Ohessa kaksi juttua gear efektistä.
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Eka juttu:
The Myth that is Gear Effect – Cause and Antidote
– by Dr. Leon Seltzer
Gear effect is a phenomenon which is the result of off-center contact between the clubface and the golf ball. When present, gear effect causes a golf ball which has been contacted off the center of the clubface to spin in such as way as to curve back in the opposite direction from which it was initially deflected. Some people seem to believe that gear effect is a result of the bulge (convex curvature) built into the face of drivers and fairway clubs. As will be discussed below, bulge is actually the antidote for too much gear effect. Properly applied, bulge keeps gear effect under control thereby keeping many golf balls out of the rough, trees and hazards.
On an off-center hit, the clubface will either open or close depending on whether contact occurs toward the toe or heel. The twist (torque) resulting from the off-center contact causes the clubhead to rotate about its center of gravity (c.g.). For example, in the case of a toe hit for a right-handed golfer, as a result of off-center contact, the clubhead will rotate clockwise. Where the c.g. is well behind the face, as in a driver or fairway club, the contact point on the clubface will not only move back, but it will also swing to the right across the back of the ball. Under these conditions the interaction between the clubface and the ball is much the same as the action that takes place between two meshed gears. Hence the term gear effect-as one turns in one direction, the other will rotate in title opposite direction. The amount of gear effect depends on the distance that the c.g. is located behind the clubface. In the case of an iron because of its relatively thin face, the c.g. of the clubhead is near the face and any gear effect will be quite small. In most cases it will not be noticeable. For a driver or fairway club, however, where the c.g. can be quite some distance behind the clubface, the effect is significant.
If the clubface of a driver (one which has its c.g. well behind the clubface) were perfectly flat, gear effect would not only reduce the spin caused by the opening clubface, but it might also completely overcome it. This could result in an uncontrollable hook from toe hits and the opposite for heel hits. Gear effect is not necessarily a user-friendly phenomenon. However, gear effect can be controlled (and actually be made to help the player on off-center hits) by the application of the proper amount of face curvature, called bulge, in the design of drivers and fairway clubs. This is the reason for the use of the word antidote in the title of this article. The antidote for excessive gear effect is clubface bulge. The radius of the bulge curvature which is built into these clubheads depends on the distance that the c.g. is behind the clubface. Persimmon and laminated maple heads have their c.g.’s well behind the face and therefore require a considerable amount of face curvature (a smaller radius) to counteract gear effect stainless steel metal woods, on the other hand, have c.g.’s closer to the face and require less bulge (a larger radius). In fact, some metal woods have too much bulge built into the design considering the c.g, location, and as a result the ball may start too far off line on off-center hits for gear effect to bring the ball back to the fairway.
The acceptable weight for drivers is approximately 200 grams (just over 7 ounces). It has been determined that during a direct impact the average force applied to the face of a driver traveling 100 miles per hour is nearly 1500 pounds. This means that the peak force must be close to 2000 pounds. The face of a driver made of stainless steel must have a face thickness of about one-eighth inch thick (0.125 inches) in order that it may withstand this enormous impact force. Some long hitters develop clubhead speeds close to 130 miler per hour and this will increase the impact force by thirty (30) percent. In order to keep a stainless steel driver with a large head within acceptable weight limits, it is necessary that the rest of the shell that goes to make up the clubhead be extremely thin. The shell thickness (crown and sides) is actually in the neighborhood of only one-thirty-second of an inch (0.030 inches). With the shell being this thin, and therefore light in weight, the c.g. of the large stainless steel driver is relatively close to the clubface and less gear effect is realized on off-center hits. Because of bulge, there may not be enough gear effect to bring the ball back to the fairway. The type of metal wood that has just been described should have a minimum of bulge built into the face. Clubheads made of materials which are lighter than stainless steel (such as aluminum, wood or graphite) can and do have the c.g. further back. The thick-walled aluminum driver is the only metal golf club which can have its c.g. located well behind the clubface. This, in turn, makes it possible to end up with a controlled amount of gear effect for the benefit of the golfer.
The bulge which is incorporated into a well designed club is the arc of a circle whose radius may be anywhere from eight to fourteen inches. The amount of bulge to be built into a particular clubhead should be determined after the c.g. location has otherwise been established. With the availability of modem mechanical ball striking machines it is not difficult to optimize this facet of golf club design.
It would be well to point out that all of the above is based on the premise that the clubface is perpendicular to the swing path as impact is reached. If the face of the club is open or closed prior to impact, then an additional source of side spin is introduced and gear effect may not occur.
Toka juttu:
A feature built into modern drivers and fairway woods intended to reduce the amount of slice or hook when the ball is propelled. Here are the details:
The face of a driver or fairway wood is designed with a subtle convex curve from toe to heel. The clubhead is weighted to keep the center of mass (yellow circle) well behind the clubface. This curve tends to compensate for sidespin that would otherwise result from striking the ball either too close to the heel or too close to the toe.
Here’s how it works. (You had better sit down first.)
Let’s say a right-handed golfer makes contact with the ball very near the toe, as in our first illustration. We’ve removed the club shaft for simplicity, leaving that small black circle at the bottom of each diagram.
Now, notice how the center of mass of the ball is not centered with the center of mass of the driver with respect to its direction of travel.
Contact by the ball with the clubface above the path of travel causes an opposing force not centered with the driver’s center of mass (big black arrow pointing right).
If you are having difficulty understanding the rotation, imagine that somebody pushes you. If that person pushed your chest, you’ve simply move backwards. But if that person shoved your right shoulder instead, your body would rotate around to the right a bit.
The fact that the big black force arrow does not point directly to the center of mass of the driver means that the driver will want to rotate in response. The club will pivot clockwise around it’s center of mass (green arrow).
The club face itself slides in the direction of the red arrow. But because the clubface of a gear-effect club is curved, it can maintain contact with the ball as the clubface slides sideways. Friction between the face and the ball act as gears meshing together.
This imparts a counter-clockwise rotation in the ball around its center of mass (indicated by the blue arrow).
Now your intuition is still correct. The ball being hit off the toe will certainly be propelled at an angle (towards the upper left of our diagram) rather than straight to the left. But the gear-effect rotation of the ball will cause it to hook during flight, making it curve back (somewhat) towards the center of the fairway.
The actual ability of gear effect to correct for slice is limited to off-center ballstrikes when the clubface is square to the line of travel at impact, as in our top illustration.
Gear effect cannot correct slice resulting from an open face at impact, nor an outside-in swing.
Gear effect is also not possible with bladed irons because the clubhead is too thin to get the center of mass as far behind the ball as would be required to induce gear effect. Besides, the face of an iron is flat and the concept still wouldn’t work.
Pari muuta linkkiä:
http://www.ottawagolf.com/swingsync/geareffect.htm
http://www.bs-sports.co.jp/english/basic_of_golf_club/basic_of_club_5.html
Lue lisää: gear efektistä