ABSTRACT
As expected for uniform shapes, the principal axes of inertia lie in the x,y and z directions, through the centre of gravity (marked ‘x’ in the figures) for all three idealised clubheads
when the shaft is not included in the model. For the blade, the moments of inertia about these respective axes are 3.208×10−5kgm2, 10-5kgm2 and 20.95×10-5kgm2. The increase for Ixx is about 70 percent for both peripheral weighted and cavity backed clubheads. The percentage increases for Iyy are 7.7 and 16.3, and for Izz are 24 and 29.7 for peripheral weighted and cavity backed respectively. Obviously, the position of the CG is considerably altered when the shaft is added but, more importantly, the variation between the I values is reduced to what at first sight appears to be an insignificant value. The consequent effect of this slight variation on the location and size of the sweet spot is discussed elsewhere but the preliminary conclusion is that either the shaft plays little role in the impact dynamics and hence on the ‘quality’ of the shot, or that the difference in the ‘feel’ and performance of the clubs is attributable to second order effects. Given the sensitivity of the human senses, the latter is not impossible. The use of lightweight materials such as CFRP for the shaft does offer the possibility of retaining more of the difference in the head characteristics at the expense of other engineering properties (and, of course, of cost).
