Understanding the Determining Factors of Ball Flight
Earlier this year I purchased a Trackman®, and working with it has allowed me to understand impact and ball flight at a new level. One of the great things about Trackman® is that it tracks the full trajectory of every shot from 6 foot pitches to 400 yard drives. It then displays the shots 3D trajectory as well as 26 impact and ball flight parameters in real time. A few examples of these parameters include: club path, face angle, attack angle, launch angle, ball speed, smash factor, spin, among many more. Basically it is an MRI for your golf swing. It tells us what your club is doing at the all important moment of impact, as well as tracking the full flight of the ball, which then allows us to figure understand the golf balls flight. More information on Trackman® can be found at www.trackmangolf.com.
Whenever I start working with a new student one of the first things that we do is discuss, in depth, the ball flight laws and the “ D-Plane”. Basically, golf in its simplest form, is the physics of the collision between the club face and the golf ball. The ball does not know, or care, if someone who has never broken 100 or a multiple major champion is holding the club. All it knows is what the club head is doing at the moment of impact.
I believe there are two crucial things that every serous golfer needs understand…Why does the golf ball curve? What are the determining factors of the golf balls flight?
Lets take a closer look at these questions.
1. Why does the golf ball curve?
Well thats an easy answer, we know that a ball curves because of side spin! Incorrect! The golf ball curves due to a tilted spin axis. There is no such thing as side spin. With the emergence of launch monitors such as Trackman®, we have come to realize that what we thought was happening isn't necessarily what is actually happening.
Trackman® defines spin axis as a representation of the amount of curvature of a golf shot. A negative spin axis represents a ball curving to the left, a positive spin axis represents a ball curving to the right, and a zero spin axis represents a shot that has no curvature.
Below (Figure 1) we can see spin axis can be associated to the wings of an airplane. If the wings of an airplane are parallel to the ground, this would represent a zero spin axis and the plane would fly straight. If the wings were banked/tilted to the left (right wing higher than left wing), this would represent a negative spin axis and the plane would bank/curve to the left. And the opposite holds true if the wings are banked/tilted to the right. In general, a spin axis between -2 and 2 can be considered a straight shot. Under normal conditions, it would be difficult to see curvature on a shot with a spin axis between -2 and 2. The higher the number of the spin axis, the more curvature that should be visible.
So, what determines the spin axis of the golf ball? That brings us to question number 2.
2. What are the determining factors of ball flight?
The quick answer to this question is… the D-Plane. Now your wondering what is the D-Plane. In 1993, Dr. Theodore Jorgensen, a University of Nebraska physics professor who had worked on the Manhattan Project during World War II, published The Physics of Golf. In it, he coined the term "D-Plane," which he called "the plane located between the intersecting lines created by the club face angle and club head path”.
Lets take a look at the two determining factors of the the D-Plane, club face angle, and club head path. These are the two determining factors of ball flight. Actually there is another determining factor in ball flight, and that a centred strike on the club face. When we do not strike the shot in the centre of the club face there is gear effect applied to the spin axis of the ball. But that is a discussion for another time. From this point on we are going to assume that the shot was a centred strike on the club face, and there was no gear affect present.
Club Face Angle
For short we will call club face angle as face angle. Trackman® defines face angle as; the direction the club face is pointed (right or left) at impact and is measured relative to the target line. Most golfers refer to this as having an “open” or “closed” club face. A positive value means the club face is pointed to the right of the target at impact (“open” for a right-handed golfer) and a negative value means the club face is pointed to the left of the target (“closed” for a right-handed golfer).Face angle is the most important number when determining the starting direction of the golf ball. Lets take a look at that last sentence again. Face angle is the most important number when determining the starting direction of the golf ball. What does this mean? The face angle, at the moment of impact, will determine the direction the golf ball will start on, It is not the only factor of where the ball will start as the launch angle will be pulled a bit in the direction of the club path, but for this discussion we are going to assume it is.
Club Head Path
For short we will refer to club head path as club path. Trackman® defines club path as the direction the club head is moving (right or left) at impact and is measured relative to the target line. Most golfers relate this number to hitting the ball “in-to-out” or “out-to-in”. A positive value means the club is moving to the right of the target at impact (“in-to-out” for a right-handed golfer) and a negative value means it is moving to the left of the target (“out-to-in” for a right-handed golfer). The difference between these 2 parameters is known as face to path, and is the primary determinant of spins axis of the ball. So lets take a look at the face to path parameter.
Face To Path
Trackman® defines face to path as the difference between the face angle and the club path. For a right-handed golfer, a negative face to path would represent a face angle that is “closed” to the path and a positive face to path would represent a face angle that is “open” to the path. A zero face to path represents a face angle and club path that have the same value.
Face to path is a key factor in determining the expected curvature (spin axis) of a golf shot. Assuming centred contact, the ball should curve towards the face angle and away from the club path (if face to path is not equal to zero).
Ok, now that we understand what each of the terms means, lets start looking at some practical examples of golf shots and what if anything may need to be worked on in each shot.
One of the great features of Trackman® is that it can overlay the target line, face angle, club path, and the flight of the ball on the video of the swing making it much easier for the student to understand what is happening at the moment of impact. You can see this below (Figure 2).
This picture shows the target line in white, the red arrow shows a face angle that is 3.9* to the right at impact, the blue arrow shows the club path going 10.2* to the left at impact, and the pink line shows the resultant ball flight of a slice to the right of the target
In all of these scenarios we are going to assume that the player is right handed.
Above we see (Scenario 1) a shot that starts at the target and flies straight at it. This students face angle was 0.2 left (closed) and his path was 0.8 right (in to out). This resulted in a ball flight that started at the target and did not curve. Great Shot!
Above (Scenario 2) we see this student is impacting the ball with a face angle 8.4* left (closed), and a path that is 8.1* left (out to in). The result was a shot that flew very straight but left of the target. In this case, we see issues with both the face angle and the path, however there could be a very simple fix for this student. What we are a seeing is a shot that is going roughly 8* off line. The fix could be as simple as aiming this student 8* to the right. This isn't always the case but it is where I would begin.
Next, lets start looking at some students who are curving the ball, In these scenarios we are going to see some students who are controlling there ball flight and some who are not.
Above (scenario 3) we see a student that is impacting the golf ball with a face angle that is 1.3* right (open), and a club path that is 14.1* left (out to in). The resultant shot has started very close to the target line but has sliced far to the right of the target. This student is controlling the face of the club quiet well (1.3* open) but definitely needs some work on his club path.
Scenario 4 Part A Scenario 4 Part B
Above (Scenario 4 Part A and B) we see a student with an interesting case and we will discuss this one a little more in depth. We see that this student has just hit a great shot (Scenario 4 Part A). The very next shot the student hit a ball that started left of the target then curved even further left (Scenario 4 Part B). Right after he struck this shot he turned to me and said, “I hate that shot! I swung over the top!” So we stopped right there and had a conversation about ball flight. It went something like this. “So you feel like you came over the top and swung to the left and that is what caused your ball to miss to the left” he said “Yes”. I then showed him that Trackman® had measured that he had actually swung the club head to the right (in to out) 1.7*, which was actually 0.9* more right (in to out) than his previous swing (Scenario 4 Part A). The reason the ball started left and curved further left is because his face angle was 7.5* left (closed), and we know that the face determines start line, and his path was 9.1* right of that (face to path) causing his ball to curve left. This was eye opening to him because his first thought was to fix his swing path. His swing path was fine. He needed work on controlling his club face angle at impact. I see this with a lot of students. There idea of what went wrong is not necessarily what is actually at fault. They then try to fix something that isn’t broken causing multiple issues in their swing. This is why Trackman® is such a valuable piece of equipment. It measures things that can not be seen with the naked eye or video.
Finally lets look at a student who is controlling his ball flight.
Above (scenario 5) we see a student impacting the ball with a face angle that is 5.6* right (open) and a path that is 10.7* right (in to out). The resultant ball flight is a shot that started right of the target and drew back to the target. This student doesn't require any adjustments to his impact parameters. His golf ball is doing what he wants it to do. That being said, I would prefer to see a path that is in the 4* to 5* to the right and a face angle that is between 2* and 3* to the right. This would reduce the amount of curve during the flight of the ball, and would be more consistent.
I realize that this article has been quite long (longer than I intended for it to be) it is my experience that understanding impact parameters and ball flight, and being able to control them, are the two most important factors of becoming a great ball striker! You do not need a club path and face angle that are directly at the target to play great golf, and I would say that nearly all of the worlds best players don’t. What these great players do understand is that if they are trying to hit a functional draw, the club face has to be open (right) at impact, and the path must be more to the right than the face, for a right handed golfer, so the ball will start right and curve back towards the target (Figure 3). If they are trying to hit a functional fade, the club face must be closed (left) at impact, and the path must be more to the left than the face, for a right handed golfer, so the ball will start left and curve back towards the target (Figure 4).
In conclusion, the easiest way to understand your golf balls flight, and impact parameters, is to remember that the club face will determine the start direction and the ball will curve away from the club path in relation to the start line. If the path is right of the club face the ball will curve left, and if the club path is left of the club face the ball will curve right.
I would like to say thanks for taking time out of your day to read my ramblings. If you have the chance to spend some time on a Trackman I would highly recommend it. Trackman will give you unbiased fact based information on what is happening during your swing. Why guess… what you can measure?
See you in the fairway…