Speed control on "pure" carving ?

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Speed control on "pure" carving ?

Postby tommy » Mon Feb 09, 2004 1:59 pm

Hi all,

first of all: I've been away for a few days, working in a small town in north of Sweden, only a few miles from the arctic circle, lat. 66.6 N. It was great to see the burst of activity on the furum during my "absence", in particular, Gravity has been a boost to this forum's activity! Great!

Anyways, I had the opportunity to ski in a very small resort up there in north, no lift lines, lots of snow, perfect grooming, firm snow, and less than 50 people sharing 8 slopes! Can't get any better than that! It was a bit cold though, -25C (-13F I think).

Now, skiing in these perfect conditions, I got the opportunity to experiment with carving. Since the firm snow allowed almost any amount of ski pressure, without any risk of the downhill ski slipping away, I "dared" to push the envelope of my carving to its limits: in normal conditions, which for me is either hard pack or ice, I simply can't stay in control while doing carving when I get to steeper slopes, e.g. black diamonds. Typically, my downhill ski will slip away if I really press to make a short turn, or the speed will build up to uncomfortable levels. But up there in north, no matter how much pressure I put to the skis, they did remain in track, even on steep slopes. However, the speed just kept increasing, even if I tried to do the turns as short as possible, and keep them "High-C-like". So, finally I got scared enough to hit the brakes!

This experience got me thinking about the physics of carving: assuming "pure" carved linked turns, as far as I can see, the only means of speed control is to aim your skis uphill ("extreme finishing of your turns"). And, if you are doing a fairly steep slope, thus gaining pretty good speed, then, in order to keep your speed within any reasonable range, you need to "pull up" quite a lot in order to keep the speed down, and you end up doing some pretty huge and ugly "non C-like" turns!?

The reasoning behind the above reasoning is that in "pure" carved turns, the only forces working against the speed buildup is the friction force from the edges cutting the snow, and the drag from air, both of which are fairly small compared to the pull of gravity. Unless you aim your skis heavily uphill, there is always a component of gravity providing acceleration downwards. Whereas in skidded turns, you can add a lot of braking power by means of friction force. So, because I'm too much of a chicken to even approach terminal speeds where the drag force would inhibit any further acceleration downwards, the only remaining option to control speed is to do these ugly "ride uphill" turns....?

Anyone having any thoughts on this ?

Cheers,
Tommy
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Postby jclayton » Mon Feb 09, 2004 3:22 pm

Hi Tommy,
sounds like a pretty good life up there . Not knowing the steepness of the slopes you are talking about it is a bit hard to make comments . I suspect that you just need to get used to travelling at high speeds , bit by bit . I find on a 30 - 35? slope that if the turns start with a "high C " and carve all the way around I have a consistent speed just finishing at 90? to the fall line more or less , if I finish higher I lose some power from the ski to start the next turn and it is difficult to get a smooth transition ( when it all works , sometimes the spring throws me quite violently into the next turn )

Also what skis were you using , perhaps try ,say, a Head chip S.L. which gives a good powerful finish while whipping around quite quickly , staying less time in the fall line than ,say , an Atomic SX 11 .

As Harald mentioned also if you stay forward during the whole turn this has a slowing effect ( a problem with some racers evidently )

Also Harald demonstrated to me that with the "high C " on steeper slopes you have to start angulating very early so in fact it feels as though you are angulating up the hill as you start the carve. It feels quite awkward but most new sensations do , especially at first when you exagerate the actions to get the "feel" of them .

I notice sometimes when I start to "freeze" at speed I tip my upper body into the slope and have to concentrate on "hanging ten" or angulating over the downhill ski ( a bit of surfing parlance from the malibu days )

These are things I have been working on this last weekend , they are not easy , but every now and then I get a hint of what they should feel like and the sensation is of a lot of power .

J.C.
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Postby tommy » Tue Feb 10, 2004 12:26 am

Hi JC,

I'd say the slopes where I started to notice the speed control problems were somewhere around 30-35?, hard to say exactly, as I don't have any better measuring tool than estimating using my poles.

Having the posts re. High-C and early angulation in mind while up there, I really tried to do my turns as C-like as possible, "showing the bases to the mountain", using weighted release to "throw" me into the next turn, and sure, at least sometimes it all worked out quite ok, but still the speed kept increasing to, for me, uncomfortable levels. Again, its hard to estimate speed, but somewhere around 40 km/h I'd quess. So, the options I found remaining were either to aim uphill at end of turn, or to put a skidding end to the turns.

As you say, as soon as you either have a traverse in between your turns, or aim uphill for a while, the ability for smooth transistions goes away; instead of "using the force" to enter the new turn, you have to do more of manual work to change edges.

You also mentioned "staying forward": I played a bit with this in the steepest section, where I noticed a tendency to "enter the backseat". In order to experiment, I forced myself forward on the skis, and explicitly "falling" downwards in transition, and this helped in the transition to some extent.

But when thinking about the physics of a pure carved turn, it appears to me that at some point, where the slope angle exceeds a certain value, the braking force created by sliding friction will simply not suffice to stop acceleration downwards, even if your turns are "perfect"; there is always a component of gravity acting downwards along your skis, and you will increase speed until the point where aerodynamic drag becomes the dominant braking force. At some point, you will reach terminal speed. It appears that the speed where this happens is beyond my current comfort zone.

Cheers,
Tommy
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Postby Hobbit » Tue Feb 10, 2004 7:08 am

Hi Tommy & JC,

Correct me if I am wrong here, but I think the way to control the speed is to make a shorter radius turns. The ski must be bent more for the shorter radius turn which would require a greater force (pressure). The ski edges will bite much more into the snow. I think this is a common pattern. Try carving turns on the green and you'll notice that shorter turns will get you going slower.
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Postby Guest » Tue Feb 10, 2004 9:16 am

Hi Tommy,
from what you say you seem to have most things dialled , I mentioned trying smaller radius slalom skis to make shorter turns as Hobbit suggested . BUT perhaps we have to realize we are only mortals ,not Hermann Maier or von Gruenigen, and there is a limit to how steep a run we can carve turns on .
OR keep extending the comfort zone .
J.C.
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Postby BigE » Tue Feb 10, 2004 9:21 am

In my opinion, a given turn shape on a given pitch will eventually result in some terminal velocity.
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Postby tommy » Tue Feb 10, 2004 9:50 am

Folks,

thanks for the input, appreciate the discussion!

JC, are you suggesting that at 43, with less than 10 years of skiing experience, I shouldn't aim for World Cup.....?! What a disappointment..;-)

Wrt. to the issue of shortening the turns: I really tried to get the turns as short as possible, and think I was succesful to some extent - at least I didn't occupy the entire width of the slope... but I also noticed that I'd probably need to start "body building" my leg, hip, stomach and back muscles - in some of the turns, I felt that I didn't have enough power to keep the ski from pushing back. And today I have a tremendeous pain in the forementioned muscles.... barely can walk nor sit....

Cheers,
Tommy
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Postby Jeff Markham » Tue Feb 10, 2004 6:05 pm

Flexing my knees more and reaching down the hill with my pole plant helps me, but I am by no means carving on the steeper stuff. I'm getting there, but am still working on it.
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Postby Bluey » Wed Feb 11, 2004 2:56 am

I can relate to the issue being addressed here.

My only input is to say Lito T-F has an interesting viewpoint on speed control on steep slopes at this web address :

http://www.breakthroughonskis.com/Pages ... ion30.html

Its titled "The myth of edging".

I haven't tried his advice in this article but is sounds like its either a plausible work-around to the issue or else it might be part of the solution.


That's my 2 cents worth.


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Postby tommy » Thu Feb 12, 2004 10:53 am

Bluey,

interesting link, it pretty much sums up the discussion. What I read Lito saying is that when the slope gets steep enough, forget about pure carving, if you want to control your speed:

["Aren't we the pure carving generation? Not entirely. Don't let carving become an ortthodox religion in your ski life."]


Unless you are willing to accept and live with the very high speeds required to make aerodynamic drag slow you down, you simply have to put some amount of skidding into your skiing in the steeps.

This is an area which I have not found very clearly explained in Harald's books/videos; my understanding from those is that Harald really wants skiers to move away from any skidding.

Harald, if you read this, maybe an idea for yet an other new chapter for the upcoming book - skiing steeps ?

Cheers,
Tommy
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From a physics point of view

Postby JimR » Thu Feb 12, 2004 10:17 pm

I find this an intriguing question, not so much from a skiing point of view but from a physics or energy point of view (and I ain't an engineer). There has to be more going on here than just snow friction and wind resistance. As you are going through the turn, there is a velocity down the hill but there is also velocity sideways. As you go through each turn, this sideways velocity is completely canceled and replaced with a sideways velocity in the opposite direction. That requires a lot of energy to stop the sideways component and turn it into the opposite direction. I think this flexing of the skis and straightening of the leg is resisting the energy created by gravity, i.e. dissipating the energy created by gravity. Maybe the reason making more turns slows you down more is that you dissipate more energy. In fact, the furrow that gets cut in the snow when you are carving burns more energy than just sliding on top of the snow on a flat ski would (which I think is only friction).

If it were only wind resistance and friction on the snow, then you wouldn't be bending your skis (which takes energy), and you wouldn't have to be resisting the G forces with you legs.

A picture comes to mind of a time that I had to follow a concrete water way (culvert) that ran down a hill. I found that I could control my velocity down the hill just by jumping from one side of the culvert to the other, absorbing the jump on each side and springing back to the other.
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Postby Bluey » Fri Feb 13, 2004 4:11 am

Hi JimR,

Your post prompted me to reply to another thread ...so I'll just kinda duplicate/elaborate on my comments in respect to your points again here......

IMHO, and I'm certainly not an engineer either, I agree with you...... I would put it this way......
I kinda think the residual energy of the pull of gravity and centifigual forces are "hiding"/being stored in the ski itself.....therefore, as the ski bends into the bottom of the turn in soaks up the energy generated from the pull of gravity, .......
The trick is to Release the energy in that very bottom part of the turn just before I head downhill again ( this last bit, is the bit I am not very elegant with ....).

How is the energy stored in the ski? I believe you're also right....... the more I can bend the ski the move energy its storing/soaking up.

How do I bend the ski?
Also, IMHO, my guess is that its by controlling my Fore/Aft balance via the pulling the hips under the body etc and thereby trying to keep centred over my ski boots as I enter the very bottom of the turn......its all about aligning the skeletal/body bits in an alignment so that the forces are acting downwards into and over the whole of the ski boot.........

To me, skiing's kinda like dancing.....they're both about balance and timing.....I wish I could translate the theory into elegant practical results on steeps (and on the dance floor)..........for me, it's about practice, practice, practice......and as someone else said, unless your practicing PMTS, you're doing it the hard way....


Gotta go...


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Postby Jeff Markham » Sat Feb 14, 2004 9:15 am

I think that JimR and the rest of you have already made a compelling argument, but I'll take a whack at different way of expressing the same ideas.

With all due respect to Mr. Tejada-Flores, who has undoubtedly forgotten more about skiing than I'll ever know, I don't believe that his article about side-slipping on a steep slope applies to Harald. I believe that Harald is carving as usual. Mr. T-F's article is probably more directed at us mortals who "tense up" and "over-edge" and allow the ski to "shoot ahead". Harald doesn't talk much about the need to be relaxed, but he definitely avoids focusing on edging and advises us to keep our feet under our hips.

Submitted for your approval: It is precisely BECAUSE Harald is carving that he is able to control his speed.

I'm going to discard the aerodynamic argument (OK, maybe Harald knows how to find thicker air <g>). Note: If I *ever* go fast enough that air drag becomes a factor in my skiing, then I'm going WAY too fast. Somebody yank my lift ticket...

Also, I'm not entirely convinced that Harald is spending any significant portion of his turns moving uphill. We've all seen him ski and I've never seen anything but beautiful lines.

Also, I'm not convinced that my skis (or my body itself) are totally storing *all* of the energy from my turns.

The question is: where is the energy going?

As others have said, I believe that it is turning itself that is slowing Harald. Although "pure" carving greatly reduces his forward resistance, it is the carving itself that allows him to apply force to the mountain to slow himself down.

A (hopefully relevant) motorcycle analogy...

Motorcycles slow down when in a curve. Motorcycling educators (e.g., MSF) advise motorcyclists to apply *more* throttle in a curve (yes, it's counter-intuitive) in order to counteract the slowing caused by turning forces. By rolling on the throttle, the desired weight distribution is maintained and the suspension remains settled. My point here is that the slowing down is a natural and unavoidable part of cornering. Unless you are a racer and you are drifting either/both of your tires in a racetrack turn, your average street rider's tires are *not* sliding (i.e., side-slipping or skidding) in a turn -- they are gripping the pavement. Yet, the motorcycle slows down unless additional throttle is added. If I keep the throttle neutral (i.e., don't add or subtract throttle), I can increase the slowing effect by taking tighter line through the curve.

(A related comment: the motorcycle's suspension compresses in a turn (which is another reason why hard parts sometimes drag), just like your skis are storing energy when bent.)

So, I think that is why Harald says that the bulletproof short turn is indispensible for steeps (and moguls and ...). Short turns allow him to get more turning performed for a given vertical distance and therefore more slowing effect. Carving these turns actually *improve* his ability to dissipate his downhill energy.

...or maybe I'm full of it. ;-)

I'm looking forward to Harald's comments on this topic.
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Postby BigE » Mon Feb 16, 2004 9:03 am

There is skidding and there is skidding. There is skidding when the edges are not engaged,and skidding because the edges no longer hold.

I submit that it is not possible to carve a pure turn on an extremely steep slope without scraping noises indicating that some sideslipping is going on due to lack of edge hold....

Or do I have some more learnin' to do :o
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Jeff, thanks for the motorcycle example

Postby JimR » Mon Feb 16, 2004 8:50 pm

Jeff's example of turning on a motorcycle really opened my eyes. I pictured a motorcycle with the wheel completely turned sideways, which would completely stop forward motion. Turned straight ahead it doesn't affect forward motion (except for friction). Turned anywhere in between it slows forward motion, the sharper the turn the more slowing. This is because the front tire grips the road and inhibits forward movement (by some amount). Imagine the same motorcycle on a wet or icy road; turning the wheel won't provide as much stopping because it will slip (or skid) (and, unless you have great balance, result in a fall :-) ?

The arcing front of the ski is performing the same function. As our skis bend, the tip impedes forward progress and redirects some of that energy in the direction of the turn just like the motorcycle tire, but anytime the skis are bent and arcing they are slowing us down. Probably the more they are bent the more they are slowing us down, the softer the snow the better grip the tips will have which means more slowing, and having two skis bent and arcing provides more slowing than one? Not carving (skidding) may be more like trying to turn the motorcycle tire on a wet road; it will slow some but not as much because there isn't as much grip.

Stemming the ski (skidding) defeats speed control because it ruins the grip of the ski, putting the ski in a sliding mode rather than a gripping mode.

This also fits well with the postings about staying forward on the tips slowing down racers. In fact I remember seeing an OLN excerpt of Bode Miller jabbing his toe as he exited the turn just to scrub a little extra speed.

So, to slow more, you turn more and you angulate more so you can get into a position where your skis bend more.

Theoretically, I guess the slopes can get so steep that the skis can't resist the downward forces, but I haven't encountered that problem on any of my green runs. Thanks Jeff (at least until someone tells us how it really works).
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