GB2387121A

GB2387121A - Golf club shaft

Info

Publication number: GB2387121A
Application number: GB0208031A
Authority: GB
Inventors: Brian Hammersley
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-04-06
Filing date: 2002-04-06
Publication date: 2003-10-08
Also published as: GB0208031D0

Abstract

A shaft, particularly for a golf club, of conventional tubular or circular cross-section is provided over at least part of its length with a fairing which substantially surrounds the shaft and is shaped to reduce the drag coefficient of the shaft as it is swung through the air. The fairing 90 may be moulded around the shaft, Fig 8 (not shown), or be in the form of members 94, 96 adhered or clipped to the shaft 92, Fig 9. The cross-section of the fairing may vary along the length of the shaft, and can be non-symmetrical; the surface of the fairing can be roughened to further reduce the drag coefficient.

Description

1 2387121

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 fable composite material and are generally circular in crosssection along the entire length of the 5 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. 15 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-iron or pitching wedge etc. but generally will taper from the grip towards the club head. As an example, a typical 7-iron may have a diameter just below the grip of approximately l5mm and a diameter just above the shank of the club-head of approximately lOmm.

20 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 25 the speed of the club head and consequently reducing the distance that the golf ball travels.

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

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

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

According to one aspect of the present invention therefore, there is provided a shaft for a golf club comprising a conventional, circular or tubular shaft, a portion of which is provided with a fairing substantially surrounding said shaft; wherein said fairing is shaped thereby to reduce the drag coefficient of the shaft.

10 Conveniently, the fairing is moulded around said portion of said conventional shaft. The shell or fairing may therefore be formed as a unitary moulding substantially encapsulating or sheathing the original, conventional shaft.

Alternatively, the shell or fairing takes the form of an ar comprising two or more pieces or members adapted to be fitted around said conventional shaft. The members maybe IS adapted to be clipped or a&Bred together around said conventional shaft. Conveniently, therefore, the members maybe preformed by a suitable technique such as injection moulding.

The fairing may be shaped with leading and trailing edges and a cambered surface profile between the edges.

The cross-section of the fairing may be symmetrical about a plane extending between the 20 leading and trailing edges. In addition or alternatively, the cross-section of the fairing may be symmetrical about a plane normal to a plane extending between the leading and trailing edges.

The fairing may have a fineness ratio (defined as the ratio of the length between a leading edge and a trailing edge of the failing to the maximum thickness of the shell or fairing in cross-section) of between 2 and 4.

The cross-section of the fatting may vary along the length of the shaft.

5 The surface of the fairing may be roughened thereby to reduce further the drag coefficient of the shaft.

The cross-section of the fatting may comprise a portion that has a nonsymmetrical cross-

section. . 10 The present invention also provides a golf club including a shaft as described in the preceding paragraphs. The present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a perspective view of a section through a preferred form of golf club shaft 15 according totheinvention; Figure 2 is a front view of a golf club having the shaft of figure 1; 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; 20 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;

l Figure 6 is a diagram illustrating the flow of air past a golf club shaft having a circular cross-

section; Figure 7 is a diagram illustrating the flow of air past a golf club shaft having a streamlined cross-section; 5 Figure 8 illustrates a first practical implementation of the shaft of the invention in cross-

section; and Figure 9 illustrates a second practical implementation of the shaft of the invention in cross-

section. It will be appreciated that the diagrams are for illustrative purposes only and are not drawn 10 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 15 of movement 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 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.

20 As shown in figures 2 and 3, illustrating a golf club employing a shaft according to the invention, the shaft has the faired, streamlined cross-section of figure 1 along most of its length, but has a circular cross-section 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 upper end region 30 is covered by a grip covering 36 in a conventional manner for gripping 25 by the golfer. 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 38 in figure 3) and in figure 5, the cross 5 section is taken at a point just above the shank of the club-head (point 40 in figure 3). It can be seen that the shaft of the present invention has a chord C (length between leading edge 22 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 ratio remains generally constant along the length of the shaft having the streamlined portion.

10 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.

15 Referring to figure 6, this shows the flow of air past a conventional circular shaft curing 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 shaft 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 20 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 anticlockwise 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 25 greatest at this point.

As the air divides, a laminar boundary layer develops over the surface of the shaft in which 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 gradient" develops between the minimum pressure 5 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 10 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 15 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 20 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 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 25 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, 5 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 10 approximately 15 mm and a maximum depth of between 4 and 8mm while near the club head the shaft could have a chord length of approximately 10mrn and a maximum depth of between 2.5 and 5mm.

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 15 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 20 must be taken into consideration when deciding on a specific cross-section.

On the other hand, in order to meet the twist and bend criteria set out in the regulations imposed by various golfing associations, such as the Royal and Ancient Golfing Society, or to ensure appropriate flexibility of the shaft in all planes, in one advantageous embodiment of the invention, illustrated in Figure 8, the shaft is formed by moulding a streamlined shell 25 or fairing 90 around a conventional, circular or tubular club shaft 92. Thus, the original steel, graphite or carbon fibre shaft 92 is retained and is surrounded by the streamlined fatting 90

such that the structural properties, and in particular the torsional and bending properties of the original shaft are substantially retained or are not disadvantageously affected.

The preferred method for the manufacture of such a shaft involves placing the original club shaft 92 in a suitably shaped mould and then injecting a suitable material into the mould to 5 form the fairing 90, for example using a generally conventional injection moulding process.

Appropriate materials may be thermoplastic materials such as polypropylene or the like, carbon fibre or any other material which can be injected into the mould and which hardens to form the fairing.

In order to ensure adhesion of the fairing material to the shaft 92, which is retained within 10 the fairing 90, the original shaft 92 may be surface treated with a suitable coating or may be physically altered, for example by pitting or roughening.

In another advantageous embodiment shown in Figure 9, it is envisaged that the fairing 90 may be in the form of a shell which is pre-formed in one, two or more pieces or members 94, 96, which members are arranged to clip or fit onto an existing shaft 92. In this manner, no 15 special treatment of the shaft is necessary and the fairing may be fitted to the shaft, and removed therefrom, by the club owner rather than requiring specialist fitting or moulding.

In particular, the fairing may be moulded from suitable material, such as those mentioned above, to form the two or more members 94, 96 and produced to specific lengths corresponding, for example, to the lengths of standard club shafts. The members 94, 96 are 20 arranged to fit around the circumference of the shaft, and along its length and can be clipped together by mechanical means or joined by a suitable adhesive. Preferably, means are provided to ensure that the fairing cannot move relative to the original shaft and in particular, is not allowed to rotate about the axis of the shaft. This can be achieved by adhering the shell parts to the shaft or by means of radially inwardly directed pins on the members 94, 96 which 25 engage in bores (not shown) formed in the shaft.

These embodiments provide a shaft for a golf club which exhibits improved aerodynamic

characteristics whilst retaining the essential mechanical properties of the original shaft. In addition, the latter embodiment allows an aerodynamic fairing to be easily fitted to an existing shaft without specialist knowledge or assistance.

Since the shape and plane of the swing may differ for different clubs, it may be that the cross-

5 section of a shaft for, say, a 3-wood may be different from, say a 5iron 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 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 10 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 15 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-to-

out swings.

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

Claims

1. A shaft for a golf club comprising a conventional, circular or tubular shaft, a portion of which is provided with a fairing substantially surrounding said shaft; wherein said fairing is shaped or faired thereby to reduce the drag coefficient of the shaft.

5 2. A shaft according to claim 1 wherein said fairing is moulded around said portion of said conventional shaft.

3. A shaft according to claim 1 wherein said fairing comprises an attachment including two or more members adapted to be fitted around said conventional shaft.

4. A shaft according to claim 3 wherein said members are adapted to be clipped or 10 a&Bred together around said conventional shaft.

5. A shaft according to any preceding claim wherein the fairing is shaped with leading and trailing edges and a cambered surface profile between the edges.

6. A shaft according to claim 5 wherein the cross-section of the fairing is symmetrical about a plane extending between the leading and trailing edges.

15 7. A shaft according to claim 5 wherein the cross-section of the fairing is symmetrical about a plane normal to a plane extending between the leading and trailing edges.

8. A shaft according to any preceding claim wherein the fairing has a fineness ratio of between 2 and 4.

20 9. A shaft according to any preceding claim wherein the cross-section of the fairing varies along the length of the shaft.

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

11. A shaft according to any preceding claim wherein the cross-section of the fairing 5 comprises a portion that has a non-symmetrical crosssection.

12. A shaft according to any preceding claim comprising first, second and third portions, the first and third portions having a circular crosssection and the second portion having the fairing and extending between the first and third portions.

10 13. A golf club including a shaft as defined in any preceding claim.

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

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

15 16. An attachment for a shaft of a golf club comprising at least one member arranged to be attached to said shaft thereby to reduce the drag coefficient of said shaft.