[Daryl]

Wow. I wrote this, then realized, it's a long and vapid post. Sorry for the inconvenience. All of the following Jorgensen quotes are from chapter 9 of his book.

I think that people who explain Jorgensens "D Plane" stretch it a bit too much.

The D Plane as a Practical Tool
The D plane for a golf swing contains the path along which the club-head is moving at impact, the normal to the clubface, and the initial path of the ball after impact. The D plane also contains the aerodynamic lift force, since the lift force is perpendicular to the axis of spin and this axis is perpendicular to the D plane

Normal to the Face. Now, I don't know about anyone else, but "Normal to the Face" is not exactly normal to the face. When the clubhead is halfway down to the ball; is the clubface square to the path of the clubhead? I don't think so. How about when the Clubhead is traveling up and in after low-point. Is the Clubface square to the path of the Clubhead? I don't think so.

So somewhere along the line, the clubface becomes square to the path of the clubhead. Does Jorgensen say where along the path the Clubface becomes square? No, but we can assume somewhere around Impact. Does he tell us "How" the Clubface became Square to the Path? No, but who's asking anyway.

Jorgensen is only stating 2-D-0:

2-D-0 DIRECTIONAL FACTORS Another need for a “perfect circle” motion is for directional control. If the Clubface is maintaining a constant relationship to the radius of its rotation – whether the face is open, closed or square – then the direction imparted at any one point of the arc will always be the same for “centered” (Sweet Spot) Impact (2-F).

Something Jorgensen said is very interesting:

Consider a collision for which the clubhead at impact is moving directly toward the chosen target and the normal to the clubface is directed to a point exactly above the target. The D plane for such a collision contains the target, and the plane is vertical. After the collision, the ball will be moving in this plane toward the target with the line of flight a little below the normal to the clubface.

He further explains:

. If the reader takes the usual stance with a five iron and swings the club directly in the direction of an assumed target with the clubface square to the target, neither toed in or toed out, then the D plane for the swing will be a vertical plane containing the velocity of the clubhead, the velocity vectors of the ball and the normal to the clubface, and the target. To illustrate this swing, the card representing the D plane should be held so that the line representing the clubhead motion points horizontally toward the target and the line representing the normal to the clubface points directly toward but above the target. For such a swing, in the absence of a crosswind, the ball will fly directly toward but above the target without a hook or a slice.

I don't know what you guys think, but after reading TGM, I would say that that Ball is going to curve.

It's not that the "D Plane" is anti-TGM, it's that Jorgensen did not consider Hinge Action. Jorgensens "D Plane" is based on "Glancing Blow" Theory. Glancing Blow theory is great for Ping Pong and Tennis Balls but the Golf Ball has a "Solid-ish" core. "Compression" theory is applicable to explain the spin cause by the collision between a Golf Ball and Club.

The Two Theories are very different. The following example can highlight their difference.

Jorgensen said:

When the ball is hit out of deep rough and a layer of grass lubricates the contact between the clubface and the ball, there may not be enough friction to give the ball the usual amount of spin. Under this condition the ball may leave the clubface along a line closer to the normal than usual.

If we view this situation using "Compression" theory, we might say that the amount of grass between the Clubface and Ball caused the Clubface to lose contact with the Impact Point before separation, which caused a loss of spin producing compression. We would also claim that the ball flight will be a little right of target for the same reason.

Consider test results when Clubface surfaces are altered. A clubface without grooves can produce nearly the same amount of spin from one with Grooves when hit from a dry and tight lie. A study I recently read, compared 3 surfaces, Smooth, roughed and grooved and under 3 different conditions, dry, oiled and oiled wiped-off. The results were not supportive of the Glancing Blow theory. In fact, there's hardly any mentionable difference in spin rates.

I think the "D Plane" is an acceptable way to explain Ball Flight for anyone that swings the Club and can hold the clubface square to the clubhead path during Impact.

I also think that "Trackman" can improve by using Low-Point of the Sweet-spot Orbit to calculate the Horizontal Swing Plane rather than the Ball Location. But their interest is explaining "How" the ball tracked, not "Why". "How" and "Why" is like "night" and "day".