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The D plane
There is an ancient proverb which says: “May you live in interesting times.”
In golf instruction these are THE most interesting times. Like any other discipline we have come of age thanks to technology; things like radar and 3D capture systems have taken much of the guesswork out and replaced it with immutable laws of physics. We started out in the “dark ages” of golf instruction using only our eyes. We, the instructors, would watch the flight of the golf ball and infer from it what the golf club might have done to cause a shot. We helped some people but there was still something missing. Then came the video era and we got at least a better look at what the body was doing in the swing, but a certain ambiguity still surrounded impact. Now we have come pretty much full circle to the enlightenment era of Doppler Radar. This article deals with some of the new findings and how the data debunks certain long held myths.
If you are a fan of this or any of the other popular golf forums, you most certainly have heard of something called the D Plane. The D Plane was popularized by Theodore Jorgenson in his seminal work “The Physics of Golf” back in 1999. He used the term D Plane because it “described” the collision of the golf club and golf ball. His findings were somewhat controversial because he took issue with prevailing ball flight and impact theories; namely the initial direction of the golf ball and the role of the clubface, path and angle of attack at impact. So let’s look into the D Plane and explain it in practical terms that you can understand and use to help your game.
D Plane definition: The wedge shaped plane between two three-dimensional directions — 1) The club head direction, which is a combination of the path AND the angle of attack; and 2) The clubface orientation, which is a combination of dynamic loft and face angle.
Interpretation: The golf club swings up, down, reaches the very bottom of its arc, and travels back up. Because we all swing on an inclined plane (somewhere between 45 and 65 degrees) when the club is traveling down it is NOT swinging at our target (assuming we are aimed parallel left of our target line). It is in fact swinging to the right of the target. And when the club is swinging up, it is actually swinging to the left of the target (stand up and try it.) The only point in the entire arc of the swing where the golf club is swinging at our aim point is at the very bottom of the swing arc, what we call low point. This might be a better way to understand it: If the golf club was swung on an entirely vertical plane (90 degrees) then ALL points in the swing, up and down, would be swinging at the target. This is physically impossible on an incline. So with that in mind, we learn something critical about the “true path: of the swing. It is not simply directional. It is a combination of the up and down in conjunction with the left and right. This is why video can NEVER show the true path. Video is a 2-dimensional representation of a 3-dimensional motion! The knowledge of this, thanks to Trackman, Flightscope, etc., has all but revolutionized teaching. Here’s why…
Technically you cannot hit a straight shot with an in-to-in path aimed at the target. The more DOWN you swing, the more you need to aim or swing left. The more UP you swing (driver), the more you need to swing or aim right. It’s that simple. Because remember: If you hit the golf ball BEFORE you reach low point, which of course you should on any shot on the ground, at impact your path is in-to-out. This will give you a clubface that is closed RELATIVE to the path, and curve the golf ball to the left (for a right handed player.) And if you hit a golf shot AFTER low point you are swinging to the left. This gives you a face that is open RELATIVE to the path. It is not the position of the clubface relative to the target but RELATIVE TO THE PATH that gives the shot its shape. This explains quite categorically how a square face draw/hook or a square face fade/slice can be hit. Very often you can look at high speed video, see the face DEAD SQUARE to the target, and watch the ball curve. Maddening!
Finally all of the information above is based on hitting the golf ball on the center of the face (Which is rare by the way). Toe hits, heel hits, high or low on the face contact, twist the golf club. Here’s where the beauty of modern golf clubs comes into play. We have what is known as horizontal gear effect, which actually helps straighten the flight of the golf ball, when hit off center. When the toe of the golf club strikes the ball, the clubface opens, and when the heel of the club strikes the ball, the face actually closes. But … here is the where the integrated help I referred to comes into play: The toe hits have hook spin and the heel hits have fade spin. So … on a toe hit the flight actually starts to the right (open face) and curving a little back to the left. And on a heel hit, we get flight beginning to the left (closed face) and curving back to the right. So here we actually observe open face hooks and closed face slices! A real true draw is hit with a slightly OPEN face with a path from the inside. And a true fade is hit with a slightly closed face and a path well outside that face. Horizontal gear effect is more built more into woods than irons, but irons have it as well. And you think this is isn’t a crazy game!
It’s difficult to understand in words but there are plenty of D Plane videos on the net, and if you like I’ll do one here on the GOLFWRX forum as well.