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# 4 Questions - Page 8

Quote:
Originally Posted by borntoski683

Just thinking out loud outside of the box for a minute.

Ok...just thinking out loud here....humor me for a sec...

In a turn, LeMaster says the front of the ski will have bigger steering angle then the back of the ski.  Makes sense.  Wait, so if the foot as it or near zero steering angle, what is the tail of the ski?  Less than zero?  Just askin'.  What about toes vs heels?

If you read my post 205 it explains that a bit....so no the tail is not less then 0.

Quote:
Originally Posted by borntoski683

But in any case, let's just imagine that the steering effect is gotten from the area just in front of the boot and skidding is gotten from the area just behind the boot.  In any given turn where the ski is redirected out of a perfect track, that steering angle at either the edge of the ski just in front of the boot or the edge of the ski just behind the boot will be different.  The front would be more than the back.

Is that significant?  I dunno, just asking...

If I understand what you are writing...I think that in part you are taling about the skis self steering effect...so yes it is very significant.

Quote:
Originally Posted by borntoski683

What if we want to increase the skidding without changing our steering angle per say.  Is that possible?

Yes you can decrease edge angle, and then compensate for the resulting less of ski bend by then increasing the amount of pivot to keep the steering angle constant.

Quote:
Originally Posted by borntoski683

Is our pivot point around which the ski steers itself always located at exactly the same spot under our foot?  Or will it be different depending on whether our intention is to steer or smear?  Or both.

We manage the pivot point through fore/aft balance and proper pivoting skills.  Many people lose sight of the fact that the main "skill" in the pivoting skill is not to simply pivot the ski...but to be able to control where that pivot point is.  So yes it changes....I would think it actually changes throughout the turn...starts under the ball of the foot, and prgressivly moves back to the heel as we adjust fore/aft balance throught turn.

By shifting weight back, we decrease the influence of the ski tip..ie.it flexes less..., thus less steering angle and the turn is released.
Quote:
Originally Posted by BigE
The method suggested above by skidude72 is fine.  It is your idea that a point NOT on the ski can say something about the steering angle of the ski that is flawed.

As to the remainder of the pics, the integration of all forces ahead of the foot vs the forces at the tail of the ski will show if the SKI turns, not if the skier turns.

I disagree.  The method Skidude is presenting simply doesn't deliver a consistent result and cannot be "independently verified" to get the same result on two different skiers, so it isn't credible.

In your second sentence, you completely misinterpret what I'm saying.  I'm the one saying that Steering Angle cannot be measured by a random point along the radius (regardless whether it's on the ski or not).  To Skidude, I'm simply suggesting a way to prove the point.

BigE,
When you say, "Reducing the edge angle also reduces the turn radius, since you've reduced the deflecting force operating on the ski underfoot -- the steering angle will have less of an effect."  I would disagree.

First, recall that I was describing a mostly flat, fully skidding ski.  Now suppose we take a perfectly smooth 2x4 with typical rounded-over edges and slid it perfectly  sideways down a mild slope.  Suppose it is well-balanced enough to continue sliding sideways for 20 feet.  Great, we have our control case.

Now we take the 2x4 back up the slope, only this time we put 10 pounds of weight directly over its CM so that it remains perfectly 'balanced' and slide it down sideways again.  Will it now rotate - or will it preform as before?  I say it will perform the same way.

This works because the friction on both ends of the 2x4 changes equally (whether it grows in total or shrinks in total doesn't matter).   It's only when we increase (or decrease) friction unevenly that we create a difference in torque.

In the skiing example BTS cited, if the skier reduces edge-angle (all else being equal, a necessary analysis constraint here) then they simply have less total friction underfoot - but distributed exactly the same way as before.  Of course, in a real world situation the skier will already be rotating somewhat and have some existing angular momentum, they may not keep their CM in exactly the same location as before, etc.

A real world skier has a tough time 'keeping all else the same' when changing edge angles even slightly.  Whether their rate of rotation increases, decreases or stays the same depends on all those other factors, not the mechanically consistent nature of 'frictional balance'.

.ma
michaelA,

If the ski is fully skidding, there is no turn.

Your need to use a flat ski does not address my statement whatsoever.
Why is skidude72's result "inconsistent" and therefore not credible? So far, all I have are your assertions, and a flawed argument which used points that were not under the ski.
Quote:
Originally Posted by michaelA

SkiDude72,

I get what you're saying but we went a bit beyond that a while back.   The problem as covered earlier arises when we try to use points along the curve as you are doing in what you just posted as example.  In your example, what would be the steering angle for a 8-foot radius turn as measured 20 feet from the point underfoot?  Does that result make any sense?

Also, similar to your example and based on the way you're calculating things ... What is the Angle of the Circle as measured from any given Point on the circle? (feel free to select any point on the circle from which to calculate it).  By attempting this problem, you'll see why I didn't like the method you're suggesting just above.

.ma

As I wrote from the beginning "Steering angle" is a concept to help us understand skiing...not a measurement tool.  I have no doubts your efforts to use it as such is causing you difficulty.

Also as I wrote earlier, and perhpas you could answer this....how would you actually measure this in practice anyway?  Would they ski with a protractro between their legs?  Would you attempt this off video with all the angle distortions?

Lets say you could measure it....and the "measure" was 12.5 degrees?  Now what?

The concept of steering angle as it sits simply allows a relative comparison.  If you took two skiers both making the same arc...one on a pair of 160cm, and one on a pair of 180cm....sure the curved nature of the ski once bent will mean the angle from toe piece to tip is different on the 180 to the 160.....but they will LOOK the same becuase they are bent on the SAME arc...it is only a pecularity of gemotery, not skiing that you are discussing.

Quote:
Originally Posted by michaelA

'Holistically' virtually everything is somehow related to everything else in skiing... but we're trying to keep the Scope of this particular discussion on the nature of Steering Angle rather than possible global outcomes.

.ma

I strongly disagree with this approach.  It is the quickest road to nowhere possible. On Epic especially many people look at minute details of skiing and come up with "theories" and names to describe what they see.  This approach invariably leads to over simplistic explanations and understnading of skiing which totally collapses when these individual theories and ideas are tried to put together into a coherant total picture.

Systems worth learning have concpets that build on each other, and support each other.  They blend seamlessly from one aspect of skiing to another.  Yes learning at this level takes more work, additionally devising theories in this manner takes WAY more work...but the rewards are worth it.  Only through this approach whiere we can tie everything back to the big picture, and drive into detail, and back...can we be truly effective pros....

Also as new theroies come up...the simplist test of whether they are bunk or not is whether or not they can be tied back into the big picture....

PS:  IF this post is shown twice I apologise...I entered it, then hit "submit"...but it seemed to disappear?  So I retyped it.
Quote:
Originally Posted by BigE
That depends on edge control. You can do 360's down the fall line just by playing with the forces on the tip and tail of the ski.  As michaelA says, the ski will supply torque to the skier, but that does not necessarily change the turn radius.

Edging is most definitely part of the equation.  In fact you have no turn and no steering angle without it, its a neccessary component.  A flattened ski has no steering angle. Edging not only initiates the local steering angle and contributes to changing the steering angle; but it also effects how efficient the steering angle will be in redirecting the CoM on a tighter radius.  Its not all or nothing, there is a continuum here.  This in, and of itself, could be its own thread, how edging effects steering.

As you have pointed out, you can do 360's down the hill by simply exploiting the self steering effect of the ski.  This is, BTW, how the BPST works without using rotary in the legs, in my view.

As Ski Dude said:

Quote:
Originally Posted by Skidude72
Many people lose sight of the fact that the main "skill" in the pivoting skill is not to simply pivot the ski...but to be able to control where that pivot point is.

That and other aspects as well, CONTROLLING the pivoting, versus twisting to pivot and forcing it all.  Pivoting or steering skills are not just about how to twist the legs, they are about how to control the steering angle effect of the skis.

Quote:
Originally Posted by Skidude72
By shifting weight back, we decrease the influence of the ski tip..ie.it flexes less..., thus less steering angle and the turn is released.

.  So in addition to tipping and pivoting, fore/aft balance can have a huge impact on how we bend the ski, or load up the front of the ski in order to increase or enhance the effects of the steering angle.

Quote:

Originally Posted by Skidude72
Yes you can decrease edge angle, and then compensate for the resulting less of ski bend by then increasing the amount of pivot to keep the steering angle constant.

Right.  like what we do with 360's on the snow.  This is where I'd like to ask what will happen at high speed if you do that?

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 infuential 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.
Quote:
Originally Posted by BigE
If the ski is fully skidding, there is no turn.
Your need to use a flat ski does not address my statement whatsoever.
1) There doesn't need to be a 'turn' - the simple information I presented is about causing our sliding 2x4 to Rotate about it's own axis based on unbalanced forces.

2) Yes, ...I think it does.     But if you want to talk about a very-tipped ski and the resulting bend and torsional changes to that ski based on context-specific forces then all bets are off since that becomes very much more complex.  Still, the fundamental concepts presented above remain valid - they just get submerged into the mess of all other things going on.

.ma
Quote:
Originally Posted by BigE
Why is skidude72's result "inconsistent" and therefore not credible? So far, all I have are your assertions, and a flawed argument which used points that were not under the ski.

The method of analysis he described is inconsistent because it is highly context dependent and we end up with different measurements for the exact same turn depending on a variety of other factors.

The whole point of defining a 'measurement' (like Steering Angle) is to pick something that will easily and consistently deliver the same results regardless how it is repeated.  If all we have to do is change our skis to get a different reading for the same radius turn then how is that consistent?  For a skidded turn, everything works great.  All I've tried to do is demonstrate that Steering Angle (as cast) simply doesn't apply to a carved turn and that trying to 'invent' a method to apply it to a carved turn is problematic at best.

I've no reasonable way to respond to your 'dislike' for the material I presented.  If it's not in agreement with what you believe, feel free to post the specific details on what you believe.  I'm only posting how I see things and you're certainly free not to see things the same way.

.ma
Skidude,

Management of 'Scope' is an absolute necessity here!  The only way to discuss a given topic with any hope of agreement is to manage the Scope of things being discussed including Context and Frames of Reference.    It's simply too easy to artificially falsify a perfectly credible position/argument by changing the surrounding context or by changing the Frame of Reference in which we're examining the idea without clearly identifying the choice to change.

Every turn in skiing is made up of many tiny, even microscopic movements.  When we examine any idea (like Tip Lead, ILS, Weight Transfer, etc) we're specifically controlling the Scope of our focus by including a whole set of those micro-movements and setting aside the other more global elements of skiing.

I would go so far as to say that surreptitiously trying to escape from an accepted scope and context in a given discussion in order to damage a particular line of reasoning is a common tactic of Sophistry.

.ma
michaelA,

What skidude72's point was that as you get closer and closer to the midpoint under the boot, the steering angle becomes smaller and smaller.  That is not an inconsistent argument, that is the behaviour of the series of numbers that occurs while taking smaller and smaller distances along the arc that the ski is creating..

We are approximating the steering angle by the angle of a chord of the arc to the direction of motion. If you wish you can anchor this directional vector to the point on the ski under the boot that is flexed furthest from the boot sole -- that would be just as likely be the midpoint, but let call it the anchor point instead. That way we avoid senseless arguments about the difference in anchor point and mid-point.

From this anchor point, the chord extends to any place on the arc and since it is on the arc, the angle from the anchor point under the foot is positive and non-zero.  That's skidude's argument -- choose any point on the arc, and it will produce a non-zero steering angle -- even if it is very very close to the anchor point.

In the limit as the length from anchor to a point along the perimeter of the arc approaches zero, so does the steering angle.  However, and this is the key point,  there is always going to be a  non-zero chord length and therefore a non-zero steering angle.

So, what to make of your distaste for infinitesimally small steering angles?

Standardize the steering angle to be anchored at midpoint of the boot and extend and arbitrary 4".  The previous example of the perfectly round 8m carve gives a steering angle of 0.72 degrees. Regardless of the length of the ski.

But how does that figure help? How would ANY figure help?
Edited by BigE - 11/9/09 at 4:11pm
BTW: The sliding non-turning 2x4 shows only that a steering angle of zero can exist regardless of how the skis are pointed.  This is the degenerate case. It does not address the case of a non-zero steering angle whatsoever.

Do you think it's new to show that imbalanced forces turn the ski?
Quote:
Originally Posted by michaelA

The method of analysis he described is inconsistent because it is highly context dependent and we end up with different measurements for the exact same turn depending on a variety of other factors.

The whole point of defining a 'measurement' (like Steering Angle) is to pick something that will easily and consistently deliver the same results regardless how it is repeated.  If all we have to do is change our skis to get a different reading for the same radius turn then how is that consistent?  For a skidded turn, everything works great.  All I've tried to do is demonstrate that Steering Angle (as cast) simply doesn't apply to a carved turn and that trying to 'invent' a method to apply it to a carved turn is problematic at best.

I've no reasonable way to respond to your 'dislike' for the material I presented.  If it's not in agreement with what you believe, feel free to post the specific details on what you believe.  I'm only posting how I see things and you're certainly free not to see things the same way.

.ma

It has been writtne so many times that Steering angle is not a measurment...that I think your continued refusal to acknowledge that is dubious at best.

But  here is somthing for you to ponder:

Regardless of how you measure it....a particular set of movements will always yield the same turn for a particular skier on a particular slope with set gear, regardless of the measurement method chosen...further the skis steering angle "will appear" idnetical to a coach, regardless of the skis size or measurment chosen becuase they are all along the same arc...so to the coach we have consistency, and to the student inputs we have concistency...the only varible is your insistance on gemotery. The only other variables we would get from above would be the standard variance that we get in all ski technique discussiions.....skiing is an open skill sport after all.
Quote:
Originally Posted by michaelA

Skidude,

Management of 'Scope' is an absolute necessity here!  The only way to discuss a given topic with any hope of agreement is to manage the Scope of things being discussed including Context and Frames of Reference.    It's simply too easy to artificially falsify a perfectly credible position/argument by changing the surrounding context or by changing the Frame of Reference in which we're examining the idea without clearly identifying the choice to change.

Every turn in skiing is made up of many tiny, even microscopic movements.  When we examine any idea (like Tip Lead, ILS, Weight Transfer, etc) we're specifically controlling the Scope of our focus by including a whole set of those micro-movements and setting aside the other more global elements of skiing.

I would go so far as to say that surreptitiously trying to escape from an accepted scope and context in a given discussion in order to damage a particular line of reasoning is a common tactic of Sophistry.

.ma

Actually, I think this happens not becuase it is false...but becuase so many ideas here are bunk.  Most of what is written here and dispelled as insight or somthing new, rarely is.  It is often taking those over views that shows bunk up for what it is.  Solid thoeries hold, no matter what.  In my view it is those theories which should get the most attention....this discussion of steering angle shows that even basic concepts are not well understood by the "epic experts".
Skidude and BigE,

I put a good deal of time into context descriptions, complete explanations and even created to-the-point diagrams to support my reasoning for review by everyone.   I've clearly stated my context(s) in line with presented arguments, followed up and answered all the legitimate questions I think necessary to comprehend what I've tried to present.

At this point it just seems to be a contest of whether you can wear me out or not.  With eight pages of this we still seem just too far apart on the concept (and even the purpose of it) so I think I'll just leave all my previous footprints, arguments and supporting evidence to be examined and judged by others as they see fit.   Perhaps we can come back to revisit these things at some future time.

.ma
Quote:
Originally Posted by michaelA

Skidude and BigE,

I put a good deal of time into context descriptions, complete explanations and even created to-the-point diagrams to support my reasoning for review by everyone.   I've clearly stated my context(s) in line with presented arguments, followed up and answered all the legitimate questions I think necessary to comprehend what I've tried to present.

At this point it just seems to be a contest of whether you can wear me out or not.  With eight pages of this we still seem just too far apart on the concept (and even the purpose of it) so I think I'll just leave all my previous footprints, arguments and supporting evidence to be examined and judged by others as they see fit.   Perhaps we can come back to revisit these things at some future time.

.ma

Thanks for the discussion Micheal.  Even thou we did not reach consensus I think it was valuable all the same.
Methinks those marbles rolling through the bowls don't have edges.
I also think I could carve with perhaps only a little difficulty with bindings mounted too far forwards.
Carry on.
Quote:
Originally Posted by michaelA

Skidude and BigE,

I put a good deal of time into context descriptions, complete explanations and even created to-the-point diagrams to support my reasoning for review by everyone.   I've clearly stated my context(s) in line with presented arguments, followed up and answered all the legitimate questions I think necessary to comprehend what I've tried to present.

At this point it just seems to be a contest of whether you can wear me out or not.  With eight pages of this we still seem just too far apart on the concept (and even the purpose of it) so I think I'll just leave all my previous footprints, arguments and supporting evidence to be examined and judged by others as they see fit.   Perhaps we can come back to revisit these things at some future time.

.ma

I am not trying to wear you out -- I'm trying to find anything of substance in your musings. Heck, it's not even clear what you are trying to say.
delete
No worries BigE and Skidude.

I just feel like we're starting to go in circles.   I do comprehend the points you're both making but I've no idea how to restate my own perspectives any better than I have.

Over time, one of us may have an epiphany and figure out something along these line that makes things perfectly clear to each other, but that isn't likely to happen right now.  If you think of something genuinely new, by all means post it when you do.

To me, these forum discussions are more about presenting and elaborating ideas - not about convincing others.  A good discussion of contrary ideas doesn't need to have a winner.   That said, I yield the floor (but not the point ).

{{ Ghost... do post that video.  It's at least an interesting thing to watch... }}

.ma
Ok Michael,
What you presented makes perfect sense to me.
If you look at the local steering angle, (edge direction compared to momentum of cm direction) it decreases to zero and goes on changing behind the boots.  The tail is still pushing the skier into the turn in a carved edge-locked turn.  Unfortunately the only way I have of explaining kinematics and dynamics is physics, including the physics of circular motion, and folks other than you don't seem to want to go there. However, since you seem interested: The whole ski is pushing the skier into the turn even those parts with negative steering angle (and I think you are the only on this thread who will even admit to the possibility of negative steering angle without catching an edge), net force is the vector integral of the pressure vector integrated over the area of contact, resulting in a force into the centre of the turn.  Steering angle is useful as a way to get a handle on how steering affects turning forces and braking forces in a steered turn, but that's likely as far as its usefulness goes.

Here's a video of some interesting circular motion.
Without knowing any better would this not be a negative steering angle ?

Edited by tdk6 - 11/10/09 at 9:38am
TDK,  Bode is lengthening the turn.
Ghost,

RE; negative steering angle.

Top which steering angle are you referring?  The steering angle that turns the skis or the steering angle that turns the skier?
IF there were negative steering angle in the tail of the ski, wouldn't it unbend?
A negative skiers steering angle would push the CM to the outside of the turn.  That is not happening.

A negative steering angle on the ski would reduce the torque on the ski.  We could say that any pressure on the tail is doing that.
Quote:
Originally Posted by borntoski683

IF there were negative steering angle in the tail of the ski, wouldn't it unbend?

Since steering angle is from cero to +90deg? then negative steering must be from cero to -90deg? Like bode in the video. I dont quite understand how it is possible to ski with negative steering except when wedging backwards.
Quote:
Originally Posted by tdk6
to -90deg? Like bode in the video. I dont quite understand how it is possible to ski with negative steering except when wedging backwards.

I'm with you on this TDK.  But things are probably more complex than any of us are as of yet explaining.

The way I see it, positive steering angle is like spreading butter.  Negative steering angle is what happens when you catch an edge.
Quote:
Originally Posted by borntoski683

Quote:

I'm with you on this TDK.  But things are probably more complex than any of us are as of yet explaining.

The way I see it, positive steering angle is like spreading butter.  Negative steering angle is what happens when you catch an edge.

Then it would be like Bode right when he looses his balance and his ski goes out to the side?
Quote:
Originally Posted by BigE

Ghost,

RE; negative steering angle.

Top which steering angle are you referring?  The steering angle that turns the skis or the steering angle that turns the skier?
The local steering angle defined as the direction of the edge measured against the direction the CoM is moving it at any particular instant in time.Drawing is ski moving toward top of page north.  Positive pointing somewhat in direction of turn at tip (top) zero at boot, pointing in outward direction at tail.  Note that normal force at all points is helping skier turn, but trying to slow northward velocity at tip and trying to increasing it at tail.
Quote:
Originally Posted by Ghost

The local steering angle defined as the direction of the edge measured against the direction the CoM is moving it at any particular instant in time.Drawing is ski moving toward top of page north.  Positive pointing somewhat in direction of turn at tip (top) zero at boot, pointing in outward direction at tail.  Note that normal force at all points is helping skier turn, but trying to slow northward velocity at tip and trying to increasing it at tail.

"Local steering angle" is a new term for me. So the steering angle is devided into sub categories..... local and ???. Anyway, I dont quite understand since steering is if I have understood it correctly tip and tail not tracking in the same groove. Not along the same rr-track in the snow. How much is determined by the steering angle. Cero steering angle would be carving rr-traxs. Now comes the "local steering angle" which suggests that steering is a relationship between CoM and how the ski tracks in the snow. Can it get much more complicated? How do you explain all this to a student in the ski school? If he/she is lets say a child?
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