 Poster: A snowHead
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Just how, exactly, did you paint the target on your fat ass. Did you use two brushes a set distance apart? Are the lines in the circle perfectly parallel? Can we have a picture of it so we can judge? 
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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I think the RSPCA should be called because of this cruelty to Masque's donkey!!!
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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.
You need to Login to know who's really who.
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Masque, Read it and was fascinated. Good work. More please to keep summer interesting.
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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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Masque, are those your tracks? That's a pretty clean cross-over.
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You'll need to Register first of course.
You'll need to Register first of course.
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rob@rar, that was knicked from the EPIC thread that martinBell referred to on the tip lead topic. Bob barnes had some very nice clear graphics that expanded on some of the ones sideshow bob had done.
Masque - agree with your conclusions. I always felt that shovel loading was the main reason for this as i can bend my ski tips with light finger pressure and as you point out a fully loaded outer ski can only bend so much.... It isnt to difficult to bend em both at roughly the same radius in grippy snow as demoed above.
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| skimottaret wrote: |
| rob@rar, that was knicked from the EPIC thread that martinBell referred to on the tip lead topic. Bob barnes had some very nice clear graphics that expanded on some of the ones sideshow bob had done. |
Thanks. I suppose I should look at EPIC from time to time.
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| Masque wrote: |
| See the deeper track of the outside ski and the inner wall of the uphill track is almost as long as the downhill demonstrating a more acute insertion angle. |
Hi Masque. Wow, what an effort you put into this,,, well done! And with all the controversialness to start the summer off right!  Question: by "more acute insertion angle" your suggesting the inside ski track indicates that the inside ski was tipped to a higher edge angle, right? That's really the only way less pressure might produce a similar width sidewall. At the same edge angle, less pressure would just mean less penetration of the ski into the snow, thus a narrower sidewall in the track. Agree?
Now lets go back to your pillow test. What happens if you put a pillow under both skis? After all, when skiing, if the pillow represents the snow, then both skis are standing on it. In my double pillow test, if you pressure one ski more than the other, and the lesser pressured ski is only loaded enough to compress the pillow about 1/2 way, which ski will bend more?
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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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rob@rar, I went to Epic once - and found that I had to pay to contribute - $20 or something like that to give free advice? I thought they were having a laugh! 
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FastMan, In the case I'm describing there is no attempt to 'drive the skis and the rider is only trying to stay neutral over the skis through the carve.. I did a lengthy post in the other thread about bio-mechanics and why when you raise your inside foot and angulate through your hips in the carve your uphill foot pronates and your foot turns (yaws) toward the inside of the turn.. Mechanically the bones in the foot and ankle form a semi-rigid structure that is laterally very stiff and resistant to the torque generated by the engaged edge of the inside ski.
Your downhill ski is attached to an extended leg with a lot of flexibility in the mechanics of the structure when stressed outward. It's much more difficult to resist the twisting moment generated by the edge of the downhill ski. Without a concious effort by the skier their downhill ski will always have a shallower insertion angle than the uphill ski.
Coming back to the pressure scenario and the pillows, the only time you have two pillows under you is when you're standing still or in transition. As you tip your skis onto their edges they cut into the snow surface and begin to compress the snow under the running surface. It's the density and structure of the snow that determines how much it deforms to provide a stable and flat surface for the ski to run on (a berm). In a carve the ski's edge is only there to ensure that the ski can cut deep enough into the surface of the snow to provide a flat running surface wide enough to support the the skier's mass and acceleration vectors of the turn.
This is where it gets interesting. At whatever speed, pressure or angle of attack of the ski to the snow there is a point of equilibrium where all the forces are in balance and ski cannot be bent any further because the all the forces are cancelled out. All the skier can do to alter the turn shape is either move the Centre of Mass insertion position (something that we can discuss later) or change the angle of the ski to the snow. This is aplicable to the complex interdependent balance mechanism that is two skis linked at your groin.
Taking a sidebar: You all know that the older straighter skis (nearly all skis throughout the sport's history have had some shaping) are a bitch to carve, taking skill and effort to do so. I'm going to speculate that it's virtually impossible to carve a consistent turn on truly parallel straight skis. It's been the advent of snowboarding's sidecut shaping that's led to the ability of skis to carve turns in the manner that's caused this debate.
And it's the sidecut that allows the inner ski to bend more than the outer whilst under less pressure. The pillow analogy is still valid as all that happens is that as you go from equally balanced on two matching pillows in the transition, the outer pillow becomes thicker as the turn develops and the inner pillow shrinks because the fulcrum points on the outer ski are closer to the Centre of Mass than those of the inner.
Geometry is a simple tool to show that a ski's sidecut means that they need very little difference in bending moment to have significantly differing turn radii and the angle of the ski to the surface combined with it's length and the size of its sidecut determines it's theoretical maximum turn rate . . . but that calculation is static and on a non-deformable surface. It's the amount of deformation under the ski that limits the ski's ability to bend and the more pressure applied the more the snow deforms until it reaches maximum density. The lesser the pressure of one side of a interdependent balance mechanism means a smaller deformation in the snow surface, less resistance and a greater bending motion to achieve equilibrium.
This is why when a skier in mid carve undergoes a sudden change in weighting from the outer ski to the inner, they experience an immediate shortening of the turn radius to the outer ski and a concurrent lengthening of the inner as the pressures and snow deformation equalise, the carve/turn radii digress and the tips cross . . . with entertaining results
The deeper the sidecut, the more pronounced and faster this happens . . .
All the above is independent of deliberate skier input, I'm still working through the mechanics of including rider input to this.
Just a PS . . . why does it need a boarder to explain to you plankers as to how you stay upright and why you fall over? 
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snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
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I still swear its all linked to cone shaped railway wheels and Dyson balls 
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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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Megamum, regrettably not unless your brakes are locked and the track is at Alton Towers. This is about flexible shapes, deformable surfaces, friction coefficients and gravity.
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Masque, well balls to that idea then (Dyson ones of course!!). 
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You know it makes sense.
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Megamum, I can see where your head's going. The vector paths of the two ski radii and the path of your CoM form cone sections if they are traversing a flat plane but that turns out not to be relevant to creating the path in the first instance . . . it's just a result that has no function in the process . . . and of course if your track takes you over a convex or through a concave surface then the cone becomes narrower or can even end up flat. . . . not important but needed to be factored before eliminating.
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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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Poster: A snowHead
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Masque, Yeah, but if the track takes you over a convex or concave surface then its only adding or subracting from the same cone argument. I think the two skis flex to sections of that cone, the one on the inside of the curve behaving slightly differently to the one on the outer edge to maintain a cone profile. In the same way the train wheel can't go round the curve if its square to the track, I doubt that skis can either. Therefore, the action of skiing must deform the skis to get round the bend in the same way as the cone shaped wheels argument. The shape of the surface doesn't affect the cone argument it just shifts the variables.
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Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
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