# Science and Golf II: Proceedings of the 1994 World Scientific Congress of Golf

By A. J. Cochran; M. R. Farrally | Go to book overview

40

An investigation of three dimensional deformation of a golf club during downswing

A.M. Brylawski

Department of Mechanical Engineering and Mechanics, Lehigh
University, Bethlehem, Pennsylvania, USA

Abstract

A study was undertaken to investigate the influence of shaft flexibility on the positioning of the club face during the downswing. To accomplish this task, a computerized model of deflections occurring in the shaft over the period of the down-swing was developed. Employing Lagrangian dynamics, equations of motion for bending and for twist coordinates of the shaft are produced. In addition to being dependent on stiffness, these deformations are a function of the forces generated by the acceleration of the shaft during the swing. To determine these forces, video images of a real swing are converted to digital data using a motion analysis software package. The equations of motion can then be solved numerically, yielding the position and orientation of the club face over the course of the swing.

Key Words: Stiffness, Shaft Deflections, Mathematical Model.

1 Introduction

Currently, golf shafts are available with different stiffness ratings ranging from regular to extra-stiff. The standard practice is to recommend a more flexible shaft for weaker players, while stronger golfers play with a stiffer shaft. Until recently there has been limited scientific insight into the rational for this advice. An investigation into the significance of shaft stiffness by Milne and Davis (1992) concluded that shaft flexibility does not play an important dynamic role in the golf swing, meaning that there is no advantage gained by a “whipping” effect of a flexible shaft. The only contribution of the deformations is to change the effective loft and lie angles of the club face at impact. This suggests that a golf club with a stiff shaft and the desired loft and lie angles will produce more consistent shots because the initial and the effective loft and lie will be the same. Of course, this is only true if the golfer is able to bring the club head back to the exact address position at the bottom of the downswing. This study is the primary step of an investigation into the magnitude of the deflections occurring in the shaft during the downswing and the effect they have on the position of the club head at impact.

A computerized model has been developed that calculates deformations due to forces and moments applied to the shaft. The computed parameters include the rotation of the shaft about its centerline, the deflection in a direction normal to the club face, and the deflection parallel to the plane of the club face. These three parameters define the position of the club face at any time during the swing.

Science and Golf II: Proceedings of the World Scientific Congress of Golf. Edited by A.J. Cochran and M.R. Farrally. Published in 1994 by E & FN Spon, London. ISBN 0 419 18790 1

-265-

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