Shiffrin free skiing

[jimtransition]

Heard of Q angle, ramp angle, steering angle, edge angle and platform angle.

What's critical angle?



Really? Resorts seem to be full of people having trouble stopping their skis from skidding unintentionally. This can be due to incorrect platform angle but it's also very commonly due to fore/aft balance issues, particularly being too far forward and pivoting the rear of the skis around a point towards the tips.

Haha, agree with this for sure, I wish my skis just locked onto an edge and stayed there without any effort.

 

[François Pugh]

Heard of Q angle, ramp angle, steering angle, edge angle and platform angle.

What's critical angle?



Really? Resorts seem to be full of people having trouble stopping their skis from skidding unintentionally. This can be due to incorrect platform angle but it's also very commonly due to fore/aft balance issues, particularly being too far forward and pivoting the rear of the skis around a point towards the tips.

There used to be a really good gif floating around epicski.com that illustrated it. Bob Barnes may have posted it. I can't recall.

In a nutshell it shows that at any given instant in a given turn you must have you skis tipped up sufficiently so that the net force you push on them is directed more down into the snow than a line that would be perfectly perpendicular to the plane of the ski. That keeps the ski in the groove. If turn forces are greater than that, the net force points more along the slope and less into the slope and your skis slip out of the groove (because that greater turn force would need a bigger "critical" angle and you haven't tipped the skis more. If you tip your ski less than the required critical angle for those turn forces, you push the ski out of it's groove. You can tip your skis more and you'll be fine; tip them less and you will skid. You can also move your centre of mass more toward the outside of the turn (angulation), changing the geometry and critical angle required, so that gravity and turn forces now point more down and not slip.

 

[Sanity]

Heard of Q angle, ramp angle, steering angle, edge angle and platform angle.

What's critical angle?



Really? Resorts seem to be full of people having trouble stopping their skis from skidding unintentionally. This can be due to incorrect platform angle but it's also very commonly due to fore/aft balance issues, particularly being too far forward and pivoting the rear of the skis around a point towards the tips.

Haha, agree with this for sure, I wish my skis just locked onto an edge and stayed there without any effort.

Well this is awkward. I figured people are looking to disagree with me no matter what I write, so I decided not to write anything at all. I copied and pasted, verbatim, Jamt's words on the matter. I thought he would recognize it as such and discuss. Instead, promisingly, he seemed to agree with himself for the most part. Unfortunately, this has created a situation where people are disagreeing with Jamt while thinking it's me. Regardless, you'll have to ask him about it, since those are his words, not mine.

 

[geepers]

There used to be a really good gif floating around epicski.com that illustrated it. Bob Barnes may have posted it. I can't recall.

In a nutshell it shows that at any given instant in a given turn you must have you skis tipped up sufficiently so that the net force you push on them is directed more down into the snow than a line that would be perfectly perpendicular to the plane of the ski. That keeps the ski in the groove. If turn forces are greater than that, the net force points more along the slope and less into the slope and your skis slip out of the groove (because that greater turn force would need a bigger "critical" angle and you haven't tipped the skis more. If you tip your ski less than the required critical angle for those turn forces, you push the ski out of it's groove. You can tip your skis more and you'll be fine; tip them less and you will skid. You can also move your centre of mass more toward the outside of the turn (angulation), changing the geometry and critical angle required, so that gravity and turn forces now point more down and not slip.

That's platform angle...

Non?

 

[François Pugh]

The two angles (platform angle and critical angle) are related, but differ slightly in definition. I don't remember the exact definitions. One may have to be greater than 90 degrees and the other less than 90 degrees. Exactly what lines define the angle differs. However, what is the same is when the ski isn't tipped enough for the net force acting (I include dynamic forces), the ski will be getting pushed out of its groove. The key determining factor being the direction of the net force compared to the plane of the tipped ski.

 

[mdf]

That's platform angle...

Non?

Critical angle is the value of the platform angle required to avoid skidding. It's still a platform angle even when it's not enough.

 

[Jamt]

Well this is awkward. I figured people are looking to disagree with me no matter what I write, so I decided not to write anything at all. I copied and pasted, verbatim, Jamt's words on the matter. I thought he would recognize it as such and discuss. Instead, promisingly, he seemed to agree with himself for the most part. Unfortunately, this has created a situation where people are disagreeing with Jamt while thinking it's me. Regardless, you'll have to ask him about it, since those are his words, not mine.

That was a sneaky thing to do, but I can understand that if you feel constant disagreement. Anyway, my response was " I don't think I said anything that contradicts this. I was primarily pointing out the difference between steering angle and rotation. ".
I then discussed some more detail of some terminology. Hope I did not contradict myself but if I did you are welcome to point it out. I'm always up for understanding more, and I'm sure I have changed my opinion on matters a number of times in the past.

Regarding the critical angle, I don't really like it because you cannot say what it is. You cannot look at a picture and say what it should be.
If the skis is digging itself deeper you have reached the critical angle, if it isn't you have not. The difficult part is the borderland, when you go from skidding to edge locked (i.e. having achieved critical angle) or vice versa. Note though according to the picture I posted that the tail locks before the tip. The key here is dynamics, i.e. "accelerating up or down always". If you are in a static turn and suddenly the edge locks you will quickly be ejected out of that turn.
Sure you can have an edge locked ski and make it slip again, but that also means that the turn forces reduce drastically and in a racing context that usually leads to a failed run.

In the Shiffrin video the edges "lock" relatively late, and thus she has a short and distinct pressure phase. As it should be.
If you lock the edges too early in a carved turn, like many do, sure you will have "early pressure", but it usually leads to a (semi) static turn without a real finish. Also the maximum pressure will never be anything near a proper SL race turn (3-5 gs)

Edit2: Most people NEVER ski with their edges locked when they have high speed. They just ski assisted by the side cut. Just because you leave tracks that looked carved does not mean the skis were edge locked.

 

[geepers]

The two angles (platform angle and critical angle) are related, but differ slightly in definition. I don't remember the exact definitions. One may have to be greater than 90 degrees and the other less than 90 degrees. Exactly what lines define the angle differs. However, what is the same is when the ski isn't tipped enough for the net force acting (I include dynamic forces), the ski will be getting pushed out of its groove. The key determining factor being the direction of the net force compared to the plane of the tipped ski.

Hmmm... Ron le Master uses the word "critical" 12 times in the 224 pages of Ultimate Skiing. But never associated with the word "angle" or "edge". He does describe platform angle and the need to keep it below 90 degrees to keep the ski in its groove.

Critical angle is the value of the platform angle required to avoid skidding. It's still a platform angle even when it's not enough.

So one is the actual angle (platform angle) and the other is the scalar quantity to achieve a desired outcome?

More accurate to describe as the "critical value of the platform angle" rather than the

critical edge angle.

since it has seems to do have nothing to do with edge angle.

 

[Jamt]

Hmmm... Ron le Master uses the word "critical" 12 times in the 224 pages of Ultimate Skiing. But never associated with the word "angle" or "edge". He does describe platform angle and the need to keep it below 90 degrees to keep the ski in its groove.



So one is the actual angle (platform angle) and the other is the scalar quantity to achieve a desired outcome?

More accurate to describe as the "critical value of the platform angle" rather than the

since it has seems to do have nothing to do with edge angle.

I don't know where the term comes from but "critical value of the platform angle" is just 90 degrees so that does not make much sense.
I'd rather see it as the "edge angle required to achieve critical platform angle (<90 deg)", but that is also exactly why I don't like the term, because it also depends on other factors. Edge locked or not edge locked is good enough IMO, but even that leaves room for interpretation.
The easiest way to get a feel for what it is is to make a hockey stop with gradually increasing edge angle. You will feel very distinctly when the ski has reached critical angle, i.e. edge lock

 

[JESinstr]

As I read all the posts above I realize how elitist (please don't take as a slur) most of you are in your mindset and basic assumptions on the process of Carving. Yes I said process, not outcome, not technique, PROCESS. I define Carving as the PROCESS of converting straight line travel (energy) into circular travel (energy) . Simple as that. This is what the tool we refer to as modern shaped ski is designed to do.

As a teacher of the sport (not just a specific niche segment such as racing or bumps), I can begin teaching this critical process at the very beginning of the learning cycle starting at the wedge.

@geepers rightfully pointed out: "Resorts seem to be full of people having trouble stopping their skis from skidding unintentionally". Well Duhhhhh. If you relegate teaching the basic critical function of the ski to only the advanced/high end skiing population what do you expect?

Other than the critical skill of building and managing edge angle the only other angle I deal with when executing the carving process is my entry (into the realm of circular travel) angle. Much like a space capsule returning from the moon into earth orbit, you need to set up a re-entry angle). IMO, this angle is instinctively and dynamically calculated based on one's level of carving process skills.

This is what you see in Shiffrin's video. As she floats from arc to arc (circle to circle) she is instinctively setting up her entry angle, based on her COM's direction of travel, so that the skis will be totally utilized in the carving process.

 

[LiquidFeet]

Heard of Q angle, ramp angle, steering angle, edge angle and platform angle.
What's critical angle?

Below is Bob Barnes' graphic illustration of "platform angle."

It is my understanding that "critical angle" often is used to mean a particular edge angle to the snow that determines whether the ski holds and thus whether it can track as in a carved turn. So "critical angle," if it means that, contradicts what Bob is indicating here.

Ron LeMaster also talks about Platform Angle as the determinant of grip in his book Ultimate Skiing, agreeing with Bob. Neither of these two talk about "critical angle" in their various writings, as far as I know, as something that determines whether a ski grips or slips.

 

[LiquidFeet]

Here's another from Bob. He makes understanding so easy.

 

[LiquidFeet]

Most people NEVER ski with their edges locked when they have high speed. They just ski assisted by the side cut. Just because you leave tracks that looked carved does not mean the skis were edge locked.

@Jamt can you say more about this? You are implying there's a difference between "carved" and "edge locked" turns which the quality of the tracks doesn't reveal.

 

[Sanity]

Below is Bob Barnes' graphic illustration of "platform angle."

It is my understanding that "critical angle" often is used to mean a particular edge angle to the snow that determines whether the ski holds and thus whether it can track as in a carved turn. So "critical angle," if it means that, contradicts what Bob is indicating here.

Ron LeMaster also talks about Platform Angle as the determinant of grip in his book Ultimate Skiing, agreeing with Bob. Neither of these two talk about "critical angle" in their various writings, as far as I know, as something that determines whether a ski grips or slips.
View attachment 133217

Lord forbid that I speak for Jamt, and perhaps he'll completely disagree with this, and I won't argue, but in my mind it has to do with speed. For a particular edge angle there's a maximum angular speed where it's impossible to maintain a platform angle where the skis will hold. For example, at 20 degrees edge angle, once you exceed a certain angular speed the centrifugal force will topple you out of the turn. In order to keep from toppling out of the turn, you have to lean your center of mass lower inside the turn. However, if you keep leaning lower (without increasing the edge angle), you'll eventually exceed the platform angle and the skis won't grip anymore like in the picture above on the right. Therefore, for any given speed, there's a minimum edge angle that must be obtained for the skis to carve according to the turning radius (sidecut) of the skis. Until you reach this minimum edge angle, the equation of centrifugul force and minimum platform angle are balanced by having the skis carve a wider arc. But, this wider arc is not the arc specified by the sidecut, so it's essentially adding in more of a skidding component.

 

[Jamt]

Lord forbid that I speak for Jamt, and perhaps he'll completely disagree with this, and I won't argue, but in my mind it has to do with speed. For a particular edge angle there's a maximum angular speed where it's impossible to maintain a platform angle where the skis will hold. For example, at 20 degrees edge angle, once you exceed a certain angular speed the centrifugal force will topple you out of the turn. In order to keep from toppling out of the turn, you have to lean your center of mass lower inside the turn. However, if you keep leaning lower (without increasing the edge angle), you'll eventually exceed the platform angle and the skis won't grip anymore like in the picture above on the right. Therefore, for any given speed, there's a minimum edge angle that must be obtained for the skis to carve according to the turning radius (sidecut) of the skis. Until you reach this minimum edge angle, the equation of centrifugul force and minimum platform angle are balanced by having the skis carve a wider arc. But, this wider arc is not the arc specified by the sidecut, so it's essentially adding in more of a skidding component.

Yes, very good. If we take skier A2 above for example. Can he ski with that edge angle and the ski will hold? Maybe for an very small time but it is quite obvious that it will not work without even considering any math. Say that he is going 70 mph, what will happen?
The ski will likely surf on the top of the snow or he will eject like a fighter pilot. This is also related to you other question above @LiquidFeet .

What is also relevant is dynamics. Say for example that skier A2 has just landed like that after dropping a jump, then the skis will of course lock in harder, but he will probably eject out of the coming turn because he did not establish edge angles.

The typical skier that does not carve edge locked does also stand significantly on the inside ski, and thus Bob's pictures are not relevant.

 

[Pdub]

Because she is free skiing I wonder what type of ski she is skiing? One wouldn't think she is not on a full race ski from her WC skis, if she just out having fun. When you figure she can have any ski she wants, what does she chose for free skiing? A while back wasn't there a thread that talked about when she took a break and she got a pair of skis from some local ski shop?

I'd bet my car she is on 157 cm FIS slalom skis.

 

[François Pugh]

Lord forbid that I speak for Jamt, and perhaps he'll completely disagree with this, and I won't argue, but in my mind it has to do with speed. For a particular edge angle there's a maximum angular speed where it's impossible to maintain a platform angle where the skis will hold. For example, at 20 degrees edge angle, once you exceed a certain angular speed the centrifugal force will topple you out of the turn. In order to keep from toppling out of the turn, you have to lean your center of mass lower inside the turn. However, if you keep leaning lower (without increasing the edge angle), you'll eventually exceed the platform angle and the skis won't grip anymore like in the picture above on the right. Therefore, for any given speed, there's a minimum edge angle that must be obtained for the skis to carve according to the turning radius (sidecut) of the skis. Until you reach this minimum edge angle, the equation of centrifugul force and minimum platform angle are balanced by having the skis carve a wider arc. But, this wider arc is not the arc specified by the sidecut, so it's essentially adding in more of a skidding component.

Yes, and the speed at which the turn forces will preclude clean arc-2-arc carving depend on the tipping angle (higher tipping angles with tighter turns will release at lower speeds) and the side-cut turn radius of the ski (release from clean arc-2-arc carving at higher speed for longer side-cut radius skis).

 

[geepers]

Shiffren’s turns in the Gellie commentary are short, pulsed slalom turns in which she is looking to be on and off the edges as quickly as possible with maximum lateral displacement for minimal time. They are not, contrary to Gellie’s view, pure, carved arcs and are not intended to be. The top of the turn is deliberately truncated to achieve her goal. That much is obvious from the tracks. It is in these kinds of turns that a transitional “float” is essential.

There is, however, another kind of transition which facilitates a more complete carved arc when that is desired. Sasha Rearick in one session I worked with him describes this as remaining “heavy” through transition. Pressure is drawn from one foot to the other by progressive shortening/lengthening of the respective legs without any period of lightness (amazing or otherwise for those of a certain vintage!). It’s a very powerful, grounded kind of transition in which the skis track throughout the entire cycle as if they’re on rails. Very different from Shiffren’s turns here but ones that she certainly employs when she has the need.

Think we are missing the key point that Tom Gellie was making. It's not whether these turns represent perfect carving. It's the timing of pressure - as per the last part of the vid title "How early is it?" Anwser: not early.

There's a good vid on BPS that's relevant. Makes the point that if we extend too early in the turn we go vertical. If we time the extension correctly the angles created results in a lateral extension.

 

[geepers]

The easiest way to get a feel for what it is is to make a hockey stop with gradually increasing edge angle.

Could also do it in a simple traverse on a slope. Which makes it easier to manage fore/aft at the same time.

Other than the critical skill of building and managing edge angle the only other angle I deal with when executing the carving process is my entry (into the realm of circular travel) angle. Much like a space capsule returning from the moon into earth orbit, you need to set up a re-entry angle). IMO, this angle is instinctively and dynamically calculated based on one's level of carving process skills.

Entry angle.... that's a new one.... It's the angle between what and what? How do we control it?

Below is Bob Barnes' graphic illustration of "platform angle."

It is my understanding that "critical angle" often is used to mean a particular edge angle to the snow that determines whether the ski holds and thus whether it can track as in a carved turn. So "critical angle," if it means that, contradicts what Bob is indicating here.

Ron LeMaster also talks about Platform Angle as the determinant of grip in his book Ultimate Skiing, agreeing with Bob. Neither of these two talk about "critical angle" in their various writings, as far as I know, as something that determines whether a ski grips or slips.

Ron le Master is quite explicit about it in Ultimate Skiing.

However, if you keep leaning lower (without increasing the edge angle), you'll eventually exceed the platform angle and the skis won't grip anymore like in the picture above on the right.

Well, we could do the sensible thing and angulate. Not sure about anyone else but I'd have to go out of my way to increase inclination of the legs/body and NOT increase edge angle. Ski boots and bindings limit the ability of the legs to incline without the ski's edge following suit.

Of course if the only way we could balance was to lean in with the upper body whilst leaving the hips to the outside you'd have a point.

If we take skier A2 above for example. Can he ski with that edge angle and the ski will hold? Maybe for an very small time but it is quite obvious that it will not work without even considering any math. Say that he is going 70 mph, what will happen?
The ski will likely surf on the top of the snow or he will eject like a fighter pilot.

Not the greatest quality vid clip from Kitz but the DH guys seem to making a pretty good job of carving it in the speed range (125kph) and inclination range (roughly A2) without much surfing or ejecting.

 

[François Pugh]

Below is Bob Barnes' graphic illustration of "platform angle."

It is my understanding that "critical angle" often is used to mean a particular edge angle to the snow that determines whether the ski holds and thus whether it can track as in a carved turn. So "critical angle," if it means that, contradicts what Bob is indicating here.

Ron LeMaster also talks about Platform Angle as the determinant of grip in his book Ultimate Skiing, agreeing with Bob. Neither of these two talk about "critical angle" in their various writings, as far as I know, as something that determines whether a ski grips or slips.
View attachment 133217

Glad you found that! Be sure and post the .gif if you find it too.
BTW I don't see the contradiction. Critical angle is either (180 - platform angle) or it's the tipping angle required to make the platform angle less than or equal to 90 degrees (I forget which). Skiers A2 and B2 has platform platform angle <90 and critical angle achieved or exceeded.