CallawayGolf.com

Aerodynamic Benefits of Seamless Molding

Aerodynamic Benefits of Seamless Molding

By: Grady Crahan, Ph.D. (Manager, Golf Ball Testing & Aero Development)

SHOP CHROME SOFT

INTRODUCTION

In order to make the cover of a golf ball, two hemispheres are joined together to produce a seam, generally at the equator. In order to eliminate the material molded at the seam, it is common to buff it off with a rough sandpaper-like material, leaving a flat surface where the material used to be. The new Chrome Soft golf balls incorporate a new revolutionary seamless molding method that has eliminated the need to buff away the seam material. This new design has decreased the variation in carry distance caused by the flat seam region by up to 40% relative to our competitors.

Aerodynamic Concepts

The idea of adding dimples to roughen the surface of a golf ball to increase overall distance has been well-known for years. This phenomena was first observed in the late 1800s when the Guttie ball would become longer as the surface of the ball became scratched and worn during play. Since that time, significant research has been completed and it is a now well-known drag reduction technique in aerodynamics.

The rough surface will cause the boundary layer to transition from laminar to turbulent at lower speeds which delays separation and decreases the size of the wake behind a golf ball. The smaller wake leads to lower drag and increased distance for a golf ball. Figure 1 shows some comprehensive wind tunnel studies that were completed in the 1970s looking at the drag of smooth and roughened spheres at multiple flow speeds. The y-axis represents the drag of the object and the x-axis represents the speed of the flow, with a highlighted grey region indicating the flow speeds seen by a common golf shot. The smooth sphere (dotted line) shows a drag coefficient of 0.5 in the speeds seen by a golf ball. In contrast, the golf ball drag (line with circles) shows drag at 0.25, a 50% decrease.

This chart shows the drag (y-axis) of a smooth and rough sphere at different speeds. The region highlighted grey indicates the speed of the flow seen by a common golf shot. [1]

As a ball flies through the air it will encounter fluid particles that flow over its surface. As shown in Figure 2, the air will hit the ball at the front (known as the stagnation point) and move around the sphere in a line of constant longitude. When this is applied to a golf ball, the fluid particle on a given streamline will be going in and out of dimples as it travels to the back of the ball. In order to produce a symmetric ball flight, it is important that each fluid particle encounters a similar dimple profile around the golf ball.

Figure 2. Streamlines going around a non-rotating sphere.

The seam of a golf ball inhibits the symmetry of these streamlines and can cause a major aerodynamic issue. As described before, a seam is created to join two hemispheres together to mold the cover of a golf ball. As the material is buffed off, there is usually a large flat circle around the golf ball that does not have dimples. Often this flat seam can be easily noticed with the naked eye, but when done correctly, it can be difficult to find. Nonetheless, even if it is not easily recognizable to the naked eye, the fluid particles traveling around the ball will find the small flat spots.

When the seam is aligned towards the target, the streamline that goes over the centerline of the golf ball will separate from the golf ball earlier than the streamlines that move around different regions of the golf ball. This occurs because this centerline region will behave like a smooth ball, while the rest of the streamlines around the ball will behave like a normal, dimpled golf ball. With non-symmetric behavior from different streamlines, the golf ball will show aerodynamic variability based on its orientation and potentially show a different result than the player is expecting. This isn’t too concerning on a tee shot where a player can orient the ball away from the seam, but when the ball is in the fairway and cannot be re-oriented, this non-symmetric result could put your golf ball in the greenside bunker.

Conclusions

The engineers at Callaway have developed a way to mold golf ball covers in a way that eliminates material at the seam without having to buff the surface and create unwanted flat spots.  The new 2018 Chrome Soft and Chrome Soft X are the first of their kind to incorporate this ground-breaking technology. Combining this seamless molding process with the patented HEX pattern synonymous with Callaway aerodynamics, our golf balls show a significant advantage in distance consistency relative to the leading competitors.  For golfers this means more consistent distance control from shot-to-shot and ultimately lower scores.

 

About the Author:
Grady received his Bachelors Degree in Aerospace Engineering at the Georgia Institute of Technology and his Ph.D. in Aerospace Engineering from the University of Notre Dame. While at Notre Dame he researched the best methods to mount a laser on an aircraft traveling near the speed of sound. He has been working on golf ball aerodynamics for Callaway since 2013.

Recent Headlines

Featured Products