The US PGA’s “Ball Flight Laws” state that the ball will start in the direction of the club path and curve if the club face is pointed in a different direction than the club path.
The D Plane shows that the ball actually starts just about where the face is pointed(approx 85% of it’s direction) and curves if the path is in a different direction than the face. The only assumption made here is solid contact. If the ball is hit off the sweetspot, the club will turn before the ball separates from the face and gear effect will affect the spin axis of the ball.
So how is the 3d path determined?
For most good players, they take a divot with an iron after the ball. This means that the ball is hit before the low point. So, relative to the ball, the 3d path is to the right of the plane line(TGM term for the base of the inclined plane) for an iron shot(see picture below). 3 dimensionally, the club head continues to travel downward, forward and outward until it reaches the lowest point. Immediately after this, the club head begins traveling inward and upward. Because of the fact of when we hit the ball relative to low point, in order to hit it straight at a target, the club must be traveling to the left of the target(for downward angles of attack) while the face is pointing at the target at the hit/seperation. We are trying to get the 3d path to point at the target not the base of the plane.
This contradicts aiming parallel left with iron shots unless a person swings left. If you aim parallel left, make a perfectly on plane swing, hit the ball with the face pointing at the target, hit it solid and take a divot after the ball the ball will start just right of the target and draw left of the target.
Obviously, the opposite is true for players that hit upward on their drives. Just reverse the above information and you’ll see you have to aim/swing right(for upward angle of attack), with a face pointing at the target, to hit it straight. Assuming again solid contact.
Looking at the picture attached you will see the target line, 3d club path(club head velocity direction for a perfectly low point strike), club face normal(3 dimensional direction face is pointed) and initial ball directon(horizontal ball velocity direction). You can see that the 3d path(club head velocity direction) is to the right of the club face and the initial ball direction is just right of the club face normal. This is the D plane of a push draw. Path is right of target, face is right of target but left of path so ball will draw.
Follow this link for a good way to visualize the D Plane.
Here’s a link to another blog where I talk about how to use the D Plane.
Check out the D Plane Page for videos explaining visually what the D Plane looks like.
Please leave me some comments if you are having trouble understanding this. Picture was provided by Mandrin from the brian manzella forum.