In my quest to hit driver farther, I've reviewed this discussion, which is great, and found this article. The original work was published by Tutelman (somewhat controversial guy but seems very open about his research and inviting others to participate) in 2007 and updated in 2011. It is from a fitter's point of view. An excerpt that coincides with Erik's Instruction and Discussion:
Angle of attack
This is not a club design issue, but a golfer-training issue. It requires learning how to hit the ball on the upswing, which implies placing it further forward in the stance and teeing it higher. It works because you can increase the launch angle without increasing loft. Every degree of angle of attack gives a degree of launch angle with no effect on spin!
How much can you gain through angle of attack? I don't have a lot of data on what golfers who try to hit up on the ball accomplish. But here are a couple of ways to estimate an answer:
- Long drive data: These guys have a lot of athletic ability, plus a strong motive to learn an upwards angle of attack; they need both in order to compete. So we can look at the actual data from the high finishers in elite long drive competition and get an idea of the AoA that they manage. I plugged the launch data from two drives from the 2006 ReMax finals into TrajectoWare (they were drives Jason Zuback and Erik Lastowka), and worked backwards to the loft and angle of attack that they must have used. In both cases, the angle of attack was under 1º. I was surprised it was so small.
- More long drive data: Tom Wishon points out that "the long drive competitors can use a head with 5-6 degs and still generate a launch angle of 11-12 degs." Even allowing for a reasonable shaft bend increasing the loft by 3º, this is still 3 or 4 degrees of upwards angle of attack.
- Geometry: If you can somehow tee up the ball 6" farther forward in your stance, the natural arc of a 45" driver will allow hitting up on the ball by an angle of 8º. That is a lot. It will also involve teeing the ball up almost a half inch higher. This is probably an extreme upper limit to angle of attack, nowhere near available to most of us.
AND THEN, OFF TOPIC, yet extremely interesting
Making use of vertical gear effect is a combination of the golfer's swing and a driver fit to that swing:
- The golfer must have a repeatable impact high on the clubface. High enough to get maximum benefit from the gear effect, but still low enough not to lose COR.
- The golfer can be helped a little by a low center of gravity for the clubhead. A low CG increases the range and efficacy of hitting "above the center".
- Shaft flex. (Finally, something we clubmakers can relate to easily.) Dana Upshaw has reported an anecdote involving a long drive champion getting much better runout after landing after going to a flexible-tip shaft (generally considered high-launch and high-spin) and a lower loft in the clubhead. The explanation Dana gives is that the clubhead was more free to rotate and exercise vertical gear effect with the tip-flexible shaft. I'm not sure if I agree; my inquiry suggests that tip stiffness has much less impact on vertical gear effect than Upshaw reports. But Dana's data is what it is, and I can think of no other explanation for it.
There are other factors sometimes cited as ways to get high launch and low spin which, unfortunately, do not do what the proponents would have you believe:
- Head weight distribution - A low center of gravity is reputed to give a high launch angle without adding spin. Vertical gear effect is a technical explanation for why that should be. A low CG enhances the vertical gear effect as noted above.
Oh yeah. There's also the possibility of raising the launch angle by moving the center of gravity back away from the face. That definitely works to raise the launch angle. But it has the same effect as loft -- increasing the spin as well -- so it's not helpful this time.
- Shaft flex - Stiff shafts, and especially tip-stiff shafts, have a reputation for being low spin. (Also low launch. That is not what we want right now, but remember that because it's important.) The biggest launch effect of shaft flex is on the dynamic loft of the clubface. So if you reduce spin, you also reduce the launch angle. The only valid use of shaft flex to reduce spin without lowering launch is as Dana Upshaw revealed; use a tip-flexible shaft in conjunction with a lower loft clubhead to take maximum advantage of gear effect. The shaft flex will increase the loft, the lower-loft clubhead will get the loft back down, and a high-face hitmight get less backspin because the shaft will allow more clubhead rotation and the resulting gear effect. (I qualify it with "might", not "will". My analysis does not support the substantial effect that Upshaw noted. So I accept his data with considerable reservation.)
Edited by Mr. Desmond - 3/6/13 at 10:19am