GB2350065A

GB2350065A - Golf club shaft

Info

Publication number: GB2350065A
Application number: GB9911277A
Authority: GB
Inventors: Brian Hammersley
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-05-17
Filing date: 1999-05-17
Publication date: 2000-11-22
Also published as: GB9911277D0

Abstract

A shaft 20 for a golf club wherein at least a portion of the shaft 20 is shaped or faired to reduce the drag coefficient of the shaft 20. The portion of the shaft 20 which is shaped or faired may have a streamlined, non-circular cross-section. The streamlined portion of the shaft 20 may be shaped with leading 22 and trailing edges 24 and a chambered surface profile between the edges. The cross-section of the streamlined portion of the shaft 20 may either be symmetrical about a plane extending between the leading and trailing edges, or be symmetrical to a plane which is normal to the above described plane, or both. The streamlined portion of the shaft 20 may have a fineness ration of between 2 and 4. The cross-section of the streamlined portion of the shaft 20 may vary along the length of the shaft 20. The surface of the shaft 20 may be roughened to further reduce the drag coefficient of the shaft 20. The cross-section of the streamlined portion of the shaft 20 may comprise a portion that has a non-symmetrical cross-section. The shaft 20 may comprise first, second and third portions. The first 30 and third 32 portions having a circular cross-section and the second portion having the streamlined, non-circular cross-section and extending between the first 30 and third 32 portions.

Description

2350065 Shaft The present invention relates to a shaft and particularly to

a shaft for a golf club.

Typically, golf club shafts are formed either from tubular steel or from a carbon fibre zn composite material and are generally circular in cross-section along the entire length of the 1: Z> shaft. The diameter of the shaft is normally at its greatest at the end of the shaft which is gripped by the user and tapers, generally uniformly, to its narrowest at the end connected to the club head. Such shafts carry the disadvantage that the circular cross-section produces relatively high levels of drag.

It is generally desirable for a golfer to be able to hit a golf ball as far as possible whilst using 10 the minimum amount of effort. In order to achieve such a shot, the golfer must ensure that the club-head strikes the ball at the highest possible speed by accelerating the club during the downswing, thus imparting the maximum amount of momentum on the ball. In general, all else being equal, the faster the club speed at impact with the ball, the further the ball will travel.

Conventional golf clubs have shafts which are circular in cross-section. The diameter of the shaft depends on the club type e.g. 3-wood, 5-i on or pitching wedge etc. but generally will taper from the grip towards the club head. As an example, a typical 74ron may have a diameterjust below the grip of approximately 15mrn and a diameterjust above the shank of the club-head of approximately 1Omm.

During the action of a swing, the shaft is moved through the air in an arc such that the direction of movement of the shaft at any given point in the swing is approximately perpendicular to the axis of the shaft at that point. For reasons which will be described below, shafts having a circular cross-section are subject to relatively high levels of drag during the swing. This drag restricts the speed at which the shaft can be swung, thus limiting the speed of the club head and consequently reducing the distance that the golf ball travels.

2 It is, therefore, desirable to minimise, or at least reduce, the drag on the club shaft during the swing.

Since the actual drag applied to the shaft is dependent on the speed at which the shaft moves 0 it is appropriate to refer to a drag "coefficient" which is dimensionless and allows a comparison to be made between different shafts.

The present invention aims to provide an improved golf club shaft.

Accordingly, the present invention provides a shaft for a golf club wherein at least a portion 0 of said shaft is shaped or faired to provide a streamlined, non-circular cross-section of the shaft thereby to reduce the drag coefficient of the shaft.

The shaft preferably comprises first, second and third portions, the first and third portions having a circular cross-section and the second portion having the streamlined, non-circular cross-section and extending between the first and third portions.

The present invention also provides a golf club comprising a shaft as described in the immediately preceding paragraph, a club head connected to the first portion of the shaft and 15 grip means located on the third portion of the shaft.

Advantageously, the second portion of the shaft having the streamlined, non-circular cross section extends almost fully between the club head and the grip means.

The streamlined portion of the shaft may have well-defined leading and trailing edges and a cambered surface profile between the edges. Conveniently, the cross section of the shaft 20 may be symmetrical about a plane ektending between the leading and trailing edges.

The present invention will now be described, by way of example only, with referen ce to the accompanying drawings in which:

3 Figure 1 is a perspective view of a section through a preferred form of golf club shaft according to the invention; Figure 2 is a front view of a golf club having the shaft of figure 1; 0 Figure 3 is a side view of the golf club of figure 2; Figure 4 shows a comparison of the cross-sections of the shaft of figure 1 and a conventional circular shaft at a point just below the grip; Figure 5 shows a comparison of the cross-sections of the shaft of figure 1 and a conventional circular shaft at a point just above the club-head; Figure 6 is a diagram illustrating the flow of air past a golf club shaft having a circular cross10 section; and Figure 7 is a diagram illustrating the flow of air past a golf club shaft having a streamlined cross-section; It will be appreciated that the diagrams are for illustrative purposes only and are not drawn to scale.

Referring to figure 1, the cross-section of a preferred form of shaft 20 according to the present invention is shown which has been developed by the applicant. The cross-section of the shaft 20 is faired to form a symmetrical aerofoil, being cambered (slightly curved) on either side from a leading edge 22 to a trailing edge 24. The arrow A denotes the direction 0 ofmovement of the shaft through the-air during the swing action. It can be seen that the shaft is substantially symmetrical about an plane extending between the leading edge 22 and the 0 trailing edge 24, parallel to the direction of movement, and also about a plane perpendicular to the direction of movement. It is preferable, but not essential, for the shaft to have its point of maximum thickness approximately half way between the leading and trailing edges.

4 As shown in figures 2 and 3, illustrating a golf club employing a shaft according to the invention, the shaft has the faired, streamlined crosssection of figure 1 along most of its length, but has a circular crosssection at its upper and lower end regions 30, 32. The lower end region 32 is inserted into the shank of a club head 34 in a conventional manner. The 5 upper end region 30 is covered by a grip covering 36 in a conventional manner for gripping bythegolfer. The faired, streamlined portion of the shaft thus extends from a point 38 just below the grip 36 to a point 40 just above the shank of the club head 34.

Referring to figures 4 and 5, a comparison is shown between the crosssection of a circular shaft and a faired, streamlined shaft according to the present invention. In figure 4, the cross- section is taken at a point just beneath the grip (point 3 8 in figure 3) and in figure 5, the cross section is taken at a point just above the shank of the club-head (point 40 in figure 3). Itcan be seen that the shaft of the present invention has a chord C (length between leading edge 22 0 Z> and trailing edge 24) approximately equal to the diameter of the circular shaft and a maximum thickness d of approximately half that of the diameter of the circular shaft. This 15 ratio remains generally constant along the length of the shaft having the streamlined portion.

0 0 As stated above, the streamlined portion of the shaft is symmetrical in cross-section about planes X and Y (parallel and perpendicular respectively to the direction of movement A of the shaft) and thus represents a symmetrical aerofoil.

It can be shown that the shaft of the present invention has a reduced drag coefficient compared with a shaft having a conventional circular cross-section.

Referring to figure 6, this shows the flow of air past a conventional circular shaft during the swing. In this figure, the shaft 60 is moving through the air in the direction of the arrow A and thus the movement of the air relative to the shaft is denoted by the streamlines 62. As the air flow makes contact with the ghaft 60 it divides, with some of the air passing around the shaft in a clockwise direction (as seen in figure 6) and some passing round the shaft in an anticlockwise direction. The streamline 62a which effectively represents the division between the air which passes around the shaft in either a clockwise or an anticlock wise direction is termed the "dividing streamline" and at the point at which this streamline contacts the surface of the shaft, the air flow becomes stationary and is termed the &&stagnation point" 64. The pressure on the surface of the shaft, termed the "normal static pressure", is greatest at this point.

As the air divides, a larninar boundary layer develops over the surface of the shaft inwhich the air moves much less quickly relative to the shaft and the air follows the contours of the shaft to a point at the top or bottom of the shaft respectively 66, 68 where the normal static pressure on the surface of the shaft reaches a minimum. Aft of the minimum pressure points 66, 68, the normal static pressure increases and tends towards the stagnation pressure at the very rear 70. Thus an "adverse pressure gradierif' develops between the minimum pressure points and the rear.

The slower air flow in the laminar boundary layer close to the surface of the shaft does not possess sufficient momentum to move against the adverse pressure gradient and the airflow is forced to detach from the surface, in a process known as "separation" at points 72, 74 (separation points) just aft of the minimum pressure points 66, 68. In the separated region R over most of the rear portion of the shaft, the static pressure is constant and equal to the minimum pressure at points 66, 68. The high pressure at the stagnation point 64 and the low pressure in the separated region R at the rear of the shaft result in an overall drag force F acting on the shaft 60.

In contrast, figure 7 shows the flow of air past the shaft of the present invention during the swing. Once again, the air divides at the leading edge 22 of the shaft 20, causing a laminar boundary layer to develop over the surface of the shaft. As in the case of the circular shaft, the air flow follows the contours of the surface of the shaft through the points of minimum pressure 76, 78 at the positions of greatest thickness of the shaft. However, since the rear of the shaft tapers more gradually than in the case of the cylindrical shaft, the adverse pressure gradient is less steep and the air does not separate from the shaft surface as early. The separation points 80, 82 thus move rearwards.

The region of low pressure R at the rear of the shaft caused by the separation of the air from 6 the surface is thus much narrower than in the case of the circular shaft. Consequently, the pressure at the rear of the shaft is greater than at the rear of the circular shaft and thus the difference in the pressures at the front and rear of the streamlined shaft is less, producing an overall reduction in drag coefficient compared with the circular shaft. This reduction in drag coefficient allows the shaft to be swung at a higher speed for a given amount of effort, thus causing the ball to travel further.

It will be appreciated that various modifications and improvements may be made to the invention.

For example, while the actual drag coefficient of the shaft must usually be determined empirically, being dependent on the exact shape of the shaft cross- section and its dimensions, there are general aerodynamic principles which it may be desirable to adhere to when generating a cross-section for the shaft.

For example, the minimum drag for a faired, streamlined section shaft occurs when the shaft has a "fineness ratio" (ratio of chord length C to depth d) of between 2 and 4. Thus in the case of a 7-iron, for example, near the grip the shaft could have a chord length of approximately 15 nim. and a maximum depth of between 4 and 8mm while near the club head the shaft could have a chord length of approximately 1Onim and a maximum depth of between 2.5 and 5min.

Aerodynamic theory suggests that a faired, streamlined shaft should possess a drag coefficient of between 15-25 times less than a circular shaft having a diameter equal to the maximum thickness of the streamlined shaft. It will be apparent that this figure will increase for a shaft where the maximum depth is less than that of the circular shaft.

It will be appreciated that the structural properties of the shaft must also be considered. For such faired, streamlined shafts, the ability of the shaft to withstand the torsional and bending moment stresses imposed on the shaft during the swing action may be compromised and this must be taken into consideration when deciding on a specific cross- section.

7 Since the shape and plane of the swing may differ for different clubs, it may be that the crosssection of a shaft for, say, a 3-wood may be different from, say a 5-iron or a pitching wedge. Alternatively, the cross section of the shaft may vary along its length since the lower end of the shaft moves more quickly through the air during the swing than the upper end -of the 5 shaft.

A further reduction in drag coefficient may be obtained by roughening the surface of the shaft, e.g by knurling or pitting. This has the effect that the boundary layer over the surface of the shaft may become turbulent. The turbulent boundary layer remains attached to the surface of the shaft for longer and thus separation occurs nearer the trailing edge of the shaft.

Thus, the low pressure region produced at the rear of the shaft is smaller and the drag coefficient is further reduced.

The shaft may have a non-symmetrical cross-section. Such a section may produce a force normal to the direction of movement of the shaft during the swing, in a similar manner to an aircraft or racing car wing, and thus affect the swing path of the club. While this may produce a lack of control of the club, it is possible that such a force on the shaft may be beneficial to certain players to produce swings of a different shape such as out-to-in or in-toout swings.

The shaft may be made of tubular or solid steel, carbon fibre or any other suitable material.

8

Claims

1. A shaft for a golf club wherein at least a portion of said shaft is shaped or faired thereby to reduce the drag coefficient of the shaft.

2. A shaft according to claim 1 wherein said portion of said shaft which is shaped or faired has a streamlined, non-circular cross-section.

3. A shaft according to claim 2 wherein the streamlined portion of the shaft is shaped with leading and trailing edges and a cambered surface profile between the edges.

4. A shaft according to claim 1 or 2 wherein the cross-section of the streamlined portion of the shaft is symmetrical about a plane extending between the leading and trailing edges.

5. A shaft according to any of claims 2 to 4 wherein the cross-section of the streamlined portion of the shaft is symmetrical about a plane normal to a plane extending between the leading and trailing edges.

6. A shaft according to any of claims 2 to 5 wherein the streamlined portion of the shaft has a fineness ratio (defined as the ratio of the length between the leading edge and the trailing edge to the maximum thickness of the streamlined portion in cross section) of between 2 and 4.

7. A shaft according to any preceding claim wherein the cross-section ofthe streamlined portion of the shaft varies along the length of the shaft.

8. A shaft according to any preceding claim wherein the surface of the shaft is roughened thereby to reduce further the drag coefficient of the shaft.

12 Slay 2

9 9. A shaft according to any preceding claim wherein the cross-section of the streamlined portion of the shaft comprises a portion that has a non-symmetrical cross- section.

10.A shaft according to any preceding claim comprising first, second and third portions, the first and third portions having a circular cross-section and the second portion having the streamlined, non-circular cross-section and extending between the first and third portions.

11. A golf club comprising a shaft as defined in any preceding claim, a club head connected to the first portion of the shaft and grip means located on the third portion of the shaft.

12. A golf club according to claim 11 wherein the second portion of the shaft having the streamlined, non-circular cross-section extends almost fully between the club head and the grip means.

13. A shaft constructed and arranged substantially as described herein with reference to figures 1 to 5 and 7.

14. A golf club constructed and arranged substantially as described herein with reference to figures 1 to 5 and 7.

1: May 20(YJ