I think probably that the toe 'up' at the start of the swing is due to the curvature of the shaft produced by the inertia of the club head as the shaft is driven downward. With a pure 'swinger' I doubt there is very much of this. At the bottom of the swing when the velocity is high there are two forces attributable to the centrifugal force on the club head - an axial tension load on the shaft produced by the mass of the club head and a toe down bending moment produced by the fact that the cg of this mass is offset from the centerline of the shaft. Because the club head cg is both toward the toe and behind the shaft axis (somewhere in the body of the head) this moment has both toe down and higher loft components. This is a very different load applied to the shaft than from the inertial of the club head during the downswing and will have a much higher oscillation frequency than the shaft fundamental, so it is possible for it to have been driven toe down and oscillated to a toe 'up' position at impact. You can see this in TT Shaft Lab data, btw.
We are defining the cycle the same way.
Regards,
Alan
At 09:40 AM 1/2/03 -0500, you wrote:
Royce and Alan The centrifugal force is certainly part of the Toe down deflection at impact. Since toe down deflection is dependent on club head speed this would make the better players with the high clubhead speeds have greater toe down deflection ( opposite True Temper results ). What I described earlier is the other component of toe down defection at impact. As can be seen in all of the Shaft Lab data there is initially a toe up deflection at the top of the swing. This deflection along with the time from the start of the down swing to impact gives the shaft time to go through 1/3 to 2/3 cycle of its natural frequency resulting in some degree of toe down deflection. This resulting defection is a function of how much the club is loaded at the top of the swing to produce the initial toe up deflection. Herein lies the difference between the good player and the others.Allen, I follow your 1/2 cycle argument and our only difference is in the definition of the cycle. As an example, if I mount the club in a frequency analyzer and pull the head down and hold it in that position before releasing it, it dose not complete a full cycle until it returns to the max down position again. A 1/4 cycle would bring it to shaft straight with max upward velocity. As in the swing I do not consider the loading of the shaft as part of the cycle because it is not a function of natural frequency or spring properties. ----- Original Message ----- From: "Royce Engler" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Tuesday, December 31, 2002 10:07 PM Subject: FW: ShopTalk: shaft flex v.s. frequency > Alan said.... > > <snip> > As far as 'toe bob' goes I am not sure that I know what you mean by > this. I think it is probably the toe down deflection of the club head > caused by the centrifugal force on the offset cg of the club head. This > force increases very rapidly near impact (it's proportional to the square > of the head velocity) and is resisted mostly by a relatively short section > of the shaft near the tip. > > </snip> > > As I understand it there are two forces acting here, both the result of the > CG of the clubhead being offset from the centerline of the shaft. First > there is a moment working to align the CG of the clubhead with the shaft, > which has the effect of rotating the trailing edge of the clubhead under. > This has the effect of increasing the loft of the club as it goes through > the ball, and acts in the plane of ball flight, commonly called dynamic > loft. According to Tom Wishon's book, moving the CG 1/8" further back from > the face will add about 7 feet to the trajectory. > > What is commonly called toe bob is the result of a similar, but orthogonal > moment trying to align the CG of the club with the shaft in the direction > from the toe to the heel. The net effect is to rotate the toe of the club > around the CG, which bends the tip towards your toes i.e. in a plane that is > orthogonal to the plane of ball flight. This is the effect that causes > dynamic lie angle to be different from static lie angle. > > All of which combines to make it amazing to me that any of us can ever hit > the ball "on the screws".... > > Royce >
