One question I've received is *why* the Attack Angle will effect the path.
Let's revisit with the attack angle is.
As the diagrams above show, attack angle is measured from the face on view and it's the angle of the clubhead coming at the ball. The problem is that when you hear somebody talk about 'coming down too steep', they often mistake an upright downswing plane (aka 'coming over the top') with the attack angle. In Trackman terms, the downswing plane is the 'vertical swing plane', but downswing plane will suffice. But that and attack angle are two entirely different aspects of the golf swing.
What we know is that if you make your attack angle steeper (for instance, a -3* attack angle becomes a -6* attack angle), that steeper attack angle will shift the path more inside-to-out. If the face is square to the target at impact and you have now made the AoA steeper, you're going to hit a draw. Conversely, if you shallow out the attack angle, the path moves more to the left.
So why is this?
The Geometry of the Circle.
Technically, the swing does not move in a circle. But it moves in something that somewhat represents a circle. The bottom of the circle is the lowest point the clubhead will be at in the swing. And as you can see, the low point is opposite approximately where the left shoulder is.
So, BEFORE the low point, the clubhead is moving downward.
But, AFTER the low point, the clubhead is moving upward
Before we go further, let's think about how that knowledge should apply to how we hit golf shots.
With irons, we hit DOWN on the ball. So, we can deduct that if the clubhead is still moving downward BEFORE it reaches the low point, then we need to have the ball BEHIND the low point at address so we can hit down on the ball. Thus, when you hear about 'moving the low point forward', it's basically trying to get the golfer to hit more down on the ball. With the hacker, it's an attempt to get them to stop flipping at impact and to get them to compress the golf ball better. But with the more advanced player, it's usually to get them to hit the ball lower.
With the driver, we *can* hit up on the ball if we choose to. This is a great way to pick up distance off the tee. If we want to hit up on the driver, we need to find a way to get the low point behind the ball. Why? Because after the clubhead reaches the low point, it moves upward.
But getting back to how and why the AoA influences the path, remember that we swing on an inclined plane.
If the ball is located before the low point, not only will the clubhead go downward after it hits the ball (until it reaches the low point), but the clubhead will also go out to the right (if you're a righty). On the flip side, if you hit up on the ball, that means the low point is behind the ball. So not only does the clubhead reach the low point and then go upward, but it goes leftward as well.
If you want to hit upward and hit a draw, which goes against the 'natural way' of hitting up on the ball, you'll need to get the clubhead pointing near the target at impact and get your 'circle' pointing out to the right.
If you want to hit down on an iron and hit a fade, which also goes against the 'natural way' of hitting down on the ball, you'll need to get the clubhead pointing near the target and get your 'circle' pointing to the left.