New Posts  All Forums:Forum Nav:

Is this aft? - Page 3

post #61 of 71

I would have tended to agree with mogulmuncher's point and say let's just call it aft. Clearly there's a differnce though between someone skiing "in the backseat" - balanced aft and what we're talking about. I like your description here:

 

 Quote:

 Now, draw a line in the direction in which the CM is moving at the same instant- note that this line points more directly downhill than the line along the skis. Extend a plane down from this CM line again passing through the balance point. Observing in this second plane shows that the CM is over or ahead of the feet.
So, which plane of reference is the correct one?
I contend that "balance" in this context has to be anticipatory and that the second frame of reference is the valid one - Barnes' concept of "balancing into the future". So, any definition of "aft" has also to specify the plane in which we are at observing the relationship.  
-HardDaysNight:
 

Would this reallyl be true though? It would be nice to have an overhead shot to confirm that in the plane the cm is traveling, it is ahead of the feet. Surely at point that significant weight returns to the skis, the cm needs to be in front of the heel binding or he's going to wheelie.

 

Is this guy aft?

He's definitely balanced while in the air!

You get a good look at how pivoting the skis in this position will engage the tips much sooner. I know Rick said above that doing this will bring him more forward. Is this simply because the tails wil engage later? If you just pivot the skis here the tails move out, but does it change the relationship of the cm to the feet?

Rebound,Web.jpg

Photo by Rick Schnellmann

http://web.me.com/rickschnellmann/Racing_Pictures/Loveland_NorAm,2010/Rebound/Rebound,Web.jpg

post #62 of 71



 

Quote:
Originally Posted by Tog View Post

 I know Rick said above that doing this will bring him more forward. Is this simply because the tails wil engage later? If you just pivot the skis here the tails move out, but does it change the relationship of the cm to the feet?

No it doesn't but that is not what it is about. It is about the force coming from the skis balancing against the forces coming from the CM, i.e. gravity and acceleration. If you pivot the skis before engagement the force will be directed more in opposite direction of these forces than if you do not pivot.

 

By the way, I added some bezier curves to Ricks montage. Note that the skis are not fully engaged in the last frame (very little spray), but it is just before that. It should be clear from this picture that there is a lot of redirection of the skis before they are engaged. Whether you want to call that carving or pivoting I leave for the other thread.

HirscherSL Montage bezier.jpg

post #63 of 71
Quote:
Originally Posted by Bob Barnes View Post

......
 
It certainly does call into question the current fad among many instructors to "move the hips over the feet," to move the hips "forward and diagonally" to the feet, or to try to "get the femurs vertical" to initiate a turn. It calls into the question the advisability of trying to "engage the tips" to start a turn as, clearly, this skier initiates the turn with a release of the edges, not an engagement--tips or otherwise! (Which is not to say that, once he enters the pressure/carving phase, his tips are not engaged; they are, due to the downhill movement of his CM).

Best regards, and Merry Christmas!
Bob Barnes


 

Bob just brought up the question that kills me for the for the last 2-3 years: Are there any other reasons to "initiate the turn by actively engaging the tips of the skis" besides "using the ski design"? What are the advantages (if they are there at all as I see only disadvantages) comparing to releasing the edge while centered over the boots?

 

My area of interest in skiing and teaching is energy conservation and finding a low impact ways to ski extreme terrain. That brings me to following conclusions:

1. Yes, if I will get my "femurs vertical" they will hurt like hell while I will extend!

2. If I load my tips too much during transitions they will dive in crud or powder

3. If I load my tips by "foreagonal" movement during transition I will go into high edges carved turn which is only good on groomed slope with packed powder (icy conditions do not support "foregonal" as aggressive engaging of edges becomes skidding - light touch is advisable).

4.  .......

 

So what happened with "versatility" all our instructors are looking to bring in their skiing and teaching? Does "initiate the turn by actively engaging the tips of the skis" support versatility?

 


 

post #64 of 71
Stroller,

A bit of a sidebar but I'll take a shot at the versatility question. My desire for Versatility is aimed at the skier and not any specific technique. We may not advocate Braking Wedges as a way to ski any more but a Braking Wedge becomes a highly useful technique when it works better than the alternatives in a given situation. The versatility is in my ability to select from a wide variety of possible techniques, not in any one technique being good for everything.

What good is "Initiating a turn by actively engaging the Tips"? Well, assuming I've already released the old edges...

** I find this method to be a simple and efficient way to ski on most firm-snow terrain. I simple tip the skis onto the new edges and the tips engage immediately if I'm in a F/A Balanced stance. This way the skis 'drive' me into a turn rather than me having to make any effort to turn the skis into the new direction. No pivot is needed. No unweighting is needed. No push-off is needed. No upper-body rotary is needed.

** I use a variation of this idea a lot in tight bumps and narrow corridors, especially when the surface is soft & fluffy (or dense and wet) and therefor doesn't permit any sort of surface pivot. Here I firmly 'pull back' both feet as I release both edges and rapidly tip my skis onto the new edges. The forward leverage on the tips pins them to the snow, partially bends the tips before edge engagement, causes the shovels to immediately engage and deflect downhill and the skis execute a very short radius turn right from that moment. (I call it a tip-carve though others have their own labels)

** I also use this idea in many drills to help students 'find' the advantage of a more centered stance. Pretty much impossible to get the tips slicing immediately if the skier is back on the tails.

---
Of course the question arises: What exactly does "initiate a turn" mean?

Is it when...
- The skis first begin turning in the new direction? (The generally accepted instructor definition)
- The skis first engage their new edges and begin driving the turn themselves? (Preferred by the general public)
- The skier's CM begins turning in the new direction? (a few on this forum have preferred this)
- The skier makes the very first movement related to the new turn? (a perspective good for analytical math)

.ma
post #65 of 71


 

I would like to point out that in order to initiate turn by loading tips of the ski one has to get VERY far forward (far beyond centered stance) in the transition. In other words skier’s hips should be way in front of ball of the foot, so he can ski from forward to extremely forward stance.

If you are in the forward stance at the end of the turn and you have to move forward even more to create pressure on your tips and unweight your tails (note you using only half of your ski surface – skis will dive in soft conditions) before you can release edges to create tip-carve. This is a valid technique, but hard on skiers quads and effective for packed powder only.

My question is why this became our Mantra for all situations? Where is our ability to select the right technique for the right situation? Also, why use something that require physical effort while easier and effective options are available?

 

See my comments embedded:
 

Quote:
Originally Posted by michaelA View Post

Stroller,

A bit of a sidebar but I'll take a shot at the versatility question. My desire for Versatility is aimed at the skier and not any specific technique. We may not advocate Braking Wedges as a way to ski any more but a Braking Wedge becomes a highly useful technique when it works better than the alternatives in a given situation. The versatility is in my ability to select from a wide variety of possible techniques, not in any one technique being good for everything.
 
No argument here!

What good is "Initiating a turn by actively engaging the Tips"? Well, assuming I've already released the old edges...

** I find this method to be a simple and efficient way to ski on most firm-snow terrain. I simple tip the skis onto the new edges and the tips engage immediately if I'm in a F/A Balanced stance. This way the skis 'drive' me into a turn rather than me having to make any effort to turn the skis into the new direction. No pivot is needed. No unweighting is needed. No push-off is needed. No upper-body rotary is needed.
 
As I said this technique is good for groomers with packed powder!

** I use a variation of this idea a lot in tight bumps and narrow corridors, especially when the surface is soft & fluffy (or dense and wet) and therefor doesn't permit any sort of surface pivot. Here I firmly 'pull back' both feet as I release both edges and rapidly tip my skis onto the new edges. The forward leverage on the tips pins them to the snow, partially bends the tips before edge engagement, causes the shovels to immediately engage and deflect downhill and the skis execute a very short radius turn right from that moment. (I call it a tip-carve though others have their own labels)

I am NOT with you on this, both carve and pivots are widely used but very inefficient in these conditions as they do not provide essential speed control! Active continues steering with elements of flotation is easier on skiers muscles (do not have to bang edges to slow down) and nerves (constant speed with no acceleration and deceleration).


** I also use this idea in many drills to help students 'find' the advantage of a more centered stance. Pretty much impossible to get the tips slicing immediately if the skier is back on the tails.

I am not in any way advocating for loading tails of the ski! Centered stance IMO works the best for any condition! My definition of centered stance is when hips are between the arch and the ball of the foot. This stance require minimal movement from turn to turn and energy efficient in any condition.



---
Of course the question arises: What exactly does "initiate a turn" mean?

Is it when...
- The skis first begin turning in the new direction? (The generally accepted instructor definition)
- The skis first engage their new edges and begin driving the turn themselves? (Preferred by the general public)
- The skier's CM begins turning in the new direction? (a few on this forum have preferred this)
- The skier makes the very first movement related to the new turn? (a perspective good for analytical math)

 

I have to blame my educational background but for me "first movement related to the new turn" is innitiation roflmao.gif

.ma

post #66 of 71
Quote:
Originally Posted by stroller View Post

I would like to point out that in order to initiate turn by loading tips of the ski one has to get VERY far forward (far beyond centered stance) in the transition. In other words skier’s hips should be way in front of ball of the foot, so he can ski from forward to extremely forward stance.

If you are in the forward stance at the end of the turn and you have to move forward even more to create pressure on your tips and unweight your tails (note you using only half of your ski surface – skis will dive in soft conditions) before you can release edges to create tip-carve. This is a valid technique, but hard on skiers quads and effective for packed powder only.


Hmmmm. Not sure you're envisioning what I'm trying to communicate further above. To achieve an effective tip-carve I don't need any tip lead nor do I need to be "severely forward" ahead of time. Below I've attempted a more clearly worded execution.

Coming out of the last turn I'm in transition at a point where my skis are nearly "flat" to the general surface (or surface underneath a covering of soft snow). My ski tips have solid support since the entire base of each tip/forebody is supported by the snow. At this moment I actively dorsiflex both feet while simultaneously pulling each foot 'back' using my knee joint. This briefly 'stalls' both skis while my upper body continues forward.

This brief move creates an overall forward rotation (of the whole skier) and because I quickly run out of dorsiflexion range, my ski tips bear the brunt of it and are 'levered' down into the snow (arresting my overall forward rotation). In this moment I'm also just engaging the new edges which then "take over" the pressuring assignment - which is good since my forward rotation has been halted by then.

In short, my momentary spurt of tip-pressure comes from a brief forward rotational momentum and not from deliberately moving (and holding) body Mass over the tips of the skis. Does that make more sense? It's basically a cheap "momentum trick" used to my advantage.

(And I agree, this idea would result in a face-plant in very deep powder! It works well on a firm surface, over a firm layer under soft snow and even in very dense wet snow if done with care.)

Quote:
Originally Posted by Stroller 
I have to blame my educational background but for me "first movement related to the new turn" is initiation
That is exactly how some people view it. But consider this, my own "first movement" related to the new turn comes at Apex where I begin to release my degree of inclination. This effort is done quite early inside the old turn. Also, I begin moving my new inside-hand/arm forward reaching for the next pole plant/touch while I'm also well inside the old turn. These (and other) movements are my own first movements related to the new turn, yet they occur well before my skis or CM get anywhere near changing direction.

.ma
post #67 of 71
Quote:
Originally Posted by michaelA View Post

Quote:
Originally Posted by Stroller 

I have to blame my educational background but for me "first movement related to the new turn" is initiation

 

That is exactly how some people view it. But consider this, my own "first movement" related to the new turn comes at Apex where I begin to release my degree of inclination. This effort is done quite early inside the old turn. Also, I begin moving my new inside-hand/arm forward reaching for the next pole plant/touch while I'm also well inside the old turn. These (and other) movements are my own first movements related to the new turn, yet they occur well before my skis or CM get anywhere near changing direction.

.ma

 

The crux of good skiing, right there. Failure to do that can result in all sorts of pushoffs, twists etc. When feel myself having a slight check at the end of the turn, it's usually because of not moving early and not skiing to finish the turn.

post #68 of 71
Quote:
Originally Posted by michaelA View Post
.....

Coming out of the last turn I'm in transition at a point where my skis are nearly "flat" to the general surface (or surface underneath a covering of soft snow). My ski tips have solid support since the entire base of each tip/forebody is supported by the snow. At this moment I actively dorsiflex both feet while simultaneously pulling each foot 'back' using my knee joint. This briefly 'stalls' both skis while my upper body continues forward.

This brief move creates an overall forward rotation (of the whole skier) and because I quickly run out of dorsiflexion range, my ski tips bear the brunt of it and are 'levered' down into the snow (arresting my overall forward rotation). In this moment I'm also just engaging the new edges which then "take over" the pressuring assignment - which is good since my forward rotation has been halted by then.
.......

 

 

You just described one more execution technique to initiate the turn by loading tips of the skis. However, independent of execution technique, whether it is extreme forward stance (PSIA-C standard) or dorsiflexion all limitations of loading the tips of the skis stay unchanged:

  1. This technique is applicable for packed powder only (as any significant amount of fresh snow will cause face plant and ice will cause sideway skidding with such a sudden and aggressive edge engagement)
  2. No matter how skier manage to load the tips of the skis, the loading and holding loaded process itself by definition require significant force applied which transfers to skier’s muscle strength and energy expansion. Overwhelming majority of our students are people with cedenary jobs, not athletes! They simply do not have required muscle strength and energy to expand, which IMO makes loading tips of the ski a very inefficient way to initiate the turn, at least for out audience.

P.S. In my attempts to find energy efficient ways to ski any terrain I seem to have more success with techniques where action happens in unloaded state and allow for muscle release and relaxation periods, therefore edge release seems to be the logical way to initiate the turn – it is unweighted action that does not require physical force – just agility.

post #69 of 71
Quote:
Originally Posted by HardDaysNight View Post

It's a great question. "Fore" and "aft" are only meaningful if we specifiy the plane in which we are making the determination. Consider, for example, a line drawn along the direction the skis are moving at the instant in question and passing through the balance point on the ground (where the balance axis intersects the ground). Extend a plane from that line through the CM. Observing in that plane shows that the CM is behind the feet. But, is this the relevant plane? Now, draw a line in the direction in which the CM is moving at the same instant- note that this line points more directly downhill than the line along the skis. Extend a plane down from this CM line again passing through the balance point. Observing in this second plane shows that the CM is over or ahead of the feet. So, which plane of reference is the correct one? I contend that "balance" in this context has to be anticipatory and that the second frame of reference is the valid one - Barnes' concept of "balancing into the future". So, any definition of "aft" has also to specify the plane in which we are at observing the relationship.  
 

Quote:

 

My reference model will still call this "aft" as a simple matter of definition:  the Centre of Mass (roughly the navel area) is behind the Base of Support (the feet).  Can you clarify for me what you would consider "aft" as a matter of definition?    

 

 

I think the planes of reference as you have described them pay more attention to the forces at work, and relative direction of travel (for CoM and BoS), and this makes sense for an overall evaluation of balance.


I've used a simpler starting  point, thinking of the planes as fixed, relative to the skier in a basic standing position.  Hopefully not oversimplified, but I'm drawing a parallel between definitions of pitch, roll and yaw axes, which remain the same for a ship or airplane even as the direction of travel changes.   Now maybe this isn't the best way to look at it, since the mass profile of a skier in motion is not as consistent as that of a ship or an airplane. 

 

For me, "fore/aft" is the plane which defines position or rotation about the pitch axis.  I'm trying to describe "Aft" in this "fore/aft" plane as a simple and objective observation, but I want to be clear that I'm not concluding that "aft" by this simple definition means "out of balance." 

 

In the Hirscher example, I would say he is aft, but still very much in control of his line and not out of balance.  For other skiers, (e.g. average recreational skiers), being in this position would be outside of the comfortable balance range.

 

post #70 of 71
Well, to be honest Stroller, I happen to be one of those self-same non-athletic sedentary folks! I'm also quite lazy when it comes to exerting myself continuously such that I try very hard to minimize the effort I put into skiing. I tend to 'relax into' each new turn whenever possible and avoid any movement pattern that doesn't add value to my intent.
Quote:
Originally Posted by stroller View Post

No matter how skier manage to load the tips of the skis, the loading and holding loaded process itself by definition require significant force applied which transfers to skier’s muscle strength and energy expansion. Overwhelming majority of our students are people with cedenary jobs, not athletes! They simply do not have required muscle strength and energy to expand, which IMO makes loading tips of the ski a very inefficient way to initiate the turn, at least for out audience.

I disagree with the bolded words above and suspect you may be misreading my posts further above. There is no 'significant force' required in what I've proposed. I was very careful to state that what I'm doing is very subtle and takes almost no energy.

That said, I'll repeat that there's no special 'muscle strength' required in what I've described. The movement isn't much more than a brief 'twitch' to pull my feet back and it takes virtually no athleticism at all (which is good because I've no athleticism available). Sure, it takes some accuracy of movement and a reasonable degree of timing, but that's it. I've successfully taught this concept to 6 year-olds, 70 year-olds, overweight people, tall kids, short kids - even kids with Chicken Pox!

The idea is not to 'crush' the tips/forebody into a major bend - it's to momentarily increase tip pressure just enough (and long enough) to get them to engage immediately in a slightly more pre-bent state than normal. After the artificially-early initial engagement, normal turning forces (CF) takes care of continued engagement pressure.

Oh - and I'm changing my story -- thinking about it further I bet it would work just fine in deep powder snow provided one is on a pair of Fat Rockered skis! smile.gif

.ma
post #71 of 71
Quote:
In the Hirscher example, I would say he is aft, but still very much in control of his line and not out of balance. For other skiers, (e.g. average recreational skiers), being in this position would be outside of the comfortable balance range.

MogulMuncher--I would say that you are correct, but not because they lack the strength or athleticism to be "comfortable" in that position. The reason is simply that that "position" is a result of the extreme forces Hirscher is balancing against in the high speed, highly dynamic turns he's making. The same is true of the degree of inclination (tipping into the turn) of World Cup racers at speed--they incline more than "average recreational skiers" because they are going so much faster and balancing against such higher G-forces in their turns. "Average recreational skiers" don't incline so far, not so much because they lack the strength and technical skill, but because at the lower speeds they're moving, that much inclination would be inappropriate--they'd be way out of balance.

It takes more strength to be out of balance than in balance. These movements are the epitome of balance on skis (in four dimensions)--they do not require strength or athleticism. If you practice these movements and you find the need to pull yourself forward with powerful leg and abdominal muscle strength, as ESA coach Squatty might say, "that ain't it"!

Best regards,
Bob
New Posts  All Forums:Forum Nav:
  Return Home
  Back to Forum: Ski Instruction & Coaching