What's essential for carving on hard snow?

Discussion in 'Ski School' started by LiquidFeet, Dec 31, 2018.

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  1. François Pugh

    François Pugh Out on the slopes Skier

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    Thanks for making the effort to explain it.

    That variety of turn radii is limited in range at the short end by reaching a point where the turn dialed up by the tipping angle required to provide the turning force without slipping up the groove requires a greater force, and at the higher end by the sidecut radius of the ski.
     
  2. skier

    skier Getting on the lift Inactive Pass Pulled

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    Geepers, ever since I told you your mogul dude is in the back seat, you've been harassing me at every chance. I'm sorry it upset you so much, but I've had enough of it, and I'm not going to stand for it any more. This is the me too era after all. The writing is on the wall, you're just not getting it, and I suspect if anyone else wrote it, you'd get it. So, back the duck up, buckle up for a ride, here we go, 100 pages and a thread lock. You're not getting the last word.:)

    Quite the opposite, it has everything to do with the sidecut. Because of the platform angle limitations, it's impossible to get enough lean to carve 16 meter turns with a 5 degree edge angle for some speeds. Is that really a surprise? Sharp turns give lots of CF. CF takes lots of lean. You can't lean past a 90 degree platform angle. If you think you can carve sharp turns with low edge angles, then it's hopeless talking to you. So, now what's the only carving solution if we can't carve sharp turns with low edge angles? It's carving large circles with low edge angles. And that's where the sidecut comes into play. The ski is not designed to carve large circles. Rsc is the largest circle that the sidecut is designed to scribe approximately. Go back and read that physics of skiing section on carving with 0 degree edge angle and see the radius that the ski is designed to follow. For larger circles the tip will not follow the tail even approximately around a circle. Don't get hung up on the zero angle though too much. You could just take the limit as the angle goes to zero, and the equations work out nicely describing a smooth transition from forward motion to edge locked carving, which is a feature by the way, not a limitation.

    1. We're stuck with not being able to exceed 90 degrees. Going less than 90 doesn't fix the problem of not being able to carve 16 m turns with low edge angles, because you must have more lean not less. A platform angle less than 90 degrees represents less effective lean, a platform angle greater than 90 degrees represents more effective lean.

    2. Two skis do not change the fact that you must have lean to counteract CF. Neither ski will have enough lean to carve sharp turns with low edge angles. Both skis are designed to carve only sharp turns edge locked.

    3. Carving a circle when the ski is shaped like an ellipse would be an approximation. Carving a 200 meter turn, when the ski is designed for a maximum of 16 meters is not an approximation.

    The Physics of Skiing book has a different section for soft snow carving. I haven't digested that yet. These equations are for hard snow, and they are absolutely true. You can turn at the top of the turn, but it starts out predominantly skidding, and then becomes less and less until you are edge locked carving a ~16 meter turn based on the sidecut of the ski. The only fallacy is your own perception of what you are doing on skis.
     
  3. François Pugh

    François Pugh Out on the slopes Skier

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    If you want to pure carve a 16 m turn at speed, just tip a 32 m radius ski up to 60 degrees. If you want to do it arc-2-arc with no skidding, make the ski go straight for that small fraction of a second it takes you to reach the critical tipping angle, while your body continues into the new turn under the action of momentum from the previous turn and gravity.
     
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  4. mdf

    mdf entering the Big Couloir Skier

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    It has been mentioned once or twice, but I think that the dynamic nature of the loads is not being given enough attention. An "adiabatic" picture, where the history is treated as a sequence of quasi-static situations, is not valid. The forces are not in balance at each individual time.
    We get light at transition to reduce the necessary loads. Our center of mass follows a less-curved path than our skis.
     
  5. skier

    skier Getting on the lift Inactive Pass Pulled

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    MDF, I believe I've worked it out where the ski cannot carve at low edge angles regardless of the weight on the ski, because the mass cancels in those equations. So, if our COM is following a less-curved path than our skis, how are the skis turning?
     


  6. skier

    skier Getting on the lift Inactive Pass Pulled

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    Francois, this is basically the solution put forth by Razie, me, Jamt, sort of MDF, and others as well, but with one caveat. Can you ski straight with your momentum going away from the skis, load the ski at an angle of 60 degrees and have the ski catch you? Some have said yes, some say no. Let's not have that argument now, but there are physics concerns with that scenario. The ski must cross the path of the skier's momentum such that it feels like the momentum is going into the skis. Jamt and the Physics of Skiing describe that there must be a steering angle before loading to make this happen. I believe this is true too. This is why I believe there is a slight rotary input for many types of turns without skidding. But, the physics gets more complicated, and it's not easy to make a clear, indisputable, argument. Even with a clear argument it can be tough, so let's not debate it. I just want to put that controversy out there, so that we can understand why some people have made certain conclusions. That's the answer to my question to MDF also, there's no way for the skis to carve themselves with low edge angles even if the skier was only 50 pounds, so if they are rotating sharply without skidding, it's because the skier is rotating them.
     
  7. markojp

    markojp mtn rep for the gear on my feet Industry Insider Instructor

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    How is it I can make low speed railroad tracks with just slight ankle tipping movements?
     
  8. Average Joe

    Average Joe Getting on the lift Skier

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    It's not possible:) We ran off the (RR) tracks about 11 pages ago.
     
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  9. skier

    skier Getting on the lift Inactive Pass Pulled

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    I don't think it's possible on hard snow. I don't even know if it's possible in soft snow, but I'll leave that for another day. The perception of what we're doing is often different than what we are actually doing.
     
  10. Thread Starter
    TS
    LiquidFeet

    LiquidFeet Out on the slopes Instructor

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    It's possible for Marko.
     
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  11. skier

    skier Getting on the lift Inactive Pass Pulled

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    Ooops, I missed the low speed part. The lower the speed, the smaller the skidding phase.
     
  12. Average Joe

    Average Joe Getting on the lift Skier

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    Embrace the possibilities.
     
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  13. Uke

    Uke Who am I now Skier

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    skier,

    Steering angle is inherent in any ski with side-cut. Once the ski is tipped to any fraction of a degree steering angle is created an the ski will begin turning, if certain conditions are met the ski will carve a pure arc (fairly easy to do) otherwise it will produce a brushed turn. Marko can do it as so can I.

    Might it be that rather than all the posters who have disagreed with you having a misconception of what is really happening that it is you who is laboring under a flawed concept of what is going on under your feet.

    One last thing. After years of exchanging posts and PMs with jamt I'm pretty sure that he would side with the majority of the poster here who disagree with you.

    uke
     
  14. skier

    skier Getting on the lift Inactive Pass Pulled

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    Uke, I am sorry that I have offended you. Please accept my humble apologies. Jamt's posts have been very important for me figuring this stuff out. He has many posts on the subject. Here's one:

    "Thus the turn will start with a steering angle and as soon as possibly the racer will increase edging and pull back the skis to remove the steering. When the skis lock in edge it is very difficult to return to steering, you are locked into the carving track. If you misjudged you are in trouble.
    The redirection/steering of the skis happen even if it looks like a pure carve, becuase you dont really carve until you have hit that critical edge angle. This has caused a lot of debate in the past because some view this as a pivot and others don't. I don't really care what its called, the important thing is what the steering angle is when the skis are engaged again. "

    Though, you are right, he will side with the majority of posters here. Let's remove him as a reference, though I wanted to give him credit, since I didn't think this stuff up myself. I originally accepted the ideas after hearing him describe it, but I hadn't worked out exactly the mechanisms until now. Honestly, I couldn't understand why he would say you don't reach edge lock until 72 degrees at gs speeds, because I didn't realize the true limitations of the turning radius equation. I always thought turning radius went up to infinity with edge angle, but now I see that's not true.

    Best regards,
    Skier.
     
  15. Uke

    Uke Who am I now Skier

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    skier,

    The quote sounds like jamt is talking about the intentional redirection that take place in almost every turn in a race course rather than the inherent 'skid' that you are arguing must take place in the beginning of any arc.

    Also, be aware that static, two dimensional depictions of a dynamic activity that take place in four dimensions can be misleading. When all factors are taken into account things, and the math, become more complicated. Like the man said "I know why the chicken crossed the road. But the answer only works for round chickens in a vacuum."

    uke
     
  16. skier

    skier Getting on the lift Inactive Pass Pulled

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    Thanks for clearing that up Uke. I'm glad to know now that perfect arc to arc carving without skidding or rotary is done regularly by experts like yourself. Forums like this are so useful, because now I know the truth where as I questioned it before. Again, please accept my apologies for disagreeing with you. I realize now it's better just to ask you than think for myself, because what good is math and physics for solving problems? Math is way too complicated for solving things like sending rockets to the moon or figuring out the carving limit of a ski. It's much better just to ask experts like you whenever we need to do things like that. Everyone, please disregard any evidence that I have presented for my points. I am clearly mistaken, because those points are meaningless next to Uke's indisputable, expert, opinion.
     
  17. Average Joe

    Average Joe Getting on the lift Skier

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    Thread closed?
     
  18. skier

    skier Getting on the lift Inactive Pass Pulled

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    That's a great idea! Let's lock the thread before Geepers has a chance to reply, and I can get the last word in for the first time ever.ogsmile
     
  19. François Pugh

    François Pugh Out on the slopes Skier

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    Or you could take a high school physics course, so as to understand the physics. You need to understand that forces are vectors, and you can at the beginning of turns, provided you have previously given your body the correct momentum, press the ski down into the snow more than you are pressing it sideways, as you tip to the critical angle, which would only take a small fraction of a second.
     
  20. skier

    skier Getting on the lift Inactive Pass Pulled

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    I will bet my life that I've taken more physics courses than you have.
     
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