Lately I've focused on the concept of 'swinging left' in order to hit the ball straight according to the studies and reseach the people at Trackman have found.
For new readers, provide that your clubface is square to the target at impact/seperation, in order to hit the ball and have it fly straight it, the club path needed depends on the angle of attack.
If the angle of attack is downward (or negative), then the golfer needs to 'swing left.' If the angle of attack is upward or positive (which would only happen with a driver), then the golfer needs to swing out to the right.
However, because of the spin axis on the ball, the amount of swinging left differs between irons and the woods. With woods it's simple. If the angle of attack is -2*, then the golfer needs to swing left 2*. However if a golfer uses a 4-iron and swings downward by -2*, then they need to swing left by HALF of that amount, which is -1*. If a golfer hits up on the driver by 3*, then they need to swing out to the RIGHT by 3*. And if a golfer hits down on an 8-iron by -5*, then they need to swing left by 2.5*.
AS OF NOW, my current thinking is this GREATLY applies to certain lies a golfer may find on the course. I haven't tested this out with Trackman, and I'm not even sure Trackman can research this, but I have done some research of my own and I keep getting the same results.
BALL ABOVE YOUR FEET = SWING LEFT
UPHILL LIE = SWING LEFT
BALL BELOW YOUR FEET = SWING RIGHT
DOWNHILL LIE = SWING RIGHT.
Playing golf in Northern Georgia, there is a lot of hilly terrain and a lot of time to practice these shots. Every time I try to hit a straight shot with these lies, the only way I could do that is if I followed the statements I capitalized above. Granted, I may have some flawed thinking or execution going on here, but as of this moment my thought process is this:
1. Ball above the feet or an uphill lie the clubhead is likely to come into contact with the ground well before the 'low point.' I believe this creates a steeper angle of attack. Thus you need to more to the left to hit the ball straight. Ever since I was in high school, these types of lies usually produce big draws/hooks. This would make sense because if I take a normal swing with a normal path I am actually swinging inside-to-out of the 'true path', which produces a hook. And to compound the issue even more, I would generally aim more to the right and swing more to the right, producing a bigger hook.
2. Ball below the feel or a downhill lie, the clubhead is likely to come into contact with the ground well after or closer to the 'low point.' Thus it's likely to flatten out the angle of attack (you won't hit up with an iron or a fairway wood or a hybrid, but you won't hit with as much of a downward strike either). These are shots that I almost always hit a big fade/slice with, probably because the 'true path' is more square to the target and I'm swinging too far left of the 'true path' causing a left-to-right spin.
So I would try it out for yourself and see what you think.
Of course, there's trying to understand the difference of 'swinging left' versus coming 'over the top.'
I struggled with this, and then Jeff Mann (http://perfectgolfswingreview.net) helped clear up this concept.
To swing left of the target, one simply reorients the baseline of the inclined plane a few degrees leftwards and one then traces the Straight Plane Line (new plane line), which is now a few degrees left of the ball-target line, as per the usual technique - thus generating the standard in-to-square clubhead arc (relative to the new plane line).
So basically the clubface is pointed at the target at address.
But the golfer just moves the incline plane to the left. Here again is the Jeff Evans video on the incline plane angle.
So basically you just move the incline plane angle in Jeff's video (albeit an imaginary one in real life) just a few degrees left if you want to hit a straight shot.
But remember this, according to a Brian Manzella post where he did some research on Trackman (http://3jack.blogspot.com/2008/12/post-of-year-by-brian-manzella.html), a 6-iron needs about -3.5* Angle of Attack for optimal height. So if you hit down by -3.5* with a 6-iron, you need to swing left by 1.75*. In case you didn't know, that is VERY miniscule. Now Brian did mention that a LW needs an angle of attack around -8*, but that's swinging left by 4*, which still is not a big amount of swinging left. Remember, coming over the top means that the club is getting above the plane on the downswing. 'Swinging left' just 'moves the swing' to the left a slight amount and the club never gets above the plane on the downswing.