Is Golf More Difficult Than Flying?
Playing golf and “driving” a ball with some degree of proficiency is difficult, and almost as time-consuming to perfect as “driving” a plane. For one, the rules of golf do not permit “Artificial Devices and Unusual Equipment which might assist [the player] in making a stroke in his play,” which essentially means that golfers don’t get the benefit of autopilot. Second, golf requires a person to stroke an object (the ball) with another object (the club head), which is attached to the end of a 40-inch shaft (+/-5 inches). This action must be performed so precisely that the ball will fly approximately 280 yards in the air, within a horizontal window of 4 degrees from the launch pad, and stay in the fairway (short grass)…only so you can find it and repeat the process with another club, resulting in a completely different trajectory.
How the Ball Flies
The complex science of aerodynamics can help us understand precisely how the air flows over the surface of the ball, allowing it to fly through the air like a plane rather than take on the trajectory of a bullet. In fact, a golf ball can travel farther than any other round object of the same size and weight launched under the same conditions.
A lot is known about how air flows over a wing, but less about how it flows around the wing tips, where it is believed the trailing vortices begin. The type of turbulence and aerodynamic forces created in this area are complex. Some have even compared the airflow surrounding a spinning golf ball to the dynamic reaction of two wing tips meeting.
Does this mean that a golf ball is in part more complex aerodynamically than the Falcon 7X, Boeing 777, or even the Concorde? The only thing that makes the golf ball a little easier to study is that it doesn’t get into the supersonic range, although it may seem like it does when John Daly or Tiger Woods hit the ball.
Discovery of the Dimple
Some 600 years ago, someone observed that an older, used ball with a roughened surface performed better than a new, smooth one – hence the origin of “dimples.” As ball construction evolved from a stitched pouch of skin stuffed with feathers to the molded, solid, natural rubber (gutta percha) ball introduced about 150 years ago, a roughened surface was recognized as an integral part of the design, even though it was not understood why or how it worked.
As soon as a golf ball is launched off a driver, it starts its trajectory straight down the runway (fairway) with lift forces greater than the weight of the ball and drag forces that will immediately start slowing it down. Yet, it is still able to cover a distance of approximately 265 yards in the air and then bounce and roll on to about 290 yards in total. A smooth ball with otherwise identical physical properties, launched in the same manner, will only travel about 140 yards.
Drag Force Barrier
Wind tunnel experiments show that the simples on a nonspinning golf ball actually decrease the drag force, allowing the ball to slip through the air with less resistance than a smooth ball, but only at speeds between about 55 mph and 300 mph. Below 55 mph, both the smooth and dimpled balls slip through the air with about the same resistance (drag force).
It is at the critical speed of about 55 mph that the nonspinning, dimpled golf ball passed the critical “Reynolds number” (aerodynamic jargon for “force barrier”), reducing the drag force significantly. The smooth ball goes through a similar force barrier, but at a critical speed of about 300 mph, and at this speed has less drag than the dimpled ball. It is at these critical speeds that the drag tail (turbulence behind the ball) suddenly decreases in size. The separation point of air causing the turbulent tail or wake rapidly moves from a point about 80 degrees from the air flow direction to about 110 degrees around the back of the ball. This is sometimes referred to as “delayed separation” (see illustration). When this happens, the drag force decreases by almost 40% of that just prior to this critical speed.
The drag force on the golf ball will then slowly increase as the speed increases. A golf ball well-struck off a driver is launched at about 160 mph and lands at about 70 mph. Thus, the ball would be in this decreased drag zone for most of its flight, taking advantage of the phenomenon.
Design by Trial and Error
Designers have taken an experimental approach and have analyzed the cause and effect of a variety of designs in search of the “perfect dimple,” which will result in an optimum trajectory.
The Ball is Going too Far?
For the last 100 years, golf’s governing bodies have been concerned by the continual improvement in distance that balls have gained through technological research.
By 1976 the “Overall Distance Standard” (ODS) was adopted. The standards were based on launching a ball using a mechanical golfer to simulate real field conditions and setting a limit on the distance under specified test conditions. Individual properties of the ball, which contributed to the overall distance, were not isolated or limited for two reasons: first, they were not understood; nor were they able to be measured at the time.
The Laws of Physics Will Govern Distance
Unfortunately for many golfers looking for an extra thirty yards, the laws of physics will limit the distance balls can travel to only a 10- to 15-yard improvement – even without existing performance standards! In other words, equipment is reaching its limit.