Energy Transfer Accelerance Theory

E.T.A.™ – Energy Transfer Accelerance
By Carter Penley 1997-2000

Over the past several years, there have been many discussions and theories on how to develop golf equipment that makes those long Par 5’s more user friendly for the average player. Advances in material, processes and club geometry have fuelled the latest technologies in golf equipment. The importance of the shaft, Penley’s area of expertise, cannot be overlooked. The shaft plays a fundamental part in golf club design because it functions as the interface (a veritable suspension system and drive train) between the player and his or her striking surface-the club head.

Think of it this way: what good is it to have a 5 liter Ferrari with the top of the line tires, linked with a poorly designed transmission or suspension system? The power of the engine and responsiveness of the tires cannot be maximized because of their weak suspension link. The correlation is the same in golf clubs. Through the shaft, the player feels and controls the shot. The full power of a player’ swing and the design virtues of a quality club head cannot be maximized unless linked with a quality shaft. That is the reason Penley has spent years developing high performance shafts. This focus has paid off-Penley is the prominent shaft in long drive championships and a leader on the PGA tour. As a leader in the golf shaft industry, Penley continues to develop state of the art, cutting-edge products delivering the highest performance and consistency on the course.

There are three fundamental parameters that characterize the performance of a golf shaft. The first, and probably most important, is the feel of the shaft. Put simply, does the club feel comfortable during the swing from address through follow through? Technically speaking, Penley has determined the best combinations and distributions of shaft weight, stiffness, torque, and dampening that yield an incredibly responsive and comfortable feeling piece. The second fundamental parameter of shaft performance is control. Does the shot go where it was intended to go? That is, for a driver, did it stay in the fairway; and for iron, did the distance and dispersion put it where desired on the green?
Through computer-aided analysis and state of the art manufacturing techniques, Penley creates the most concentric shafts on the market. This translates into unparalleled accuracy and consistency from club to club, shot to shot. The final factor of shaft performance is distance. This can be quantified by determining how much of the club’s energy during impact is transferred to the ball. Designing shafts that maximize these three-performance parameters-feel, control, and distance-requires some extremely complex and creative engineering solutions.

Fortunately, Penley is solving many of these engineering and design challenges through high-tech analytical, high-speed computer programs (one such program requires 900,000 calculations per individual shaft design) developed and written in house. One program is Energy Transfer Accelerance (ETA), which, pertains to the distance portion of shaft design. In this program, we address the much asked question, “how much energy can or does a player transfer to the ball?”

Early in 1997, Penley sports determined that the next level of shaft design had to incorporate energy transfer. But since there was little or no data about this topic, we had to develop the data ourselves. The scope of this ETA research and development project was to derive a theory about energy transfer efficiency, prove and apply the theory, then generate data about shaft efficiency through a test phase using a mechanical hitting device. If successful, we would go to the field for human testing (staff personnel and our full time PGA Tour Van.)

ETA focuses on the efficiency of the club to ball energy transfer. A hypothesis was developed stating: For longer drives and less human effort, the maximum amount of energy transfer must take effect between the club and the ball. Assumptions were made that maximum energy transfer will occur if the club head is square and at its maximum velocity just prior to ball impact (1-3 milliseconds.) Shafts, therefore, can be designed to unload into the squared position (while generating maximum club head velocity) according to a player’s swing speed and tempo.

With the hypothesis and assumptions formulated, the engineering staff was able to construct a mathematical model of how energy is transferred from the club to the ball. The theory was successfully tested, so the engineering staff created a parametric computer model of the ETA derivation. A mechanical hitting device and high-speed cameras were then used to demonstrate and apply the practicality of the ETA computer program. Some sample results follow:

Player #1 (Class ‘A’ Player)
• Club Head Velocity: 101 mph
• Ball Velocity (at launch): 149 mph
• Back Spin: 4800 rpm
• Side Spin: 646 rpm
• Effective Mass of Club: 231 g
Energy transferred is 74.443 Ft-Lb.
Percentage of energy transferred from the club to the ball is 21.44%

Player #2 (Staff Player-Long Drive Specialist)
• Club Head Velocity: 140 mph
• Ball Velocity (at launch): 210 mph
• Back Spin: 4200 rpm
• Side Spin: 598 rpm
• Effective Mass of Club: 220 g

Energy transferred is 148.620 Ft-Lb.
Percentage of energy transferred from the club to the ball is 23.42%

This type of testing and analysis explains not only the energy transfer efficiency of a particular shaft, but offers insight into where the energy losses occur. Through the use of high-speed cameras, deformations of the ball, shaft, and head at impact can be detected and analyzed. The amount of energy loss due to heat, ball spin, and elastic waves within the ball, head, shaft, and grip can then be determined. This data is used to understand how and through which method a shaft absorbs and dissipates energy. Future designs incorporate this information to maximize energy transfer while minimizing energy losses in the shaft.

The ETA program also allows Penley’s research and development staff to:

• Demonstrate to prospective customers which combination of shaft and club head will transfer
the highest percentage of energy to the ball with the most effective spin rates.
• Develop and apply data that can be used to create improved materials and processes.
• Develop and apply data that can be used to reduce fatigue rates of shafts.
• Develop and apply data that can be used to reduce interlaminar shear loads in shafts.
• Develop and apply data that can be used to enhance micro mechanics for maximum shaft load
transfer.

• Develop and apply data that produces a more consistent performing shaft or set of shafts.

As shown, the ETA program is an extremely powerful analytical tool. It clearly defines the “distance performance” of a shaft while giving insight into many other mechanical properties of a shaft.
This, however, is only the tip of the iceberg when looking at the hi-tech design and analysis techniques used by the Penley Sports engineering staff.

Other static and dynamic swing analysis programs that process immense amounts of data include a Spine Reduction System (SRS) and Lamination Theory Analysis (LTA) package. The SRS ensures a concentric, symmetric shaft. This minimizes or effectively eliminates any dominant spine while maximizing the consistency and control factor of the shaft. The LTA package allows shafts to quickly be designed with the desired torque, stiffness, dampening, and mass distributions. This program facilitates the design of shafts or sets of shafts that have a specified “feel”. The Penley Sports engineering staff wrote all of these programs in house, then combined them to create a design and analysis package that maximizes the fundamental variables of shaft performance-feel, control, and distance. Needless to say, this design approach has been extremely successful.


Penley creates the highest quality, best performing, most consistent shafts in the industry. Using Penley shafts, golfers can increase their confidence and overall performance on the course. The top competitors on PGA tour and in long drive championships prove this point. All golfers can benefit from the power of Penley.

Contributions by Pete Wagner, Staff Engineer

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