ADAM’S GOLF
A
sk most golf club designers what the ultimate goal of
a good driver — the club used to blast off the tee on everything but the shortest of holes — and the answer is: Distance, distance and (more) distance.
Golf club drivers have dramatically increased in size in recent years as a result of developments in material and manufacturing technology, always with an eye on the ultimate goal of distance. The performance of golf club driver heads has been studied extensively by the golf industry and has led to design targets for certain physical properties of the club head. For example, recently manufacturers have been targeting a high rotational moment of inertia (MOI) of the club head to decrease the energy loss for off center impacts. The rapid increase in size led the United States Golf Association to establish design constraints incorporated into the rules governing golf equipment. These constraints include: • A displaced volume limit of 460cc • A notional “box” with dimensions of 5 x 5 x 2.875 in. within which the club head must fit • And a moment of Inertia limit about the vertical axis of 5900 kg mm2 The major challenge faced by designers is that a 460 cc driver head cannot be easily designed to hit the dimensional and MOI limit without resorting to unusual club head shapes. Moreover, during a golfer’s swing the club head is exposed to wide variations in wind speed and orientation. During the first part of arm rotation, the club is plowing the air with the heel of the club, from which it is rotated rapidly to impact, During that time, the air stream rotates from the heel of the club to the face plane — a total orientation change of 90 deg. Additionally, as the club is moving thru these orientations, it also increases in velocity from zero to over 100 mph — more with professional golfers. Since its introduction, the Speedline driver has been in the bag of multiple winners on the LPGA tour and on the Champions tour with Bernard Langer (this picture and right)
2009 | WIND TUNNEL INTERNATIONAL
After extensive study of the performance ramifications of driver heads near these maximum dimensions, one extremely important and somewhat unexpected performance issue was identified. By having golfers swing different driver designs and measuring the club head speed they obtained just before ball impact, it was determined that the external shape of the driver head had a significant influence on the measured club head speed. Broadly speaking, higher clubhead speeds result in higher ball speeds, which in turn lead to longer drives. With this in mind, an initial design was conceived to conform to the dimensional and MOI rules and the prototype (called the “Bullet”) was typical in having a somewhat unusual head shape. While the design did have some desirable properties, player testing revealed that golfers’ maximum club head speeds were reduced with this club by approximately three percent versus a “traditionally” shaped 460 cc driver — a major disadvantage off the tee. A generally accepted rule of thumb is that, for instance, a three-percent drop in club head speed leads to a three-percent reduction in total drive distance. This result was unexpected and led to a study of the aerodynamics of golf club heads both in “During (the swing), the air the wind tunnel and stream rotates from the heel using computational of the club to the face plane — fluid dynamics a total orientation change of (CFD) analysis. It 90 deg. ... and (the club) also led to the Adams increases in velocity from Speedline driver, now zero to 100 mph” in production. An extensive series of wind tunnel tests were conducted at the Oran W. Nicks Low Speed Wind Tunnel at Texas A&M University. The driver heads were mounted on a short portion of a shaft connected to a balance to measure forces and moments. The heads could 31