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Start the Turn - Page 2

post #31 of 46
I don't disagree that consistency could be a sticky wicket with divisions too, but I theorize that what's needed is to focus attention on, as Harald Harb is wont to say, THE SINGLE MOST IMPORTANT THING. In divisions, I submit that's education. For PSIA national, I say it's upholding the national standards--concerning BOTH member instructors and member schools.

Who knows, maybe schools would step up if PSIA had a tete a tete with the insurance folks about the risk benefits of retaining experienced, certified instructors. I feel that the insurance industry is more likely to drive improvements in the instructor's state of being than our bosses' good will and humanitarianism.

I should note that I have zero support for my point of view amongst any of the aforementioned stakeholders...
post #32 of 46

I should note that I have zero support for my point of view amongst any of the aforementioned stakeholders...
And we come back to our industry's major problem, apathy by the powers that be.

post #33 of 46
Bob; I love your description of "offensive turning" It's really hard for me (and most people, I expect} to take complex descriptions and translate them into action; But the idea of starting a turn as an acceleration I totally get.. I do this in combination with working on riding out the arc; the idea being not to hook it but riding it smoothly as far around as you wish to control speed then dropping into the next turn by lightening and tipping the downhill ski and accelerating back into the fall line..
post #34 of 46
In "linked" turns, the new turn should be started before the old turn ends. In other words the body should be moving into the new turn before the previous turn is ended. Beginning and ending a turn are ovelapping processes.

Physics Man
"...so you will have a positive steering angle near the tip and a negative angle near the tail with an average value again equal to zero."

I thought a ski would have a natural non-zero steering angle that comes from the taper angle?
post #35 of 46
...oversimplified "average angle" that I tried to get away with...
Nope--you can't get away with ANYTHING around here!

Nice explanations, Tom. To me, the only thing that makes sense, at least "practical" sense, is to consider only what happens directly beneath my foot, where the forces that apply to me actually apply--the point of the ski over which I'm balanced, and through which the "line of action" applies--where "action meets reaction." The line of action indicates the direction of the forces that apply to me, and in a (theoretical) circular pure-carved arc, that direction is directly sideways, perpendicular to the direction I'm traveling at any given moment. And the ski, of course, is going the EXACT direction I'm traveling--at this point beneath my foot--representing a ZERO steering angle.

The rest of the ski--tip and tail--really doesn't affect ME. It can influence that steering angle under my foot in several ways, but it does not affect ME. It really doesn't matter what happens to the rest of the ski as far as its effects on me go--it can tighten or straighten its arc, as long it doesn't change that angle beneath my foot--witness the incredible flapping and gyrations of the ski in a slow motion film of a downhill racer. It doesn't matter how LONG the ski is, either, although the angle of the tip of a longer ski in the same carved arc is obviously different than the angle of a short ski. Again, the only steering angle that matters is the angle at the point I'm standing on, the direction the ski pushes on ME.

Of course, in that theoretical perfect carve again, the steering angle changes constantly, as does my direction of travel, as I go through the turn. I like the image of a ball-bearing rolling around in a bowl. The circular sides of the bowl provide a continuous centripetal force, pushing the ball at right angles to its direction of travel (at any instant). The tangent of the bowl's arc at the point where the ball contacts it represents the direction the ball is traveling at that moment, and (obviously) also represents the steering angle. The bowl is like a very long ski, so long that it bends 360 degrees and describes the entire circle.

Another applicable image is the ball on a string, swinging in a circle. Here, the STRING represents the centripetal force. Obviously, it always pulls directly toward the center of the circle, along the line of the string (the only direction it CAN pull). And that direction is always perpendicular to the direction the ball is traveling, represented by the tangent of the arc--which again represents a ZERO steering angle.

Perhaps these illustrations can help:

Good theoretical stuff. I'm not sure it lends any more real insight into how to start a turn than the little side-track about teaching that we switched to above, but it's good to understand!

Best regards,
Bob Barnes
post #36 of 46
Hi Bob -

I really like your simplification of the issue down to the question of whether or not your foot is pointed in the same direction as it is moving. It's the same thing, but MUCH clearer than my statement,

>"...define the "effective" steering angle as the angle between the direction your foot is moving and the centerline of the ski..."

since in mine, the reader has to realize that the centerline of the ski IS the direction your foot is pointed. I strive for clarity, and unfortunately, usually wind up with verbosity, whereas you always seem to achieve it on the first shot. I guess its one of the curses of being a geek - arghhhh.

Unfortunately, I've got to point out a spot in your post where I think you may have misspoken:

>"...in that theoretical perfect carve again, the steering angle changes constantly, as does my direction of travel, as I go through the turn. ... represented by the tangent of the arc--which again represents a ZERO steering angle..."

Since we seem to be in agreement that a decent definition for the steering angle is the angle between the direction your foot is going and the direction it is pointed, in a perfect carve, that number is always exactly zero (as you said in the last part of the above quote). However, in the first part of the quote, you say it changes constantly. I suspect that all you meant was that the direction of travel changes constantly.

All the best,

Tom / PM

PS - You lucky dog, I hear there was snow out in your neck of the woods this AM - WOOHAAA!!!!

PS#2 - re your last comment, that all this theory doesn't really tell you how to start a turn: Yup, this discussion got waaaay too technical even for me. The only reason I persued Fox's comment back on 8/18 was that there seems to be an oversimplification or dated remark in LeMaster's book where he essentially says that to start a turn, you must establish an initial steering angle away from the direction you are going, ie, you *must* initially skid or hop your turn around.

This clearly isn't required in a modern carved turn, this was misleading Fox, and looked like there was a good chance it confuse other people as well who use this book as a reference. Hence, the start of this subthread on this one small issue. Maybe Epic needs footnotes like scientific literature (...just kidding...)

PS#3 - I loved your new illustration. Are we going to find bowls like this in every terrain park next year? ... You know, sort of like those games / exhibits in shopping malls & museums where you roll a penny around a curved surface that gets steeper and steeper the closer you get to the center?

[ August 22, 2002, 10:47 AM: Message edited by: PhysicsMan ]
post #37 of 46
Oops [img]redface.gif[/img]

[ August 22, 2002, 11:27 AM: Message edited by: John Cole ]
post #38 of 46
Originally posted by Ydnar:
Neither has PSIA on either the national or the divisional level and I see no reason to hope that the situation is going to improve. So where does that leave us except up chit creek without a paddle, and the damn canoe is leaking.

I cannot agree that National and Division have not done their best to educate the instructor. Look at wealth of educational materials available from National and yet how many even on this site have the latest manuals? My Division, Central, offers a tremendous array of clinics and yet most instructors only attempt to stay current. Can all of this be improved? Absolutely! For one the cost of clinics could be lessen so more might participate and educational materials could be changed and possibly improved to assist the newer instructor. Yet there is only one person that can make it happen, the instructor! Participation is the only real true answer. The instructor’s demand to the organization will change the organization. The instructor’s participation is what will improve the instructor and the organization.

Have a GREAT day!
post #39 of 46
Originally posted by NordtheBarbarian:
...I thought a ski would have a natural non-zero steering angle that comes from the taper angle?
Actually, what's going on is this: The curved edge of a tipped ski in reverse camber forms a curve that closely approximates a circle whose radius equals the sidecut radius, and whose center is located on a line perpendicular to the centerline of the ski and passing through the ski waist.

In a theoretically pure carve, the above curve forms a replica of itself in the snow, and this is the precise path that your ski takes.

Since the center of this curve is also out on a perpendicular from the ski waist at every point in time, the centerline of the ski is exactly parallel to the tangent to the curve describing your path at the ski waist. Thus, if you define the "effective" steering angle as the angle between the direction your foot is moving and the centerline of the ski, this effective steering angle is exactly zero by the above geometrical argument.

Unfortunately for me, in my earlier post, not wanting to bore people more than I usually do , I gave an overly simplified explanation of this:

"...so you will have a positive steering angle near the tip and a negative angle near the tail with an average value again equal to zero..."

You very sharply picked up on the slight difference between the effective steering angle and the oversimplified "average angle" that I tried to get away with in my previous post.

FWIW, this difference is only about 0.16 degrees, so I throw myself on the mercy of the court and plead leniency.

This 0.16 degree number can be estimated as follows. The difference between tip and tail widths on most skis is usually about 10 mm. Only half of this appears on one edge. This 5 mm difference occurs over something like 175 cm, leading to a taper angle of ~0.16 degrees relative to the center line of the ski. This minute angle should be compared to the hundred times larger (ie, 10-20 degrees) steering angles involved in most scarved turns.

Its a tiny effect, but I've got to hand it to you for picking up this discrepancy.

Tom / PM

PS - BTW, this sort of problem is why I dislike using any sort of an average steering angle and referring angles to the centerline of the ski. I *much* prefer to think in terms of the local steering angle relative to each point along the edge. In these coordinates, by definition, the local steering angle in a carve is identially equal to zero along the entire length of the ski, so no sort of averaging or "effecive" arguments need to be made.

[ August 22, 2002, 12:43 AM: Message edited by: PhysicsMan ]
post #40 of 46
Thanks Tom--yes, you are right--the steering angle in that perfect carved turn remains zero throughout, even as both your direction of travel--and the direction the skis point RELATIVE TO THE EARTH changes constantly. Once again, we have gotten into that area where the truth depends on your frame of reference, eh? Thanks for the clarification.

This may help only a very few people start at a better turn, but it can help pass the time until we CAN start a turn!

Best regards,
Bob Barnes
post #41 of 46
Physica Man

You said
"This is because in a turn that is truly carved from start to finish, you need to keep the steering angle equal to zero throughout the entire duration of the turn. Zero steering angle IS the definition of carving. Starting turns with a non-zero steering angle (ie, skidding or hopping the starts) used to be the only way to get them going, and is still by far the most common way you'll see on the slopes, but it certainly isn't necessary to start turns this way, and isn't even desirable in many cases."

For this to be true, for a ski with a wider tip than a tale would have to be steered opposite the direction of the turn to make "your" theoretical perfect carved turn. I don't think this "countersteer" ever happens, thus I don't think your perfect turn exists.

Also, If there is no inital steering angle, What bends the skis?
post #42 of 46
Originally posted by NordtheBarbarian:
For this to be true, for a ski with a wider tip than a tale would have to be steered opposite the direction of the turn to make "your" theoretical perfect carved turn. I don't think this "countersteer" ever happens, thus I don't think your perfect turn exists. Also, If there is no inital steering angle, What bends the skis?
Take a look at this schematic representation of a ski. You can think of it as either as one quadrant (ie, the inner, forebody) of a longer ski, or as the inside half of an oddball ski whose waist is located waaaaay to the rear of the ski.

<img src = "http://groups.msn.com/_Secure/0QgAAAK4XDBQr5XKPRlaNUXaoPad8yf2o9XvukglTkG5FGJI!P IxvJ2uZ6TyCB!FRauNmJjOwKWodSUG!WdIBKKkFdLOCzGGJhHs nhnBf7!c/CardboardShapeOfSki01-small.jpg">

Now, the center of the boot for this ski will located at the upper RH corner of the green area, with the toe pointed towards the tip.

In a pure carve, the boot will be moving directly forward, exactly tangent to the curve of your path directly underneath your boot. There is no small angle between the direction you boot is pointed and the direction it is actually moving at that moment - the steering angle is zero.

I suspect that what you are thinking is that if you would make a stiff cardboard cutout in this shape, edge it, put it in reverse camber, and push it along a surface, the tip and waist would somehow be the only points that would contact the surface, and "hence", the ski would actually be traveling on a straight line defined by the tip and waist contact points, ie at a non-zero angle to the centerline. While this conceivably could happen with an extremely light skier on an absurdly stiff ski, obviously, this is not what happens when in a normal carving situation and the ski is in contact with the snow at many points along its length.

With respect to your final question about what bends the ski, obviously, your weight pressing down on it bends it.

Hope this helped,

Tom / PM

[ August 23, 2002, 11:03 AM: Message edited by: PhysicsMan ]
post #43 of 46
What I meant to talk about is the initial stering angle. I agree with steering angle being zero during the carve. That is true by definition of a carved turn.
What I saying is you need some initial steering to start the carve. A very small steering angle will work, even the amount given by the taper angle of the ski. That's how you make a DH turn.
Skis pointed down fall line ski rolled onto edge, then Ski shape causes it to turn.
post #44 of 46

Sorry - I thought you were asking about the steering angle during a carved turn, not the initial steering angle often used to initiate it.

With respect to the latter, I maintain that while most people start their turns using an initial steering angle, it is not at all necessary.

To see this, lets use exactly the example you suggested, namely, a situation where you start from a straight downhill schuss and then do nothing more than roll your skis up on edge as in the recent discussion of RR track turns.

At the point you edge your skis in this example, your skis and boots are both pointed in the same direction, exactly down the fall line (ie, at zero steering angle), and you have just begun your arc to the L or R. It is exactly like the diagram in my previous post with the addition of now imagining that the fall line is to the left in that diagram.

For simplicity, lets imagine doing this on hardpack and you quickly roll your skis up on edge. As soon as you do this, your tip, waist and tail all contact the snow at three points which form an arc with your instantaneous velocity pointing along a tangent to it. This happens no matter if there is normal, zero, or reversed taper, and certainly without turning the centerline of the ski even an iota from the path that it had been taking a moment earlier. This is the whole purpose of the RR track exercise.

I will go even further and say that if you do start a turn with some non-zero initial steering angle, ie, a bit of a skid, it actually will be somewhat more difficult to convert your subsequent motion into a pure carve because your skis are already brushing sideways over the snow to some degree. The only ways out of this (ie to convert it to a carve) are:

1) Increase your "critical edge angle" to the point where your skis have a chance of holding on the little ledge of snow they are trying to create under themselves. Do this too abruptly and you will either do an old-fashioned edgeset or get thrown over the handlebars if you are not set to absorb the shock.

2) Use very fine rotary skills to line your skis up in the same direction that you are going at a particular moment and then lock in your edging.

3) (The most common) Gradually increase your edge angle to the point where it quenches any sideways motion and carve from that moment onwards.

Personally, I think that if you can, its better to start the carve right from the start, and not have to deal with any of the above.

Now, I used as an example a carved turn which starts without any skidding from a straight run down the hill. If you are starting your carve from some orientation other than straight down the fall line, you can still do it, but it gets more difficult the further away from the fall line you get. For example, if you try to do this from a pure 90 deg traverse, you would have to go quite a few degrees beyond flat to have your downhill edges lock in adequately. On other than very modest slopes, people usually don't have sufficient flexibility to do this (to say nothing of the unusual balancing act required).

In that case, you are stuck, and you would pretty much have to revert back to the normal routine of flattening your skis as much as you can, let them drift towards the fall line as you continue to move forward, and then getting on the new edges as soon as possible.

Since the skis are not locked onto an edge during this phase of the turn (the approach to the fall line), you have the option of using rotary input to keep the skis pointed in the direction they are moving in a very carve-like manner. Note, however, that its not a carve in the usual sense because your edges are not locked in to a particular path.

In other words, all carves have zero steering angles, but not all conditions of zero steering angles are carves (eg, flat ski skiing with "manual" control of the direction the ski is pointing).

Obviously, from a traverse, you always have the option of doing exactly what you said - you can always twist the skis around by 20 or 30 degrees while you are still heading across the hill, jam on the edges and start carving. The bottom line is that this is not necessary, just one of your options.

Any clearer or did I make it even worse - grin?

Tom / PM

[ August 23, 2002, 02:26 PM: Message edited by: PhysicsMan ]
post #45 of 46
Tom, congratulations, you have succeded in making my eyes glaze over. :
post #46 of 46
LOL - That'll teach him to ask a question - I'll yack him to death.

Besides, I'm not responsible (...obscure reference to another thread on Epic...) for how much I write - it must be genetics.

Tom / PM
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