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本帖最后由 lupo 于 2014-1-31 19:20 编辑
Ski Bending
http://www.paullorenzclinics.com/#!ski-bending/c6l1
One often sees skiers from the chairlift locked on their edges but travelling relatively straight or on a very large arc. This is called “railing”, or “parking and riding”, and is unfortunately what a lot of skiers are out there doing. Some of these skiers may not be aware that they are railing and others may not be capable of skiing at a higher performance level. The ultimate ski performance requires the ski not only to be locked on the edges, but also requires the ski to bend or flex along its length progressively throughout the turn to create an arc that decreases in radius. Bending or “working the ski” is what all advanced skiers, ski instructors and professional racers are striving to achieve. So, how do you bend a ski and what is the purpose of doing this?
While the ski can, and does bend when it is skidding, steering, carving and railing - “bending/working the ski” is most commonly referred to when “pure” carving. Purely carving the ski means that the ski is slicing into the snow through the turn with zero skidding. The tail of the ski follows the exact same path as the tip, a pencil thin line is left as a track and the ski is progressively bending through the turn. When skiing with this performance, progressively bending the ski allows the skier to shorten the radius of the arc/turn therefore giving the skier control over the turn shape and speed. It also creates a stronger and more manageable build up of centripetal force and “rebound” effect. The following diagram shows 2 skis, one is bending more than the other and means that the arc that it is travelling on is tighter.
Without bending the ski at this performance, a skier is simply relying on the shape/side cut of the ski to turn and is not truly controlling the shape, speed and direction of the turn (otherwise known as "railing" or "parking and riding"). The skier is simply a passenger being taken for a ride by the radius of the ski. The smaller the radius of the ski, the smaller the turn, and the larger the radius - the larger the turn. Unfortunately, most of the skiing population are not able to progressively bend the ski when turning, and are subsequently railing.
You will hear a lot of people saying that to bend a ski you need to press/push on it, or put as much weight as possible on it and it will bend. This is logical but is only a very small part of the process. If the ski is flat on the snow then all the weight in the world is not going to bend it along its length. The most important ingredient when bending the ski is the edge angle you create through the turn. The higher the edge angle, the more the ski is capable of bending. Increasing the ski's edge angle throughout the turn, along with the natural weight of the skier balancing on the ski is all that is required to sufficiently bend a ski through a turn. Lets have a look at this in the below diagram.
As you can see from this image the ski has a small amount of edge angle. Without weight on the ski, the ski’s tip and tail are touching the ground and the middle is in the air due to the shape of the ski (image showing middle of the ground). You can see the gap between the middle of the ski and the ground. If pressure is applied to the middle of the ski, it would start to bend and form a slight arc in the snow (as can be seen in the above image). Now if this amount of edge is held throughout the entire turn then one would be “railing”. This ski would have enough edge to slice the snow, or lock on the edge, but the radius would not change. It would only be turning as a result of the sidecut (meaning the more sidecut, the more of a gap there would be under the middle of the ski and the tighter the arc it would bend into).
However if the skier tips the ski further onto its edge and increases the edge angle through the turn as in the next image, you can see that the tip and tail are still the only parts of the ski touching the ground and there is now an even larger gap under the middle of the ski. This means that with the added weight of the skier, the ski would now bend into a much tighter arc.
So as you can understand from these images, bending the ski predominantly comes from increasing the edge angle through the turn, along with balancing on the ski. As mentioned above, one can put all the weight in the world on the ski, but without the ski's edge angle increasing you will not be bending the ski any more.
This is where skiing gets really cool. When a ski bends it can give a similar feeling as when you land on a trampoline. It too can create the feeling of a rebound effect similar to a trampoline mat bending and rebounding you back up into the air. The stiffer the ski, the more of a rebound affect the ski can produce, which is one of the reasons why most race skis are rather stiff (also with the pressure involved at race speeds the ski needs stiffness so it doesn't bend into a circle like a noodle).
When a ski’s edge angle is increased progressively the skier is more able to deal with the built up of pressure and turn radius tightening. The skier can then use this pressure to “rebound”, or push their Centre or Mass across the hill. This is one of the most exhilarating feelings in skiing. It is also one of the most important and useful skills in ski racing, as the more the ski is rebounded or pushed across the hill the less the skier has to turn the skis across the direction of travel (or the bottom of the race course).
When a ski is on edge, the snow exerts a centripetal force more or less perpendicular to the direction the ski is travelling. Have a look at the below diagram to see which way the ski/skier is being pushed by centripetal force through the turn as the ski bends.
After looking at the above diagram, you can see that it would make sense to attempt to bend the ski early in the turn to create acceleration down the hill. While some people will tell you that a ski racer is trying to bend the ski before the middle of the turn to produce a "rebound" effect down the hill, this is very difficult as there is not very much edge angle and pressure created at that point. One is trying to bend the ski in this phase of the turn to simply get the turn going. The more you bend the ski above the fall line the more quickly a turn will commence.
It is also important to note, that the centripetal force from the snow pushing on the base of the ski after the fall line (middle) is acting adversly to the skier's general travel down the hilll. A ski racer (and high level skier) should therefore be trying to build up enough “rebound” pressure (centripetal force) before and through the middle of the turn. As the ski starts to point back across the hill (not long after the middle) the skier should start releasing the edge, or decreasing the edge angle. If done correctly, this should to allow the “rebound” or pressure to push the skier across the hill without disrupting travel down the hill. Ideally one is trying to minimise the amount of centripetal force acting heavily on the ski when it is pointing across the hill as the pressure created is difficult to manage and is heavily slowing the skiers speed down the hill.
I hope this has given some food for thought for the next time you have a wide open groomed trail and freshly tuned skis strapped to your feet!
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雷达卡
发表于 2013-12-12 19:41:08
显身卡
楼主
