 Poster: A snowHead
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| ansta1 wrote: |
| I also like the sidecut idea and was going to suggest it but thought I'd ask what You'd already covered. |
We will be putting a bit in the next newsletter (goes out around the end of March) next year about how and why skis turn.
To start you off, here is a ski radius / edging / sidecut - spreadsheet/calculator.
You will need excel on your PC to download it.
The page was only put up this morning in response to a discussion someone (?) had on facebook so it will be made to look better.
But the spreadsheet download works fine.
I hope you find it interesting.
http://www.brentaski.com/skiradius/
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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Is a certain physicisteo behind this? Beyond geeky for any normal punter.
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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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and maeningless given that the most important factor, being how bent the ski is under stress, is incalculable... 
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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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Sidecut Radius and Turning Radius:
It's an interesting subject that many skiers choose to ignore.
I would say that all but the most casual of skiers need to understand how a carving ski works.
Variable Turn Radius
The fact is that if it's carving, the track can be curved by clean edging. The turn can be tightened in the carve by edging progressively more.
"Ordinary skiers" can learn this. It is a progression to more "output focused" which starts with looking at the inputs:-
If there are three steering elements (edge, pressure and rotation) then only edge need be actively applied by the skier and the pressure can be allowed to build up on its own. This pressure needs to be managed rather than applied. If the skier tries to actively apply pressure, the ski will break away. Rotation of the ski in a carved turn is to be completely minimised to as close to zero as possible.
Skilful skiers don't make semicircular turns. Turns start with a long radius and tighten down to a minimum - then they expand out again on the progressive release of the edge angle.
The more the carving ski is edged, the tighter the carved radius becomes.
The maximum carve turn radius will be the ski's sidecut radius. That's the fixed radius that's marked on the ski. Normally Slalom skis are 11m Rsidecut and today's FIS GS competition skis are 35m Rsidecut with Recreational GS skis around the 20m mark. (Note that Rsidecut of a ski is ski-length dependent. You'll find that a shorter length in the same make and model of ski has a smaller Rsidecut).
Bending a ski that is carving
The bend that can be put on to the ski is variable: It can be closely approximated to :-
Rsidecut times the cos of the angle of inclination.
(Where Rsidecut is the fixed sidecut radius designed into the ski. This is very frequently referred to incorrectly as the "turning radius" of the ski. If more people understood that error, there would be more expert skiers on the slopes).
Assuming you can ski on that bent ski, you'll carve a turn whose radius at any point will be the same as the bend radius of the ski.
It's obviously a theoretical value and it is to miss the point if one tries to derive an accurate value of radius. The point is that the radius of the carve turn is a variable that is a factor of the angle of inclination. The maximum turn radius is Rsidecut. The minimum is a small number of metres and is skier-dependent.
Practically
Intuitively, one can see that as the ski is tilted (try it on the kitchen table) a gap opens up under the mid-point. Pressing down to close the gap makes the ski bend.
Geeky? Not really...
The reason we need to know this is that it can be shown that a GS ski has a more versatile carving radius range than a Special Slalom ski (or other short Sidecut-radius ski); in that edging the longer-sidecut radius ski can give you solid carve grip at the top of the arc with minimal turning at low angles of inclination. (In GS you don't want to be in the fall line till you are near the gate. So you want to de-couple the job of gripping from the job of turning.
Why are GS cut skis more versatile?
Roll the GS ski on to a large edge angle progressively, and then roll it off again as soon as possible after the fall line and you have an expert's GS race turn. Such a GS carved turn can tighten right down to a radius of only 2 metres or so. It is an impulse that lasts a fraction of a second.
Why do untrained skiers need to understand this if they want to become experts?
Most untrained skiers only edge after the fall line and then get trapped on the increasing edge as the pressure builds up. They carve up the hill to give speed control. Also, they "park'n'ride" i.e they don't progressively increase and decrease the edge angle, but try to hold a constant small edge angle. Hence the popularity of turny, short-sidecut radius skis.
Expert skiers get off the edge at or just after the fall line. And that is much less tiring and allows higher speed, controlled skiing. The different factors of speed control and direction control can be therefore separated.
Once an intermediate skier can grasp the concept, they will quickly improve. Once they learn how to sharpen their skis that is. 
Graph of edge angle vs ski-bend radius for a given fixed sidecut radius.
http://www.epicski.com/content/type/61/id/107371/width/500/height/1000/flags/LL
From this can be seen that there is - at the GS end of the family - a greater rate-of-change of output radius for a given edge angle. (The curve is steeper) i.e. there's a grater sensitivity.
Epic Ski thread
http://www.epicski.com/t/113663/relationship-of-carved-turn-radius-and-ski-sidecut-radius#post_1526489
Last edited by Anyway, snowHeads is much more fun if you do. on Sun 27-09-15 20:41; edited 7 times in total
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| SkiPresto wrote: |
The reason you need to know this is that it can be shown that a GS ski is more versatile than a Special Slalom ski; in that edging the longer-sidecut radius ski can give you solid carve grip at the top of the arc with minimal turning at low angles of inclination. |
... or you could learn to ski.
My slalom skis don't have any problem carving the whole arc.
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| rjs wrote: |
| SkiPresto wrote: |
The reason you need to know this is that it can be shown that a GS ski is more versatile than a Special Slalom ski; in that edging the longer-sidecut radius ski can give you solid carve grip at the top of the arc with minimal turning at low angles of inclination. |
... or you could learn to ski.
My slalom skis don't have any problem carving the whole arc. |
RJS you say
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| "My slalom skis don't have any problem carving the whole arc" |
I have no doubt that this is true. If you read again, I'm discussing something beyond that. It's understood that the whole arc is to be carved.
e.g.
1) Being on the edge all the time is slow. Racers and high performance skiers like to glide between turns.
2) I'm discussing an arc that is not semicircular. It's a continuous carved track that tightens and loosens (opens up again). Slalom skis start to carve at 11m which is less versatile than starting the carve at 25m and tightening the arc.
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@SkiPresto, have you not just eloquently described why a ski radius calculator is a bit pointless?
Even more so when you take into account variable contact points due to rocker profile. Nothing wrong with favouring tight radius skis - not everyone wants to hoon around bending GS skis.
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You'll get to see more forums and be part of the best ski club on the net.
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@SkiPresto, uhhh, the maximum carve radius is infinite.
being a straight line and all...
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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| under a new name wrote: |
@SkiPresto, uhhh, the maximum carve radius is infinite.
being a straight line and all... |
Yes you are mathematically correct, but (in the case of a finite sidecut radius) only if the inclination angle is zero. In that case, I would argue that "carving" is not occurring.
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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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You know it makes sense.
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I get to 90+ regularly and sometimes 180+.... Though more often than not those angles don't allow recovery to <20 without a yard sale..... (for more often than not read never) 
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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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@ansta1, if standing on the ski =0 degrees, 180 degrees = upside down
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Poster: A snowHead
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Hi @skimottaret 😊
Yes your math is good, but I think your angles will be more than 60 degrees. It's only for a split second and the turn is between the 45's in terms of direction change.
If you are with JJC in Saas-Fee in November, let's see what we can do.
😉
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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yeah having a crack at some more GS but looking at video from last year a lot to work to do and dartfish is showing me at 66 deg on my good side and 55 on my weak side in the fall line
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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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What I see is that people who try to explain a ski carving still don't get it.
The ski acts as if it is a continuous procession of segments.
Not a cookie -cutter stamp tool.
If the sidecut profile isn't a semicircle, then that's ok.
The tip starts the groove and all the parts of the edge follow behind. The sidecut radius simply allows the ski to bend into its own radius.
Like a long railway train approaching a curve. The fore part of the train can be on the curve while the guards van is still on the straight.
Similarly, the shovel of the ski can be at any instant bent into a tighter bend than the tail.
The GS turn is over very quickly. Less than a second at the gate. The rest of the GS turn is setup and crossover.
The rate of change of direction accelerates positively and then negatively. The direction change starts slow, and gets faster and faster, then gets slower again.
The GS turn is parabolic in shape. Not constant radius.
Only in this way can the momentum be harnessed to linearly accelerate out of the turn.
Semicircular turns would force the skier to grind the edge in after the fall line at the very point where the edge angle should be coming off.
Last edited by You need to Login to know who's really who. on Mon 28-09-15 17:08; edited 2 times 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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| under a new name wrote: |
| @ansta1, if standing on the ski =0 degrees, 180 degrees = upside down |
Yep!
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You'll need to Register first of course.
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Nice paper there @philwig. Good to credit Skiing Mechanics, John Howe 1983, even if there were very few Snowboarders then. I have a copy.
I'd say that the accuracy of the calculations isn't the point. The main point to get over is that the Output radius is a function of edge angle. Further, that there is one best radius / edge angle pair that doesn't break away. (A bit like the classroom mech eng excercises of railway trucks on an inclined plane, where the force is straight into the rail - rather than pushing the rail in or out).
I'd not get too hung up on the shape of the side-cut. This is not the curve that is ridden on a bending board. The side-cut initiates bending.
Straight boards can be made to bend without a sidecut (we used to call our skis "a pair of boards" in a long-gone halcyon era before snowboarding). We pressed tip and fore-part, then middle and then "jetted" the tails to make the ski work when we had 90m sidecut radii.
Last edited by After all it is free  on Mon 28-09-15 19:56; edited 1 time in total
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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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im gonna regret this but here is a photo of me not bending the skis very well and highlighting different edge angles on strong and weak footed turns.. pretty tough to get over 70 degrees I recon for most non racers
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| skimottaret wrote: |
im gonna regret this but here is a photo of me not bending the skis very well and highlighting different edge angles on strong and weak footed turns.. pretty tough to get over 70 degrees I recon for most non racers
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Looking at that, I'd say your turn to the left (Right footed) looks more effective, as you've got more of a turn completed.
Maybe if you took the inside foot away - to commit 90-odd percent on to the outside ski, you'd get more angle / leg inclination. And more force available to bend the outside ski. Ted's inside knee is pointing skywards - it's so far "out of the way".
Maybe you are turning too far round the curve - rather than flattening off on to a 45Degree traverse to the next turning point.
Obviously, it's the hardest thing to do as the tighter the turn, the more the force, and the faster the speed - well the force increases by V Squared.
The answer lies in making the skis change direction at a point of your choosing, but without breaking away.
This is indeed speed control.
This is what the nay-sayers to the so-called "Speed-Test" don't 'get'. It's not about more speed. It's about the correct speed for the conditions and the amount of edge inclination. Skiers who have poor technique can't control the speed without exhausting their physical strength owing to having to soak up the big forces late-on in their heavily-edged phase-3 of their turn, whereas expert skiers are off the edge by then and don't take nearly so much force in phase-3.
The references to body Inclination/ Angulation earlier reinforces what we have already learned that Body Inclination is "stance of strength", but it's not agile. So we compromise by angulating at the various joints - to get the job done in time.
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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Gosh ... how can I ever enjoy skiing again?
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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 still haven't seen a description of anything that isn't just as easy to do on SL skis as on GS ones.
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You know it makes sense.
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| rjs wrote: |
| I still haven't seen a description of anything that isn't just as easy to do on SL skis as on GS ones. |
The thing is that: on slalom skis, as soon as you stand on the edge at any nonzero angle of inclination of the ski, you send the ski into a tight turn of about 11m radius.
This could whip you in to the fall-line too early. Especially if you put an increasing amount of edge on.
This doesn't let the skis run. So you can end up slowing down.
Slalom skis are great for rapid short arc, short deflection turns - i.e. turns of short radius, but not too much offset.
GS skis allow the non-expert much more time to establish edge grip high up in the arc.
GS Skis allow the expert to have more edge-sensitivity and get to play with the instantaneous radius all the way from Rsidecut all the way down to a couple of metres radius when they are laid out.
Slalom skis are limited/ optimised to about 30mph - or they'll just put you on your back if you try to put a big edge on at speed.
GS skis allow the good skier to go much faster - but under full early edge grip, controlling speed and direction continuously through the turn, and a flexibility to turn as tightly as your skill allows.
Last edited by You know it makes sense. on Mon 28-09-15 23:42; edited 3 times in total
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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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I think SP's point is that a GS ski is more versatile in that you can arc bigger radius turns and if you put big edge angles on and pressure the ski correctly you can make arced short radius turns using GS skis. You cant arc turns with a radius bigger than the size of turn you are trying to make so turn shape using SL skis is limited.
Last edited by Otherwise you'll just go on seeing the one name: on Mon 28-09-15 23:20; edited 1 time in total
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Poster: A snowHead
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@ Skimottaret - That's right. The biggest radius you can carve cleanly is Rsidecut. I think the bind that the intermediate gets into is that they can't finesse a turn on slalom skis because they are far too turny, and unless you are a world-cupper, you don't have time to control them at high speed.
"You can't clean-carve an arc with an instantaneous radius greater than Rsidecut". Slalom skis are stuck at 11m starting radius and can only clean-carve at or tighter than that.
GS skis allow the non-expert to decouple the establishment of grip from the direction change.
Once you have grip you are much more under control. You can then remove the support foot (old outside ski-becomes new inside ski)(see Ligety image) allowing inclination to commence and allow the turn to start way before the fall-line, get right over into the turn, widen the stance (see Ligety's stance when he's at max inclination) allowing maximum long outside leg and short inside leg. The skis carve tighter and come underneath the centre of mass - allowing the upper-body to angulate at femur-tops and in the spine too, whilst the pressure comes off the outside ski early and transfers on to the outside edge then the flat of the inside ski - allowing the availability of the new inside edge of the new uphill ski after the crossover to make the new turn grip early.
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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@SkiPresto, disagree. but have neither the mental capacity nor bandwidth now to understand clearly myself nor explain, but given I think (!) a descriptive equation could include a flat ski and an inclined ski then your statement implies a pretty nasty discontinuity.
someone else (better qualified than myself) has almost certainly run the mechanics and mathematics...
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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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@underanewname
It's an interesting test to take the problem to the end points like you have attempted to do.
You say "
| Quote: |
uhhh, the maximum carve radius is infinite.
being a straight line and all..." |
You can suggest a radius of infinite length. That's all very interesting but it isn't all that useful if you are a skier.
They say parallel lines meet at infinity. That's fine too. Because they'd never reach infinity.
If you are suggesting a circle of infinite radius, I'm saying that it doesn't meet the requirements of a circle in that the circle must enclose an area. If I remember this area is pi *r squared.
Your infinite radius cannot enclose an area because the ends of the line would never meet.
A circle of infinite radius is a straight line of infinite length.
I go back to the.practicalities:
Skis have a sidecut radius that is finite not infinite.
So the maximum radius that can be carved is the sidecut radius, because the bend on the ski would be approximately the same as the sidecut radius at the smallest nonzero edge angle.
Last edited by Well, the person's real but it's just a made up name, see? on Tue 29-09-15 8:36; edited 1 time in total
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You need to Login to know who's really who.
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@SkiPresto, but you are ignoring torsion on the ski. and softness of snow...
I submit that you can go smoothly from a straight line through to some maximum tightness of turn without having a sidecut radius "jump". Skis just don't automatically assume the "Rsidecut" carve you are suggesting. IMHO :SH:
I also have empirical evidence (albeit somewhat specific and a single instance) that it is entirely possible to ski faster on SLs than SG or DH boards in a downhill.
Conscious that this is possibly getting tedious for the audience, can I park my argument for the moment (I'm at a conference and rather distracted) and I promise to resume tomorrow afternoon, by PM if better?
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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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@underanewname
| Quote: |
| "but you are ignoring torsion on the ski. and softness of snow... " |
Yes. I am doing that. These are my reasonable assumptions for the purposes of discussion. These factors may well be present in practice. The principle we're discussing here is the main thing, and these factors can safely be parked.
We assume here that the ski is gripping on a surface that cannot be deformed to any great extent more than is necessary to hold a minimum amount of edge.
These points illustrate my descriptions:
A flexing ski starts to carve when the angle of tilt is increased from zero such that the ski bends.
A ski will carve (i.e. Tail follows in a groove made by the tip) in an output turning radius that can be considered to start at Rcarvemax= Rbendmin = Rsidecut.
A skilful skier can bend the ski more by increasing the lean (edge angle) and that the output turning radius can be approximated to be equal the bend on the ski.
The bend on the ski can be approximated to Rbend = Rsidecut times Cos(edge angle).
The skilful skier can increase or decrease the amount of edge angle at a progressively rapid rate, and continue to carve a curved groove that at any point has an instantaneous radius that is becoming smaller (or larger) than that at a previous point.
The ski is like a flexible beam for the purposes of analysis. It can be considered to be suspended between its two initial points of contact, and pressed into a curve.
Rsidecut is a constant. It is the radius cut into the side of the ski. As the skier does not actually ski on the side of the ski, we must use the sidecut simply as a design feature that facilitates the ski to bend and flex along its length.
Older designs of skis can be carved too, but there is no simple Edge-to-turn mechanism. Older skis have to be pressed at front, then middle then tail in order to make them flex.
Practical skis can be considered as flexible - in other words each element over the length of the ski can be flexed at a minutely different amount.
The ski does not work as a guillotine blade.
Other models can be considered... e.g. a cantilevered beam. In practice, this can be seen in GS racing at the end of the turn where the tips of the skis are off the snow, and the curve is being made by the tails of the skis. This could be considered as a single-point of suspension - rather like a diver's springboard.
(In order to ski, it is not necessary to know all this.
Many skiers consider that they ski long turns on a long side-cut radius ski, and in order to ski tighter turns then new short side-cut radius skis are required.
This isn't helped by Rossignol who this year have LT skis and ST skis (Long Turn and Short Turn)).
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(Politely..) Perhaps it would be possible to make what you're trying to say simpler? I do have some materials science background, probably more than the vast majority of skiers, and if I can't understand the point then probably most people won't.
"You can recognize truth by its beauty and simplicity. When you get it right, it is obvious that it is right ..."
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| Quote: |
The tip starts the groove and all the parts of the edge follow behind
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Nice thread, maybe worth adding that many all mountain and other ski profiles its not always the tip that starts the turn, the widest part of the ski could be well back from the tip, therefore the greater the edge angle achieved the great amount of ski in contact with the snow, therefore enabling a very diff radius from one ski.
On purer SL and GS skis its a great deal easier to work out whats going on though?
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Hi @philwig
I agree with you. It could be written more simply.
What's holding you back?
Lets see your take on it.
I've not made it simplistic. That's where many skiing books and even expert studies lead the unwary down the path of constant radius turns. That leads to static skiing.
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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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Hi @livetoski
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On purer SL and GS skis its a great deal easier to work out what's going on though?
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I agree with that.
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Edge angles are great, but to be most effective a skier should be able to balance against the ski(s) when they are at the angle. On soft snow that isn't too difficult as snow pressure builds up against the base, but on hard snow it requires accurate management of the upper body mass. Example below, one turn well balanced and the other not so:
On the left the skier (me!) is properly balanced against the outside ski which is bending nicely at the apex of the turn, just above the gate, while on the right the outside ski is yet to de-camber leaving a lot of work to do after the gate, and losing speed. Skis are Dynastar ladies FIS from 2013 with r 25m (length 182).
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FAQ
I recon I can get to about 60 on a good day and if my maths are right my turn arc would be half the sidecut radius. is that a fair assessment? if so no excuses now 
