I can quite see why this discussion and others like it can be quite helpful.
thats why i selfishly started the thread in the first place....
I am a BASI L2 instructor and just passed the L1 coach course. Started working towards my ISIA this year with a few courses under the belt and hoping to get ISIA license in the next two years or so if my old bones with get me there.
Again, good luck with that.
A few years ago I did a weeks intensive tuition with a BASI 1 instructor (John Angela) with a view to not only reconstruct my skiing (boy did it make a difference) but to see whether it was reasonably feasible to take BASI 3. He reckoned it was. Alas circumstances changed, so I never pursued it. It's probably something I'd really enjoy and get immense satisfaction from.
Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
Mark Hunter, You can take the 5 day L1 now at a snow dome... THe standard isnt too hard and once you get that you can have a go at teaching, if you enjoy it do your L2 in the mountains.... Im 45 and just got into it for fun and a challenge but have to say i enjoy teaching more than i thought i would.
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?
and describes exactly the things I was trying to explain earlier about how the inside ski has to either diverge, be rotated slightly or put on a more extreme edge angle than the outside ski (hence tighter radius turn!) for it to be carved. I agree with everything said in FastMan's post. Great reading, and links to some excellent photos showing how the top guys do it.
No, Uvavu, incorrect!
Again, there is always the danger of using photos of WC to try and justify a position, you never know if it is intent or outcome. Those two photos in Fastman's post show racers moving to the inside to get the line, with the consequence that they are on the inside ski causing it to diverge! It is not an intent in good 2 footed carving.
Look at this youtube video - good 2 footed carving, with no inside ski divergence. Both skis doing exactly the same thing for much of the turn. Good arc to arc skiing.
And just to show you can use WC imaged to prove any point you want, here is Ligety and Raich skiing GS without and inside ski divergence nor scissoring.
Scissoring is NOT part of modern clean arc to arc skiing or carving technique!!
Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
OK, ready to be enlightened. The first clip, skiers 3 or 4 and 5 seem, whilst demonstrating arc to arc skiing, to have some tip lead especially in the final 3rd (mostly I think) of the turn. In one case, Guay, it appears that he has tip lead during the first 3rd of the turn. I fully appreciate that the camera angle may create the illusion, hence being prepared for enlightenment.
Mark Hunter, i will probably get shot down in flames for this but some tip lead is inevitable but it's when you have too much that it becomes a problem. i'll let someone else define "too much"
Then you can post your own questions or snow reports...
Then you can post your own questions or snow reports...
veeeight wrote:
Scissoring is NOT part of modern clean arc to arc skiing or carving technique!!
Scissoring is one way of allowing a clean arc to be carved. The other ways will involve either some rotating or steering of the inside ski (easier if it has less weight applied) or the inside ski being edged at a greater angle to the outside ski. One may also see the inside and outside ski come together in a slight 'snowplough' shape at the end of the turn.
The photos demonstrated a number of top-end racers scissoring. Other photos show athletes with some rotation of the inside ski and others show a wider stance at mid turn than at initiation and convergent skis to the end of the turn. All tools for the job. An awful lot of the photos demonstrate an amount of inside-ski lead. I'd also argue that in the fifth top-most image of Ligerty his tips are (albeit slightly) further apart than his tails and skis diverging, and the same with Raich in the fourth image above the first gate. Below the gate, the tails are further apart than the tips and the skis are converging
As GrahamN showed with his links, the geometry of parallel curves means that one the inside curve has a tighter effective radius. How do you make that inside ski track a tighter radius? Remember, it's skis reacting to the snow that creates a turn, so it's a tighter radius relative to a point on the snow. It has to be rotated ever so slightly or put on a tighter angle. The WC guys are expert at doing the former with minimum of slip/obvious rotation and a lot of steering the ski with the feet through the turn, but it's still being done.
What points of FastMan's post do you not agree with?
After all it is free
After all it is free
Arno, funny, that is what I would have thought.
Analysing my skiing, I am aware of tip lead, but I couldn't honestly say when, although at a guess it would be in the first 3rd of the turn. Watching many instructors arcing down a shallow gradient piste, I have been struck by the evident way they almost seem to push forward the uphill ski as they transition it to the downhill. It might be an illusion, but I am conscious of doing something similar. I think!
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.
Mark Hunter, look at the edge angles they are achieving - tip lead is always present at high edge angles (or inclination, counter etc.). The aim is not to eliminate tip lead, but to manage/reduce it.
Quote:
Scissoring is one way of allowing a clean arc to be carved.
If you are scissoring (defn: diverging inside ski or diverging outside ski), you are NOT carving clean arcs. Mutually exclusive. End of.
Quote:
How do you make that inside ski track a tighter radius?
As long as you continue to believe that the inside ski tracks a tighter radius, this debate is pointless.
Ski the Net with snowHeads
Ski the Net with snowHeads
If it tracks the same radius, then mechanics will ensure that tip lead develops as the turn progresses the inside ski travels a shorter distance, unless you somehow pull the ski back and slow it down.
snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
I agree that the thread title should perhaps be changed to "Reducing tip lead".
I don't think we should be using racers (in a race situation) as examples. Their motivation is purely to get from A to B, there are no style marks and as we have seen they often exhibit non-parallel skis, non-parallel shins, and varying stance widths. In that free-skiing clip, things are a little different, that is a clip of racers trying to ski "neatly" rather than simply going balls-to-the-wall.
If you want to see neat or "pretty" matching arcs, you're better studying ski instructor "final forms" rather than race sequences.
By the way it may be difficult to really define a turn "radius", because according to "Physicsman", a carved turn is not a circle but a "sinusoidal curve", whatever the hell that is
More details for geometry freaks here:
http://forums.epicski.com/showthread.php?t=42263
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.
Quote:
As long as you continue to believe that the inside ski tracks a tighter radius, this debate is pointless.
Apologies to the rest of the forum, but as a mathematician this gets my goat.
So, the inside ski neither converges nor diverges but stays the same distance apart throughout the turn (where the distance is greater than 0), but the turn radius is the same for both skis? Sorry, that's absolutely mathematically impossible. GrahamN posted a link to the proof.
So if you're just off somewhere snowy come back and post a snow report of your own and we'll all love you very much
So if you're just off somewhere snowy come back and post a snow report of your own and we'll all love you very much
Quote:
but the turn radius is the same for both skis?
Is it, if both ski arcs have different centres (your hip sockets).
Quote:
So, the inside ski neither converges nor diverges but stays the same distance apart throughout the turn
That's why it's called a parallel turn.
Quote:
but as a mathematician this gets my goat
And this is why I am a skier, not a mathematician.
You know it makes sense.
You know it makes sense.
So why does an inner ski usually have a greater angle to the snow than the outer ski?
Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
Frosty the Snowman, I think I know what you are saying, yes, which is why managing tip lead by keeping the hip square to the skis in a longer turn is desirable, which is why many drills/exercises in reducing tip lead involves pulling back the inside ski and/or pushing forward the outside ski throughout the turn.
Where do you find that the inner ski has a greater angle than the outer ski? When that happens (biomechanically difficult at higher angles) then the inside ski will start to diverge into the turn, and you are no longer skiing clean parallel arcs.
MB, that's the Physicsman's spreadsheet I've been trying to find!
Poster: A snowHead
Poster: A snowHead
veeeight, I thought I had seen it in many photos, but this one appears to show something totally different. It appears that the skier is actaully angulating the outer knee to the hill, but the inner one AWAY from the hill
Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
veeeight wrote:
Quote:
but the turn radius is the same for both skis?
Is it, if both skis have different centres (your hip sockets)
And if we draw a line across your hip sockets, this line will rotate perpendicular to the direction of skis throughout the turn, right? This line will describe an evolute for the turn.
What makes your hips rotate? The turning effect of the skis.
Let's imagine a skier carves a perfect circle on a flat bit of piste. Let's look at the tracks for each ski. It may help if you get a piece of paper and draw this out, two circles, same centre, slightly different radii. A pair of concentric circles. With me so far?
Now for a ski to carve and for no slipping whatsoever, the skis must have been bent through each circle. The tip, middle and tail of the ski will pass through the same points on the circle, agree?
Let's say it's a really really tight turn, and the skis are flexed through 60 or even 90 degrees. Now let's draw where the length of each ski is are on each curve at a single point in time when this 360 was carved. Do it in thick marker pen. Mark the tip and the tail of each ski. As we're carving, every point on the outside ski must lie on the outside circle. Every point on the inside ski must lie on the inside circle. After all we've got perfect tracks with no slipping, right?
Now, which is the tighter circle? Which ski is making the tighter turn, and hence which ski is turning with a shorter radius? As we're carving both skis, the only thing making the ski turn is reaction with the snow. The tighter the turn relative to how far apart the feet are, the more difference between turn radius.
I can't upload images at the moment so I can't draw it out, but I will tonight when I'm home.
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?
FtS, That's because at those edge angles and with that amount of angulation it becomes biomechanically difficult to maintain completely parallel shins and identical edge angles.
Let's imagine a skier carves a perfect circle on a flat bit of piste.
Except, that that is only possible in academic world. Never in the real world. As alluded by Martin Bell above, skiers don't really ski according to circles, more in a sinusoidal curve, with dynamic increasing and decreasing and ever changing edge angles. The only point you can reasonably establish a "radius" of anysort is at the apex of the turn.
Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
Frosty the Snowman, I think this was mentioned earlier in the thread as something that does occur. Personally I do it also, but more out of the need to have somewhere more solid to rest my gut...
Let's imagine a skier carves a perfect circle on a flat bit of piste.
Except, that that is only possible in academic world. Never in the real world. As alluded by Martin Bell above, skiers don't really ski according to circles, more in a sinusoidal curve, with dynamic increasing and decreasing and ever changing edge angles.
Do you agree for that theoretical example the inside ski has a tighter radius though?
It's the same issue whatever parallel curve you carve. It's just easier to imagine with a circle, or with an arc. You'll find the geometry is the same. To keep the curves a set distance apart, the inside curve must be tighter than the outside.
Quote:
The only point you can reasonably establish a "radius" of anysort is at the apex of the turn.
Not really. There's the center of curvature, which moves throughout the turn to form the evolute. For parallel curves, the evolutes are identical.
Then you can post your own questions or snow reports...
Then you can post your own questions or snow reports...
Question: If one was to exert enough pressure on the downhill ski to cause it to carve it's smallest possible radius turn, then, if the above comment is true, it wouldn't be possible to have a parallel course from the uphill ski?
After all it is free
After all it is free
Quote:
Do you agree for that theoretical example the inside ski has a tighter radius though?
IF you consider that the inside hip socket is the centre of the concentric circle, YES, you will get two concentric circles of which the inner circle will have a smaller radius.
BUT
We NEVER ski like that in real life - the two hip sockets are describing a sinusoidal pattern, parallel with the ski tracks.
Consider the hips sockets (or knee joints if you like) as the centres of the two sine wave tracks being left by the skis, and suddenly perfectly parallel, identical carved arc to arc ski tracks are possible.
PS: Think railway tracks. Do you really consider that the inside track in a curve has a smaller radius than the outside track, or that the railway tracks are parallel?
Last edited by After all it is free on Wed 16-04-08 18:54; edited 1 time in total
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.
Mark Hunter wrote:
Question: If one was to exert enough pressure on the downhill ski to cause it to carve it's smallest possible radius turn, then, if the above comment is true, it wouldn't be possible to have a parallel course from the uphill ski?
AHA!!! At last!!! Finally!!! Someone is starting to think about the effects of what happens about when you have a dominant outside ski (as per norm in high performance skiing)
Ski the Net with snowHeads
Ski the Net with snowHeads
Mark Hunter wrote:
Question: If one was to exert enough pressure on the downhill ski to cause it to carve it's smallest possible radius turn, then, if the above comment is true, it wouldn't be possible to have a parallel course from the uphill ski?
The arc you bend a ski into is not just a factor of pressure, more edge angle and sufficient pressure (if we're negating depth the ski cuts into the snow). If you set two skis parallel to each other two feet apart at the same angle with the same pressure applied and apply no rotational/turning forces, they'll turn the same radius of curve, which will result in the skis' paths converging. Of course, the two skis are linked by the skier's hips, which applies turning forces to the uphill ski, making it track a tighter radius by turning/steering it.
snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
double post
Last edited by snowHeads are a friendly bunch. on Wed 16-04-08 19:10; edited 1 time in total
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.
[quote="Sideshow_Bob"][quote="veeeight"]
Quote:
PS: Think railway tracks. Do you really consider that the inside track in a curve has a smaller radius than the outside track, or that the railway tracks are parallel?
That's exactly what I was going to ask you to think of! The inside track most definitely has a smaller radius! This doesn't stop them being parallel though, where we define parallel as separated by a fixed distance from the normal to the curve! Think of a circular section of railway line. Each track is a fixed distance at the normal from the other all the way through the turn, but the inside track definitely has a smaller radius and is turning quicker.
Do you think if you took the inside rail and moved it so it was on top of the outside rail, they'd overlap exactly?
So if you're just off somewhere snowy come back and post a snow report of your own and we'll all love you very much
So if you're just off somewhere snowy come back and post a snow report of your own and we'll all love you very much
I'm obviously overlooking something here. If one did as you suggest, why would the skis' paths converge? I would have thought that an equal pressure and distance between the skis would ensure that the paths didn't converge. I think I'll bow out and leave the radius discussion with your good self and veeeight
You know it makes sense.
You know it makes sense.
veeeight wrote:
Consider the hips sockets (or knee joints if you like) as the centres of the two sine wave tracks being left by the skis, and suddenly perfectly parallel, identical carved arc to arc ski tracks are possible.
PS: Think railway tracks. Do you really consider that the inside track in a curve has a smaller radius than the outside track, or that the railway tracks are parallel?
Not sure if you can really call the hip socket the "centre" - if that were true, the radius would be the length of the leg, and the foot would rotate while the hip remained stationary.
Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
Chasseur wrote:
I'm obviously overlooking something here. If one did as you suggest, why would the skis' paths converge? I would have thought that an equal pressure and distance between the skis would ensure that the paths didn't converge. I think I'll bow out and leave the radius discussion with your good self and veeeight
What causes the skis to remain the same distance apart though? Start the skis the same distance apart, and just edge them the same, so they turn the same radius. You'll find that a tighter radius is needed for the inside ski to keep it the same constant distance from the outside ski.
Poster: A snowHead
Poster: A snowHead
Sideshow_Bob wrote:
If you set two skis parallel to each other two feet apart at the same angle with the same pressure applied and apply no rotational/turning forces, they'll turn the same radius of curve, which will result in the skis' paths converging.
Martin, I don't believe true racing turns look exactly like that. I think that the skis do actually converge and diverge a little bit during the turn, and the skis are further apart in the fall line than at turn initiation. There's also either an amount of steering of the inside ski to make it track a tighter radius or some minor scissoring.
However if you imagine a turn where the skier always has their feet the same width apart, then yes, it'd look like that.
If one exerts sufficient pressure on the downhill ski to ensure it reaches it's minimum turn radius in a carve, the reality is that the uphill ski will also carve a parallel line with considerably less pressure.
To be clear (for the less educated like me), is the suggestion therefore that the difference of degree of edge to the slope between both skis compensates for the carved lines to not diverge? I'm not sure that makes sense, but it has been a long day!
Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
Chasseur, can you talk about inside and outside skis? Makes it easier to think about, as (usually at least!) the uphill ski at the start of the turn is the downhill ski at the end of the turn.
Just back in from mowing the lawn, but pondering this equal diameter question for the inside & outside ski.
Thinking about what the inside ski would have to do to have a tighter track than the outside ski (and still be 'carving') it would have to be either,
Tilted \ edged \ angled more than the outside one - I don't believe that is the case, certainly in my skiing.
and / or
Bent \ Pressured \ curved more the outside ski - I don't believe that is the case, unless things are going badly wrong for me
we can pivot or turn the ski under foot, but that would not be 'carving'.
So it figures that the inside and outside must have the same diameter track ??
Then you can post your own questions or snow reports...
Then you can post your own questions or snow reports...
david@mediacopy, well that's what I'm having a problem getting beyond to understand Sideshow_Bob's position.
Sideshow_Bob, you probably gathered that just to add to the confusion a change occured a few posts ago - apologies.
And yes, outside ski = downhill ski etc - will aim to keep the vernacular.
After all it is free
After all it is free
Interesting spreadsheet - and it shows that veeeight is actually way out of his depth here, having misinterpreted many of the results and concepts. First off - two conceptual errors.
a) Curves do have well defined centres of curvature pretty much all the time (other than places like when when turning at a point - pivoting), even if that point is moving. As previously mentioned, the mathematical definition of that is the evolute curve.
b) As Martin Bell rightly queried, the hip sockets have no relation to the centre of curvature. That's defined by the geometry and edge angle of the skis.
Now misinterpretations of the spreadsheet.
1) The sinusoid is not a prediction, but an assumption of the model. Yes it's a mathematically easy function to deal with, and has the benefit of matching reality in being straightish at the transitions and pointy in the middle, so a good starting place.
2) The model is also that - a model, and models what each ski would have to do to "carve" a pure sinusoid given desired separations at apex and transition. It is NOT saying what actually happens, just what has to happen to fit to those requirements. It quite explicitly shows that each ski is doing something different at pretty much all points along the path.
3) The model itself allows for the fact that the tracks are almost never parallel, by asking you to specify leg separation independently for transition and apex - and gives you a graph of that variation in separation as you go through the turn. It also explicitly tells you how much yours skis are diverging at the transition. (It's a shame the graph is in Y axis rather than normal to the curve though)
4) The radii of curvature are different for inside and outside skis pretty much throughout.
5) Yes the inside ski may have a longer radius than the outside, but only for a short period near the apex of the turn, when the outside ski radius is still dipping, but the inside has limited. Throughout the vast majority of the turn the outside ski has a shorter radius than the inside
6) For the turns I looked at (SL-type), the sinusoidal model shows that the ski is actually carving for only about half the turn. In the params I entered, the inner ski was carving from about 0.23 to 0.76 and the outer even less than that. This was commented on in the associated thread by PhysicsMan, and is probably where the sinusoidal model deviates pretty badly from reality.
Probably a load more, but I've got to stop now, as I'm late for skiing (now even later).
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.
GrahamN wrote:
Probably a load more, but I've got to stop now, as I'm late for skiing.
A far more useful activity
In the end, these little "thought experiments" are diverting but often bear little relation to reality. I was chuckling, over lunch, imagining a young BASI trainee being told to do railroad turns with parallel shins and parallel skis, and saying "but sir, that's mathematically impossible". I can imagine the answer he would get from some wizened old Scottish BASI trainer - it would probably contain plenty of the kind of words that you could hear late at night in the "Winkie"!
Would I recommend the mathematical approach to passing instructor exams? No, just regurgitate whatever technical buzz-words are in fashion that season in that country, and try to copy the skiing style of your examiner, based on whichever national association you're taking the exam with...
Ski the Net with snowHeads
Ski the Net with snowHeads
Quote:
and it shows that veeeight is actually way out of his depth here
FAQ
Poster: A snowHead
