club head  100  positioned at the center  123  of the striking surface  122 . 
     The head origin coordinate system defined with respect to the head origin  160  includes three axes: a z-axis  165  extending through the head origin  160  in a generally vertical direction relative to the ground  117  when the club head  100  is at the normal address position; an x-axis  170  extending through the head origin  160  in a toe-to-heel direction generally parallel to the striking surface  122  (e.g., generally tangential to the striking surface  122  at the center  123 ) and generally perpendicular to the z-axis  165 ; and a y-axis  175  extending through the head origin  160  in a front-to-back direction and generally perpendicular to the x-axis  170  and to the z-axis  165 . The x-axis  170  and the y-axis  175  both extend in generally horizontal directions relative to the ground  117  when the club head  100  is at the normal address position. The x-axis  170  extends in a positive direction from the origin  160  towards the heel  126  of the club head  100 . The y-axis  175  extends in a positive direction from the head origin  160  towards the rear portion  132  of the club head  100 . The z-axis  165  extends in a positive direction from the origin  160  towards the crown  112 . 
     D. Center of Gravity 
     Generally, the center of gravity (CG) of a golf club head is the average location of the weight of the golf club head or the point at which the entire weight of the golf club head may be considered as concentrated so that if supported at this point the head would remain in equilibrium in any position. 
     Referring to  FIGS. 4-6 , a CG  150  is shown as a point inside the body  110  of the club head  100 . The location of the club CG  150  can also be defined with reference to the club head origin coordinate system. For example, and using millimeters as the unit of measure, a CG  150  that is located 3.2 mm from the head origin  160  toward the toe of the club head along the x-axis, 36.7 mm from the head origin  160  toward the rear of the club head along the y-axis, and 4.1 mm from the head origin  160  toward the sole of the club head along the z-axis can be defined as having a CG x  of −3.2 mm, a CG y  of −36.7 mm, and a CG z  of −4.1 mm. 
     The CG can also be used to define a coordinate system with the CG as the origin of the coordinate system. For example, and as illustrated in  FIGS. 4-6 , the CG origin coordinate system defined with respect to the CG origin  150  includes three axes: a CG z-axis  185  extending through the CG  150  in a generally vertical direction relative to the ground  117  when the club head  100  is at normal address position; a CG x-axis  190  extending through the CG origin  150  in a toe-to-heel direction generally parallel to the striking surface  122  (e.g., generally tangential to the striking surface  122  at the club face center  123 ), and generally perpendicular to the CG z-axis  185 ; and a CG y-axis  195  extending through the CG origin  150  in a front-to-back direction and generally perpendicular to the CG x-axis  190  and to the CG z-axis  185 . The CG x-axis  190  and the CG y-axis  195  both extend in generally horizontal directions relative to the ground  117  when the club head  100  is at normal address position. The CG x-axis  190  extends in a positive direction from the CG origin  150  to the heel  126  of the club head  100 . The CG y-axis  195  extends in a positive direction from the CG origin  150  towards the rear portion  132  of the golf club head  100 . The CG z-axis  185  extends in a positive direction from the CG origin  150  towards the crown  112 . Thus, the axes of the CG origin coordinate system are parallel to corresponding axes of the head origin coordinate system. In particular, the CG z-axis  185  is parallel to z-axis  165 , CG x-axis  190  is parallel to x-axis  170 , and CG y-axis  195  is parallel to y-axis  175 . 
     As best shown in  FIG. 6 ,  FIGS. 4-6  also show a projected CG point  180  on the golf club head striking surface  122 . The projected CG point  180  is the point on the striking surface  122  that intersects with a line that is normal to the tangent line  127  of the ball striking club face  118  and that passes through the CG  150 . This projected CG point  180  can also be referred to as the “zero-torque” point because it indicates the point on the ball striking club face  118  that is centered with the CG  150 . Thus, if a golf ball makes contact with the club face  118  at the projected CG point  180 , the golf club head will not twist about any axis of rotation since no torque is produced by the impact of the golf ball. 
     II. Exemplary Embodiments of High Loft, Low CG Golf Club Heads 
     A. Z-Axis Gear Effect 
     In certain embodiments disclosed herein, the projected CG point on the ball striking club face is located below the geometric center of the club face. In other words, the projected CG point on the ball striking club face is closer to the sole of the club face than the geometric center. As a result, and as illustrated in  FIG. 7 , when the golf club is swung such that the club head  100  impacts a golf ball  200  at the club head&#39;s center  123 , the impact is “off center” from the projected CG point  180 , creating torque that causes the body of the golf club head to rotate (or twist) about the CG x-axis (which is normal to the page in  FIG. 7 ). This rotation of the golf club head about the x-axis is illustrated in  FIG. 7  by arrows  202 ,  203 . The rotation of the club face creates a “z-axis gear effect.” More specifically, the rotation of the club head about the CG x-axis tends to induce a component of spin on the ball. In particular, the backward rotation (shown by arrows  202 ,  203 ) of the club head face that occurs as the golf ball is compressed against the club face during impact causes the ball to rotate in a direction opposite to the rotation of the club face, much like two gears interfacing with one another. Thus, the backward rotation of the club face during impact creates a component of forward rotation (shown by arrows  204 ,  205 ) in the golf ball. This effect is termed the “z-axis gear effect.” Because the loft of a golf club head also creates a significant amount of backspin in a ball impacted by the golf club head, the forward rotation resulting from the z-axis gear effect is typically not enough to completely eliminate the backspin of the golf ball, but instead reduces the backspin from that which would normally be experienced by the golf ball. In general, the forward rotation (or topspin) component resulting from the z-axis gear effect is increased as the impact point of a golf ball moves upward from (or higher above) the projected CG point on the ball striking club face. Additionally, the effective loft of the golf club head that is experienced by the golf ball and that determines the launch conditions of the golf ball can be different than the static loft of the golf club head. The difference between the golf club head&#39;s effective loft at impact and its static loft angle at address is referred to as “dynamic loft” and can result from a number of factors. In general, however, the effective loft of a golf club head is increased from the static loft as the impact point of a golf ball moves upward from (or higher than) the projected CG point on the ball striking club face. 
       FIG. 8  is a schematic side view  800  illustrating trajectory  800  of a golf ball hit by a driver having a projected CG that coincides with the geometric center of the striking surface. The launch conditions created from such a driver typically include a low launch angle and a significant amount of backspin. The backspin on the ball causes it to quickly rise in altitude and obtain a more vertical trajectory, “ballooning” into the sky. Consequently, the ball tends to quickly lose its forward momentum as it is transferred to vertical momentum, eventually resulting in a steep downward trajectory that does not create a significant amount of roll. As illustrated by  FIG. 8 , then, even though some backspin can be beneficial to a golf ball&#39;s trajectory by allowing it to “rise” vertically and resist a parabolic trajectory, too much backspin can cause the golf ball to lose distance by transferring too much of its forward momentum into vertical momentum. 
       FIG. 9 , by contrast, is a schematic side view illustrating trajectory  900  of a golf ball hit by a driver having a lower center of gravity in accordance with embodiments of the disclosed technology. In  FIG. 9 , the static loft of the golf club head is assumed to be the same as the driver in  FIG. 8 , although the static loft can be higher, as more fully explained below. The launch conditions created from a driver having a lower center of gravity includes a higher launch angle and less backspin relative to the driver having a projected CG that coincides with the geometric center of the striking surface. As can be seen in  FIG. 9 , the trajectory  900  includes less “ballooning” than the trajectory  800  but still has enough backspin for the ball to have some rise and to generally maintain its launch trajectory longer than a ball with no backspin. As a result, the golf ball with trajectory  900  carries further than golf ball with trajectory  800 . Furthermore, because the horizontal momentum of the golf ball is greater with trajectory  900  than with trajectory  800 , the roll experienced by the golf ball with trajectory  900  is greater than with trajectory  800 . 
     B. Exemplary CG z  and Static Loft Values 
     In some embodiments described herein, a golf club head for a driver has a higher static loft, a lower center of gravity, or both a higher static loft and a lower center of gravity than conventional drivers. For example, for golf club heads having lower centers of gravity (e.g., centers of gravity that result in a projected CG on the striking surface of the club face below the geometric center of the club face), the backspin of a golf ball struck by the golf club head can be reduced, thereby allowing the golf ball to travel a greater distance (e.g., according to a trajectory similar to the trajectory shown in  FIG. 9 ). Further, for golf club heads having both a higher static loft and a lower center of gravity than conventional drivers, the backspin produced may not be less than a conventional driver (since the higher static loft significantly contributes to increased backspin), but the reduction in backspin produced by the lower CG helps the golf club head reduce the backspin from that which would otherwise be experienced. As a result, greater distance can be obtained from the golf club head. Moreover, for some players, a golf club head having a higher static loft and a lower center of gravity than conventional drivers can produce greater overall driving distances. 
     For example, certain players having swings with slower head speeds (e.g., less than 100 or 90 mph) achieve greater driving distances from a golf club head with a high static loft and low center of gravity. For instance, simulation results indicate that for a club head speed of 80 mph (typical of many amateur golfers), the distance obtained from embodiments of the disclosed golf club heads having a CG z  of −15 mm or less and a static loft of 18° is substantially the same or greater than the distance obtained from a driver having a CG z  of −5 mm and a static loft of 12°. Additional simulation results are shown in the graphs presented in  FIGS. 12 and 13 , which show total distance (carry plus roll) for golf shots struck at a club head speed of 80 mph.  FIG. 12  shows total distance versus CG z  location for golf clubs having lofts of 12°, 15°, and 18°, and also showing shots struck at centerface relative to shots struck at 7.5 mm above centerface.  FIG. 13  shows total distance versus static loft for golf clubs having CG z  locations ranging from −5 mm to −15 mm, also showing shots struck at centerface relative to shots struck at 7.5 mm above centerface. 
     From the information shown in  FIG. 12 , the golf club having a 15° static loft provides higher values for total distance over the reported range of CG z  values relative to golf clubs having either higher loft (18°) or lower loft (12°). Moreover, from the information shown in  FIG. 13 , the optimum static loft value for obtaining maximum distance over the reported range of CGz values is between about 14° and about 15°. 
     Additionally, players sometimes have a preference for clubs having higher static lofts. For instance, many players hit higher lofted clubs more consistently than lower lofted clubs. Thus, many players will benefit from having a driver with a higher loft and a lower center of gravity, even if the overall distance from such a club may be slightly less than the conventional driver. 
       FIGS. 10 and 11  are graphs  1000  and  1100  showing exemplary values of CG z  and static loft for embodiments of the disclosed technology. In particular,  FIGS. 10 and 11  are graphs having an x-axis showing CG z  values measured in mm from the geometric center of the club head face, where the geometric center is determined in the manner described above. Thus, the value of CG z  measures the distance between the geometric center and the CG along the z-axis originating at the geometric center.  FIGS. 10 and 11  also have a y-axis showing static loft values for the club head face, where the values represent the static loft angle (illustrated in  FIGS. 1-3  as loft angle  115 ) measured in degrees. Also shown in  FIG. 10  is an area  1002  that represents a range of CG z  and static loft values for golf club heads according to the disclosed technology. Similarly,  FIG. 11  includes area  1102  that represents a range of CG z  and static loft values for golf club heads according to the disclosed technology. 
     Certain embodiments of golf club heads designed in accordance with the disclosed technology have values of CG z  that are less than −7.0 mm. For example, and depending on the overall size of the club head, embodiments of the disclosed technology can have a CG z  value between −7.0 mm and a value representing a z-axis location of the center of gravity just inside the club head body adjacent to its sole. In specific embodiments, and as illustrated by area  1102  in  FIG. 11 , the CG z  value is between −7.0 mm and −40.0 mm, while in other embodiments illustrated by area  1002  in  FIG. 10 , the CG z  value is between −7.0 mm and −20.0 mm. Any other range of values between −7.0 mm and a value representing a z-axis location of the center of gravity just inside the club head body adjacent to its sole is also possible and contemplated by this disclosure. For example, certain embodiments of the disclosed technology have a CG z  of between −9.0 mm and −20.0 mm. 
     Certain embodiments of golf club heads designed in accordance with the disclosed technology also have static loft values that are greater than 11.0°. For example, and as illustrated by area  1102  in  FIG. 11 , embodiments of the disclosed technology have a static loft of between 11.0° and 33.0°. In specific embodiments, and as illustrated by area  1002  in  FIG. 10 , the static loft is between 11.0° and 19.0°. Any other range of values between 11.0° and 33.0° is also possible and contemplated by this disclosure. For example, certain embodiments of the disclosed technology have a static loft of between 15.0° and 19.0°. Still other embodiments of golf club heads designed in accordance with the disclosed technology have static loft values between 5.0° and 11.0°. 
     C. Using Discretionary Mass to Lower the Center of Gravity 
     Lower center of gravity values can be attained by distributing club head mass to particular locations in the golf club head. Discretionary mass generally refers to the mass of material that can be removed from various structures providing mass and that can be distributed elsewhere for locating the club head center-of-gravity. 
     Club head walls provide one source of discretionary mass. A reduction in wall thickness reduces the wall mass and provides mass that can be distributed elsewhere. For example, in some implementations, one or more walls of the club head can have a thickness less than approximately 0.7 mm. In some embodiments, the crown  112  can have a thickness of approximately 0.65 mm throughout at least a majority of the crown. In addition, the skirt  116  can have a similar thickness, whereas the sole  114  can have a greater thickness (e.g., more than approximately 1.0 mm). Thin walls, particularly a thin crown  112 , provide significant discretionary mass. 
     To achieve a thin wall on the club head body  110 , such as a thin crown  112 , a club head body  110  can be formed from an alloy of steel or an alloy of titanium. In other embodiments, the thin walls of the club head body are formed of a non-metallic material, such as a composite material, ceramic material, thermoplastic, or any combination thereof. For example, in particular embodiments, the crown  112  and the skirt  116  are formed of a composite material. 
     To lower the center of gravity within the club head body  110 , one or more portions of the sole  114  can be formed of a higher density material than the crown  112  and the skirt  116 . For example, the sole  114  can be formed of metallic material, such as tungsten or a tungsten alloy. The sole  114  can also be shaped so that the center of gravity is closer or further from the golf ball striking club face as desired. 
     Golf club heads according to the disclosed technology can also use one or more weight plates, weight pads, or weight ports in order to lower the center of gravity to the desired CG z  location. For example, certain embodiments of the disclosed golf club heads have one or more integral weight pads cast into the golf club head at predetermined locations (e.g., in the sole of the golf club head) that lower the club head&#39;s center-of-gravity. Also, epoxy can be added to the interior of the club head through the club head&#39;s hosel opening to obtain a desired weight distribution. Alternatively, one or more weights formed of high-density materials (e.g., tungsten or tungsten alloy) can be attached to the sole. Such weights can be permanently attached to the club head. Furthermore, the shape of such weights can vary and is not limited to any particular shape. For example, the weights can have a disc, elliptical, cylindrical, or other shape. 
     The golf club head  100  can also define one or more weight ports formed in the body  110  that are configured to receive one or more weights. For example, one or more weight ports can be disposed in the sole  114 . The weight port can have any of a number of various configurations to receive and retain any of a number of weights or weight assemblies, such as described in U.S. Pat. Nos. 7,407,447 and 7,419,441, which are incorporated herein by reference. Inclusion of one or more weights in the weight port(s) provides a customized club head mass distribution with corresponding customized moments of inertia and center-of-gravity locations. Adjusting the location of the weight port(s) and the mass of the weights and/or weight assemblies provides various possible locations of center-of-gravity and various possible mass moments of inertia using the same club head. 
     In further embodiments, one or more openings in the walls of the golf club head body are formed. For example, the crown of the golf club head can include an opening. A lightweight panel can be positioned within each opening in order to close the opening. By selecting a material for the panels that is less dense than the material used to form the club head body, the difference between the mass of the body material that would otherwise occupy the opening and the panel can be positioned elsewhere in the club head. For example, by strategically selecting the number, size, and location of the openings, the center of gravity of the golf club head can be lowered to a desired position within the club head body. The panels may comprise, for example, carbon fiber epoxy resin, carbon fiber reinforced plastic, polyurethane or quasi-isotropic composites. The panels can be attached using adhesive or any other suitable technique. 
     In addition to redistributing mass within a particular club head envelope as discussed above, the club head center-of-gravity location can also be tuned by modifying the club head external envelope. For example, the club head body  110  can be extended rearwardly, and its overall height can be reduced. In specific embodiments, for example, the crown of the club head body is indented or otherwise includes an at least partially concave shape, thereby distributing the weight of the crown lower into the club head body. 
     D. Mass Moments of Inertia 
     Referring to  FIGS. 4-6 , golf club head moments of inertia are typically defined about the three CG axes that extend through the golf club head center-of-gravity  150 . For example, a moment of inertia about the golf club head CG x-axis  190  can be calculated by the following equation 
         I   xx =∫( z   2   +y   2 ) dm   (1)
 
     where y is the distance from a golf club head CG xz-plane to an infinitesimal mass, dm, and z is the distance from a golf club head CG xy-plane to the infinitesimal mass, dm. The golf club head CG xz-plane is a plane defined by the golf club head CG x-axis  190  and the golf club head CG z-axis  185 . The CG xy-plane is a plane defined by the golf club head CG x-axis  190  and the golf club head CG y-axis  195 . 
     The moment of inertia about the CG x-axis (I xx ) is an indication of the ability of the golf club head to resist twisting about the CG x-axis. A higher moment of inertia about the CG x-axis (I xx ) indicates a higher resistance to the upward and downward twisting of the golf club head  100  resulting from high and low off-center impacts with the golf ball. 
     In certain embodiments of the disclosed golf club heads, the moment of inertia I xx  is at least 250 kg-mm 2 . For example, in certain embodiments, the moment of inertia I xx  is between 250 kg-mm 2  and 800 kg-mm 2 . It has been observed that for embodiments of the disclosed golf club heads in which the projected CG on the club head face is lower than the geometric center, a lower moment of inertia can increase the dynamic loft and decrease the backspin experienced by a golf ball struck at the geometric center of the club. Thus, in particular embodiments, the moment of inertia I xx  is relatively low (e.g., between 250 kg-mm 2  and 500 kg-mm 2 ). In such embodiments, the relatively low moment of inertia contributes to the reduction in golf ball spin, thereby helping a golf ball obtain the desired high launch, low spin trajectory (e.g., a trajectory similar to that shown in  FIG. 9 ). In still other embodiments, the moment of inertia is less than 250 kg-mm 2  (e.g., between 150-250 kg-mm 2  or between 200-250 kg-mm 2 ). Adjusting the location of the discretionary mass in a golf club head using the methods described above can provide the desired moment of inertia I xx  in embodiments of the disclosed golf club heads. 
     E. Delta 1 
     Delta 1 is a measure of how far rearward in the club head body  110  the CG is located. More specifically, Delta 1 is the distance between the CG and the hosel axis along the y axis (in the direction straight toward the back of the body of the golf club face from the geometric center of the striking face). It has been observed that for embodiments of the disclosed golf club heads, smaller values of delta 1 result in lower projected CGs on the club head face. Thus, for embodiments of the disclosed golf club heads in which the projected CG on the ball striking club face is lower than the geometric center, reducing Delta 1 can lower the projected CG and increase the distance between the geometric center and the projected CG. Recall also that a lower projected CG creates a higher dynamic loft and more reduction in backspin due to the z-axis gear effect. Thus, for particular embodiments of the disclosed golf club heads, the Delta 1 values are relatively low, thereby reducing the amount of backspin on the golf ball and helping the golf ball obtain the desired high launch, low spin trajectory (e.g., a trajectory similar to that shown in  FIG. 9 ). For example, in certain embodiments, the Delta 1 values are 25 mm or lower (e.g., in the range of 10-25 mm). Adjusting the location of the discretionary mass in a golf club head as described above can provide the desired Delta 1 value. For instance, Delta 1 can be manipulated by varying the mass in front of the CG (closer to the face) with respect to the mass behind the CG. That is, by increasing the mass behind the CG with respect to the mass in front of the CG, Delta 1 can be increased. In a similar manner, by increasing the mass in front of the CG with the respect to the mass behind the CG, Delta 1 can be decreased. 
     F. Bulge and Roll 
     Bulge and roll are golf club face properties that are generally used to compensate for gear effect. The term “bulge” on a golf club refers to the rounded properties of the golf club face from the heel to the toe of the club face. The term “roll” on a golf club refers to the rounded properties of the golf club face from the crown to the sole of the club face. In certain embodiments of the disclosed technology, the “roll” or “roll radius” of the golf club head is designed to improve the trajectory of a golf ball when stricken at the geometric center of the club, which in certain embodiments of the disclosed technology is off-center of the projected CG on the ball striking club face. The roll radius R refers to the radius of a circle having an arc that corresponds to the arc along the z-axis of the ball striking club face. Curvature is the inverse of radius and is defined as 1/R, where R is the radius of the circle having an arc corresponding to the arc along the z-axis of the ball striking club face. As an example, a roll with a curvature of 0.0050 mm −1  corresponds to a roll with a radius of 200 mm. 
     The roll of the golf club head can contribute to the amount of backspin that the golf ball acquires when it is struck by the club head at a point on the club face either above or below the projected CG of the club head. For example, shots struck at a point on the club face above the projected CG (e.g., at the geometric center  123  above the projected CG  180  in  FIG. 7 ) have less backspin than shots struck at or below the projected CG. If the roll radius of the club head is decreased, there will be a decreased variance between backspin for shots struck above the projected CG of the golf club face and shots struck below the projected CG of the ball striking club face. 
     In certain embodiments of the disclosed golf club heads, the roll radius is relatively large (e.g., greater than or equal to 300 mm). Thus, for embodiments of the disclosed golf club heads in which the projected CG on the ball striking club face is lower than the geometric center, the higher roll radius operates to enhance the z-axis gear effect when a ball is stricken at the geometric center, thereby reducing the amount of backspin on the golf ball and helping the golf ball obtain the desired high launch, low spin trajectory (e.g., a trajectory similar to that shown in  FIG. 9 ). Furthermore, in certain implementations of the disclosed golf club heads, the golf club face is flat or concave in order to further reduce the backspin imparted on a golf ball having a relatively high static loft. In other embodiments, the roll radius is less than 300 mm. In certain embodiments, for example, the roll radius is between about 100 and 150 mm. 
     G. Volume 
     Embodiments of the disclosed golf club heads disclosed herein can have a variety of different volumes. For example, certain embodiments of the disclosed golf club heads are for drivers and have a head volume of between 250 and 460 cm 3  and a weight of between 180 and 210 grams. Other embodiments of the disclosed golf club heads have a volume larger than 460 cm 3 . If such a club head is desired, it can be constructed as described above by enlarging the size of the strike plate and the outer shell of the golf club head. Furthermore, such “large” club heads allow for greater opportunity to achieve a lower CG z  in the golf club head. It should also be understood that golf club heads that have volumes or dimensions in excess of the current U.S.G.A. rules on clubs and ball are possible and contemplated by this disclosure. 
     H. Exemplary Embodiments 
       FIGS. 14A-C  illustrates an embodiment of a golf club head having a relatively high static loft and relatively low center of gravity.  FIG. 14A  illustrates a toe side elevation view of the golf club head  1400 ,  FIG. 14B  illustrates a top plan view of the golf club head  1400 , and  FIG. 14C  illustrates a front and toe side perspective view of the golf club head  1400 . As discussed above in relation to the golf club head embodiments shown in  FIGS. 1-3 , the golf club head  1400  includes a hollow body  1410  defining a crown portion  1412 , a sole portion  1414 , and a ball striking club face  1418 . The ball striking club face  1418  can be integrally formed with the body  1410  or attached to the body. The body  1410  further includes a hosel  1420 , which defines a hosel bore  1424  adapted to receive a golf club shaft. The body  1410  further includes a heel portion  1426 , a toe portion  1428 , a front portion  1430 , and a rear portion  1432 . 
     At normal address position, the club head  1400  is positioned on a plane  125  above and parallel to a ground plane  117 . As shown in particular in  FIG. 14A , at the normal address position, the sole portion  1414  of the embodiment shown is inclined at a sole angle  1438  relative to the plane  125  such that a rear portion  1442  of the sole is positioned lower than a front portion  1444  of the sole. In some embodiments, the sole angle  1438  is between about 5° to about 40°, such as from about 7° to about 30°, such as from about 10° to about 25°, or from about 15° to about 22°. 
     A three-dimensional model of the golf club head  1400  of the embodiment shown in  FIGS. 14A-C  was created and subdivided into sections corresponding to the crown portion  1412 , the sole portion  1414 , the ball striking clubface  1418 , and the hosel  1420 . Each section was then constructed in the model to have the materials, thicknesses, and other properties listed in Table 1 below: 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Example 1 
                 Example 2 
                 Example 3 
                 Example 4 
                 Example 5 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Mass 
                 199.7 
                 g 
                 200.8 
                 g 
                 200.4 
                 g 
                 201.4 
                 g 
                 200.3 
                 g 
               
               
                 CGx 
                 1.3 
                 mm 
                 0.9 
                 mm 
                 1.2 
                 mm 
                 1.0 
                 mm 
                 0.7 
                 mm 
               
               
                 Delta 1 
                 14.4 
                 mm 
                 12.7 
                 mm 
                 14.2 
                 mm 
                 18.1 
                 mm 
                 16.3 
                 mm 
               
               
                 CGz 
                 −10.4 
                 mm 
                 −14.9 
                 mm 
                 −11.1 
                 mm 
                 −15.3 
                 mm 
                 −19.6 
                 mm 
               
               
                 Face Thk 
                 2.5 
                 mm 
                 2.5 
                 mm 
                 2.5 
                 mm 
                 5.0 
                 mm 
                 5.0 
                 mm 
               
            
           
           
               
               
               
               
               
               
            
               
                 Face Mtl 
                 Ti alloy 
                 Ti alloy 
                 Ti alloy 
                 Composite 
                 Composite 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Crown Thk 
                 1.0 
                 mm 
                 1.5 
                 mm 
                 1.5 
                 mm 
                 1.0 
                 mm 
                 1.5 
                 mm 
               
            
           
           
               
               
               
               
               
               
            
               
                 Crown Mtl 
                 Ti alloy 
                 Composite 
                 Al alloy 
                 Ti alloy 
                 Composite 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Hosel Thk 
                 1.0 
                 mm 
                 1.0 
                 mm 
                 1.0 
                 mm 
                 1.0 
                 mm 
                 1.0 
                 mm 
               
            
           
           
               
               
               
               
               
               
            
               
                 Hosel Mtl 
                 Ti alloy 
                 Ti alloy 
                 Ti alloy 
                 Ti alloy 
                 Ti alloy 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
            
               
                 Sole Thk 
                 1.45 
                 mm 
                 2.1 
                 mm 
                 1.55 
                 mm 
                 2.0 
                 mm 
                 2.6 
                 mm 
               
            
           
           
               
               
               
               
               
               
            
               
                 Sole Mtl 
                 Ti alloy 
                 Ti alloy 
                 Ti alloy 
                 Ti alloy 
                 Ti alloy 
               
               
                   
               
            
           
         
       
     
     In Table 1, the materials listed include Titanium alloy (“Ti alloy”) having a density of approximately 4.5 g/cc 3 , a carbon fiber epoxy composite (“Composite”) having a density of approximately 1.5 g/cc 3 , and an aluminum alloy (“Al alloy”) having a density of approximately 2.8 g/cc 3 . As noted in the Table, the foregoing exemplary embodiments included designs having values for CGz ranging from about −10.4 mm to about −19.6 mm. 
     I. Concluding Remarks 
     Having illustrated and described the principles of the illustrated embodiments, it will be apparent to those skilled in the art that the embodiments can be modified in arrangement and detail without departing from such principles. For example, although the embodiments disclosed above are made primarily with reference to drivers and driving-wood-type clubs, any aspect of the disclosed technology can be incorporated into a fairway wood having a smaller volume and/or greater mass. For example, a fairway wood or rescue wood having any of the disclosed low CG and/or static high loft characteristics are considered to be within the scope of this disclosure. For instance, embodiments of fairway woods incorporating any one or more aspects of the disclosed technology have a volume between about 130 and 220 cm 3  and a weight of between about 190 and 225 grams, whereas embodiments of rescue woods incorporating any one or more aspects of the disclosed technology have a volume between about 80 and 150 cm 3  and a weight of between about 210 and 240 grams. 
     In view of the many possible embodiments to which the principles of the disclosed invention(s) may be applied, it should be recognized that the illustrated embodiments are only preferred examples and should not be taken as limiting the scope of the disclosure. Rather, the scope of the disclosure is at least as broad as the following claims and their equivalents. We therefore claim all that comes within the scope and spirit of these claims and their equivalents.