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# Ski technique - Page 39

Quote:
Originally Posted by Ghost

If you are using a ground reaction force to make you turn with 3g of centripetal acceleration and you suddenly remove that force (eg by flexion), your body will continue along a path tangent to the turn at the point of time it is released.

yeah - a lot more lateral than down...? you time that right, you're sending the body straight over the skis into the next turn - did I get that wrong?

math is not my forte, but it figures that 70 degrees of 90 max is 80% or so off the force vector. G never changes so I'm left with a missing what 2.7g lateral acceleration? How much do the skis need to keep turning during the non-instantaneous release for the body to cross in a somewhat "down the corridor" direction?

How long does a typical SL retraction turn transition take (in seconds)?

Quote:
Originally Posted by razie

Quote:
Originally Posted by Ghost

If you are using a ground reaction force to make you turn with 3g of centripetal acceleration and you suddenly remove that force (eg by flexion), your body will continue along a path tangent to the turn at the point of time it is released.

yeah - a lot more lateral than down...? you time that right, you're sending the body straight over the skis into the next turn - did I get that wrong?

math is not my forte, but it figures that 70 degrees of 90 max is 80% or so off the force vector. G never changes so I'm left with a missing what 2.7g lateral acceleration? How much do the skis need to keep turning during the non-instantaneous release for the body to cross in a somewhat "down the corridor" direction?

Even more so if your reference system / point of view is moving with the skier and skis (and continuing to move with the skis).   Still you have to have some support going on in the vertical direction during transition, albeit not much.  Otherwise your trajectory would move you straight at that point on the snow where the outside edge you are balancing on meets the snow (a=F/M in the direction of net force of those diagrams of which you spoke).  Only question is how much vertical support is needed?  Probably more than it seems to you, but still not "heavy".

Quote:
Originally Posted by Ghost

Even more so if your reference system / point of view is moving with the skier and skis (and continuing to move with the skis).   Still you have to have some support going on in the vertical direction during transition, albeit not much.  Otherwise your trajectory would move you straight at that point on the snow where the outside edge you are balancing on meets the snow (a=F/M in the direction of net force of those diagrams of which you spoke).  Only question is how much vertical support is needed?  Probably more than it seems to you, but still not "heavy".

The amount of vertical support that you need to keep the COM from dropping is body weight.  The amount of time you have to catch yourself when retracting the legs is very very short, shorter than an SL transition time.  When you have some upward acceleration to make you weightless then the time is much longer.  Stand and retract the legs and try to move them to the side and catch yourself.  Then give a little hop before doing the same, and you'll see that just retracting the legs without upward acceleration is not what's happening in floating transitions.

Yes, but the CM needs to drop as I'm moving downhill, and I want to set up a big angle quickly in the new turn, so less than body weight.

Quote:
Originally Posted by Ghost

How long does a typical SL retraction turn transition take (in seconds)?

Let's see, a 60 gate slalom race with a time of about 60 seconds = about one turn per second.  YM

So about 0.2 seconds for the transition?

Giving a  10 cm drop while pushing up with half your weight, or a 20 cm drop while not pushing at all.

10 cm seems about right for that last bit of the turn where you step onto the old inside skis LTE.

Quote:
Originally Posted by Ghost

Quote:
Originally Posted by razie

Quote:
Originally Posted by Ghost

If you are using a ground reaction force to make you turn with 3g of centripetal acceleration and you suddenly remove that force (eg by flexion), your body will continue along a path tangent to the turn at the point of time it is released.

yeah - a lot more lateral than down...? you time that right, you're sending the body straight over the skis into the next turn - did I get that wrong?

math is not my forte, but it figures that 70 degrees of 90 max is 80% or so off the force vector. G never changes so I'm left with a missing what 2.7g lateral acceleration? How much do the skis need to keep turning during the non-instantaneous release for the body to cross in a somewhat "down the corridor" direction?

Even more so if your reference system / point of view is moving with the skier and skis (and continuing to move with the skis).   Still you have to have some support going on in the vertical direction during transition, albeit not much.  Otherwise your trajectory would move you straight at that point on the snow where the outside edge you are balancing on meets the snow (a=F/M in the direction of net force of those diagrams of which you spoke).  Only question is how much vertical support is needed?  Probably more than it seems to you, but still not "heavy".

think impulse, impulse - too much static diagraming... the true mark of the expert skier is stealing just enough impulse from the turn: not less and not more... well, certainly hard to control that +/- x% that might get you airborne in a WC turn, but anyways, you get the picture...

Quote:
Originally Posted by The Engineer

Dropping into the turn happens as centrifugal force is building, so it's also not light, in fact as you are dropping in the turn the pressure on the skis increases.

Not unless the skier is pushing against the upside down skis and even then any pressure introduced at that point is small and short lived because the skier is really just pushing their CoM further down the hill. Real pressure builds once the ski tip hooks up.

Quote:
If it is fact that flexion allows the CoM to move towards the base of support then it is also a fact that removing the base of support via flexion causes a transition.

This is not true. Removing the bos of support may allow the com to move across the skis but it does not automatically (magically) cause an edge change. Which is the only absolute that needs to happen during transition. Think of a high side fall. There is more to transition than just having the com cross the bos. And while zen is correct by saying
Quote:
And yet flexing or extending can both have a direct influence on the chosen method of turn entry as well, in regards to steered, pivoted, tipped. The details will lie in the
The thing that is most important changing edges which requires the com moving over the bos but that is not the cause of the edge change. Simply flexing or extending does not cause an edge change either. In fact you have 3 options during transition and those are flexing, extending or neither, think white pass turn. The more correct description of this would be flexion/extension During transition.
Also a release of the edge or com may or may not result in a transition. Again transition requires edge change. Edge change is done through femur rotation and adduction/abduction.
Quote:
Originally Posted by loki1

Simply flexing or extending does not cause an edge change either.

That may be true if you consider synchronized leg actions, but if they are independent they most certainly can cause an edge change. ILE and OLF are two common examples.

Quote:
Originally Posted by Ghost

So about 0.2 seconds for the transition?

Giving a  10 cm drop while pushing up with half your weight, or a 20 cm drop while not pushing at all.

10 cm seems about right for that last bit of the turn where you step onto the old inside skis LTE.

The fastest racers have the CoM moving up and down in the order of 50 cm.

Any sane person should understand that this is impossible if you are heavy in transition.

Quote:
Originally Posted by Ghost

Even more so if your reference system / point of view is moving with the skier and skis (and continuing to move with the skis).   Still you have to have some support going on in the vertical direction during transition, albeit not much.  Otherwise your trajectory would move you straight at that point on the snow where the outside edge you are balancing on meets the snow (a=F/M in the direction of net force of those diagrams of which you spoke).  Only question is how much vertical support is needed?  Probably more than it seems to you, but still not "heavy".

You don't "need" any vertical support. You want some ski-snow contact but you don't "need" it.

Again this is the typical vertical support in an SL turn, about 25%.  It also gives an answer to you previous question about how long the transition is. If we assume 1 second in this picture the transition is about 0.5 seconds ( if we further assume transition=initiation+completion).

Quote:
Originally Posted by Jamt

The fastest racers have the CoM moving up and down in the order of 50 cm.

Any sane person should understand that this is impossible if you are heavy in transition.

You're going to have to explain this. It may be obvious to you but not to everyone else. How does it relate to these transitions, and are they heavy or light?

Photos by Ron LeMaster
Full images here:
http://www.ronlemaster.com/images/posted-11-2015/content/Ligety-Vail-2015-GS-2A-11x14_large.html
http://www.ronlemaster.com/images/posted-11-2015/content/Hirscher-Lenzerheide-2014-GS-1-13x13-B_large.html
Quote:
Originally Posted by Tog

You're going to have to explain this. It may be obvious to you but not to everyone else. How does it relate to these transitions, and are they heavy or light?

Photos by Ron LeMaster
Full images here:
http://www.ronlemaster.com/images/posted-11-2015/content/Ligety-Vail-2015-GS-2A-11x14_large.html
http://www.ronlemaster.com/images/posted-11-2015/content/Hirscher-Lenzerheide-2014-GS-1-13x13-B_large.html

There are different rates of edge change from high-siding to highly skidded patient turns. Heavy can refer to how your skis feel or how your body feels (bos or com). Keeping contact with snow may feel light on the bos, but perhaps not in the com - like the feeling when skiing upside-down.

It really is not that much about if you are heavy or not at transition. Its more about how big edge angles you can pull off.

Quote:
Originally Posted by Tog

You're going to have to explain this. It may be obvious to you but not to everyone else. How does it relate to these transitions, and are they heavy or light?

Get on a bathroom scale and start in a deep squat. Rise 60 cm and back again a few times and see if you can do it fast without getting light at the highest point.

Edit.

Just to understand what it takes to move up and down in a short time, lets assume that a skier has a light vertical state during half the turn, and an opposite and equal magnitude upwards acceleration during the other half of the turn.

The time it takes to make this movement can then easily be calculated as, if the CoM rises up and down X m we get the time

t=4 * Sqrt[X/a]

For example if we rise 60 cm and the acceleration is a=g (i.e. as light as you can get.)

t=4*Sqrt[0.6/9.81] =0.99

If we have e.g. a=g/2 and X=50 cm, this is still light.

t=1.3 seconds.

If you are heavy, e.g. a=0.2g and x=0.5:

t=2.0 seconds.

Edited by Jamt - 1/11/16 at 6:03am
Heavy in the com has a lot to do with getting those angles. Phil said it at the end of the video. That's what it's about.
Quote:
That may be true if you consider synchronized leg actions, but if they are independent they most certainly can cause an edge change. ILE and OLF are two common examples.

This is simply not true.
ILE will move the com further inside the turn and away from the bos. It will also transfer pressure from the outside ski to the inside ski.
OLF will move the com towards the bos and towards the outside of the turn. This may eventually cause the com to cross the bos but only after the range of flex has been exhausted. It still will not cause and edge change.
Remember in a turn the outside leg is extended more than the inside. Also the only time ILE and OLF make the com move laterally to effect edge angle is when in a wedge.

When the skier is balanced traveling around a circle, the forces are aligned with the body.  When the base of support is removed the initial momentum is pointing towards the ground on the edge of the circle.  As the body begins to move towards the outside edge of the circle on the ground (i.e. skis) gravity keeps pulling downward.  So, the COM will always land inside the circle.  It’s impossible to travel balanced in a circle, retract the legs, and cross the skis that are continuing in the circle.  Something else has to happen.  When falling like a rock, there is no time for anything else to happen.  In order for retraction to be the cause of weightlessness for the vast majority of turns, you would have to see the COM drop nearly a foot after the release for just about every transition.  That’s not happening, folks.  In many transitions that I’ve looked at, the COM is rising as the outside leg is flexing.

Sit in a chair that can spin.  Hold something down at an angle pointed towards the outside edge of a circle.  Spin around as fast as you can.  Drop the item.  See where it lands.  What you’ll see is that the item immediately leaves the hand straight in the direction it’s pointing (relative to the rotating person, the object continues on the tangent), and then curves downward to land inside the outside edge of the circle that the hand is pointing at.

Edit:  There are problems with this experiment.  What you need is a mass on a string that can automatically adjust to it's natural angle based on gravity and centrifugal force to be like the balanced skier.

Quote:

Originally Posted by Jamt

The fastest racers have the CoM moving up and down in the order of 50 cm.

Any sane person should understand that this is impossible if you are heavy in transition.

Before apex, the COM is still dropping, but yet the pressure on the skis is much greater than gravity.  Just because the COM is dropping at various times in the turn cycle does not mean that there is no pressure on the skis.  The COM must drop before centrifugal forces build during transition to be evidence of weightlessness during transition.  Sometimes that happens, sometimes that doesn’t happen.  Therefore, sometimes the skier is weightless; sometimes the skier is not weightless.

Quote:
Originally Posted by Jamt

Get on a bathroom scale and start in a deep squat. Rise 60 cm and back again a few times and see if you can do it fast without getting light at the highest point.

This is an up-unweight move that has nothing to do with the conversation at the moment.  The conversation at the moment is if you can get weightless to transition merely by retracting the legs.  For some reason people want to rehash old arguments in this thread that have already been pretty well settled, just because we are discussing the possibilities of retracting both legs to get weightless to transition.  I see many transitions where skiers are not retracting both legs, so whether they can get weightless to transition merely by retracting the legs or not has no bearing on whether skiers are heavy or not in transition.  Do we really have to keep arguing about whether there are heavy transitions or not?  We've each made our case.  We're not going to convince each other.  Let's drop it.

Edited by The Engineer - 1/11/16 at 9:11am
Quote:
Originally Posted by Ghost

Yes, but the CM needs to drop as I'm moving downhill, and I want to set up a big angle quickly in the new turn, so less than body weight.

We already talked about this earlier in the thread.  Heavy as possible includes lightening by accelerating down the slope, so ~2/3 weight is even heavier relative to what's possible, though not by a whole lot.

Quote:
Originally Posted by loki1

This is simply not true.
ILE will move the com further inside the turn and away from the bos. It will also transfer pressure from the outside ski to the inside ski.
OLF will move the com towards the bos and towards the outside of the turn. This may eventually cause the com to cross the bos but only after the range of flex has been exhausted. It still will not cause and edge change.
Remember in a turn the outside leg is extended more than the inside. Also the only time ILE and OLF make the com move laterally to effect edge angle is when in a wedge.

No simple truths. If you transfer weight from an extended outside to the inside the CoM comes closer to the BoS, because the BoS moves from the extended outside to the flexed inside.

You also change the balance state so that you will "vault" towards the next turn.

You don't even have to do any flexing or extending or edge moves, just like PSI man.

Quote:
Originally Posted by loki1

This is simply not true.
ILE will move the com further inside the turn and away from the bos. It will also transfer pressure from the outside ski to the inside ski.
OLF will move the com towards the bos and towards the outside of the turn. This may eventually cause the com to cross the bos but only after the range of flex has been exhausted. It still will not cause and edge change.
Remember in a turn the outside leg is extended more than the inside. Also the only time ILE and OLF make the com move laterally to effect edge angle is when in a wedge.

This bears repeating, as it is something that again anyone reading this can experience.  In this case, I'd recommend an uncrowded green or mellow blue with room to roam to get this sorted, but it is another basic fact.

Quote:
Originally Posted by CTKook

This bears repeating, as it is something that again anyone reading this can experience.  In this case, I'd recommend an uncrowded green or mellow blue with room to roam to get this sorted, but it is another basic fact.

Paging @HeluvaSkier ! Please come and fix this train wreck that Loki, CTKook and TE have created.
Quote:
Originally Posted by loki1

Removing the bos of support may allow the com to move across the skis but it does not automatically (magically) cause an edge change. Which is the only absolute that needs to happen during transition.
The thing that is most important changing edges which requires the com moving over the bos but that is not the cause of the edge change. Simply flexing or extending does not cause an edge change either.

yup - these are related and both necessary - edge change can't happen without crossing and crossing can't happen without edge change (or results in a thud).

There is a way though where the first bit about the COM causing the edge change, say in speed skiing, there's so much time and such big forces that you can simply wait for a passive extension of the leg because of the COM crossing - often resulting in that bit of A-frame we see in COM releases... but that's not in the scope of this discussion, for sure.

Otherwise, yes, flex/extend is the required thing (I never really agreed with the old coaching adage with inclination of COM causing edging, still present in many manuals). We disagree some, I think, on the I guess ratio of ankle to femur work involved in tipping the skis on edge at different places in the turn, but yeah.

Quote:
Originally Posted by Jamt

Quote:
Originally Posted by loki1

This is simply not true.
ILE will move the com further inside the turn and away from the bos. It will also transfer pressure from the outside ski to the inside ski.
OLF will move the com towards the bos and towards the outside of the turn. This may eventually cause the com to cross the bos but only after the range of flex has been exhausted. It still will not cause and edge change.
Remember in a turn the outside leg is extended more than the inside. Also the only time ILE and OLF make the com move laterally to effect edge angle is when in a wedge.

No simple truths. If you transfer weight from an extended outside to the inside the CoM comes closer to the BoS, because the BoS moves from the extended outside to the flexed inside.

You also change the balance state so that you will "vault" towards the next turn.

You don't even have to do any flexing or extending or edge moves, just like PSI man.

"no simple truths"  - No kidding... I don't particularly fancy much the ILE. There is a fine line between transferring early to the inside leg, which will be the new outside leg and then extending it. The question is really one of when the extension happens: before or after skis flat. If it's before, which I think an ILE is, then it does push the body back up the hill and slows things down...

If you just transfer some weight to it and the extension is after skis flat, then it's what Ted does and it's fine. The point of that is that when transferring to the uphill edge of the inside ski, the balance is changed drastically like Jamt noted, as that's well under the COM and that is one of the benefits of doing that.

The bold part is interesting - haven't actually thought of it that way, but of course.

I think we're missing this picture from our own animation master when talking about releases of COM and skis and force vectors and why things cross:

Some (TE?) seem to equate the arc and path of the skis with that of the COM - that's barely true in low level skiing... and far from reality in high end skiing...

If one simply removes the support of the COM, the paths will cross just because they were never the same...

Edited by razie - 1/11/16 at 8:26am
Quote:
Originally Posted by Jamt

Quote:
Originally Posted by Tog

You're going to have to explain this. It may be obvious to you but not to everyone else. How does it relate to these transitions, and are they heavy or light?

Get on a bathroom scale and start in a deep squat. Rise 60 cm and back again a few times and see if you can do it fast without getting light at the highest point.

Edit.

Just to understand what it takes to move up and down in a short time, lets assume that a skier has a light vertical state during half the turn, and an opposite and equal magnitude upwards acceleration during the other half of the turn.

The time it takes to make this movement can then easily be calculated as, if the CoM rises up and down X m we get the time

t=4 * Sqrt[X/a]

For example if we rise 60 cm and the acceleration is a=g (i.e. as light as you can get.)

t=4*Sqrt[0.6/9.81] =0.99

If we have e.g. a=g/2 and X=50 cm, this is still light.

t=1.3 seconds.

If you are heavy, e.g. a=0.2g and x=0.5:

t=2.0 seconds.

hey - I was going to bring that up when everyone was tired... stole my thunder, you... thunder stealer...

we should keep the simple physics truths for the end, when all other arguments have been exhausted

Quote:
Originally Posted by Pacmantwoskis

Paging @HeluvaSkier ! Please come and fix this train wreck that Loki, CTKook and TE have created.

It is strange that factual posts about skiing would be characterized as a train wreck.  When reality is different from preconceived notions of "float" being some sort of goal or signpost for high-level skiing, certainly having to do a bit of brain-floss might be an adjustment.  When what is left is a better understanding of technique that more closely ties in to what is getting coached by the best coaches in the world, there should be no wreckage.

None of those technical arguments handy, Mr Kook? Back to brain-flossing, are we?

Edited by razie - 1/11/16 at 9:45am
What about the images of Ligety and Hirscher above?
-Are they heavy or light?
- Is the inside leg, or both, extending before transition or not?

Still don't get the scale business. They are up before transition in those photos. So...?

As for the other, without functioning legs it would seem psiman couldn't ski.

https://vimeo.com/9872613
Quote:
Originally Posted by Tip Ripply

I was letting Razie know that "forward" was digested pages ago. It seemed like he had an epiphany. Haha

HA. If "forward" was digested by enough skiers, we could put a lot more of them on the WC.

Epiphany? From what? I have many coaching tools in my coach bag and I use them as needed... including the dreaded "transfer early and push yourself forward"...  as I said what, 4 times already? I was just proving that point I guess. I don't have just one big heavy transition like some, but a lot of other stuff.

Quote:
Originally Posted by Tog

What about the images of Ligety and Hirscher above?
-Are they heavy or light?
- Is the inside leg extending before transition or not?

Still don't get the scale business. They are up before transition in those photos. So...?

As for the other, without functioning legs it would seem psiman couldn't ski.

https://vimeo.com/9872613

hey, do you know that psiman skis like Ted? He transfers to the inside ski quickly and that's how his COM tumbles over... otherwise he'd be stuck... watch closely on which ski he's actually turning on in the high speed slow mo turn sequence towards the end, when he actually does a few turns.

and.... that's like a flexed release (removing the outside leg support)

cheers

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