At 08:56 AM 10/30/2010, Don M wrote:
There is a lot of interesting stuff in there. I do not understand
#6. Anyone?
OK, I'll take a shot at it. Not sure this is what they had in mind,
but it makes geometric sense...
Think about the swing plane. For purposes of this discussion (and,
frankly, for all practical purposes, even though that's not usually
the way we think about it), the swing plane is the plane containing
the clubhead during its approach to the ball. And, with anything but
a pathological swing plane, all the head positions (measured at the
clubhead's CG) are in a plane for the last 100msec or so of the downswing.
How do we find the direction of that plane. It is the direction the
clubhead is moving at the bottom of the arc defined by those clubhead
positions approaching impact. It's the tangent to the arc at the
bottom of the swing.
IF IMPACT OCCURS AT THE BOTTOM OF THE ARC, a couple of things are true:
(1) The clubhead is moving in the same direction as the
direction of the swing plane.
(2) The angle of attack is zero.
This is just geometry. Think about it for a while. It's essential to
visualize this before going on to Trackman's Fundamental #6.
OK, what happens if we HIT UP THROUGH THE BALL, like a driver on a
high tee? That's a positive angle of attack. Getting back to the
geometry of the swing plane, we are now getting impact after the
bottom of the arc. (Let's call this "late impact" for this
discussion.) That is geometrically essential to get a positive angle of attack.
Well, if we are past the bottom on the vertical direction (positive
angle of attack), we are also past the swing plane direction in a
horizontal plane as well. For a right-hander, the clubhead is past
the swing plane direction and traveling to the left. So, if we want
the clubhead to be going down the line with a positive angle of
attack, we have to adjust the swing plane to the right, in order to
oppose the leftness due to late impact.
The same argument applies to hitting down through the ball. A
negative angle of attack implies "early impact" -- impact before the
bottom of the arc. So the clubhead, in addition to traveling
downwards, is traveling to the right -- inside to out. We need an
outside-in swing plane to counteract this, for the clubhead to travel
straight down the line at impact.
That's my take on it. I believe it is also Trackman's intent. I ran
their numbers, using this explanation, and they're pretty close.
Also, a question I've had for a long time is, <all else being
equal>, does a straight ball go farther than a curving ball? We
have been conditioned to "know" that draws go farther. Because they
fly lower and/or run out more. But, if a person is fitted so that
his draw starts with the same launch angle and other launch numbers
as a straight hit, wouldn't the straight hit actually go farther?
In other words, the only reason a draw or pull goes farther and a
push or fade goes shorter than a straight ball is because of the
change in effective loft at impact? And if you make that effective
loft equal across all cases, the straight ball HAS to go the
farthest. This is what I think I've seen in a seat of the pants way.
I agree completely. I know Roy has already agreed. BTW, I discussed
this on my web site several years ago; see
<<http://www.tutelman.com/golf/design/swing4.php#drawRollsMore>http://www.tutelman.com/golf/design/swing4.php#drawRollsMore>.
Cheers!
DaveT
