 Poster: A snowHead
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| veeeight wrote: |
| Martin Bell, for every photo you produce with scissoring, I will be able to match with parallel skis, you know that! |
The difference is that neither Martin nor anyone else is saying that skis must never be parallel. So, producing a picture of parallel skis does not contradict anybody. However, you have maintained that they must never diverge/converge: so one picture (never mind a dozen or more) of someone doing it while winning a world cup race disproves your assertion.
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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laundryman, whilst winning a world cup, the last thing on any racers mind is to keep perfectly parallel skis, nevermind producing two lines in the snow.
As I said on page 6 (and countless people on Epic) - If people really want to use WC Racers as a model for technique we probably should be looking primarily at their practice runs rather than when they're going for broke in a real race. There's efficient skiing and then there's winning. Sometimes the 2 meet.
Last edited by Obviously A snowHead isn't a real person on Sun 20-04-08 18:07; edited 1 time in total
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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Well the one thing I've learned from this debate is that it's pointless arguing with V8. I'm sure he's a much better skier than many of us here (certainly myself), but he's clearly not in any position to enlighten us on this subject. Certainly not after 14 pages of highly dubious theory, explanations, blatant contradictions and a good deal of complete bullshitting. Well it's not fooling me or anyone else as far as I'm aware in this debate.
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| Quote: |
| laundryman, whilst winning a world cup, the last thing on any racers mind is to keep perfectly parallel skis, nevermind producing two lines in the snow. |
veeeight, why is the concept of 'perfectly parallel skis' so important then?
Last edited by You need to Login to know who's really who. on Sun 20-04-08 17:58; edited 1 time in total
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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veeeight, that is quite possibly correct and definitely irrelevant.
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| PJSki wrote: |
| Quote: |
| laundryman, whilst winning a world cup, the last thing on any racers mind is to keep perfectly parallel skis, nevermind producing two lines in the snow. |
veeeight, why is the concept of 'perfectly parallel skis' so important then? |
Are you asking because you don't know or are you asking because you want me to explain myself? There's at least two links I've references to on this thread explaining that, and it's relevance when racing.
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| laundryman wrote: |
| veeeight, that is quite possibly correct and definitely irrelevant. |
It's not actually irrelevant - there are lots of WC photomontages being thrown around in here, whilst the crux of this discussion is about analysing the two clean lines in the snow (what radius they are).
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uktrailmonster, do you accept that the inner ski does not track a tighter radius than the outer ski?
This is skiing related - please do not ever think that the inside ski has to track a tighter radius (bend more) than the outside ski - if you set out with this train of thought, your skiing will fall apart.
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You'll get to see more forums and be part of the best ski club on the net.
You'll get to see more forums and be part of the best ski club on the net.
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| veeeight wrote: |
| uktrailmonster, do you accept that the inner ski does not track a tighter radius than the outer ski? |
Well that just depends on the nature of the tracks left in the snow i.e. parallel or diverging. But as you clearly don't understand the maths I don't see any further value in discussing it with you.
I'll take my chances regarding my skiing falling apart. It might come as a big surprise, but not all instructors agree with your "theory".
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| veeeight wrote: |
| PJSki wrote: |
| Quote: |
| laundryman, whilst winning a world cup, the last thing on any racers mind is to keep perfectly parallel skis, nevermind producing two lines in the snow. |
veeeight, why is the concept of 'perfectly parallel skis' so important then? |
Are you asking because you don't know or are you asking because you want me to explain myself? There's at least two links I've references to on this thread explaining that, and it's relevance when racing. |
But you have tried to say that the concept of parallel lines doesn't apply to curves only straight lines. Again you wobble from one doggy assertion to another. Your concept of the hip joints being at the centre of rotation is also completely wrong.
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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I think you'll also find, that in the haste to reload bullets into rifles, a few other people on here have also 'wobbled', and rapidly picked up another weapon to fire when one such rifle shoots the operator in the foot.
I'll say again - my original assertion (where all this started on page 1) - is that the inner ski does not track a tighter radius than the outer ski, and that you do not need to scissor/diverge your (inner) ski in order to produce clean carved lines (anything going beyond recreational carving speeds things change, and I have said so as much).
The fact that the innerski does not track a smaller radius has been demonstrated by the results of the experiment.
Now, somewhere along the line various independent arguments broke out about radius, parallel-ism, identical-ness, edge angles, loading etc. and if everyone calms down in a few days I might demonstrate (as I have done with identical radii) that you can achieve much of all the apparent bending of maths and physics, without actually doing so.
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And love to help out and answer questions and of course, read each other's snow reports.
And love to help out and answer questions and of course, read each other's snow reports.
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veeeight, yes it does... 
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veeeight,
| Quote: |
| The fact that the innerski does not track a smaller radius has been demonstrated by the experiment. |
If you're talking about the potted graph you posted, that experiment hasn't been peer reviewed has it? It certainly shows convergence and divergence. Anyone can see that by looking at the plot.
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You know it makes sense.
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| veeeight wrote: |
| Now, somewhere along the line various independent arguments broke out about radius, parallel-ism, identical-ness, edge angles, loading etc. and if everyone calms down in a few days I might demonstrate (as I have done with identical radii) that you can achieve much of all the apparent bending of maths and physics, without actually doing so. |
If those were independent arguments you engaged in them:
| veeeight wrote: |
Take a snowboarder craving down a perfectly groomed piste, laying down near-sinusodial arcs.
Take a second snowboarder, laying down those arcs side by side, matching every peak and trough - laying down identical, but parallel arcs. |
If you could repudiate your notion of "identical but parallel arcs" (which runs counter to the received wisdom of mathematicians for 300 years and which you have avoided restating in your recent posts), we really could make some progress, because I don't believe that anyone maintains that the inner track radius is less than the outer track radius for identical arcs; only for parallel arcs (which can never be identical).
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Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
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| veeeight wrote: |
| I might demonstrate (as I have done with identical radii) |
really, don't waste your time.
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Poster: A snowHead
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veeeight, It does and you haven't. And - the inner edge of the ski is on a tighter radius than the outer edge too... (unless the ski is banked at 90 degrees...) 
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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| veeeight wrote: |
| Scissoring...... as defined on page 1 - refers to the angles of each ski to the other, I have never referred to scissoring as varying track widths. I have also likened scissoring = diverging skis many many times in this thread, never about the track width. |
So you admit that the track width must vary for the arcs to be identical - that's a start at least.
But...how can the track width change from narrow to wide, without the skis diverging (or "scissoring") at some point? That is a physical impossibility...
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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You need to Login to know who's really who.
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Martin, you are such a minx using WC montage to justify a position!
Here's Marlies Schild having a wider transition, and a narrower apex of the turn!!!
Last edited by You need to Login to know who's really who. on Mon 21-04-08 9:23; edited 1 time in total
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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Another deviation from parallel then. You have yet to show us an example of parallel tracks with equal radius of curvature throughout. Show us just one, and you are right and we are wrong.
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I bet there's a lot of pivoting and a bit of slipping in that turn (quite a bit of snow's being kicked up). The tip of the left ski at transition is in the air, as is the tail of the right ski.
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veeeight, Suggest you edit the skier's name! 
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Caveat: You shouldn't really use WC montages to justify a position......this one's pretty nice:
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You'll get to see more forums and be part of the best ski club on the net.
You'll get to see more forums and be part of the best ski club on the net.
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easiski, sorry, my child like mind again.
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| veeeight wrote: |
| this one's pretty nice: |
Yep, looks pretty nice, with a smaller radius for the inside track - though to tell anything for sure we'd need another one of your plots, like the one that showed convergence/divergence and lead/lag.
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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| Quote: |
with a smaller radius for the inside track
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Only if you are considering that both tracks share a common centre.
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And love to help out and answer questions and of course, read each other's snow reports.
And love to help out and answer questions and of course, read each other's snow reports.
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I don't consider that. They may do though - if there is no/lead lag or convergence/divergence at all. At all events, the centres will be close.
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| Martin Bell wrote: |
But...how can the track width change from narrow to wide, without the skis diverging (or "scissoring") at some point? That is a physical impossibility... |
V8 won't bother himself with trivial detail like that. His theories don't need to conform to real world maths/physics. I think that's clear from the discussion so far.
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You know it makes sense.
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laundryman, (a genuine question) why do you not consider them as two identical arcs, displaced by the stance width of the skier?
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Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
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They can't be identical and be displaced by the stance width unless the stance does not rotate at all. Janica's hips definitely rotate.
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Poster: A snowHead
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| Martin Bell wrote: |
| Sideshow_Bob wrote: |
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For me, the above diagram is one of the most important to have come out of this lengthy discussion. (Thanks Bob.)
It may closely reflect what often (not always) happens in WC GS turns. With similar edge angles, and little scope for extra ski flex (because the hard surface does not allow for any extra snow compression), inside and outside ski are often (not always) going to be carving on similar radii.
So the effect in the diagram above, where the radii are identical,is likely to happen: the skis diverge in the early part of the turn, and converge in the latter part of the turn. (One major difference to the diagram is of course that the racers' curves are sinusoid, as the edge angle progressively increases and then decreases before and after the apex.)
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I think this makes a lot of sense for such a scenario. When the skis are pure carving identical radii this divergence/convergence has to happen because of the simple geometry of the resultant tracks. If it doesn't then the radii simply cannot be identical. Only V8 seems to disagree with this simple fact.
The other scenario being discussed is that of pure carving perfect parallel curved tracks, which by its very definition requires the inside ski to track a tighter radius. Again if it doesn't then then the tracks will not be parallel. Another simple fact that only V8 would disagree with. In fact he has implied that it would be virtually impossible to load the inside ski in such a way as to carve a tighter radius (which I disagree with), which would therefore make it impossible to produce such parallel tracks. Yet his own observations show that it is possible. The contradiction is impossible to ignore and certainly hasn't been overlooked here!
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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laundryman, Thanks for answering my question about varying radii with your maths on page 14. I have continually tried to steer the maths argument into practical examples so that what we see on the mountain has some context within the geometry arguements. Grahams calcs of 1-2 degrees edge angles are very telling. Your summation of with skis 40cm apart one ski is at 25.0 M and the other 22.1 (assuming tip lag) and without lag must be 21.5M to me AGAIN shows just how little the differences are. Another even simpler way of looking at this is if i want to be parallel and the inner ski is tracing an arc of 25.0 the outer only has to be 25.4 assuming a .4 ski width. b**ger all....
V8 These examples show that in order to maintain the geometric absolutes one only has to make relatively tiny changes during the turn. Your actual skier model to me demonstrates what everyone else is saying, not your position. So what if at a point in time the outer ski has a smaller radius than the inner, that proves nothing. Each skis turn Radius varies all the time in the real world, as does convergence as does edge angle as does ski bending as as does tip lead/lag as do occasional tiny pivots.... All these things together allow us to make near perfect carves that conform to the geometrical absolutes.
V8 the geometric facts cannot be ignored, however why they don't fit exactly with what you think you see in a "perfect" turn can be easily explained, cant you just accept this
I am repeating myself on this thread so it is over and out time for me.... but it has been at times informative, thanks all.
MartinB sums it up very well.. I would add a fourth
| Quote: |
think from all this debate, we must conclude:
1. Either you carve true PARALLEL tracks – in which case the inner radius is smaller.
2. Or you carve IDENTICAL tracks – in which case the ski width must vary throughout the turn.
3. Or you can even carve tracks where the outer radius is smaller (because of greater weighting of the outside ski), in which case divergence/convergence, and/or inside ski steering, become even more necessary. |
4. A skillful skier can make continual small adjustments during the turn to carve near perfect identical parallel tracks in the snow.
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Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
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skimottaret, Another sensible summary, thanks.
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You need to Login to know who's really who.
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One last comment, at over 5,000 views this has been the most watched thread on bzk's in years, definately some pent up geekery
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Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
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| uktrailmonster wrote: |
| skimottaret, Another sensible summary, thanks. |
Hear, hear. The summary is also a particular pleasure for me, since it confirms that I have managed to keep up with at least some of what I've been reading! Thank you, it's been most instructive and, at times, very entertaining. Yeaaay, geekwatching rocks!
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skimottaret,
That's interesting. Where do you find that info?
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| veeeight wrote: |
| laundryman, (a genuine question) why do you not consider them as two identical arcs, displaced by the stance width of the skier? |
Wot sideshow bob said (and which has been said in one form or another over and over):
| Quote: |
| They can't be identical and be displaced by the stance width unless the stance does not rotate at all. |
I might come up with a simple proof (good enough for an applied mathematician, if not a professor of mathematical reasoning) later today if I can make the time.
Meanwhile, the various summaries are good.
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| laundryman wrote: |
What if there is no lead/lag? The outside ski is travelling at a faster linear speed than the inside ski to keep up. It's slightly easier to consider this case angular velocity w (measured in radians/second) - which, in this case, will be equal for both skis - than linear velocity. They are linked by w = v/r. Substituting this into Equation (3), we get:
tan(A) = (r.w**2)/g
Since r will be smaller for the inside ski, then tan(A) and hence (A) will also be smaller. (I must admit to finding that counter-intuitive; maybe grahamN or sideshow bob will spot a flaw in the logic.) Anyway, according to that, A will be 21.5 deg approximately. |
Interesting, it may be counter intuitive that you need a smaller angle for the inside ski, but if you accept that its linear speed is slower then it does make sense. That's why a banked track needs a higher inclination on the outside than the inside. This may well be a key to understanding why the inside ski does not necessarily have to be more inclined than the outer.
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You'll get to see more forums and be part of the best ski club on the net.
You'll get to see more forums and be part of the best ski club on the net.
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uktrailmonster, yes, I'd convinced myself of that in the meantime. The same maths models banked cars (I live near Brooklands, and you're right) and planes.
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| uktrailmonster wrote: |
Interesting, it may be counter intuitive that you need a smaller angle for the inside ski, but if you accept that its linear speed is slower then it does make sense. That's why a banked track needs a higher inclination on the outside than the inside. This may well be a key to understanding why the inside ski does not necessarily have to be more inclined than the outer. |
Let's not get banking for balancing the forces mixed up with angling a ski to create a deeper sidecut. Laundryman's calculations refer to the centre of mass of the skier. You can work out how angled towards the centre of the turn the centre of mass has to be to balance out the forces, but remember that there are two skis involved here in a linked system and so long as the effective weight is between these two skis you'll not fall over either to the inside of the turn or to the outside. Angling the hips can create a greater edge angle while maintaining the same effective angle for the centre of mass necessary to keep the forces aligned.
Last edited by Ski the Net with snowHeads  on Mon 21-04-08 12:22; edited 1 time in total
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