What's essential for carving on hard snow?

[Tony S]

My take atm is that these 2 are impatient and are trying to make something happen. Rather than just let it happen. I'm doing nothing but tip and balance. Absolutely no rotary.

So... There's slow and there's slow. Instructors love to say "learn it slow before you learn it fast." My observation is that there are lots of skiers who can't muster the faith to make railroad track turns even at the minimum speed required to bend the ski. They're just too uncomfortable with the speed, so they bail out, as you describe. I suspect the solution is to spend lots more time doing it on REALLY flat terrain and only VERY GRADUALLY moving to steeper green or easy blue terrain. In other words, skiing by yourself.

 

[skier]

Yep, my experience is different.

Starting from gentle groomers (as per JB vid).... I don't find it at all hard to make RR tracks. Tip (with angulation to avoid falling over!) and the skis just carve. As speed increases we get to incline against the centripetal forces but still with angulation. I do not feel any critical angle - the ski is engaged immediately the edge is on the snow and it just carves an arc.

Now I watch my wife trying to replicate that. And she inevitably moves to the inside or twists her hips or some other piece of weirdness that requires her to rotate the skis to avoid falling over. Funnily enough, when she thinks about it, she can carve the last 1/2 of a turn (after the fall line). I also have a ski instructor buddy whose CSIA L2 and I have never seem him initiate a turn without some rotary.
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My take atm is that these 2 are impatient and are trying to make something happen. Rather than just let it happen. I'm doing nothing but tip and balance. Absolutely no rotary.

Will write more on this later - day time here and got to do some stuff.

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Well, I'm not prepared to argue much for the existence of the critical angle other than The Physics of Skiing talks about the skidding phase, people on this forum talk about the critical edge angle being true, the ski is made to ease into turns by smearing for stability which gives merit to the critical edge angle concept, and I can feel it on the skis. So, I'm left either having to question all that, or believe you and others aren't aware of the steering..... Tough call? I think the thing to do would be to point out a reference disputing the critical edge angle or the skidding phase, but I don't think there is one.

Anyway, I think we've beat this horse enough.

 

[dbostedo]

...the ski is made to ease into turns by smearing for stability...

Do you have a reference for this? That part's got me especially curious. Is it from ski manufacturer's POV? Or an instructor's assumption/take?

 

[Johnny V.]

So... There's slow and there's slow. Instructors love to say "learn it slow before you learn it fast." My observation is that there are lots of skiers who can't muster the faith to make railroad track turns even at the minimum speed required to bend the ski. They're just too uncomfortable with the speed, so they bail out, as you describe. I suspect the solution is to spend lots more time doing it on REALLY flat terrain and only VERY GRADUALLY moving to steeper green or easy blue terrain. In other words, skiing by yourself.

Pretty much sums it up Tony. I have the luxury of skiing during the week and our hill has a long green with decent pitch. With few skiers on it it's a great place to practice carving and you can develop enough speed to really bend the skis and vary the turn radius while still making clean carves/railroad tracks.

Ditch your ski buddies for a while and work on stuff-it's very rewarding!

 

[François Pugh]

There is no need to smear turns. You can carve arc-2-arc turns leaving clean tracks. The left edge track will overlap the right edge track by abought a ski length, with the two tracks being nearly two straight parallel lines. The critical angle is an obvious fact for any engineer. What you have to realise is at transition when you are swapping edges you are between turning left and turning right; turn force is zero and critical angle (the angle you need to tip past to not skid) is also zero at that point. No skidding required.

 

[skier]

Do you have a reference for this? That part's got me especially curious. Is it from ski manufacturer's POV? Or an instructor's assumption/take?

I could probably dig one up, but it's just the concept of rocker vs. a ski that hooks up too quickly. For slight perturbations of the snow, if the ski edge locked, then you'd always be fighting to turn back on course and you'd overshoot leading to instability. The ski must not edge lock for slight angles otherwise, it wouldn't be stable.

 

[James]

So... There's slow and there's slow. Instructors love to say "learn it slow before you learn it fast." My observation is that there are lots of skiers who can't muster the faith to make railroad track turns even at the minimum speed required to bend the ski. They're just too uncomfortable with the speed, so they bail out, as you describe. I suspect the solution is to spend lots more time doing it on REALLY flat terrain and only VERY GRADUALLY moving to steeper green or easy blue terrain. In other words, skiing by yourself.

I don't think it's necessarily a speed issue. People are just so ingrained to having to do something to make the skis change direction. Their "psychological brain", (phrase from a nyc cab driver years ago), doesn't accept just putting a ski on edge. You show them, have them do itstanding still, demo it moving- even just with one ski! And then they go... and twist the ski into a turn. They don't even know they're doing it often.

Honestly I think if you can sideslip till your bored to death but looking downhill, and do railroad tracks in a limited width trail, you're in goodshape.

 

[skier]

There is no need to smear turns. You can carve arc-2-arc turns leaving clean tracks. The left edge track will overlap the right edge track by abought a ski length, with the two tracks being nearly two straight parallel lines. The critical angle is an obvious fact for any engineer. What you have to realise is at transition when you are swapping edges you are between turning left and turning right; turn force is zero and critical angle (the angle you need to tip past to not skid) is also zero at that point. No skidding required.

This makes no sense Mr. Pugh. At transition your edge angles are zero. Let's say the critical edge angle is 10 degrees. You have to go from 0 to 10 degrees of ski tip before the ski will edge lock. From 0 to 10 degrees the ski will partly carve and partly skid. So, how do you go from transition to 10 degrees while carving a perfect arc when the ski will skid for those angles in between? (assuming the existence of a critical edge angle.) Also, OP is talking hard snow. The critical edge angle is related to the holding force of the snow, so for hard pack there will be a higher critical edge angle which is maybe one reason RR tracks are harder on this surface. Does anyone have photos of RR tracks on this hard snow? On some of the snow I ski on, there's no possibility with lazy tuning. Most of the RR photos I see are in the absolutely best conditions where the snow grip is the absolute maximum and the critical edge angle is the smallest. People are probably floating with a little rotary, or adding in a little steering for these pristine conditions, to get past just that small skidding phase, but on WC courses, I don't think there are many pencil lines. Pencil lines aren't really useful for much anyway other than a cool photo on pristine blues. It's not worth this much discussion.

 

[James]

Critical edge angle is the angle the ski holds in the snow. Technically, it's where the line between the com and the edge is 90 deg or less. More and the edge slips. Note it is not the angle of the ski to the snow. Read that again @skier , as your def refers to the angle of the ski to the snow.

Ironically, you have to have some small degree of angulation to achieve it on the outside ski. Pure inclination, as if the person was rigid, won't achieve it.

Perhaps @François Pugh can comment.

See this thread post and thread.

Well, you're actually right! Sorry I dismissed it as absurd. Essentially when I said that I operated in the "I've always thought..." mode which has no bearing on reality.

If one is technically only inclining, like a stick, (which you said and I ignored), you can not get less than 90 deg of platform angle on the outside ski. Thus it won't hold. The inside would, but we're not talking about skiing on the inside ski. One would need a little...angulation in the system to get below the critical edge angle of 90deg. It's not much, but more than a rigid stick could manage.

Here's the diagram. (Illustrator wishes to remain anonymous)
View attachment 37390
So on a 65mm ski we, the stick figure, need to find 4.2 deg of angulation in order for the ski to hold.
Arrrgh! This critical edge angle stuff is so non-intuitive. At least to me.

So, @Jilly , you were right!

 

[Tony S]

Pencil lines aren't really useful for much anyway other than a cool photo on pristine blues. It's not worth this much discussion.

Well, here's where it comes up in my world: You've got a hundred beer leaguers racing. Maybe twenty of them have any clue how to change direction quickly and effectively on demand, on hard snow ... especially with minimal speed loss taken into account. Maybe ten of these have more than just a clue. The other 80 are always whining about one thing or another. Some of the kvetching is relevant (poor tunes). Most of it isn't. The bottom line is that they don't have a foundation of arc-to-arc skills to draw on when they need it.

 

[James]

The bottom line is that they don't have a foundation of arc-to-arc skills to draw on when they need it.

No pencil sharpener, no pencil skills...

 

[Tony S]

No pencil sharpener, no pencil skills...

I see what you did there.

 

[Johnny V.]

The other 80 are always whining about one thing or another.

Ain't it the truth!

 

[Josh Matta]

So... There's slow and there's slow. Instructors love to say "learn it slow before you learn it fast." My observation is that there are lots of skiers who can't muster the faith to make railroad track turns even at the minimum speed required to bend the ski. They're just too uncomfortable with the speed, so they bail out, as you describe. I suspect the solution is to spend lots more time doing it on REALLY flat terrain and only VERY GRADUALLY moving to steeper green or easy blue terrain. In other words, skiing by yourself.

Truth...

you can railroad track on a dead flat by pushing with your poles

 

[skier]

Critical edge angle is the angle the ski holds in the snow. Technically, it's where the line between the com and the edge is 90 deg or less. More and the edge slips. Note it is not the angle of the ski to the snow. Read that again @skier , as your def refers to the angle of the ski to the snow.

Ironically, you have to have some small degree of angulation to achieve it on the outside ski. Pure inclination, as if the person was rigid, won't achieve it.

Perhaps @François Pugh can comment.

See this thread post and thread.

It looks like we're thinking of different uses of the term. I'm using it to describe the transition point between the skidding phase and the carving phase as described in "The Physics of Skiing". I'm calling it the critical edge angle to use the same terms I've seen in forums. There's not a lot of use of this term out there, so I searched around to see where I picked it up, and apparently it's from reading Jamt's posts, probably dating back to Epic days. It appears I've picked up the term from him and have come to many of the same conclusions based on it's existence. Here's an excerpt from one of his posts I just found:


"Thus the turn will start with a steering angle and as soon as possibly the racer will increase edging and pull back the skis to remove the steering. When the skis lock in edge it is very difficult to return to steering, you are locked into the carving track. If you misjudged you are in trouble.
The redirection/steering of the skis happen even if it looks like a pure carve, becuase you dont really carve until you have hit that critical edge angle. This has caused a lot of debate in the past because some view this as a pivot and others don't. I don't really care what its called, the important thing is what the steering angle is when the skis are engaged again. "


http://www.skiervillage.com/archive/index.php/t-856.html


So, there is a question if the Physics of Skiing is still relevant, and since the "critical edge angle", as I'm using it seems to be predominantly from one source, @Jamt, I would have to leave it for him to clarify or point us to another reference.

 

[James]

These discussions go well back to epicski. Probably 15 years. Or more. Francois was there under a different username. Shame Vail destroyed the archive. Back then or earlier was a guy username Physicsman. He did a sidecut radius calculator for the site. He probably disappeared from epic over 10 years ago but I don't know. Before jamt came I'm pretty sure but not certain. I don't know if Physicsman/Tom discussed critical edge angle. He was s very good poster.

Your quote of jamt has little to do with the critical edge angle definition. He's aligned with the definition, I'm pretty sure, and he didn't invent it. But he'd have to answer. Bob Barnes did an animation probably ten years ago of critical edge angle. That was on epic. Barnes is the first source I heard it from, again probably 15 years ago or more but he didn't invent it either afaik.

Physicists and skiing are not always aligned with each ither. We've had phd's arguing violently on centrifigul force. (Epicski)

 

[dbostedo]

Bob Barnes did an animation probably ten years ago of critical edge angle. That was on epic.

I was hoping it was out on his Vimeo page now, but I don't see it... I did see this though :

 

[mdf]

Physicists and skiing are not always aligned with each ither. We've had phd's arguing violently on centrifigul force. (Epicski)

Well, that was only because they were very, very wrong.

I've never thought about how you get to critical angle before. That's an interesting question. My hunch would be that on a gradual tipping-only initiation the ski just doesn't have much sideways force on it yet, so it doesn't want to get squeezed up out of the snow. It's a race between increasing angles and increasing forces. But I haven't thought it through carefully yet.

The fast transitions have other things going on -- either classic rotary, or the ellipse traced by foot squirt with a laterally tilted lower leg, hinged around a tilted knee.

 

[razie]

I also have a ski instructor buddy whose CSIA L2 and I have never seem him initiate a turn without some rotary.

I'm a CSIA 2 as well. That is all steering. If you carve at the exam, you fail.

Their manuals used to say all turns start with pivoting and continue with ski design, but they've evolved past that now. For sure there are generations of instructors with that principle carved into their brains though

Now it's all steering, you see.

I've never thought about how you get to critical angle before. That's an interesting question. My hunch would be that on a gradual tipping-only initiation the ski just doesn't have much sideways force on it yet, so it doesn't want to get squeezed up out of the snow. It's a race between increasing angles and increasing forces. But I haven't thought it through carefully yet.

Exactly. The ideal simplistic models used on average are not describing anything except a steady state where you are in the middle of the turn with a given radius, which requires a given centripetal force, which results in a given platform angle.

Reality is much more interesting. When you're gliding between turns, there is no centripetal force. You are just about to create it by getting the ski on edge, to bend by interacting with the snow.

The skill is to not apply too much pressure for the angle you have at the moment, so the angle you have is still under the platform angle for that force that you have. If the ski is at 10 degrees, it's possible to even calculate the maximum force you can apply to it to have 10 degrees be the critical angle I think you called it here.

This is why the name of the game is quick angle creation while in balance and without a platform underfoot, balance will be harder.

The equations describing the turn do not take into account technique either. There are good skiers which can apply certain inputs that make the ski carve more than others, or that can make the ski have bigger angles sooner etc.

A full model must take skier skill and technique into account. You don't need physicist to create the good models, you need great skiers to create good models. Unfortunately, not many great skiers write manuals or books... and even less are interested in mathematical modeling.

 

[jack97]

Do you have a reference for this? That part's got me especially curious. Is it from ski manufacturer's POV? Or an instructor's assumption/take?

As mentioned, "Physic of Skiing" Lind and Sanders. Below are options for used books. The main author is a retired Prof from the Univ of Colorado, Boulder. I have high regard to the University given it did a lot of research on Physical Science that relates to my field.

https://www.amazon.com/gp/offer-lis...d_used_olp_sr?ie=UTF8&condition=used&qid=&sr=

The main take away is given the skis are designed with a camber along with the side cut (of the ski), some skidding is involved to get the tip to bite which starts the carve. A force is needed to bend that ski and directed to cause an edge angle. Its this application of force which causes a lateral movement until that ski gets locked into the groove.


BTW, the author concludes there is no such thing as a pure carve. My take is this could be approximated and we are just arguing for the past 15 years about how to achieve this approximation.