Ball Flight Curvature

Two frequent questions golfers have when they look at a ball in flight are: what made the ball curve like that, and how do I get the ball to curve like that? The good news is that the same principles answer both questions, and that's what we'll consider briefly here.

Spin axis of rotation is the key to understanding the curvature in ball flight trajectories. Spin is generated by friction of the ball sliding up the clubface at impact causing backwards rotation of the ball to provide lift. When we see the ball curve right (fade or slice) it means the spin axis is tilted right (positive). A ball flight that curves to the left (draw or hook) means the spin axis is tilted left (negative). Launch monitor data shows for every 5 degrees of spin axis tilt the ball curves about 3.5 yards to the side of the tilt.

Tilt in the spin axis occurs when the club face angle and the club head path direction are different at impact with the ball. An open face angle tilts the spin axis to the right (as in the above illustration), and a closed face angle tilts the spin axis to the left. The spin direction, the lift force vector, and the D-plane (descriptiove plane of T. Jorgensen, 1999) are perpendicular to the spin axis.

.An off-center ball contact location on the club face has an important effect on the spin axis. The effect is greatest with the driver due to bulge and roll curvature of the clubface. The curvature makes the ball and the clubhead behave like connected gears that have opposite rotational actions. This gear effect somewhat counteracts frictional ball spin and modifies spin axis tilt. 

An interesting point about gear effect is the role of club head center of gravity (CoG). At impact, the club rotates around its CoG. Since the CoG of irons is relatively close to the clubface in most club head designs, gear effect is minimal with these clubs. The CoG in drivers is further away from the club face making gear effect more significant. Ball contact a half-inch off the center of a driver club face can tilt the spin axis about 20 degrees. Bottom line, it's best to avoid an off-center hit.

Rotating the club head quickly through impact can have a modest effect on spin axis tilt. The distance of the club head CoG from the face acts to resemble a heel contact gear effect when the rate of club head closure is quick. The result will be a fade even when ball contact is directly in line with the CoG. 

Ball Flight Direction

Direction and distance are what we want to control when hitting the ball. Here we describe factors that influence ball flight direction immediately after impact of the ball with the club head.

Traditional golf instruction focused on club path through impact and misunderstood the role of face angle. We now know from launch monitor data that face angle is the major factor influencing ball direction immediately after impact. 

The orientation of the club face is about four times more important than club path in determining the initial direction of the ball at impact. It accounts for approximately 85 % of the initial direction and club path for drivers and about 75 % for irons. Knowing the relationship between face angle and swing plane can affect on how golfers change the movement of their arms and wrists when making an adjustment to their swings to control ball flight. 

Face angle is the horizontal angle of club face at impact relative to the intended target line. The flat face of an iron makes it easier to see the face angle at impact. The bulge and roll of the driver club face adds a complication: the radius of curvature (11-13 degrees in most drivers) can add up to 3 degrees or more to the apparent face angle when ball contact is not at the center of the face. In an off-center hit with a driver, face angle direction will be different at the ball contact point than at the center of the club face.

Club path shows the direction of the swing but it's also affected by angle of attack of the club head at the ball at impact and the swing plane vertical angle. The direction of the swing: e.g., straight, from inside the target line to outside, and from outside the target line to inside is the basic view of club path. However, it's helpful to consider the bottom of the swing arc relative to the vertical plane of the swing for a more complete understanding of club path.

Control of the angle of attack (AoA) is important in optimizing ball flight distance with a driver --- hitting up on the ball allows for using lower lofted club heads to minimize spin as swing speed is increased. Hitting up on the ball places the bottom of the swing arc before impact and results in a slight outside-to-in club path.

The magnitude of the AoA effect on club path direction depends on the vertical swing plane. The flat swing plane of a driver will have a greater effect on direction than a more vertical plane typical of shorter clubs.

We'll conclude our discussion of factors that affect ball flight control in our next blog.

Ball Flight Distance

Optimizing ball flight is a common goal of clubfitting and instruction. Using a radar launch monitor allows us to analyze the factors that maximize distance and make the ball curve or go straight to achieve the ball flight we seek. Here's a brief rundown on what's important for increasing ball flight distance.

Maximizing distance requires a different optimum launch angle and spin rate for any given ball speed. Changing one factor counteracts or enhances the other factors. For example, a slower clubhead speed should be balanced by increased spin rate and higher loft angle to achieve a high enough launch angle that will maximize ball carry distance. 

Spin is generated by friction of the ball with the clubface at impact. The ball spins towards the clubface around a rotational axis that influences lift and determines ball direction. Ball spin rate is influenced by the interacting effects of clubhead loft, speed, angle of attack, contact position of the ball on the clubface, and friction between clubface and ball. 

Angle of attack (AoA) of the clubhead center of gravity into the ball combines with clubhead loft at impact (dynamic loft). We can think of the combined effect as spin loft, and it's equal to the dynamic clubhead loft angle minus angle of attack. It means that hitting up on the ball (positive AoA) decreases the spin loft, allowing us to use a lower lofted driver to reduce spin and maximize distance for any given swing speed.

The clubhead will have a tendency to rotate around its center of gravity (CoG) when the ball contacts the clubface off-center. Bulge and roll of the driver clubface generates a gear effect on the ball that modifies the spin axis. 

Contact of the ball in the center of the clubface always generates the most efficient transfer of swing energy to the ball and results in maximum distance. This contact efficiency effect is usually termed "smash factor" and provides a useful indicator for clubfitting and instruction. Smash factor equals ball speed divided by clubhead speed. The maximum smash factor is 1.50.

We'll discuss additional factors that control ball flight direction in our next blog.

The Curiosity of JT

Here's what our friends at Alpha Golf wrote about JTClubs and what makes us unique.

 http://blog.alphagolfclubs.com

Why Swing Analysis?

A major goal of swing analysis is to help golfers play better golf by understanding the ways their swing mechanics, clubs, and range-of-motion interact to determine how well they play. Golfers learn what is rate limiting in their performance and what's needed to improve instead of grooving a swing problem with clubs that don't fit and range-of-motion problems that limits their ability to swing the club efficiently.

Accurate swing analysis requires technology: 3D motion capture, video, and functional movement assessments allow us to translate numbers, graphs, and images into practical applications for your game. Feedback jump-starts training and yields huge benefits to playing. Linking the analysis to launch monitor data from the same swings takes guesswork out of understanding what limits performance on the course. 

Measuring the kinematic sequence of your swing with our K-Vest 3D motion capture system identifies how efficiently you rotate major body segments in the swing. Here is the kinematic sequence of a low-handicap player who is not achieving the distance that's predicted by club performance analysis with our FlightScope radar launch monitor.

The kinematic sequence acceleration curves indicate the pelvis is not able to remain stabile in the first part of the downswing. Further analysis shows how segmental weakness and lower body stability issues may lie at the heart of the problem. We can analyze in more depth to reveal the physical limitations responsible and how it limits the ability of this player to transfer power efficiently to the club.. 

We find for this player that a combination of over-rotation of the upper body in the backswing, inefficient transition mechanics from backswing to downswing, and instability in the lower body contribute to the power loss that keeps the player from achieving his distance potential. Quantifying the way the player bends and rotates in the swing gives specific targets for training that can be monitored periodically with biofeedback from the K-Vest system. 

Over-rotation in the backswing by strong and flexible players is a frequent problem that is difficult to overcome in the transition and downswing. It translates into less distance and wider shot dispersion. Understanding the underlying cause and using K-Vest biofeedback forms a solid foundation for developing an effective game improvement strategy.