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Philpug

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If a ski moves me, I will turn it.
 

karlo

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The statement in the Facebook post that drew my attention is,

"On hard snow once a ski is tipped on edge and then the camber taken out so the whole ski edge contacts the snow, it cannot bend further"

I get that more tipping doesn't necessarily mean tighter turn on account of more bend. But, still, more bend does mean tighter turn, I'm pretty sure.
 
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HardDaysNight

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The degree to which it is possible to bend a ski is related to the angle to which that ski is tipped. This is a basic and elementary relationship. Why the hell don’t people who purport to be instructors know this?
 

Rod9301

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The statement in the Facebook post that drew my attention is,

"On hard snow once a ski is tipped on edge and then the camber taken out so the whole ski edge contacts the snow, it cannot bend further"

I get that more tipping doesn't necessarily mean tighter turn on account of more bend. But, still, more bend does mean tighter turn, I'm pretty sure.
Actually, the more you tip the ski, the shorter the turn radius is.
 

JESinstr

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Poor level of training?
Not so much poor training UKE but IMO, the lack of proper training, For so long, and for reasons unknown, any attempt to educate instructors (God forbid the customer) on the most basic elements of physics was verboten. How many on this forum do you see referring to centrifugal force as the force that turns? And when you try and tell them that it is centripetal force and that centrifugal is the equal and opposite, you get a "Whatever....".

The modern shaped ski is an incredible circular travel tool. I find it disappointing that many instructors don't have a basic understanding of the turning force, how it works, how it is generated, how it pushes vs pulls, and how its existence is totally dependent on the skier taking constant action.
 

Missile Bandits

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philpug is demonstrating how to get the most bend out of your ski. And it's not even on edge. So not only skis on edge bend. You can bend a ski more if it's not on edge.
 

markojp

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Dunno... I guess we're lucky to hang out with folks who actually get physics so quick references are no big deal if needed or useful on the chair ride up. Lots of Boeing engineer folks, architects, lawyers, etc... on ski school staffs out here. Most of my favorite divisional staff folks have race backgrounds, so this is pretty straight forward. I will say though, I'm always amazed how some will always mangle, misconstrue, and misinterpret what has been clearly and susinctly stated, beautifully demoed, and understood by the rest of the group in a lesson or clinic* . It is what it is. Some folks just take awhile. It usually isn't a matter of basic intelligence, but simply ego standing firmly in the path of experimenting with the unfamiliar.

* both giving and receiving
 

dbostedo

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For people who would say that skis can turn the skier without the skier turning the skis, and without the skis carving an arc-to-arc turn, how so?

I'm late to this thread, but I've been thinking about this. When I started taking lessons a few seasons ago, I was a terrible backseat z-turner, and couldn't carve at all. Even now, I struggle with it, though I've improved a lot.

But relevant to your question @LiquidFeet, I feel like if I'm trying to carve, and not doing it successfully, the resulting turn is a skidded turn, but without forced rotary movements (so it's still what I would call "the ski turning me"). The skidding would come from my weight (or consequently my pressure on the skis) probably being too far back or forward, so the skis don't "hook up"; But I'm not consciously rotating my legs or upper body.

At least, that's what it seems like, sitting here in the summer. I could be wrong and I'm actually forcibly steering - my self-awareness of what I'm doing isn't always the best.
 

Steve

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@dbostedo when I'm struggling with getting a nice arc-to-arc sequence of turns going, I'll stop trying. I'll ski wide steered turns and really get comfortable with some speed on them and let the carving come naturally, which it usually does. Rhythm, commitment and flow are absolutely necessary to carve, and when you start out "trying" to carve it can at times interfere with those tactical aspects.

Other times of course carving just comes right away, but it's a nice thing to keep in mind. Stop trying. Get some speed. Allow the carves to come.
 

François Pugh

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Trying to carve a turn without a high enough edge angle, i.e. less than the "Critical Angle", results in skis turning skier without carving arc-2-arc and without skier turning skis.
https://www.pugski.com/threads/glossary-of-skiing-terms.4753/
"Critical Edge Angle

Related to "Platform Angle" (both terms coined by Ron LeMaster), this concept describes the edge angle of the ski not in terms of its relation to the slope, but relative to the force the skier applies to it. Critical edge angle denotes the minimum platform angle that enables a ski to hold—or the angle at which the ski releases its edge grip and allows the ski to slip downhill. While edge angle relative to the slope, combined with sidecut and appropriate pressure to bend the ski, determines the radius of the bent ski's arc and, therefore, its "turning radius," Platform Angle determines whether or not the ski will hold or slip sideways. Essentially, a ski tipped to a 90 degree angle or less (an acute angle) to the force applied to it (a line from the Center of Mass to the ski's edge) will tend to grip; when tipped to greater than 90 degrees, it will release and slip. A platform angle of 90 degrees to the applied force, then, is "Critical Edge Angle"--the minimum angle for a ski to hold. Note that this angle is independent of the angle of the ski to the snow surface, which depends on the skier's inclination angle and the angle of the slope, as well as the skier's angulation.Platform angle depends only on the degree of angulation."

Note that if you try to carve a turn wider than your side cut radius, you will also not be carving arc-2-arc.
Note that if you are going too fast for your ski's side cut and desired tight turn shape you will also not achieve critical angle; tipping skis to critical angle results in a smaller turn that required a higher critical angle, which requires a smaller turn, which....
 
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LiquidFeet

LiquidFeet

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@François Pugh, thanks for bringing that up. Do you teach?

Here's platform angle explained in pictures by Bob Barnes. I don't hear the phrase "platform angle" used very often. Sometimes people say "critical edge angle" but don't explain that it isn't the ski's angle to the snow surface, but to where the CoM is above the foot. I think a lot of people think the ski's angle to the snow, and the pressure underfoot, together determine whether it holds. So they push their feet out harder, farther, in order to get grip. Platform angle needs to be 90 degrees or less. It doesn't matter what the ski-snow angle is - according to Ron LeMaster.

Bob Barnes' simple diagram for platform angle and angulation copy.jpeg
 
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cantunamunch

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and the closer the critical angle is going to be to 90 degrees.

Have you tried solving for the static case yet to figure out what the margin of error is?

The expression mg cosΘ < μ * mg sinΘ simplifies to tan Θ> 1/μ

For μ values of 0.15 to 0.25 (dry Ptex on Steel ) we get 76 degrees. In other words, a park rat on a super-cold day needs a rail of more than 14 degrees to slide at all. For wet ptex, of course, that value drops by a factor of 10.
 
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François Pugh

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No but one thing I did explore on the hill and in Excel with regards to tipping angle and turn radius dialed up, is because it is approximated by a cosine function, the further along you are on the curve (i.e. greater tipping angle) the greater the effect of just a little bit more tipping. Probably why you see so many folk getting launched by their SL skis when they begin to explore high edge angles.
 

karlo

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You turn the skis vs the skis turn you. Ah, so desu ka?

“You turn the skis”
“I loll the ball down the hill”; “The ball lolls down the hill”. The only way we can loll the ball down the hill is if we give it more impetus than gravity. If it is just gravity, then we have dropped it or let it go, and “the ball lolls down the hill”. Can we give impetus to the skis? When we steer, we can. We can, as others have described, store energy with an inwards counter and, in the unwind, make the ski turn faster and at a tighter radius than it would on its own. However, in a pure park-and-ride carved turn, we give it no more impetus than gravity and the ski solely turns on account of its design and snow interaction; we cannot turn the skis; in fact, our intent is for the skis to turn themselves. Thus, in a steered turn, we turn, or help turn the skis; in a carved turn, we do not turn the skis; the answer depends on the type of turn we are making.

“The skis turn you”
We can steer it, but, based on its design, it will go where it will go on account of gravity and snow interaction. We can tip it into a carve; it will still go only where it can go based on design, gravity, and snow interaction. We may have the intent to travel from point A to point B, but the course of travel to B is predetermined, as it is when we step onto a train. Despite the fact that we chose the train, the train turns us; we do not turn the train.

Sumimasen, “You turn the skis vs the skis turn you” is, as cantunamunch said, a false dichotomy, because “The skis turn you” is always true and never false. “You turn the skis” has no single answer; the answer can be both true or false.

“I've done this because, philosophically, I'm sympathetic to your aim. I can tell you, with no ego, this is my finest ski. If, on your journey, should you encounter God, God will be cut.” - Hattori Hanzo(?)
 

François Pugh

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FIFY
In a pure, BUT NOT park-and-ride, carved turn, we TIP THE SKIS, tip THEM into a carve; THEY will go only where WE TIP THEM TO GO, based on HOW MUCH WE TIP THEM, SKI design, gravity, and snow interaction. We may have the intent to travel from point A to point B, AND the course of travel to B is determined, BY HOW WE TIP THE SKI, as it is when WE PUSH ON THE HANDLE BARS ON A BICYCLE.
:P

Do not mistake the finger pointing at a park and ride turn for a pure-carved arc-2-arc turn.
 

karlo

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Enjoyed reading up on Hattori Hanzo over lunch and came across the clip. YouTube comments are illuminating.


So, with our finest skis, are they the instrument, or are we?

for Liquidfeet, from karlo. :toast
 

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