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4 Questions - Page 10

post #271 of 509
Quote:
Originally Posted by BigE View Post
If I'm reading this right, it's the local steering angle under the mid-body that does the turning.  Pretty cool I think.  

This is what I take issue with E.  I feel that statement from LeMaster has been taken to an extreme on this thread, as I tried to point out earlier in this thread here:


Quote:
Originally Posted by borntoski683 View Post
I would also like to point something else out.  Some people have really gotten onto the mode of thinking that there is this point under their foot where they think the steering angle is zero or nearly zero and that this is the only part of the ski that is having an effect on their CoM.  I would caution that this is not nearly the case, in my view.  That is far too simplistic.  While the very tip and very tail of the skis probably do have little influence directly on redirecting the CoM, as you move closer and closer underfoot, the steering angle present will have an increasing effect on redirecting the CoM.  In truth, the entire front of the ski will load up, bend and have a steering angle effect on the CoM and redirect their mass.  That is why if you bend the ski more, you carve a tighter turn.  Its not just some little tiny point under your foot and everything else doesn't matter.  Rather, as you get closer and closer to your foot, the steering angle present would have an increasingly influential role in moving your CoM.  The reason the tip and tail have less influence is mainly due to the fact that the ski flexes.  The entire front of the ski as a whole influences this.  It does not merely pivot the ski around an imaginary pivot point as if pinned into the snow there.

Another point I'd like to make is that if there is no point on the ski with less then zero steering angle, and if the tail has a smaller steering angle then under foot, then under foot can simply not be zero.

In short, I think its highly overly simplistic to assume that only the area directly under your foot represents the steering angle that moves the body.  I do like the concept that the local steering angles of the tip and tail can pivot the ski.  However, I feel that pivoting force is not as big as some may imagine.  Otherwise in all of our arcing turns we'd be experiencing that phenomenon a lot more then we do.  I think mainly skis are designed such that this local steering angle will enable them to more easily establish an over-all steering angle effect on the skier.  But I do not necessarily think that angle is determined by one spot right under the foot.  I feel the entire front of the ski loads up in a bent shape with a range of steering angles.  The closer to the foot, the less the ski's flex will dampen the effect, but to a certain point I'd say once the ski is bent, then would not the tip also have a levering effect on the skier?  I think in this case LeMaster's explanation is over simplified, perhaps on purpose in order to discuss steering angle as more of a concept than as a property in a physics equation.

I think skis are mostly designed so that the local steering angle will facilitate just enough to initiate clean arcs, not necessarily enough to create big skidding or larger steering angles that go beyond clean arcing.


Quote:
Originally Posted by BigE View Post
I agree completely with your opinion on brushing the carve.  I'll hazard a guess as to why that is so... It's because the focus on outcomes ignores mechanics.

Because its actually pretty dead simple to carve a ski these days.  It takes almost no ski training whatsoever to the skier that is not afraid of some speed.  Meanwhile those afraid of speed are just focused on that, slowing down any way they can.  The blending of rotary, edging, pressure control and balance to produce steering, smearing, brushing or whatever variation you want to refer to it as, an advanced skill.  It requires the mastery of many movements in coordination, because if you overdue it in the blending, the results will be choppy, sloppy and visibly ineffective.

Quote:
 
Brushed carving is considered skidding through a turn, that if you were a better skier, you'd carve instead.  Skidding through a turn is considered an elementary "problem" that resolves itself over time.  

There are a number of schools of thought, most of them missing the big picture.  One group says you have to do it this way and ignores some other possibilities.  Another group says no it has to be done another way, and they ignore possibilities.  I don't want to limit this discussion to one group's "brushed carving" approach, which is one approach to some situations, but not necessarily effective for all situations and not the only valid approach.  Its also not what this thread started out discussing about, "steering", something verboten in the "brushed carve" concept.
 

Quote:
Originally Posted by BigE View Post
In thinking about the notion of the negative steering angle just choose one side of the ski to have positive angles, the other negative.  So, if my skis are pointing to the right side of the path of the CM, the steering angle is positive, if left it is negative.  Skis aligned with CM is zero.  It is arbitrary, but more correct that saying a 1 degree steering angle can turn you either left or right.

Its not as simple as only if your ski is pointing outside of the CM path.  If your CM crosses over, your skis will be tipping and when they tip they will engage the sidecut and create a steering angle which is inside of the CM's path.  If they don't successfully do that, they will not turn.  This is why shaped skis make it a lot easier to initiate those turns without having to do a pivot to get the skis into a positive steering angle.  What would happen if you didn't either pivot them or have some sidecut there to create the steering angle?  You would high side(ie, catch an edge)


 
post #272 of 509
Quote:
Originally Posted by borntoski683 View Post

Quote:
 


Off the top of my head I can't think of any other reason to want to skid other than perhaps because you  need to turn tighter and slowing down from skidding is an unavoidable consequence.
 

It depends on how you define skidding but since you had no objection to my definition that skidding is whenever there is a skidding angle present I must make the conclusion that you think that there could never be any intent of not carving.

Quote:
Originally Posted by borntoski683 View Post

Quote:
 

no, Steering angle is not the side cut, though sidecut can contribute to it.  Its been explained in the this thread a few times.  Read again and/or get LeMaster's book.  Local steering angle is a bit more broad than just the tip I think, but what I read it was used only in reference to the tip.  I think the general consensus of this thread so far is that local steering angle may have to do with the steering angle effecting one particular part of the ski, as opposed to the overall steering effect on the skier.  But don't quote me on that please.
 

Cant you just give me the description. Short one to match the list. My brouser is sooooo slooooow. And I dont have the book right here.

Quote:
Originally Posted by borntoski683 View Post

Quote:
 

brushed carving is a very high level skill and yes, a lot of people today are clueless because they have not really learned that skill.  They can edge lock arc or swivel around, but have no idea whatsoever what it means to truly steer a turn.  That is my opinion.
 

I dont know if its such a high level skill. Problem is that nobody practises it. Nobody teaches it. And now since the new carving skis came its like a forbidden word. Go to any ski school and ask for an advanced lesson with no carving and they will look at you like you were from outer space. They will most probably reply that all skiing today is carving. Disclaimer, I could be wrong. In fact if you read this and other forums and magazines etc you will find it nearly extingt. But, people carve down WC SL, GS, SG and DH race tracks.... down double black diamond runs, bumps, powder, crudd, ice.... short turns, long turns you name it, its all carving.
post #273 of 509
Quote:
Originally Posted by tdk6 
It depends on how you define skidding but since you had no objection to my definition that skidding is whenever there is a skidding angle present I must make the conclusion that you think that there could never be any intent of not carving.
 


 I most definitely have not made that absolute statement.
post #274 of 509
LeMaster explicitly makes the statement that the tips and tails are too weak to turn the skier -- instead, they turn the ski.  I know that you've made the comment before in this thread that the tips/tails do affect the path of the CM.  I for one, can't see how any part of the ski other than underfoot will turn my 250 pounds.  The ski is simply not strong enough to deflect it.  It will apply a torque to me, but not a deflecting force.

I know we're miles apart on this, and that's fine.  The trouble I see is that by thinking that the tips will turn you, a skier might adopt a very forwards state of balance, overpressure the tips late in the turn, auger in and break a leg.

If the turning forces are located underfoot, then staying centered during the control phase becomes a goal supported by the physics of what is happening underfoot.  I like very much that the physics leads to this technique/state of center balance.

Re: Brushed carve. 

If steering is nothing more than manipulation of steering angle, then the brushed carve qualifies as a steered turn.  It sounds like I am playing with definitions, but bear with me.  

So far, steering has been limited to something akin to steering a car.  Grab the wheel and twist it to change the direction of the wheels.  Same with skiing -- twist the legs to change direction of the skis and yourself.

People may think my agenda is to promote a particular school of skiing with the idea of letting the skis turn you, but PSIA posted a video with that exact title.  So no, promotion of PMTS is not my goal.  

Rather, my goal is to elevate edge control to become competitive and actually more useful than steering by twisting the legs can be.  Our reliance on throwing the skis sideways abandons the purpose of the shape ski -- to turn itself!

Re: negative CM.  I really don't understand how high siding fits in.  All I suggested was to arbitrarily make one direction from the path of the CM produce positive angles, the other negative.  Then there is a difference in a left and right steering angle.  

Obviously, you'll have equilibrium when the body is on the same side as the steering angle.  But, whether or not the body is in the correct position to remain upright is irrelevant.  That is just not part of the definition.  
post #275 of 509
Quote:
Originally Posted by BigE View Post

LeMaster explicitly makes the statement that the tips and tails are too weak to turn the skier -- instead, they turn the ski.  

Well first of all, I don't take every word from LeMaster as gospel as if the golden secret nuggets of skiing are contained in every word he writes.  He's just one more opinion.  A very good one at that, but not the last one.  His words can be and often are taken out of context.

Second of all, where does the tip end and the tail end?  What about one inch in front of the boot?  two inches in front of the boot?  You don't think those parts of the ski effect the skier?  How far up the ski until it ceases to be significant?  What if the ski is fully bent?

Quote:
 
I know we're miles apart on this, and that's fine.  The trouble I see is that by thinking that the tips will turn you, a skier might adopt a very forwards state of balance, overpressure the tips late in the turn, auger in and break a leg.

I don't think we're as miles apart as you seem to think we are. 

I am not saying the tips turn you, I don't think I ever said that.  What I'm saying is that its not that simplistic.  Its not so black and white.  Its not like the only part of the ski that pushes the skier is under the foot and the only thing the tip and tail do is spin the ski around an imaginary axis.  I'm saying the entire front of the ski contributes to pushing you into the turn, with yes, most of the push coming from under the foot, of course.  But what is under your foot is attached to the front, not by a wet noodle, but by a rigid device.  I say, that there is an area, its not a point, but an area....and it extends ahead of your foot, that has significant effect on pushing the skier.  How far ahead?  I have no idea.  The point I'm making is that its not a pinpoint.  Its not all or nothing.

 
Re: negative CM.  I really don't understand how high siding fits in.  All I suggested was to arbitrarily make one direction from the path of the CM produce positive angles, the other negative.  Then there is a difference in a left and right steering angle.  

Obviously, you'll have equilibrium when the body is on the same side as the steering angle.  But, whether or not the body is in the correct position to remain upright is irrelevant.  That is just not part of the definition.  

 If the edge is not engaged then its a moot point, there is no steering angle.  if the edge is engaged and its a negative steering angle then you crash.  That is the point.

Negative steering angle is not present in good turns.  The only reason I posed that question earlier was in hopes that people would realize it does not exist and should be ruled out from the attempt to understand what steering angle is how and how it effects turns. 
post #276 of 509
BTW: I'd take the word of LeMaster over most others.  

 OK so for you, negative steering angle means on the opposite side of from the CM.   That's fine too.  

But you can have that in a pre-turn - the body has crossed the skis and the skis are still on their old edges.  It does exist in some "good" turns too.

Back to the steering angle notion.  

Let's take a simple case -- our CM is center balanced in a turn with 100% of the force on the outside ski.  

It is a given that it is the reaction force from the snow that makes the skier turn.  Said differently, the reaction force that contributes to the turning is directly underfoot.

The reaction force from the bent shovel/fore-body of the ski would be largely balanced by the reaction force from the bent tail/aft-body of the ski.  These reaction forces would sum to a force located underfoot which is turning the skier.

Any unbalanced forces will be operating as pure torque on the skier.

So in that light, we're both right.  The tips and tails do contribute to the turning of the skier, as their reaction forces will sum to a force underfoot.  It is BOTH the tips and tails that have to be included.  My error was thinking about only the tip.  

Does the inclusion of these two forces,one from the fore-body one from the aft body make a significant difference?   I suppose it can if the ski is stiff enough.
post #277 of 509
Quote:
 
But you can have that in a pre-turn - the body has crossed the skis and the skis are still on their old edges.  It does exist in some "good" turns too.

pre-turn the skis are on the old edges and you still have a positive steering angle happening on those edges.  Just because the CM has passed the skis is not important...its the direction the CM is traveling that matters.  

To have a negative steering angle the CM has to be traveling in the same direction as the side of the ski that is edged, I guess anywhere within that 180 degrees.  In other words, if your left edge is engaged, and your CM is traveling on a path 1 degree to the left of the direction of the left engaged edge, then you'd have a negative steering angle.

In the above example, as a pre-turn, your right edge would still be engaged, so not negative.  As soon as you tip over to the left edge, then you have the POTENTIAL for a negative steering angle, and if you achieve it, you will catch an edge.  To avoid catching an edge you either pivot enter the turn or you make use of the side cut to establish positive steering angle.

 
Quote:
Back to the steering angle notion.  

Let's take a simple case -- our CM is center balanced in a turn with 100% of the force on the outside ski.  

It is a given that it is the reaction force from the snow that makes the skier turn.  Said differently, the reaction force that contributes to the turning is directly underfoot.

The reaction force from the bent shovel/fore-body of the ski would be largely balanced by the reaction force from the bent tail/aft-body of the ski.  These reaction forces would sum to a force located underfoot which is turning the skier.

Any unbalanced forces will be operating as pure torque on the skier.

So in that light, we're both right.  The tips and tails do contribute to the turning of the skier, as their reaction forces will sum to a force underfoot.  It is BOTH the tips and tails that have to be included.  My error was thinking about only the tip.  



This is how I see it:

The delta (not summation) of the reaction forces between the front and back is what causes the ski to pivot at all from the steering angle effect.  Its like an airplane wing.  An airplane wing has more pressure on the bottom then on the top due to the curve on top of the wing that creates a vacume of air pressure above.  The air is only pushing from one direction to accomplish this.  Its the delta that causes the plane to rise.

On the bent/sidecut ski in a turn, the steering angle near the tip is more than the steering angle at the tail.  More steering angle means more force.  If there is more force on the tip than on the tail, then the tail will tend to pivot out relative to the tip.  

Assuming the turn is carved, what actually happens is that the tip is pushing towards the center more than the tail is, the tail is not actually moving OUT.  If there is more skidding then it becomes debatable about whether the tail is actually moving out or just moving in less than the tip is.  

Around what axis?  I think that depends on your foreaft balance.  We see that generally speaking the ski will have a progressive decrease in steering angle from front to back, which makes it hard to determine an exact pivot point.  Its not a teeter-totter. It will depend a lot on your foreaft balance too.  

And further more I am thinking, if the ski is bent, then this pivoting effect could theoretically be following the same shape of the bent ski, which would be zero skidding.  See what I mean?  The ski redirects itself throughout the turn, even when pure arcing.

As far as a "summation" of forces moving the CoM towards the center of the turn:  All of the forces coming from the snow are trying to push both the tip and the tail towards the middle of the turn.  While the delta of the two determines if there will be some kind of rotational redirection of the ski during the turn, the summation of the two causes an overall push towards the center.

The entire length of the ski will have this progressive steering angle and force thereof, from back to front, with most of the effective pushing pressure coming from the mid area of the ski, determined mostly by the fore-aft balance.  I'm sure ski designers must have a better idea about how much any particular point on the ski actually pushes a skier versus contributing to the pivoting effect.  Any given point has an angle and magnitude in this regard.  The closer you get to the mid area, the more magnitude it contributes to this summation that pushes the skier with a certain overall magnitude and direction.   

EDIT: And in addition, edging and snow conditions will contribute to the magnitude factors.

In the end, all of the points along the ski add up to some kind of summation angle and magnitude that determine how the CoM will be pushed inside, and yes, the mid area of the ski will obviously have a lot more impact on this then the tip and tails.  The mid area does not have to be right under the foot though.  Could be bigger than your foot and your fore-aft balance may move it forward or back as well, the area that contributes most to this summation.

Quote:
 
Does the inclusion of these two forces,one from the fore-body one from the aft body make a significant difference?   I suppose it can if the ski is stiff enough.

Or perhaps bent enough?  As the ski become more bent, it will become more rigid.

There is a lot we don't understand.  My only point is that I don't think its accurate to make it so absolute as to say that the none of those forces outside of the area directly under your foot contribute to pushing the skier.  Yea, most of the push will obviously come from there and perhaps some kind of summation steering angle could be determined which is MOSTLY located in the mid area of the ski, depending on our fore-aft balance.

When we start speaking in absolutes, that is generally when we will start to neccessarily start simplifying the physics down in order to try to understand it, and when we do that, it will often lead to incorrect assumptions about how skiing works.  Skiing is very complex.  There is a lot going on.  
Edited by borntoski683 - 11/11/09 at 2:39pm
post #278 of 509
The question I have now after all this bickering and postulating is:  

Are we now finally ready to come back and address the question about whether its possible for a steering angle to be different than a skid angle?

What about controlling the amount of skidding WITHOUT adding any additional "angle" above and beyond the steering angle?  I believe that is the "brushed carve" concept by the way.

When might you want to add a bit of skidding by adding some skid angle, if such an angle can even exist, beyond steering angle?
post #279 of 509
Good input everybody. 

Ghost, please continue posting on things as I think you're making better headway than I.  A key point is realizing that a "Steering Angle" can exist with minimal or no impact on direction change.  "Local Steering Angle" refers to what exists at a specific Point (any point) along the ski. 

It is the SUM of all local steering angles that matters to the mix of Braking vs Turning as modified by engagement and pressuure.

<<  I'm unable to participate anywhere for a while as my ISP of fifteen years may just have 'Gone Under' .  My DSL and Dialup have suddenly died and their support phones are all down.  Email is gone.  Stored files are gone.  Not pretty.  Might be unavailable for a while as only the neighbor's DSL is sustaining me while I find a new ISP. >>

.ma
post #280 of 509
 ma, that sucks.  Sorry to hear it.
post #281 of 509
Quote:
Originally Posted by Skidude72 View Post




I actually do think you are perhpas onto somthing here...but what is the point beyond and academic one?
The point is academic, but well worth noting. If you take a theory founded on the idea of an edge angled across the path of the cm and across the direction of motion (of that edge) and then apply it to a situation where the entire ski is in fact pointing across the cm's path and the direction of motion it works very well; if you attempt to apply that same theory to the case of an edge-locked carving ski, you will have some problems.  That's why Ron came up with the marbles. 
post #282 of 509
 It's also why he came up with the local steering angle.  However, the braking by the tip and acceleration by the tail of the edge locked ski cancel out to a large extent.  Considering that they are torques anyway (force normal to the ski with tips pushing up on the toes and tails pushing up on the heels) if they are in balance they are converted to forces under the foot that deflect the skier.

So regardless of their origin, a skier that is center balanced will feel all of the forces underfoot.  Would it be an oversimplification to use just the mid-body when teaching then?  I don't think so.
post #283 of 509
As an oversimplification it would be inaccurate to not take advantage of the large steering angle presented with the ski tip in 3D snow. It's that element of depth that makes the steering angle found in the tip such a strong turning tool. Just the touch of a little toe edge of the tip will generate the beginning of a turn you need and following with the skis major steering ability found it's decambering or found already in a rockered ski.
On hard surfaces the tip is not so much a factor but in deeper snow the tip is a tool not to be ignored.
post #284 of 509
 Whoa there GarryZ.  The tip does not turn the skier.  It turns the ski. 

There is a cascading effect of the tip turning the ski which alters the steering angle underfoot which turns the skier. (That's pure LeMaster.)

The force at the tip alone, and far away from the foot cannot deflect the skier, it can only apply torque.  That torque is lifting the tips/closing the ankle.  Even though it is not twisting the leg, it's still a torque -- it's a lever.  It gets balanced with the torque from the tail of the ski which is lifting the heel/opening the ankle. 

The resultant is a force underfoot.

LeMaster's bowl and marble doesn't address this directly.  It focusses on the force underfoot.

I really don't think that increasing the complexity of turning beyond the force underfoot is necessary.  Oh sure, we're all very clever about how that works, yet there is no mathematical model in existence that can predict the outcome of any given turn on any sort of snow.  We're better off to leave that alone -- we don't gain anything by including tip and tail in providing turning forces.  
post #285 of 509
There is a force under the foot yes. But there are forces all along the whole ski from tip to tai. Only the biggest force lies under foot. Thats pritty obvious since the ski flexes. But skis flex differently. On a stiffer skis the tip and the tail carry more load. On softer skis less.
post #286 of 509
Seems we may be in the same weight class, but regardless of that the tip and tail do have influence in the turn, torsional rigidness as well as tension are the two most important factors. We should not forget that there are actually only shaped skis out these days and there is a good reason for that. 
However what fades out more these days is that you do not have to load the weight onto the shovel or tip of the ski anymore as you had to do in the past. So that will focus more in the center of the ski which is right under your foot. The skier itself however will influence through weight, technique and a given speed and terrain how that turn will shape in the snow. Maybe that is what LeMaster wants to point out? And there really is no such thing as a carved turn on the edge alone, they are all skidded or brushed if you will. So you can get close to being perfect, but so far nobody is perfect.

MfG.
post #287 of 509
 simplyfast !
post #288 of 509
However, this here thread shows that imbalanced steering angles can be used to propel the skier in the forwards direction -- a bit more emphasis on the tail at turn completion and you'll get a speed increase on turn exit.  Advanced moves? Yes, but fully supported by the above analysis.

 http://www.epicski.com/forum/thread/32654/speed-gaining-turns/0

post #289 of 509
Quote:
Originally Posted by simplyfast View Post

Seems we may be in the same weight class, but regardless of that the tip and tail do have influence in the turn, torsional rigidness as well as tension are the two most important factors. We should not forget that there are actually only shaped skis out these days and there is a good reason for that. 
However what fades out more these days is that you do not have to load the weight onto the shovel or tip of the ski anymore as you had to do in the past. So that will focus more in the center of the ski which is right under your foot. The skier itself however will influence through weight, technique and a given speed and terrain how that turn will shape in the snow. Maybe that is what LeMaster wants to point out? And there really is no such thing as a carved turn on the edge alone, they are all skidded or brushed if you will. So you can get close to being perfect, but so far nobody is perfect.

MfG.
 

One thing that is very overlooked everywhere, here too, is the mounting place for the binding in the fore aft plane. Some brands are mounting their bindings way too far back. Head now ships their competition skis without plate. Looks like I was not the only one not satisfied. I once had a pair of Head skicross GS skis that were totally crap to ski. Stumbled onto the Ball Of Foot measurement consept on the net and tried it out. I turned out mooving the binding 40mm forwards of its original location according to the boot center mark. At the same time I changed the plastic plate to a vist racing plate and those skis rocked like no other. I moved on to a different brand where I could easily mount my binding the way I wanted. Now I can stand more center on the skis and still have pressure on the tip. And the tail holds great.

I strongly have to dissagree with your statement that a skier hardly ever carves. This might be true if you look at the masses offcourse but if you take advanced skiers that know how to carve they do it with cero skidd or steering. However, if you want to look at it through a microscope I think you are missing the forrest .
post #290 of 509
Actually I take our guys in the WC Team here in Austria. Fact is that there will always be skidding, cannot be avoided. The easiest way to spot this is to see how much snow you can see coming off of the edges in a turn. That is caused by skidding. Partially because the skier wants a certain radius in a certain situation and partially because the snow of course has some give. Hey I am not the one that will just blame the skier only here.
The only time when you can perhaps truly carve a turn flawless is at low speed at an easy terrain for demo purposes. When you look back and you see just one line in the snow then you actually carved a turn without skidding. Picture perfect.

MfG.
post #291 of 509
I think that although the whole ski is contributing to the turn, the pressure is directed in the normal direction to the ski surface, so only that component that is in the direction of the turn (left or right) will help the skier turn.  At the boot centre the normal direction is more or less straight right or left, as you get farther away the direction changes, but there is still a large component of the force that is helping the skier turn.  The amount of force coming from near the tip and tail is significant, more so on my stiff Kästles than on a softer pair of SLs but still significant.

Despite the above, all the force comes up through the boot, and it is not an oversimplification for the student to just concentrate on the push coming from underfoot. 

What is harder for some people to understand is how a force can make them turn when there is no steering angle on the ski where the force is coming from.

Think about what would happen if you were traveling in a straight line beside a very icy wall that was exactly parallel (zero degrees, infinitesimally smaller than infinitesimal) to your direction of travel, and you pushed it.  You would move away from the wall; you would accelerate. You would turn.  The dynamics of circular motion are similar, you push sideways to your direction of travel, and the acceleration keeps you in the turn, even if you don't extend.  The curved shape of the groove the skis are in ensures that an instant in time later you are still able to push against that icy wall, because although you may have moved away from where it was, it is now still beside you and you can still push it.
post #292 of 509
Quote:
Originally Posted by simplyfast View Post

Seems we may be in the same weight class, but regardless of that the tip and tail do have influence in the turn, torsional rigidness as well as tension are the two most important factors. We should not forget that there are actually only shaped skis out these days and there is a good reason for that. 
However what fades out more these days is that you do not have to load the weight onto the shovel or tip of the ski anymore as you had to do in the past. So that will focus more in the center of the ski which is right under your foot. The skier itself however will influence through weight, technique and a given speed and terrain how that turn will shape in the snow. 

  In the past people put extreme pressure on the shovels primarily to initiate the turn and perhaps to shape it.  That did not neccessarily mean that the shovel was primarily pushing the skier throughout the turn, nor did they ride the shovels through the whole turn.  However with less sidecut they would neccessarily need to bend the shovel more to get the ski into a positive steering angle without having to pivot, and initiate a carved turn.  

Today with shaped skis, it does not take nearly as much shovel bend to create the positive local steering angle in the shovel that will initiate a carved turn.  For this reason it is not as much neccessary to do such exagerated pressure on the shovel like in the old days.  The shovel can still be used to shape turns by moving your weight more onto the shovel and getting more bend in the shovel, as well as causing that area of the ski to have more influence on the OVERALL summation steering angle, you'll be getting more steering angle and create a tighter turn shape, but overall, you're right, the focus should be more on being relatively center balanced today.

Quote:
Originally Posted by simplyfast View Post

Actually I take our guys in the WC Team here in Austria. Fact is that there will always be skidding, cannot be avoided. The easiest way to spot this is to see how much snow you can see coming off of the edges in a turn. That is caused by skidding. Partially because the skier wants a certain radius in a certain situation and partially because the snow of course has some give. Hey I am not the one that will just blame the skier only here.
The only time when you can perhaps truly carve a turn flawless is at low speed at an easy terrain for demo purposes. When you look back and you see just one line in the snow then you actually carved a turn without skidding. Picture perfect.

MfG.

 Absolutely!


 
post #293 of 509
Quote:
Originally Posted by BigE View Post

However, this here thread shows that imbalanced steering angles can be used to propel the skier in the forwards direction -- a bit more emphasis on the tail at turn completion and you'll get a speed increase on turn exit.  Advanced moves? Yes, but fully supported by the above analysis.

 http://www.epicski.com/forum/thread/32654/speed-gaining-turns/0


My feeling right now is that the tail of the ski has the closest you're ever going to get to a zero steering angle.  During any given turn, the further back along the ski you look, the lower the steering angle will be, approaching zero.  When you shift your weight back you essentially lose some of the overall summation steering angle, which would like up the direction steering angle closer to the direction the CoM is moving, which should allow you to go faster, I agree.  Interesting concept to think about it this way.  Makes complete sense to me though.  

It would depend a lot on the taper of the sidecut in the tail too, as well as the torsional stiffness of the ski, edging skills, other factors.  I would expect the turn radius to widen as well, all else being equal.


 
post #294 of 509
Quote:
Originally Posted by Ghost View Post
Think about what would happen if you were traveling in a straight line beside a very icy wall that was exactly parallel (zero degrees, infinitesimally smaller than infinitesimal) to your direction of travel, and you pushed it.  You would move away from the wall; you would accelerate. You would turn.  The dynamics of circular motion are similar, you push sideways to your direction of travel, and the acceleration keeps you in the turn, even if you don't extend.  The curved shape of the groove the skis are in ensures that an instant in time later you are still able to push against that icy wall, because although you may have moved away from where it was, it is now still beside you and you can still push it.

I suspect this phenomenon, if true, would only be a factor during the impulse around the apex.

 At a recent presentation, Ron LeMaster discussed that many WC coaches are talking about the actual carving part of the turn being very short in duration.  See this post of a casual summary from that presentation(thanks SkiRacer55):

http://www.epicski.com/forum/thread/87267/balance-inefficiency-in-the-last-1-3-of-the-turn-in-advanced-to-expert-skiers/0#post_1144239

Also, where does the PUSH come from to push off the wall?  On one hand you're saying that the curved path is created by a push, but its the very same curved path that creates the centripetal reaction.  Its a chicken or the egg problem.  You won't get the centripetal force without something else causing the curved path to take place.  That is steering angle and that is where the push comes from.
post #295 of 509
BigE and BTS and I almost see it the same way. 
BigE - the steering angle at the tip turns the ski, the ski turns the skier.
BTS - You won't get the centripetal force without something else causing the curved path to take place.  That is steering angle and that is where the push comes from.

Me - Agreed!  Putting it in motion, the ski moves forward along a path lead by the steering angle at the tip, creating a groove.  The skier is turned by the ski using a sideways push against the groove, including all parts of the groove, even those with negative local steering (not skid) angle.  AS TIME ADVANCES the direction of the push changes because the ski MOVES along the curved groove, but the push is always at 0 degrees to the mid-ski and skiers current real-time direction of motion.

Note: the push in a constant radius turn does no work on the skier, being 90 degrees from the direction of motion except for slight friction.  Hence no loss of speed (except for slight friction).  In decreasing radius turn, skier speeds up - slingshot effect if exited suddenly.  What say you?
post #296 of 509
 The only problem is I don't believe in negative steering angle..   
post #297 of 509
Quote:
Originally Posted by Ghost View Post

Note: the push in a constant radius turn does no work on the skier, being 90 degrees from the direction of motion except for slight friction.  Hence no loss of speed (except for slight friction).  In decreasing radius turn, skier speeds up - slingshot effect if exited suddenly.  What say you?

I don't mean to be a prick, but what physics and mechanics do you see in play here?  The "exit suddenly" is kinda vague.  I'd love to explore this more....
post #298 of 509
BTS,
How about the rudder of a ship?  It has a definite 'negative' steering angle, deflecting water toward our desired direction of travel - but at the rear of the ship.

---
WHEEEeeeee, my ISP of 18 years is alive once more!  Connectivity, Emails and Files being restored -  even a new investor to help bring things back to solidity again!   I'm still struggling to get caught up on all manner of things and will need to re-read much of the new material here (only briefly skimmed it) since my window on the world closed for a while. 

---
The more I think about it, the ideas we're talking about here are more useful than I'd thought earlier (at least to me). 

When noodling these things, be sure to mentally separate direction of Forces from direction of the Ski/Skier.  As in the 'Wall Example' by Ghost, the resulting direction of our Skier depends on the direction and Magnitude of Force applied *and* for how long.  There isn't a merely a one-for-one relationship to consider.  Trying to find a Chord between points in our turn radius that points somewhere directionally useful is problematic for this reason. 

.ma
post #299 of 509
Nope I don't think the tail of the ski acts like a rudder.   NOT AT ALL.

And yea I think also its important to distinguish the difference between the direction of force and the direction of movement...absolutely.....  If you have some specific ideas in that regard, please share.
post #300 of 509
Sorry, didn't mean to imply Rudders and Skiing go quite together - just that Rudders do in fact demonstrate the effect of a Negative Steering Angle creating motion in the desired direction.

Again, I'm just coming off severe Withdrawal symptoms from 3 days without email or Internet access so pretty busy catching up on other things, so more thoughts later.  Ghost already started down that path pretty well.  There are many implications in what he's already posted worth re-reading and envisioning. 

.ma
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