Calculating optimal physical driver loft

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Clubdoctor
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Calculating optimal physical driver loft

Post by Clubdoctor » Mon Jul 02, 2007 11:17 pm

I've only played around with the program for about 20 minutes, so maybe I've missed something.

I understand dynamic loft and I'm starting to understand (I think) how I might use the program to optimise the dynamic loft that any player needs to maximise carry distance.

Where I'm struggling at the moment is that, having identified the optimum dynamic loft, I can't quite see how I convert that to a physical static driver loft, which I obviously need to do, given that, as far as I am aware, all OEMs and component suppliers measure their lofts statically ....
Richard Kempton

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Re: Calculating optimal physical driver loft

Post by dtutelman » Tue Jul 03, 2007 8:00 pm

Clubdoctor wrote:I understand dynamic loft...
Where I'm struggling at the moment is that, having identified the optimum dynamic loft, I can't quite see how I convert that to a physical static driver loft, which I obviously need to do, given that, as far as I am aware, all OEMs and component suppliers measure their lofts statically
Hi, Richard!
You're absolutely right. And that's why a launch monitor is such a valuable clubfitting tool. If you're going to work from impact parameters, you're stuck with doing relative numbers "all other things being equal", not absolute numbers.

Let's look at all the things you would have to take into consideration in order to convert the supplier's rated loft into the dynamic loft -- which is the only thing the ball knows when it is struck:
  1. The tolerance between the rated loft and the actual loft for this specimen. That is at least +- 1 degree, and sometimes more.
  2. The difference between the rated loft and the designed loft. This is a "dirty little secret" in the industry; I call it "vanity lofts". Unfortunate, but real for some suppliers -- and not a problem for many suppliers.
  3. Shaft bend. This depends on the golfer's swing, as well as the flex and bend profile of the shaft.
  4. Where on the clubface the ball is struck. On modern drivers, there could easily be 8* of loft difference between ball-on-face low on the face and high on the face. You might determine this with impact tape. But, if the tape shows you that the golfer is inconsistent, you're fitting to an average that won't necessarily reflect any given swing.
  5. Wrist bend at impact. This can add (or occasionally subtract) a surprising amount of loft. I often see seniors hitting a 10* driver much too high. I know they're not doing it with shaft bend. There might be a little vanity loft or high-teeing at work, but I'm sure that wrist bend is adding more than 5* of loft.
As a clubfitter, you can deal with items #1 and #2 using a specs gauge. If you go with impact tape for #4, you can use the specs gauge to measure at the impact point instead of the middle of the face. #3 is harder to quantify; my NeuFinder profiling work is aimed at deciphering this riddle, but it's a long-term goal. And #5 can be a big issue with some golfers, and is very hard to measure.

I wish I could give you a better rule for this, but I can't.

Good luck,
DaveT

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Re: Calculating optimal physical driver loft

Post by Clubdoctor » Wed Jul 04, 2007 1:40 pm

Hi, Richard!
You're absolutely right. And that's why a launch monitor is such a valuable clubfitting tool. If you're going to work from impact parameters, you're stuck with doing relative numbers "all other things being equal", not absolute numbers.

Let's look at all the things you would have to take into consideration in order to convert the supplier's rated loft into the dynamic loft -- which is the only thing the ball knows when it is struck:
  1. The tolerance between the rated loft and the actual loft for this specimen. That is at least +- 1 degree, and sometimes more.
  2. The difference between the rated loft and the designed loft. This is a "dirty little secret" in the industry; I call it "vanity lofts". Unfortunate, but real for some suppliers -- and not a problem for many suppliers.
  3. Shaft bend. This depends on the golfer's swing, as well as the flex and bend profile of the shaft.
  4. Where on the clubface the ball is struck. On modern drivers, there could easily be 8* of loft difference between ball-on-face low on the face and high on the face. You might determine this with impact tape. But, if the tape shows you that the golfer is inconsistent, you're fitting to an average that won't necessarily reflect any given swing.
  5. Wrist bend at impact. This can add (or occasionally subtract) a surprising amount of loft. I often see seniors hitting a 10* driver much too high. I know they're not doing it with shaft bend. There might be a little vanity loft or high-teeing at work, but I'm sure that wrist bend is adding more than 5* of loft.
As a clubfitter, you can deal with items #1 and #2 using a specs gauge. If you go with impact tape for #4, you can use the specs gauge to measure at the impact point instead of the middle of the face. #3 is harder to quantify; my NeuFinder profiling work is aimed at deciphering this riddle, but it's a long-term goal. And #5 can be a big issue with some golfers, and is very hard to measure.

I wish I could give you a better rule for this, but I can't
DaveT:

Pity.

I already routinely measure static driver loft (which eliminates points 1 & 2 above) and am usually able to get most golfers hitting on or close to face centre by adjusting MOIs and eliminating spine-induced impact variations.

Point (3) is more difficult, but the effective range of shaft bend any golfer is likely to achieve can be estimated within quite fine limits by having him or her hit two otherwise identical drivers (same loft & FA, length & MOI), but fitted with totally different shafts (X-flex, low launch vs. A or L flex, high launch).

If dynamic loft at impact is a function of Shaft Bend Angle (SBA) + A of A + Static Loft at Point of Impact, logically it should be possible to calculate any one of those parameters if the other three are known.


BTW, if I understand it correctly, Wishon's Trajectory Profiler assumes a fixed relationship between a specific static loft and launch angle for any given A of A and shaft bend angle - e.g. for a static loft of 12º, 0º A of A and 0º shaft bend angle, LA will be 1.6º lower and change by 1º for every 1º change in A of A or SBA; for a static loft of 8º, 0º A of A and 0º shaft bend angle, LA will be 0.9º lower and change by 1º for every 1º change in A of A or SBA. Is that correct?

So - and I should possibly post this on the 'Improvements' section of the forum - is it possible to enhance the program to allow clubmakers to try 'What If?' scenarios by entering values for LA, Static Loft, A of A, SBA and Dynamic Loft?

I should also have thought that possibly the golf ball used could affect LA and Spin Rates somewhat. I know for a fact that some golf balls give me significantly different launch angles from my wedges (4º or more measured indoors by noting the vertical impact points on a vertical net from the same launch point, in addition to taking LM readings) and I would expect some effect with drivers, albeit of a smaller magnitude.

Thus far, the above points - and what someone suggested with respect to low-spin driver heads - are the only quibbles I have with Trajectoware Drive. Otherwise, it's a great piece of software - AND it's FREE!!!
Richard Kempton

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Re: Calculating optimal physical driver loft

Post by dtutelman » Wed Jul 04, 2007 10:11 pm

Clubdoctor wrote:I already routinely measure static driver loft (which eliminates points 1 & 2 above) and am usually able to get most golfers hitting on or close to face centre by adjusting MOIs and eliminating spine-induced impact variations.

Point (3) is more difficult, but the effective range of shaft bend any golfer is likely to achieve can be estimated within quite fine limits by having him or her hit two otherwise identical drivers (same loft & FA, length & MOI), but fitted with totally different shafts (X-flex, low launch vs. A or L flex, high launch).
I agree with you on these points.

But you left out an unfortunate and very common swing characteristic -- wrist bend (bowing or cupping) at impact. I don't know of any way a clubmaker can readily measure this, though it can probably be estimated. For instance, with all the things you talk about measuring above, what is left is likely either very small or the wrist behavior of the golfer.
If dynamic loft at impact is a function of Shaft Bend Angle (SBA) + A of A + Static Loft at Point of Impact, logically it should be possible to calculate any one of those parameters if the other three are known.
IOW, static loft can be derived from A of A

BTW, if I understand it correctly, Wishon's Trajectory Profiler assumes a fixed relationship between a specific static loft and launch angle for any given A of A and shaft bend angle - e.g. for a static loft of 12º, 0º A of A and 0º shaft bend angle, LA will be 1.6º lower and change by 1º for every 1º change in A of A or SBA; for a static loft of 8º, 0º A of A and 0º shaft bend angle, LA will be 0.9º lower and change by 1º for every 1º change in A of A or SBA. Is that correct?
'Fraid not. SBA behaves like a change of static loft. AoA does not.
  • LA changes one-for-one with AoA. That's simple geometry and physics.
  • LA changes less than one-for-one with static loft. That is fairly well-known.
  • LA changes less than one-for-one with SBA. From some analysis I've done, it looks like a mix of static loft and AoA, but with over 90% of the effect looking like static loft.
A few years ago, I shared this analysis with Tom Wishon; I believe the discussion took place in the Spinetalkers forum. Apparently he came to the same conclusion, because his Trajectory Profiler software behaves as if a change of SBA is a change of loft. If you have the software, play with it a bit and you'll see that's the case.

If you want more on the analysis involved, look at the Help for TrajectoWare Drive. The page on "Understanding the Science" has links to a number of articles I've written, giving the equations the program uses to go between impact conditions and launch conditions.

One of the articles compares our behavior with the Wishon Trajectory Profiler in impact/launch behavior. They're pretty close -- too close for that to be a big difference between the programs. A much bigger difference is in the aerodynamics at high ball speeds and at high spin rates. TrajectoWare Drive is more accurate at high ball speeds, and Trajectory Profiler is more accurate at high spin rates. (One of our high-priority items for version 2 is to make the program deal with irons as accurately as it now deals with drivers -- basically a spin rate issue.)
So - and I should possibly post this on the 'Improvements' section of the forum - is it possible to enhance the program to allow clubmakers to try 'What If?' scenarios by entering values for LA, Static Loft, A of A, SBA and Dynamic Loft?
I guess I'm confused. I thought TrajectoWare Drive already does an admirable job of "What if?" scenarios; I use it that way all the time. As far as I know, its limitations are:
  • Spin rates over 4000rpm lead to loss of accuracy.
  • SBA, which we don't include. If you include it in dynamic loft, you'll be treating it correctly -- and exactly as Trajectory Profiler does.
Could you please explain better what you are looking for.
I should also have thought that possibly the golf ball used could affect LA and Spin Rates somewhat. I know for a fact that some golf balls give me significantly different launch angles from my wedges (4º or more measured indoors by noting the vertical impact points on a vertical net from the same launch point, in addition to taking LM readings) and I would expect some effect with drivers, albeit of a smaller magnitude.
We would like to account for ball differences some day. It is not our top priority for version 2. BTW, ball differences leading to different launch conditions are smaller than those due to aerodynamics. We expect to learn more about aerodynamics in order to deal with irons, making it likely that we will deal with ball-affecting trajectory differences before we deal with launch differences.

Thanks for the kind feedback.
DaveT

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