Drive Golf Performance Blog

Drive Golf Performance Blog

Tuesday 14 May 2013

Understanding Ball Flight - Why Did the Ball Go That Far?

The three questions that have been looked at to understand ball flight have been:

1. Why did the ball start there?
2. Why did the ball curve that way?
3. Why did the ball go that far?

The last two blog posts answered question 1 and 2. This post will answer question 3, why did the ball go that far?

There are several factors that effect distance that the golfer has no control of. These include wind, temperature, humidity, altitude, moisture, ground conditions etc.

There are equipment factors that influence distance which include golf ball design (materials, dimple design etc.) and golf club design (head, shaft, length, weight etc.)

The three factors that influence distance which a golfer can control are

1. Spin Rate
2. Launch Angle
3. Ball Speed

Long distance comes from high ball speed, a high launch angle and a low spin rate. These factors can be changed by altering swing mechanics. Let's take a closer look at the factors.

Spin Rate

The main factors that will affect the spin rate are

1. Dynamic Loft
2. Attack Angle
3. Club Speed
4. Impact Position
5. Friction between ball and club face

The factors all influence each other and it's the combined effect of all five that result in the total spin of the ball. The ball spins backwards through the air, backspin is a good thing and like all good things too much or too little can be bad!! There is an ideal range of backspin for each club, it is higher for wedges and lower for drivers. Players with lower swing speeds need higher spin rates to keep the ball in the air longer. Players with higher swing speeds require less spin.

Dynamic Loft

Dynamic loft is the vertical club face orientation at the center point of contact between the ball and club face at the maximum compression of the golf ball. This is basically the loft of the club at the impact point on the face. Due to vertical roll on the club face, a ball hit higher on the face has a higher dynamic loft, a ball hit lower on the face has a lower dynamic loft. In general the higher the dynamic loft the higher the spin rate.

Attack Angle

Attack angle is the vertical direction of the club head's center of gravity movement at maximum compression of the golf ball. A lower attack angle can create more spin and a higher attack angle can create less spin. However attack angle and dynamic loft together directly influence spin rate. This relationship is called spin loft.

Spin Loft 

Spin Loft is defined as the angle between the direction of the club head's center of gravity movement (attack angle and club path) and the club face orientation at the center point of contact between club and ball (dynamic loft and face angle) at the maximum compression of the golf ball. In essence it is the difference between dynamic loft and attack angle, but differences between path and face can influence it as well.






This picture from www.trackmangolf.com illustrates spin loft. In the two examples different dynamic lofts and attack angles produce the same spin loft and the same spin rate.

Spin Rate can be calculated from club head speed x spin loft x 2.3 (driver) or club head speed x spin loft x 2.6 (iron).

Impact Position

Impact position on the face impacts spin rates through vertical gear effect. With the club rotating around it's center of gravity, impacts above the center of gravity have reduced spin and below have increased spin.

Friction

The total amount of friction between the ball and the club face will effect spin. A good example would be the 'flier' i.e. when there is grass or moisture between between the ball and club friction is reduced and the ball 'jumps' or has less spin and travels further than expected..

Club Speed

Higher club speeds have greater potential to generate more spin.


Launch Angle 

For any given ball speed and spin rate there is a corresponding launch angle that will maximise distance. Launch Angle will always fall between dynamic loft and attack angle of the club. The dynamic loft has a greater influence. For drivers 85% and for irons 75% of the launch angle is accounted for by dynamic loft. If friction is reduced the dynamic loft can have an even greater influence.


 Here's a chart from http://www.planetruthgolf.com/PlayerResources/Forums/tabid/77/aft/28402/Default.aspx showing optimal launch parameters for maximum carry. Bear in mind that for maximum overall distance less carry and more roll may work better.

Ball Speed

The last factor that effects distance is ball speed. There is a relationship between club head speed and ball speed. The efficiency of speed transferred from the club to the ball is Smash Factor. If a player has 100mph club head speed and 150mph ball speed the smash factor is 1.5. The closer the smash factor is to 1.5 the better. The best way to increase ball speed is to improve center face contact.

For this reason shorter shafts in drivers may be better. Shorter clubs are easier to control and as a result easier to hit out of the center of the face. The very minute loss of club head speed is more than made up for in the more centered strike with a resultant increase in accuracy.


Summary

The three factors, Ball Speed, Launch Angle and Spin Rate, combined explain the distance any golf shot goes. Spin Rate is calculated by speed x spin loft x 2.3/2.6 (driver/iron). Launch angle is influenced by 85%/15% dynamic loft/attack angle for a driver and 75%/25% for an iron. Ball speed comes from club head speed with a centered contact.

A high ball speed, derived from a centered strike with high club head speed, with a high launch combined with a low spin rate will mean long distance with the driver. A golfer looking to maximise their driver distance should look to improve strike and then optimise their launch conditions and spin rate. Launch Monitors such as Trackman are great tools to find the numbers to optimise your driver distance. If you get a chance to use one, do, you might end up hitting drives you never dreamed of.

Other ways of increasing distance include playing in warm conditions, with the wind at your back, at altitude with dry firm fairways!!

As always comments and questions are appreciated.


Monday 6 May 2013

Understanding Ball Flight - Why Did the Ball Curve That Way?

In order to understand ball flight there are three questions to ask.

1. Why did the ball start there?
2. Why did the ball curve that way?
3. Why did the ball go that far?

In the last blog post, the first question, why did the ball start there?, was answered, in this post the second question, why did the ball curve that way?, will be answered.

Of the five impact factors, clubhead speed, club path, club face angle, angle of attack and centeredness of strike the main ones that affect ball curvature are club path, face angle and centeredness of strike.

Spin Axis

What causes a ball to curve is a tilt in it's Axis of Rotation. The axis of rotation is the axis in which the ball is spinning around. The ball spins around one axis, sometimes people believe there is a combination of backspin and sidespin, but this doesn't happen.




The line going from left to right is the axis the ball is back spinning around. The axis is also tilted to the right in this photo meaning the ball will move from left to right in the air.






Imagining an airplane turning is a good way to see how a tilt in the axis of rotation will affect the flight. With the wings tilted to the right in this photo the plane is turning right. A ball with a tilt to the right will move from left to right and a tilt to the left will have the ball moving right to left.

Trackman figures show that for every 5 degrees of tilt in the spin axis the ball will curve approximately 3.5 yards to the side for every 100 yards of carry.


Spin Axis tilt is caused by a difference between club face angle and club path, Trackman names this difference as Face to Path. If the face is open to the path, the spin axis will tilt to the right and the ball will move left to right. If the face is closed to the path, the spin axis will tilt to the left and the ball will move right to left. 

Gear effect on clubs, mainly woods, also has a major influence on spin axis. Heel strikes tilt the spin axis to the right, resulting in left to right shots. Toe strikes tilt the spin axis the the left, resulting in right to left shots.

Influence of the D-Plane on Spin Axis Tilt

The D-Plane or Descriptive Plane was coined by Theo Jorgensen in his book 'The Physics of Golf'. The easiest way to describe D-Plane is it is the plane that contains the initial flight of a golf ball after impact with the club face. The D-Plane is created by the club path and the club face orientation at impact.




This picture from www.brianmanzella.com is a good illustration of the D-Plane. The face is closed to the path, causing the spin axis to tilt to the left, the ball will move from right to left and initial starting point is closer to the clubface than the club path.

Gear Effect

Earlier on it was mentioned that the strike point on the face would affect the spin axis. This is due to Gear Effect. A golf club will rotate around it's center of gravity. A golf ball that impacts on the face in line with the center of gravity will have not have any face rotation due to the contact collision. Is the ball strikes more towards the toe the club face rotates open and vice versa for a heel strike.

Gear effect is the counter rotation inflicted on the golf ball due to the interaction of the rotating face on the golf ball. A toe strike causes the spin axis to tilt to the left and a right to left ball flight. A heel strike causes the spin axis to tilt to the right and a left to right ball flight.

For irons the center of gravity is close the the club face and irons exhibit minimal gear effect. With woods the center of gravity is quite far from the face and woods exhibit significant gear effect.

For a driver Trackman indicates that an impact that is 0.5 inch from the center will impart 20 degrees of spin axis tilt. This is quite a large number and is a major factor in ball flight. It can override the influence of the D-Plane at times.

Here is a photo from www.tutleman.com illustrating gear effect.


Face Closure Rate

One other factor that effects curvature is the rate of closure of the clubface through impact. If the face is closing around a point behind the face it will impact the spin axis like heel contact gear effect.

Summary


The factors that determine curvature of the ball are the difference between the club path and club face orientation at impact. The D-Plane illustrates this. Gear effect also has a big impact on spin axis and how the ball curves. The least known factor is the face closure rate, a the face is closing around a point behind the face it will impact the spin axis like heel contact gear effect.

As a result the main way to hit a straight golf shot is to have a centered strike with little face closure combined with a club path and face angle that are pointing in the same direction at impact. A straight shot can also be obtained when a non centered strike counteracts a face to path difference.




Any questions and comments are always welcome.