What's essential for carving on hard snow?

[skier]

Thank you James. (And Ron...)

My take:
If a skier can hold an edge traversing the conditions then it is physically possible to carve those conditions.

I'm sorry - I don't understand your point. There is this force called gravity on the hills I ski. It is certainly trying to take the skis sideways - just flatten your skis to the slope to see.[/QUOTE]

That's funny. You just answered your own question. Traverse across an icy slope with nearly flat skis. What happens? You'll go across somewhat and you'll skid down somewhat. On a really icy slope, you won't even make it across, you'll just skid down. This is analogous to turning with low edge angles at the top of the turn where you'll turn somewhat and skid somewhat. Sounds like in your mind you were comparing traversing with high edge angles with turning with low edge angles, and that's not valid. We're only considering the skidding phase of the turn where the edge angles are still low.

I think you helped me clear up another concern though. At low edge angles the centrifugal force is low, but very soon you start turning across the hill, and then gravity adds in with the centrifugal force, so there can be quite a bit of force that needs to be held with a low edge angle ski.

 

[LiquidFeet]

....
Anyone have the 1999 The Skier's Edge by Lemaster handy? Possibly there he uses critical edge angle?
He uses the term platform angle in 2010.

I've got that book. On pages 19-20 he explained the concept and labled it the "critical edge angle."
In the next book, Ultimate Skiing, he explained it the same way but changed what he calls it to "platform angle."
I suspect he did this because people continued to think it had to do with edge angle to the snow despite his explanations to the contrary.
Confirmation bias at work.
Or difficulty seeing in the mind's eye the two lines that create the platform angle.

 

[James]

No
Edge lock!

Tips follow tails, One clean line per ski

Happens all the time

Edgelocked = carving = turning = going uphill = stopping.

You're turning across the slope.

 

[James]

I've got that book. On pages 19-20 he explained the concept and labled it the "critical edge angle."
In the next book, Ultimate Skiing, he explained it the same way but changed what he calls it to "platform angle."
I suspect he did this because people continued to think it had to do with edge angle to the snow despite his explanations to the contrary.
Confirmation bias at work.
Or difficulty seeing in the mind's eye the two lines that create the platform angle.

Well, finally! A source. At least we go back 20 years with the term. I think your right about why he changed it as it is stil causing confusion.

 

[Uke]

Gravity does not pull you or your skis down the hill. It pulls you toward the center of the earth. Ground reaction force pushes you off the slope and down the hill.

uke

 

[razie]

A stivot is just one type of redirection. Read page 34 in the linked document. Make sure to read both the initiation phase and the turning phase. From your posts, I've gathered that you view minor redirections as just carving and then have a separate category for stivots, but in reality there's a broad spectrum with many turns that have minor redirection at the top of the turn.

https://ussa.org/moodle_instances/m...b/9e/fb9e887f4144659d041bb4dd791b085c7a650292

Ok... thanks, I guess? It seems they completely agree with me that stivots (pivot and skid hard to dump speed) are not quite redirection:

Emphasis on "slightly".

It's interesting though about your inference from my posts. I think I only had that argument once, a long time ago on epic, with Rick, about a specific turn of Hirscher, which he used as an example of redirection, but I begged to differ - that was a turn where the skis were indeed not engaged and turning, but I argued that they did not alter the line, so it wasn't an actual intentional redirection...

But... tomato, tomahto - I don't see slight redirections that do not affect materially the line as a different technique. I see them as either normal adjustments that one makes automatically - or the result of a loss of control / focus when the racer is focused on something else - these breakdowns in technique are normal when you push the limits of skiing.

It's not like I'm a "redirection denier" or something , but I do take issue with it being proposed as the only technique that matters... which seems to be your position - similar to Rick's in that regard, from what I remember - I think he was suggesting this technique will change skiing forever or something like that.

 

[razie]

That's funny. You just answered your own question. Traverse across an icy slope with nearly flat skis. What happens? You'll go across somewhat and you'll skid down somewhat. On a really icy slope, you won't even make it across, you'll just skid down. This is analogous to turning with low edge angles at the top of the turn where you'll turn somewhat and skid somewhat. Sounds like in your mind you were comparing traversing with high edge angles with turning with low edge angles, and that's not valid. We're only considering the skidding phase of the turn where the edge angles are still low.

Not true. When skidding across an icy slope, you have weight/pressure that causes the skid. At low angles at the top of the turn, you'll skid only if you push into the skis laterally. Otherwise, they have no reason to displace laterally. It's like my fridge: it will stay in place if nobody is pushing it around.

 

[François Pugh]

Tip rocker on hardpack will result in a brief skidding phase at the tips as the tips are introduced to the snow or ice.
Also when skis are running flat going straight ahead direction of travel does not match the curved edge except at one point.

The above are not the "skid phase present in all carved turns" which refers to the traditionally taught method of turning 40 years ago and still enshrined in many teaching systems, unwheighted pivot to a steering angle prior to tipping to carve while bending the tips with tip pressure.

Even back then there was another option, bend the tips then tip with no pivoting. This other option required more skill, but provided more DH wins.

 

[dbostedo]

... It's like my fridge: it will stay in place if nobody is pushing it around.

It stays in place? Really? My refrigerator always seems to be running.

 

[skier]

Not true. When skidding across an icy slope, you have weight/pressure that causes the skid. At low angles at the top of the turn, you'll skid only if you push into the skis laterally. Otherwise, they have no reason to displace laterally. It's like my fridge: it will stay in place if nobody is pushing it around.

The moment you begin a turn there is a force called centrifugal force that pushes laterally on the skis. At the top of the turn, the forces are small, but so is the grip of the ski, because the edge angles are very low, and the edges haven't dug in yet to make a deep groove. Also, depending on where you're turning there could also be a significant component of the force of gravity pushing laterally as well.

 

[geepers]

That's funny. You just answered your own question. Traverse across an icy slope with nearly flat skis. What happens? You'll go across somewhat and you'll skid down somewhat. On a really icy slope, you won't even make it across, you'll just skid down. This is analogous to turning with low edge angles at the top of the turn where you'll turn somewhat and skid somewhat. Sounds like in your mind you were comparing traversing with high edge angles with turning with low edge angles, and that's not valid. We're only considering the skidding phase of the turn where the edge angles are still low.

I think you helped me clear up another concern though. At low edge angles the centrifugal force is low, but very soon you start turning across the hill, and then gravity adds in with the centrifugal force, so there can be quite a bit of force that needs to be held with a low edge angle ski.

You've avoided answering my question: is it easier to traverse a gentle icy slope or steep icy slope?

In the case above - flattening the skis - the platform angle goes greater than 90 degrees and the skis slip.

 

[LiquidFeet]

The moment you begin a turn there is a force called centrifugal force that pushes laterally on the skis. At the top of the turn, the forces are small, but so is the grip of the ski, because the edge angles are very low and the edges haven't dug in yet to make a groove. Also, depending on where you're turning there could also be a significant component of the force of gravity pushing laterally as well.

Solution: skis need sharp edges to penetrate hard snow, skier needs to angulate/inclinate appropriately to establish a platform angle less than 90 degrees from the very start of the turn, skier must avoid twisting the foot (or feet) or pushing it/them outward, skier also needs to avoid allowing the upper body to twist to point in the direction of the new turn, which transfers into twisting the skis. Do all this and don't do it in a jerky way, and the groove will be cut even with the skis at a low edge angle. Oh, and the skis need torsional stiffness (so they don't let go at tip and tail), and preferably a shape made for carving.

You're right about centrifugal force aka momentum tending to keep the skier to moving in a straight line to the side of the trail. But the effect of gravity's pull is in the opposite direction at the top of the turn. Gravity doesn't pull the ski to the outside of the new turn and combine with momentum, but towards the inside of the new turn. They counter each other.

When I see a skid (or feel my skis skidding) at the top of the turn, it's usually to the outside of the turn, opposite of what gravity would promote. The skier (could be me) is usually rotating or pushing the ski unconsciously, or failing to establish that platform angle. If it's my turns that are behaving badly, I tend to keep my new inside foot up under me more, and that takes care of the platform angle (well, usually).

 

[geepers]

Gravity does not pull you or your skis down the hill. It pulls you toward the center of the earth. Ground reaction force pushes you off the slope and down the hill.

uke

And there's no such thing as sunrise. The Earth rotates to the east.

 

[razie]

The moment you begin a turn there is a force called centrifugal force that pushes laterally on the skis.

Not true. The presence of a centripetal force causes circular motion, i.e. a turn. The turn does not start by magic... it requires a centripetal force. That's Newtonian physics

Quote:

the moving object is undergoing acceleration by a centripetal force in the direction of the center of rotation. Without this acceleration, the object would move in a straight line, according to Newton's laws of motion.​

https://en.wikipedia.org/wiki/Circular_motion

To clarify again: centrifugal force is a result of circular motion and circular motion is a result of a centripetal force. Good physics lead to good skiing.

(trick ?) question: where does the centripetal force come from?

p.s. centrifugal force it is not even real. It's just inertia in a rotational frame of reference

 

[François Pugh]

Which frame of reference is the "real" one?

 

[skier]

You've avoided answering my question: is it easier to traverse a gentle icy slope or steep icy slope?

In the case above - flattening the skis - the platform angle goes greater than 90 degrees and the skis slip.

If the gravitational force vector along the slope for a 3 degree slope for example was equal to or greater than the centrifugal force for a turn with an edge angle of 3 degrees then it seems to me that my explanations for the skidding phase was probably invalid. Too lazy to do the calculation. But, I'm just speculating on why that skidding phase exists. That section in the Physics of Skiing was written after the invention of parabolic skis and they do mention that technology. So, I don't have any good reasons to say it's outdated. I don't think we're going to answer this with thought experiments back and forth. We've done a few and there are potential flaws in all. I think it could go on forever. Again, good time to stop....

 

[razie]

Which frame of reference is the "real" one?

Mine, of course!

 

[razie]

But, I'm just speculating on why that skidding phase exists. That section in the Physics of Skiing was written after the invention of parabolic skis and they do mention that technology. So, I don't have any good reasons to say it's outdated. I don't think we're going to answer this with thought experiments back and forth. We've done a few and there are potential flaws in all. I think it could go on forever. Again, good time to stop....

That section was copied from / based on a 1987 study of a turn where a racer had to skid the top. Of course it includes a skidding phase. Here's the author's explanation...

 

[geepers]

If the gravitational force vector along the slope for a 3 degree slope for example was equal to or greater than the centrifugal force for a turn with an edge angle of 3 degrees then it seems to me that my explanations for the skidding phase was probably invalid. Too lazy to do the calculation. But, I'm just speculating on why that skidding phase exists. That section in the Physics of Skiing was written after the invention of parabolic skis and they do mention that technology. So, I don't have any good reasons to say it's outdated. I don't think we're going to answer this with thought experiments back and forth. We've done a few and there are potential flaws in all. I think it could go on forever. Again, good time to stop....

No reason to just do thought experiments - this is skiing, not theoretical physics.

Try this practical experiment to determine if it is your "edge angle" or Ron LeMaster's platform angle which is really the most important in whether or not a ski slips.

Traverse an easy blue icy pitch without slipping - this will require angulation, upper body leaning out from the hill to keep weight over the downhill ski.
Now without changing the angle of the skis to the snow straighten up, inclining body to the vertical and then into the hill. At some point the downhill ski will slip even though there is no change in the ski/snow angle.

 

[James]

No reason to just do thought experiments - this is skiing, not theoretical physics.

Try this practical experiment to determine if it is your "edge angle" or Ron LeMaster's platform angle which is really the most important in whether or not a ski slips.

Traverse an easy blue icy pitch without slipping - this will require angulation, upper body leaning out from the hill to keep weight over the downhill ski.
Now without changing the angle of the skis to the snow straighten up, inclining body to the vertical and then into the hill. At some point the downhill ski will slip even though there is no change in the ski/snow angle.

The stick figure posted several pages back need 4deg of angulation to get the platform angle to hold. The interesting, and non intuitive thing is besides edge angle not being the main determinate, slope angle is not involved.
Here it is again:

So the stick figure needs 4.2deg of inclination for his left ski to hold. Note his right ski would hold in a traverse but there's no knee bend.

More than enough angulation.

This is how Reid defines knee angulation.
2010 Thesis:
https://brage.bibsys.no/xmlui/bitstream/handle/11250/171325/reid phd 2010.pdf?sequence=1&isAllowed=y

There's one thing that I don't believe was taken into account with that description, and it's maybe the most important factor. This is the holding force of the snow. Sometimes the snow just breaks away, and I think that's the main contributor to the skidding phase. Right when the turn starts, there's very little groove, and in some conditions that snow will hold, but in other conditions the snow breaks away causing skidding.

Lemaster gets to that on the next page.