Teaching with the New Ball Flight Laws
In the Winter 2010 issue of Golf Teaching Pro, the article “Ball Flight Laws: A Scientific Approach” was printed on pages 26-27. The article dealt with the fact that traditional understanding of why the ball does what it does is flawed.
Even today, most golfers and teachers are under the impression that the clubhead path determines a ball’s initial direction, regardless of clubface orientation. Recently, research by TrackMan™ and others shows that this is not the case, as the clubface angle at impact is about 75-85 percent responsible for the ball’s initial direction. The orientation of the clubface angle at impact overwhelmingly determines the initial direction of the ball. So, how does this affect our teaching?
One of the major changes is in our understanding of why a ball starts straight and then curves away from the target. Previously, we thought the clubhead path was down the target line at impact while the clubface angle was open or closed. Now, we know that the clubface angle is relatively square with the target line while the clubhead path deviates from it.
For example, let’s say a ball starts straight and then curves to the left. We now know that the clubface angle is somewhat square with the target line while the clubhead path is to the right. This is an important distinction as compared with the old ball flight laws for obvious reasons. If we are still operating under the false assumption that the clubhead path dictates initial direction, we would then say that the clubhead path is okay but the clubface angle is flawed. This teacher would then incorrectly work on changing the orientation of the clubface angle while not changing the direction of the clubhead path.
Instead, with our accurate knowledge of the ball flight laws, we would have to work on changing this student’s clubhead path through impact. This is perhaps the trickiest part of working with the accurate understanding of the ball flight laws. It may not look it visually, but balls that start straight and then curve are the result of a swing path that is incorrect. Since visually it may not make sense that the clubhead path is flawed, some teachers may not believe it and not work on the clubhead path. Of course, this would be a mistake.
Another tricky change would be with a ball that starts either left or right of the target line and then curves farther in that same direction. For a shot that goes “right to right,” for example, we previously would have said that the clubhead path was to the right of the target line with an open clubface. The result? A push-slice. Yet, this explanation is incorrect. For such a ball flight, the clubhead path is actually to the left of the ball’s initial direction, and in fact it could well be either down the target line or even left of it. The hard part with such a ball flight is that we actually don’t know exactly what the clubhead path was through impact, unless we have a TrackMan or some other launch monitor that can accurately measure this. A good way to estimate what the clubhead path was doing is to see how much the ball curves, and then assume the clubhead path was going an equal amount in the opposite direction from the ball’s initial direction. The only other way to estimate is to look at the orientation of the divot, if there is one.
Here’s another way our understanding changes, but this time not necessarily how we teach. Now let’s say our student hits pull-slices, with the ball starting left of the target line and then curving to the right of it. It might be hard to believe, but this student’s clubface orientation at impact is probably closed to the target line! The key, though, is the orientation in relation to the clubhead path. Of course, it is open, which means that the clubhead path is even farther to the left of the target line than the ball’s initial direction. For teaching purposes, though, we would still deal with this student the same way that we did before.
To sum up, the way that the clubhead path and clubface angle affects ball flight is more complicated to understand than yesterday’s simplified, but totally incorrect, method. Pay close attention to the ball flight and go from there. In the vast majority of cases, we can easily see what we need to correct, such as with pullslicers, and the methods of dealing with them have not changed. For the more tricky ball flights, as outlined above, be more diligent in ascertaining the causes and needed cures.
LAUNCH ANGLE: THE VERTICAL COMPONENT
Let’s shift our focus to clubface loft and whether the clubhead is ascending or descending into the ball, and how this affects initial trajectory. A typical driver might have 10° of loft. Assuming the clubhead is coming into the ball flat, neither ascending or descending, the ball’s launch angle will be approximately 8°. Yet, no club fitter worth anything would be happy with such a launch angle, so how can we get that launch angle up into the 12°-14° range? Well, here’s where it gets tricky again.
According to prominent clubmaker and clubfitter Ralph Maltby, many drivers’ stated lofts are not the actual lofts. There are also different ways to measure loft. You can do it in relation to the club shaft or in relation to the club soled on the ground. But, a driver may have a somewhat curved sole, so when is the club considered soled? When the middle part is flush to the ground? When the leading edge is flush to the ground? As you can see, measuring driver loft is not an easy thing, and different manufacturers measure loft with different methods. This may help explain why one company’s 9° driver goes higher than another company’s 10°. For consistency, Maltby advises measuring driver loft from the middle of the clubface while the shaft is vertical as you are looking at the driver from the toe end.
Another factor is the clubface roll. All driver clubfaces have a curvature from heel to toe (bulge) and from top to bottom (roll). This means the top of the clubface is more lofted than the middle, and the middle is more lofted than the bottom. Thus, a ball hit on the upper part of the clubface will be launched higher, all other things equal, than a ball hit on the middle of the clubface.
Back to the question of how do we get a 10° driver to launch in the 12°-14° range, which is what most people require. The first thing we need to do is to contact the ball on the clubface higher than in the middle. This will produce a couple of extra degrees of launch angle than a ball struck in the middle of the face. Finally, we need to hit up on the ball. Some people do this incorrectly by releasing the clubhead early (another issue entirely), but the proper way to do this with a good swing is to play the ball farther forward in the stance compared to shots played from off the ground.
The result: Assuming we hit the ball on the clubface slightly above center with an ascending angle of attack of 3°, this will produce a launch angle of approximately 13°. Another factor which is not figured in here is the shaft bend at impact. You might have seen some pictures of tour players at impact with the shaft bowing backwards. This also will add a couple of degrees of launch angle, but since the average golfer can’t bend the shaft (even with regular flexes) like a tour pro, we won’t worry about this.
How about a descending blow with the clubhead? This is what is required with irons. Assuming we hit a 7-iron with a loft of 35° on the sweet spot with a descending angle of approach of 7°, our launch angle will be approximately 22°. So, to hit a ball lower, we can do one of two things: We can use a lower-lofted club, or we can increase the angle of descent into the ball. Usually, the latter is accomplished by playing the ball back in the stance.
A surprising find by TrackMan is that hitting more “down” on the ball does not in itself produce more backspin! What produces more backspin with an iron is hitting the ball lower on the clubface, below the sweet spot (technically known as the center of percussion). Conversely, a ball hit above the sweet spot will produce less spin. This goes for all clubs and is regardless of whether the clubhead was ascending or descending.
If you are interested in exploring TrackMan’s research further, please go to http://trackman.dk/media/newsletter.aspx and a list of their technical bulletins will appear.