Understanding impact

[tongzilla]

Please answer if you are pretty sure of the facts and not speculating. I'm sure this has been discussed before but I still don't quite understand the topic fully.

During impact, can the clubface twist open or close? I know the golfer cannot influence the impact dynamics during impact, but I'm just asking if the clubface can twist open or close during impact.

What is the cause of hook spin when the ball is struck towards the toe of the clubhead? Is it caused by the clubface twisting (open) during impact or something else?

 

[Jim Kobylinski]

Please answer if you are pretty sure of the facts and not speculating. I'm sure this has been discussed before but I still don't quite understand the topic fully.

During impact, can the clubface twist open or close? I know the golfer cannot influence the impact dynamics during impact, but I'm just asking if the clubface can twist open or close during impact.

What is the cause of hook spin when the ball is struck towards the toe of the clubhead? Is it caused by the clubface twisting (open) during impact or something else?

The clubface twists based on where you hit the ball in relation to the exact sweetspot. The hook or fade spin created from off center hits is due to gear effect. More with a driver and less with the irons.

 

[Matt Bryda]

Tong,
Ever hit a shot and feel the club twist in your hands? Don't you think some of the
twist feel could be caused by contact away from the CoG of the club head?

 

[birly-shirly]

Absolutely, the clubhead can twist. Whack most things off-centre at 100mph and they'll twist - clubheads are no different.

Hook spin from a toe hit is an indirect consequence of the clubhead twisting. The clubhead twists around its centre of gravity. If the CoG is set back away from the face, then when the clubhead rotates, the whole clubface will move laterally across the back of the ball. It's that lateral movement of the clubface that imparts the hook spin.

If you can lay hands on a copy of The Search for the Perfect Swing, there's a very good discussion there.

 

[dschultz6072]

What do you "feel" more? Pure shots or mishit shots?

 

[tongzilla]

Tong,
Ever hit a shot and feel the club twist in your hands? Don't you think some of the
twist feel could be caused by contact away from the CoG of the club head?

I know the club does twist when you make an off center hit. But I wonder does it twist- 1) during impact, 2) enough during impact to have an effect on ball flight, 3) if answer to last question was no, then what's causing the side spin.

 

[cwdlaw223]

There's no side spin. Only spin and axis tilt. Impact is 1/2000th of a second. There has to be some movement of the clubhead during this time interval. Gear effect most certainly affects ball flight and IMO, can "override" the face to path numbers you see on Trackman. How much? That's some heavy science. There are a number of different variables affecting impact (or programming the ball for flight) such as gear effect, launch angle, attack angle, face angle, attack angle, clubhead speed, ball speed, dynamic loft, etc. Gear effect, face angle and resultant (3D) path are clearly the biggest factors with respect to tilting the axis.

 

[Brian Manzella]

The IMPACT INTERVAL is .00045 second

The BALL gets its marching orders from the clubhead near the middle of the interval, around .00023

The CLUB can twist during the interval.

The BALL spin axis is programmed from Clubface Normal near the middle of the interval (which will be different than Clubface Normal at first touch) and the 3D path of the center of mass of the clubhead.

 

[tongzilla]

The IMPACT INTERVAL is .00045 second

The BALL gets its marching orders from the clubhead near the middle of the interval, around .00023

The CLUB can twist during the interval.

The BALL spin axis is programmed from Clubface Normal near the middle of the interval (which will be different than Clubface Normal at first touch) and the 3D path of the center of mass of the clubhead.

I'm literally getting orgasms from this answer.

Let's establish more facts...

Assuming on center hit, that would by definition mean no twisting during impact. So the 3D face direction (taking into account both direction and loft) would remain the same at 0.00045s and at 0.00023s. And the 3D path would also be the same during this period give the massive arc relative to impact interval.

Either way, trackman measures the face and path at 0.00023s right?

Also impact interval is ~0.00045s for putter/9iron/driver? I'm asking because I wonder how trackman knows which part of the impact interval to use for its face/path measurements. I suspect it's not a pure measurement and has some formula/calculation involved.

Edit- one more way to look at it is, if gear effect is factored into the d-plane, it's hard to imagine how trackman can make a pure measurement on d-plane without some additional calculation.

 

[Kevin Shields]

Take a cold shower

 

[tongzilla]

To what extent does the D-plane take into account misaligned COGs?

To be more specific, at mid-impact interval (which I assume to be point of maximum deformation of ball), is the clubface normal the top of the D-plane even if impact was off centre?

EDIT- Another thought/question- with no wind etc, will the entire ball flight from launching off the ground to landing lie on the D-plane? Seems like it would if everything is just a % of the top and bottom directions of the D-plane.

 

[birly-shirly]

[...]

EDIT- Another thought/question- with no wind etc, will the entire ball flight from launching off the ground to landing lie on the D-plane? Seems like it would if everything is just a % of the top and bottom directions of the D-plane.

Yes - on perfectly straight shots. Otherwise, no.

 

[birly-shirly]

[...]
Either way, trackman measures the face and path at 0.00023s right?

Also impact interval is ~0.00045s for putter/9iron/driver? I'm asking because I wonder how trackman knows which part of the impact interval to use for its face/path measurements. I suspect it's not a pure measurement and has some formula/calculation involved.

Edit- one more way to look at it is, if gear effect is factored into the d-plane, it's hard to imagine how trackman can make a pure measurement on d-plane without some additional calculation.

D-plane is a model linking impact conditions and ball flight. TM isn't directly measuring path and face angle. Measured ball-flight (including spin) is used to back-fill or flesh out what can't be measured directly and with sufficient accuracy, including face angle. But the point isn't the method, the point is the validated accuracy - which I believe to be good.

Off-centre impacts, as far as I understand it, require some skill and experience on the part of the TM operator to correctly interpret the data.

 

[wulsy]

If the CoG is set back away from the face, then when the clubhead rotates, the whole clubface will move laterally across the back of the ball. It's that lateral movement of the clubface that imparts the hook spin./QUOTE]

Birls, isn't it the ball which , moves laterally along the clubface?

 

[tongzilla]

some people say D-plane is all the programming the ball 'knows' for its ball flight (ignore wind etc). Even if D-plane sort of takes into account gear effect it still doesn't take into account the amount of friction between clubhead and ball which also significantly influences ball flight. I may be wrong, but wasn't D-plane originally just 2 vectors- the clubface normal and the instantaneous path of the clubhead during impact...now we have to talk about COG etc to make D-plane "work".

 

[Frans@France]

...it still doesn't take into account the amount of friction between clubhead and ball which also significantly influences ball flight.

Yes, it does. Go to the Technical Appendix - Section 3 and enjoy reading about the forces of friction...

I may be wrong, but wasn't D-plane originally just 2 vectors- the clubface normal and the instantaneous path of the clubhead during impact...now we have to talk about COG etc to make D-plane "work".

Yes, you are wrong. When Jorgensen defined his d-plane and tried to "catch" the math behind it he understood completely that the math would be much more complicated if he would had to involve mishits. So in order to have a go at it he stated that

In considering what happends when the clubhead meets the ball, we have assumed that the ball makes contact with the center of the clubface, at the "sweetspot" For such a shot there is no torque about the shaft of the club to produce.....

 

[Frans@France]

EDIT- Another thought/question- with no wind etc, will the entire ball flight from launching off the ground to landing lie on the D-plane? Seems like it would if everything is just a % of the top and bottom directions of the D-plane.

EUh..why would that ever be the case? The D-Plane is descriptive of the collision between the clubhead and the ball NOT about the aerodynamics of the golfball

 

[tongzilla]

EUh..why would that ever be the case? The D-Plane is descriptive of the collision between the clubhead and the ball NOT about the aerodynamics of the golfball

I did some reading since that post and figured out that the D-plane is supposed to predict the initial launch of the ball before air resistance causes ball to slow down and fall.

 

[Frans@France]

I know the club does twist when you make an off center hit. But I wonder does it twist- 1) during impact, 2) enough during impact to have an effect on ball flight, 3) if answer to last question was no, then what's causing the side spin.

(T)His site has been mentioned more then once (Dave Tutelman) Link: All about Gear Effect
Very nice resource about this kind of things

 

[mgranato]

What do you "feel" more? Pure shots or mishit shots?

My pure shots have an almost indescribable feel of weightless nothingness to them. With a pure drive, you virtually don't feel the ball.

The opposite I can feel in my teeth.