Off-center Gear Effect Driver Impact Affects the D-plane ....

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SteveT

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FYI ... here is an excellent explanation of gear effect for drivers and irons.

By Tutelman -- Design Notes - Golf Physics p2

Gear effect is sidespin which is the result of an off-center hit with a club whose center of gravity is well back from the clubface. Without both these conditions, gear effect does not happen.

Let's see what causes gear effect. In the picture at the right, we have two off-center impacts, one on an iron and the other on a driver. Both are toe impacts, which means it is to the toe side of the center of gravity of the clubhead. (The CG is denoted by the four-quadrant black-and-white circle; it's a pretty common notation for CG.) What does Newton say about such an impact? The CG wants to continue moving forward in a straight line, but there is a force on the clubhead that is off that line. That creates a torque that wants to twist the club. The result is that the CG keeps moving forward, but the club rotates around the CG in a clockwise direction (red arrows).

The CG of the iron is close to the clubface. So, where the clubface and ball meet, this rotation (the red arrow) consists of the clubface "falling away" from the ball. This results in loss of distance (the momentum transfer is not as complete as it should have been), and perhaps the ball flying somwhat to the right as the face opens. But there isn't any special effect on spin.

The driver is a completely different story. Its CG is well behind the clubface. When the driver head rotates around its CG, the whole face of the club moves sideways. Look at the direction of the red arrow where the clubface and ball meet; it is mostly parallel to the clubface, with only a bit of "falling away".

So the club's face is moving to the right while the ball is compressed on it. The result is that the ball starts to rotate so its surface doesn't slide along the clubface; remember it's compressed so sliding is difficult. This rotation is the blue arrow in the picture. If the clubhead is rotating clockwise (as in the picture), then the ball rotates counter-clockwise. It's as if the clubhead and ball were a pair of gears, with their teeth meshing where they meet.

That's why a toe hit with a driver tends to hook. For all the same reasons, a heel hit with a driver tends to slice. You don't have this effect with an iron.

Click to expand...

Driver gear effect adds another force vector to the ball that may diminish or accentuate D-plane analysis results since it affects the ball spin rate and axis.

Therefore, current D-plane analysis only applies to driver sweet spot Impact. How does TrackMan compensate for off-center driver hits?
 
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SteveT

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Yup ... the bulge & roll of the driver face is calculated to gently push or pull the ball ... push if hit towards the heel and pull if hit towards the toe.

Again, this means another force vector that affects the D-plane vectors and directional lines.

How would this affect TrackMan data ?
 
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dannyc

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Trackman would give data that didn't "match" the flight, revealing that the ball had been struck towards the toe or heel.

This topic was discussed in one of trackman's newsletters.
 
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cwdlaw223

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SteveT -

Does Tutelman use the word sidespin to mean axis tilt? The blue line looks like true sidespin and Trackman speaks of axis tilt.
 
gmbtempe

gmbtempe

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Jim Kobylinski said:
Doesn't the bulge/roll on the face of a driver also help (not cause but help) with gear effect as well?
Click to expand...

I think it does Jim, I joked around that after switching to a driver with very little face bulge to one with I noticed that off center hits just seemed never move that much off line. Now I had gotten better but I doubt that was the total explanation.
 
duckjr78

duckjr78

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SteveT said:
Yup ... the bulge & roll of the driver face is calculated to gently push or pull the ball ... push if hit towards the heel and pull if hit towards the toe.

Again, this means another force vector that affects the D-plane vectors and directional lines.

How would this affect TrackMan data ?
Click to expand...

Steve, you seem to be intent on pointing out all the different factors that can affect the D-plane for some reason. I think we all know that shots hit away from the sweet spot will not fly exactly as intended. But, if we are able to better understand and control the Dplane that creates a particular shot, the ball will finish closer to target than otherwise.

If I create the D-plane for a perfectly straight shot to go in the hole, but I hit the ball on the toe and it finishes 2 yards short and 2 yards right of the hole, I'm still sitting pretty with a birdie putt. Remove the understanding of the Dplane, and now I have hit a pull hook with the same club and hit it off the toe, so I'm burried in a bunker, over the green with no chance to get it up and down.

You keep asking, "How does this (whatever your current needle is) affect the D-plane?"

The answer is, it doesn't.
 
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softconsult

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"Remove the understanding of the Dplane, and now I have hit a pull hook with the same club and hit it off the toe".

That presumes you didn't know how to hit a straight shot pre-D Plane knowledge. Obvious that pre and post D-Plane people figured out to hit good golf shots.
 
duckjr78

duckjr78

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softconsult said:
"Remove the understanding of the Dplane, and now I have hit a pull hook with the same club and hit it off the toe".

That presumes you didn't know how to hit a straight shot pre-D Plane knowledge. Obvious that pre and post D-Plane people figured out to hit good golf shots.
Click to expand...

I had no flippin' idea how to hit a straight golf shot until 2010. Armed with D-plane understanding when I took up the game 17 years ago, I coulda' been a contenda'.

That is why I don't understand SteveT's rational. For 16 years, the shots that I knew I had put a good swing on were pull hooks with my irons. I was long and left on many holes. And those were my good shots. When I hit it poorly, look out. Now, my poor shots tend to find the green and my good ones are flagged.

SteveT seems to be arguing that because there are so many other factors that affect ball flight, D-plane knowledge is not as important as we are saying it is. I, for one, don't think he could be any more wrong. I believe that because there are so many factors, it is of vital importance to understand the most important of these, which, to me, has been proven to be the D-plane.

SteveT seems to be of the opinion that because there are so many other factors that influence movement and transportation, we should disregard our knowledge of the wheel.
 
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softconsult

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"That is why I don't understand SteveT's rational. For 16 years, the shots that I knew I had put a good swing on were pull hooks with my irons. I was long and left on many holes. And those were my good shots. When I hit it poorly, look out. Now, my poor shots tend to find the green and my good ones are flagged."

It's great that D-Plane has helped you so much. I would simply offer this thought. Apparently, you simply could not figure out what you were doing over those 16 years. Information was available in the form of books, lessons, etc. that could have helped you straighten out your golf swing.

I mean, if you are hitting pulls it should be intuitively logical that the face is pointing left at impact and if it's not curving then the path is also going left. Not trying to be overly critical, but I'm sure I figured that out early on based on some sort of early 60's book, or books I read in my late teens. That sure doesn't mean I didn't hit some pulls and slices, but I knew what was happening.

It's not like people can't be good golfers, unless they understand the D-Plane.
Good golfers have figured out how to get the job done. D-Plane should help, but it's
not a panacea.
 
duckjr78

duckjr78

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softconsult said:
"That is why I don't understand SteveT's rational. For 16 years, the shots that I knew I had put a good swing on were pull hooks with my irons. I was long and left on many holes. And those were my good shots. When I hit it poorly, look out. Now, my poor shots tend to find the green and my good ones are flagged."

It's great that D-Plane has helped you so much. I would simply offer this thought. Apparently, you simply could not figure out what you were doing over those 16 years. Information was available in the form of books, lessons, etc. that could have helped you straighten out your golf swing.

I mean, if you are hitting pulls it should be intuitively logical that the face is pointing left at impact and if it's not curving then the path is also going left. Not trying to be overly critical, but I'm sure I figured that out early on based on some sort of early 60's book, or books I read in my late teens. That sure doesn't mean I didn't hit some pulls and slices, but I knew what was happening.

It's not like people can't be good golfers, unless they understand the D-Plane.
Good golfers have figured out how to get the job done. D-Plane should help, but it's
not a panacea.
Click to expand...

It's not a panacea and plenty of amazing players have figured it out without this knowledge written down somewhere. But when you make a swing that is as sweet as you know how and you get your path straight at the flag and clubface dead at the flag and the ball doesn't go at the flag, it doesn't make sense. It becomes maddening. So, using the old ball flight laws, I would adjust my path. Little did I know the clubface has been the culprit the entire time.

Also, had I known about swinging left when starting, I wouldn't have developed the little flip I have fought for entire time as well.

But I know now, and that is what matters. Once my son grows up and I have a bit more time to practice, I'll start my training for the Senior Am. Only 18 years left!
 
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cwdlaw223

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SteveT-

Is the axis tilted with the off center hit or is there really sidespin? Trackman says that side spine doesn't exist. I know that your photo wasn't three dimensional and I suspect a three dimensional view would show the axis tilting but I want to be sure.
 
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