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Lengthening the tops of your turns - Page 4

post #91 of 100
It is supposed to be zero. The published radius is the radius of the circle that best fits the arc of the ski when the ski is flat on the snow.

Now, 51 deg is not problem. What of a 48 or 64m ski? What is the radius?

16m = Cos(edge angle) x 64

16/64 = 0.25 = cos(edge angle) => edge angle = 75 degrees

for 48M, we have 0.33 = cos(edge angle) => edge angle = 70 degrees.

How fast am I trying to negotiate that 16M turn? Am I strong enough? Are we booting out yet?

That's my point. I can bend that ski in the garage, but not on the hill.
post #92 of 100
Quote:
Originally Posted by tdk6 View Post
Just out of curiosity, how big edge angle is the 26m radius calculated at?
Like Big E said, the sidecut most closely approximates part of a circle of 26 m when the ski is flat, and a circle of 26 m * cosine of tipping angle when the ski is tipped.

Eventually you run into problems because the ski is too stiff to bend without great forces on the edges and the edges break loose. Other complications arise because the shape is not perfect, and there has to be some give to it to allow the shape to change progressively as the ski enters and leaves a corner, to say nothing of the snow/ice surface being inconsistent. To a 1st approximation, the above equation is pretty good on a really hard surface.
post #93 of 100
Nice math BigE. Like you say, can you bend that ski out on the slope like you can in the garage? IMO a ski turn radius is a combination of sidecut, stiffness, boot placement, edge tuning, how much it is pressued etc. and we never judge the turn radius by theoretical numbers but on how they ski at appropriate speed on appropriet surface. For a SL or GS race ski there is allways speed enough to tip the ski onto its edge to at least 30 deg. The turn radius will allways be less than what is printed on top.
post #94 of 100
Of topic again guys? Yes an engaged ski can be bent into a tighter radius, exactly how much depends on the skill and fitness level of the skier, hardness of the snow, and the amount of dampening and flex built into the ski/binding/boot set up. 27 to 11 was the specific example TDK put out there. Most everyone seems to agree that the snow would need to be pretty hard to support bending the skis into a deep enough arc to make that turn. A couple questions that occurred to me are...
Is boilerplate were we would be teaching someone to lengthen their turn entry? Probably not.
Is driving the skis into that much reverse camber how we would teach lengthening the turn entry? Seems to me that is the opposite of the objective in the OP.
post #95 of 100
Yes. We are off topic.
I prefer the reverse fan approach, mentioned earlier wrt the railroad exercise. Start with a figure 11, and proceed to make a sine curve down the mountain keeping the amplitude small, but gradually increasing it. BUT that's just me.
post #96 of 100
Back to original topic.....

The problem with lengthening the top of the turn is that in order to be able to stay in balance and not fall down hill at transition as our skis come flat perpendicular to the snow surface and our CoM is being moved outside and downhill of the supporting plane of our skis we need to quickly generate the centrifugal force that is required to resist gravity pulling us downhill (skiing in a traverse). The centrifugal force is determined basicly by two things, turn radius and speed. The bigger the turn radius the more speed we need in order to generate the required centrifugal force.

A quick and dirty way of cheeting is to drift/steer our skis into a skidd/brush. The resulting excess friction will boost our centrifugal force. This is tempting since most skiers use this friction for balancing purposes. Its a direct way of adjusting our skis to support our balance. If our skis lock into a carve we have to adjust our body with movements for balance purposes. Note that if we are skidding/drifting/brushing/steering at even turn radius with no change in the offset of the tip and tail radius we need to use body movements in order to stay in balance just like if we were locked into a carve.

So the challange with lengthening the tops of the turns is that we need to match ski turn radius with speed and inclination in order to keep our skis running along their edges. Early counter and angulation is needed for proper edge hold and balancing. Be aware that the edge angle should be incresing as the centrifugal force starts to build up. Especially in the low c part of the turn were centrifugal and gravitational forces join in pulling in the same direction. In high performance skiing it is possible to save that upper body counter untill after the fall line and use it to increase your edge angles when needed the most. In this case you do not form that traditional "upside down" position where your back is turned downhill. You remain with your upperbody facing downhill. This is called anticipation and is used in short turn skiing and carving such as SL. Check out how WC skiers do it:
http://www.ronlemaster.com/images/20...005-sl-1c.html
post #97 of 100
Quote:
Originally Posted by Tdk6
Very interesting...... maybe its possible to turn a GS ski at 15.5m but would not speed have anything to do with it?
I wasn't moving the ski forward at all when I bent it to that degree.

Forward Speed has no relationship to the turn radius of a ski. High Speed around a turn may provide the opportunity to pressure the ski more than otherwise, but Speed is not necessary. We can "carve" a ski at 1 mph on flat terrain merely by tipping it around 5-degrees and carefully riding the sidecut.


JASP,
I think it's rather easy to bend a soft-flexing ski into a short radius carved turn with very little effort. Sure, the stiffer the ski; the more difficult it becomes to bend the ski and therefore more difficult to consistently carve that ski at that radius though it depends a bit on surface conditions.


BigE,
I have wide feet and wide boots (often pressed out for my wide forefoot) so I do have problems with boot-out. Still, in softer snow I'm able to keep the ski well-bent and carving despite the sides of my boots dragging through the snow. All that matters is that the Tip and Tail stay properly engaged to keep the ski bent.

Sidecut only becomes the critical factor when on very hard surfaces like ice or near-ice. Remember that the middle of a ski will nearly always penetrate more deeply than the tip and tail even for a straight-sided classic ski. This is because of pressure distribution along the ski.

I seem to recall a spreadsheet or calculator program somewhere that provides the turn radius if you enter the ski characteristics along with a tipping angle. Anyone remember where that is?

---
Tdk6,
All this side talk about Speed, Sidecut and Turn Radius has a direct impact on Lengthening the Top of our Turns.

As you correctly state above...
Quote:
The bigger the turn radius the more speed we need in order to generate the required centrifugal force.
This is important to consider at turn entry. Often, too much of the skier's momentum is downslope rather that across the slope during transition and this inhibits their ability to carve into turn entry forcing the skier to twist the skis and make a sharper turn entry.

In this respect, Forward Speed (across the slope) does become a factor in how well the top of the turn is executed.

.ma
post #98 of 100
Quote:
Originally Posted by michaelA View Post
Tdk6,
All this side talk about Speed, Sidecut and Turn Radius has a direct impact on Lengthening the Top of our Turns.

As you correctly state above... This is important to consider at turn entry. Often, too much of the skier's momentum is downslope rather that across the slope during transition and this inhibits their ability to carve into turn entry forcing the skier to twist the skis and make a sharper turn entry.

In this respect, Forward Speed (across the slope) does become a factor in how well the top of the turn is executed.

.ma
post #99 of 100
Mike,
In the example TDK mentioned he was talking about a GS race ski, not the softer ski you mentioned. In that context the idea of an 11 meter carved turn means working it pretty hard. IMO allowing the skis to slip a bit makes that turn more doable. Which might be as simple as making the forebody carve but not worrying so much about the tail. Not that the skier would push the tails out, just that they would load the front half of the skis more but only so the tip and the boots pass through the same place in the snow. Which wouldn't be a pure carved turn per se.

In so far as the speed through the transition, the skier still needs to move forward with the ski regardless of their overall speed. We can use forward momentum to help us accomplish this movement but the unbalanced position you mentioned is the direct result of the pelvis and torso not moving diagonally forward into the new turn. Another way to say this is they are making a lateral move instead of a diagonally forward and lateral move. Which creates the need for the pivot to maintain (or in this example regain) a balanced stance.
IMO this is an easy to spot sign that the skier isn't moving their body with the skis and thus becoming too static during the last half of the turn. The prescription is to slow down and work on more range of motion in the torso and pelvis rather than pivoting the skis to change their balance point on the skis. Once a skier gets comfortable with this increased range of motion and moving their hips and torso forward with the skis (through the transition), the pivot entry isn't needed because they aren't in the back seat trying to catch up with the skis.
post #100 of 100

I like it

Quote:
Originally Posted by RayCantu View Post
LiquidFeet,

To carve a turn the student must commit to the turn and yet be patient and allow it to happen. Many find it difficult to blend these two concepts which seems to be mutually exclusive but are part of the carved turn.

The skier must commit to the turn in order to get a high enough edge angle to allow the ski to carve while at the same time must be patient and inhibit the desire to twist the ski in response to the acceleration they feel as they begin to enter the fall line.

Note: though the speed (a constant) they are traveling is well within their comfort range it is the acceleration (open ended) that they have difficulty with. The exponential component, i.e., 4mph then in a few seconds 8mph then in another few seconds headed towards 16mph is enough data for their mind to extrapolate that 32mph shortly followed by 64mph and 128mph can't be far off so putting on the brakes (skid, twist the ski or what ever you want to call it) is their default position and is better applied sooner rather than latter. If you recall they most likely learned the Double Twisting Opposing Skidded Safety Position (DTOSSP or more commonly called the snow plow) on day one.

We found that using what we call an "in-rigger" the skier could get the high edge angle (a commitment) at a low speed without compromising the proper body position they would need later to move to more dynamic skiing. Of course once the high edge angle is achieved twisting the ski won't do much even though they may try.

I uploaded a clip from a DVD we gave to our alignment clients after we set up their boots. It is a drill to help them better understand the body positions necessary to deal effectively with the loads and forces developed in modern skiing.
You may find it useful in getting your students to linger a little longer letting them lengthen the tops of their turns.

http://www.youtube.com/watch?v=HO0hjU5Vmuo


Let me know if you think it might be helpful.


Ray
I use similar tasks. Wide track uphill christys fanned progressively into cowboy turns. My one point of contention is the amount of inside ski lead demonstrated and how it contributes to excess countering. I also use patience turns, having students count to three as their skis approach the fall line.
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