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Fischer Dual Radius Technical Question

post #1 of 27
Thread Starter 
Question for the gurus and experts:

Reagrding the dual radius found on the Progessor line, how is it possible to carve out a clean edge on a ski with more sidecut in the tip than the tail? Since the rear of the ski has a different sidecut, won't the tails start to drag along the snow instead of slice the same path as the tips, once the sidecut in the front engages? Likewise, if you engage the mid-section of the ski and the skis follows the longer sidecut of the tail, won't the tips smear instead of slice?

It obviously works as many seem to report carving clean; but physically, it doesn't seem possible unless the rear and front of the skis have totally different flex patterns and can change shape to adjust. Is this what's going on?  
post #2 of 27
Quote:
Originally Posted by MojoMan View Post

Question for the gurus and experts:

Reagrding the dual radius found on the Progessor line, how is it possible to carve out a clean edge on a ski with more sidecut in the tip than the tail? Since the rear of the ski has a different sidecut, won't the tails start to drag along the snow instead of slice the same path as the tips, once the sidecut in the front engages? Likewise, if you engage the mid-section of the ski and the skis follows the longer sidecut of the tail, won't the tips smear instead of slice?

It obviously works as many seem to report carving clean; but physically, it doesn't seem possible unless the rear and front of the skis have totally different flex patterns and can change shape to adjust. Is this what's going on?  

I owned them and your making an issue out of something this is a non issue.

carving isnt some magical act, it doesnt require things to be exact at all. The simple answer is the skis are decambered while carving so the sidecuts of the ski really doesnt matter. the ski is bent into the actually shape of the turn. It can be much shorter than either posted sidecut FYI.

almost any ski can lay railroad tracks from SL carvers to the Progressor, to mid fat twin tips to enomous reverese cambered boards like the hellbents. You dont even need good technique, there are tons of people out there that can lay railroad tracks down but cant ski worth a damn.

also relize that snow even in its hardest forms is still a 3d surface. and physics when it comes to something like this only really needs to be on tim the tool man taylor basis of understanding.
post #3 of 27
Thread Starter 
I am not making an issue out of it -- just was wondering. I was reading the reviews at Realskier as I am interested in the Progressor 8. I got to thinking about the whole dual radius concept and how the ski reacts on the snow. It just seems like the tail would skid, as opposed to arc, if it was forced into a path that does not match the shape of the front of the skip when the entire ski decambers -- 3D terrain or not. It seems like it would be analogous to a steering system in a car where the rear wheels do not take the same steering angle as the front. The front rear tires would, for example, only rotate 5 degrees if the front tire roates 8. It seems like there would be some skidding involved and the car would be incapable of making a clean turn with no skidding.
post #4 of 27
Quote:
Originally Posted by MojoMan View Post

I am not making an issue out of it -- just was wondering. I was reading the reviews at Realskier as I am interested in the Progressor 8. I got to thinking about the whole dual radius concept and how the ski reacts on the snow. It just seems like the tail would skid, as opposed to arc, if it was forced into a path that does not match the shape of the front of the skip when the entire ski decambers -- 3D terrain or not. It seems like it would be analogous to a steering system in a car where the rear wheels do not take the same steering angle as the front. The front rear tires would, for example, only rotate 5 degrees if the front tire roates 8. It seems like there would be some skidding involved and the car would be incapable of making a clean turn with no skidding.

niether of your assumptions is true.

car doesnt skid jsut because the rear tires dont exactly follow the front, they just take a different path. You know that cause you most likely drive and dont go fishtaling around every turn.

so the tail would skid due to being a different radius? well at least thats you assumption. i have used the ski and they do not skid if you dont want them to. What law of physics states that the tail would have to skid?

basically your arguement is null because whats your talking about doesnt happen niether of the above things happens in our world. it would be like me argueing with the world we see the sun everyday it must be rotating around us.

again this is the simplest answer to your disprove your wrong assumptions.

The ski is decambered while carving the radi at this point  dont matter because the shape and size of the arc match the shape and the size of the ski. the ski will bend how ever much it needs to be to make the desired turn shape.

really is that so hard to understand and take as fact?
post #5 of 27
Thread Starter 
Then why do skis have sidecut at all, if the dominate factor is how the ski bends when it decambers? Would not the ski take whatever shape the skier decides to place on the ski after tipping and applying pressure?

Also, I am looking for a conversation, not a prelude to an argument -- really. If you want to argue or throw out the usual banter and insults, there are plenty of people here who will oblige. I am just looking for a discussion.
post #6 of 27
I think that what Josh is trying to say is that the sidecut of the ski creates the corresponding decambering of the ski, so the difference in the "flare" of the sidecut doesn't really matter once the ski is put on edge - it skis like one ski with a continuous sidecut instead of two different skis stuck together under the bindings. That said, I think they are probably great skis and that you're reading too much into a sidecut that was probably named by marketing after it was developed by engineers.
post #7 of 27
Quote:
Originally Posted by MojoMan View Post

Then why do skis have sidecut at all, if the dominate factor is how the ski bends when it decambers? Would not the ski take whatever shape the skier decides to place on the ski after tipping and applying pressure?

Also, I am looking for a conversation, not a prelude to an argument -- really. If you want to argue or throw out the usual banter and insults, there are plenty of people here who will oblige. I am just looking for a discussion.



 

nah no need to argue you have made it much more clear what your looking for. I was trying to get you to ask the right questions. Your getting closer....

skis have sidecut to make turn initiation easier, also when on lower angle of edge input the sidecut helps the ski track on that sidecuts radius easier but the ski is still decambered. The ski being decambered is the key to why the ski actually can carve a clean arc and its quite easy to decamber a ski.

the skis sidecut is a contributing factor to the shape of the carved turn but since the ski is decambered you cna have dramatically different sidecuts and still have a clean carved turn. In fact though good pressure control you can have entirely different skis on each foot and still railroad track turn. Its should be noted that a good railroad track turn leaves far from parallel tracks.

It should be noted that predecambered skis that still have a traditional eliptical sidecuts can leave railroad tracks as well the skis might feel skiddish untill the entire ski is engaged in the snow.
post #8 of 27
Quote:
Originally Posted by HeluvaSkier View Post

I think that what Josh is trying to say is that the sidecut of the ski creates the corresponding decambering of the ski, so the difference in the "flare" of the sidecut doesn't really matter once the ski is put on edge - it skis like one ski with a continuous sidecut instead of two different skis stuck together under the bindings. That said, I think they are probably great skis and that you're reading too much into a sidecut that was probably named by marketing after it was developed by engineers.

yep.
post #9 of 27
Quote:
Originally Posted by BushwackerinPA View Post

 Its should be noted that a good railroad track turn leaves far from parallel tracks.

 

How would you describe what it does leave?

I understand that parallel applies specifically to straight lines, but it also defines the lines as being equidistant which railroad track turn arcs, are.
post #10 of 27
Progressors are excellent carving skis.  They are easy to make a clean carve with.  Progressor 9 is stiffer and little more GS oriented, and the Progressor 8 is more like all-mountain slalom ski.  Try them out, I think that you will like them very much.
post #11 of 27
Thread Starter 
Quote:
Originally Posted by HeluvaSkier View Post

I think that what Josh is trying to say is that the sidecut of the ski creates the corresponding decambering of the ski, so the difference in the "flare" of the sidecut doesn't really matter once the ski is put on edge - it skis like one ski with a continuous sidecut instead of two different skis stuck together under the bindings. That said, I think they are probably great skis and that you're reading too much into a sidecut that was probably named by marketing after it was developed by engineers.
 


Hi, thanks for the explanation, and Josh as well. 
post #12 of 27
Thread Starter 
Quote:
Originally Posted by BushwackerinPA View Post




nah no need to argue you have made it much more clear what your looking for. I was trying to get you to ask the right questions. Your getting closer....

skis have sidecut to make turn initiation easier, also when on lower angle of edge input the sidecut helps the ski track on that sidecuts radius easier but the ski is still decambered. The ski being decambered is the key to why the ski actually can carve a clean arc and its quite easy to decamber a ski.

the skis sidecut is a contributing factor to the shape of the carved turn but since the ski is decambered you cna have dramatically different sidecuts and still have a clean carved turn. In fact though good pressure control you can have entirely different skis on each foot and still railroad track turn. Its should be noted that a good railroad track turn leaves far from parallel tracks.

It should be noted that predecambered skis that still have a traditional eliptical sidecuts can leave railroad tracks as well the skis might feel skiddish untill the entire ski is engaged in the snow.





 


With the Progressor, is it easier to vary the radius mid-turn , than on a traditional sidecut? I assume shifting your weight rather than pressing would have a more prondounced effect, or am I off track? 
post #13 of 27
I think it's a very good question.  My first impression is that the ski would have a harder time holding on to a turn when pressed to the limit and the arc wouldn't be as pure, but I haven't thought it through.

The sidecuts aren't exactly circular anyway, the snow/ice surface has some give to it the ski flexes a bit torsionally to accomodate some play, but still if you were to tip the ski and bend it along a carpeted floor or hard rubber surface, you would likely see the front half and rear half of the ski take up different radii with the edge solid against the floor.

Now the question is, "What would it look like with the ski pressed out along the groove cut by the front half of the ski?"

My brain is a little tired and I don't think I can visuallize it completely right now, but I'll make a half-hearted effort.  Let's see sidecut is not as deep as would be required to have solid edge contact at the given tipping angle, meaning that the tail isn't trying to lift the centre off the snow as much as it would if the flare were more pronounced at the tail.  So either the ski rides along without the tail edge riding up and not digging the grove deeper or the ski rotates a bit in the plane of the ski to put the edge down into the groove.  Probably the latter.  The ski is tail is essentially describing a bigger arc than the tip, but it's arc is not in the same plane as the one carved by the tip.  But now since it is one ski the front half of the ski must rotate too.  lifting the front of the ski out of the groove. 

Yup, it makes it harder to hold onto a tight turn, but makes it easier to get out of a turn.

Don't forget that to maintain a turn the tail edge doesn't need to reach the bottom of the groove you cut with the tip, the base just has to stay in the groove.
post #14 of 27
I love how this site can take the simplest thing and turn it into something that is completely incomprehensible.
post #15 of 27
How is this the simplest thing?  There's physics involved.  At least there's some visualization involved.  I'm pretty sure everything is complicated if you care to actually look at it.  Like say ... your car.  How much of that do you understand?  Or your TV?  

But anyway, great discussion.  I've thought it's weird too, but people seem to think it works.  I'd agree that it *should* make it harder to maintain a clean carve, but perhaps carves aren't as clean as I visualize them.  Or maybe the ski is shaped differently than I picture.  We need mythbusters to take this up and put their high speed cameras to work watching skis in the midst of an arc.  Or anybody with a high speed.

And as for tires on a car, perhaps that's a bad example because they inherently slip.  When you make a hard turn on smooth pavement, you can hear your rear tires slipping on the ground.
post #16 of 27
The harder to hold onto an edge-locked turn probably wouldn't be that noticeable except on ice.
The easier to get out of the turn would be obvious everywhere, not so much releasing the tails as might be easily inferred, but in freeing the tips as you launch off the tails.  Should be quite fun actually.
post #17 of 27
Quote:
Originally Posted by evonitzer View Post

How is this the simplest thing?  There's physics involved.  At least there's some visualization involved.  I'm pretty sure everything is complicated if you care to actually look at it.  Like say ... your car.  How much of that do you understand?  Or your TV?  

But anyway, great discussion.  I've thought it's weird too, but people seem to think it works.  I'd agree that it *should* make it harder to maintain a clean carve, but perhaps carves aren't as clean as I visualize them.  Or maybe the ski is shaped differently than I picture.  We need mythbusters to take this up and put their high speed cameras to work watching skis in the midst of an arc.  Or anybody with a high speed.

And as for tires on a car, perhaps that's a bad example because they inherently slip.  When you make a hard turn on smooth pavement, you can hear your rear tires slipping on the ground.

me and helva pretty much made it as simple as possiable....
post #18 of 27
Quote:
Originally Posted by HeluvaSkier View Post

I love how this site can take the simplest thing and turn it into something that is completely incomprehensible.
Diversity of opinion never simplifies but can often compose a fuller understanding if you choose to look past the obvious.  Simplicity is in the  mind  of one who makes a judgment from the information presented.

 You prefer sites with less diverse opinions ?   That's a much simpler solution than sifting through the thoughts of others .
post #19 of 27
Quote:
Originally Posted by GarryZ View Post



 You prefer sites with less diverse opinions ?

Really Garry? It would be really interesting to hear your opinion on the matter so I might learn what information you're using to decide that is true.
post #20 of 27
Thread Starter 
The reason I visit this site is for infromation. It also makes for interesting reading at the office.  You have to sift through a lot but that's true anywhere online. 

Regarding this subject, I never really gave much thought to the behavior of a ski from a theoretical perspective. What is happening to the ski on the snow when it unbends? My assumption was that the ski simply decambers and attempts to follow the sidecut of the ski as it is put on edge with minimal twisting. When the issue of dual sidecut entered into the picture, like Ghost, I tried to visualize it, but it seemed to contradict my assumptions. My mind tries to visulaize the path of the tip and tail, and it doesn't add up, so I asked for information. That was the reason for the question, really. I know it's making a mountain out of a molehill, but it's interesting to think about, for me, at least.
post #21 of 27
Quote:
Originally Posted by HeluvaSkier View Post




Really Garry? It would be really interesting to hear your opinion on the matter so I might learn what information you're using to decide that is true.


 
It was a question .Hence the question mark . If  you prefer information  handed down in an edict or  collected by group discussions would reflect how you like to process information. It's up to you and not for me to judge since I'm not you and cannot know but may have an idea collected from your words. It's all we have to go by.
post #22 of 27
Quote:
Originally Posted by MojoMan View Post

The reason I visit this site is for infromation. It also makes for interesting reading at the office.  You have to sift through a lot but that's true anywhere online. 

Regarding this subject, I never really gave much thought to the behavior of a ski from a theoretical perspective. What is happening to the ski on the snow when it unbends? My assumption was that the ski simply decambers and attempts to follow the sidecut of the ski as it is put on edge with minimal twisting. When the issue of dual sidecut entered into the picture, like Ghost, I tried to visualize it, but it seemed to contradict my assumptions. My mind tries to visulaize the path of the tip and tail, and it doesn't add up, so I asked for information. That was the reason for the question, really. I know it's making a mountain out of a molehill, but it's interesting to think about, for me, at least.

Bump . Sorry Mojo
post #23 of 27
Quote:
Originally Posted by GarryZ View Post



It was a question .Hence the question mark . If  you prefer information  handed down in an edict or  collected by group discussions would reflect how you like to process information. It's up to you and not for me to judge since I'm not you and cannot know but may have an idea collected from your words. It's all we have to go by.
 

We could always talk about skiing instead.
post #24 of 27
Regarding the dual side cut there is another way to look at it. Mojoman is is concerned with how a ski can have 2 different side cuts. I think that wat is actually occuring is a continuous variation in sidecut along the ski length. Consider the following. A single side cut ski would have a curvature described by a circular arc of a certain radius that has the same instantaneous curvature (Radius) everywhere on the arc. Some skis have a parabolic arc which is slightly different from a circular arc in the sense that it has a different instantaneous radius at different parts of the arc. You can still define an equivalent single best fit radius. If you extend this and deviate from a circular arc even further so that the curve is described by a higher order polynomial or other mathematical curve such as an exponential, you get a curve that has a distinctly different curvature (equvalent radius) at different parts of the ski. If you pick two sections, say the front half and the back half and fit a best fit circle to that section you can define two different radii for the ski even though the curve is smooth. If you are old enough, think of the shape of the french curve used for drafting years ago.  Ignoring the bending of the ski, all it means is that when you carve an arc you will carve a groove in the snow that is non-circular. By pressuring the front, middle, or tail of the ski you can have the radii of that section of the ski dominate that particular turn shape. As Bushwacker mentiioned you can also change the shape and tighten the radius by bending the ski. You can increase the radius of the turn by letting the ski slip a little. I hope this helps a little.
post #25 of 27
The sidecut on the Explosiv, burgundy with the budha, is pretty unique. It's more of an angle, just behind the heel of the boot, two very long arcs intersecting at the waist of the ski, looking almost like to straight edges. I always thought the design was for short swing steep terrain skiing, slip and check windshield wiper turns.  By comparison, my B-Squads are one long arc, fairly cut (130 to 100)

and a cosmetic change is the only difference between the burgundy model and the first cloud blue models, with the wizards being a different design through the middle years. wierd.
Edited by davluri - 11/12/09 at 8:25pm
post #26 of 27
Side cuts are the personality of the ski. If you look at Realskiers where they post the ski in a box you can easily see all the different combos the sidecut designers  come up with .
This should create differences that appeal to the personality and skiing style of the skier and to market them properly these differences need to be pointed out. I don't see this sidecut presentation as being that unique .

If the first half sidecut is straighter it will engage that part as a unit first if evenly pressured so forward pressure would engage this first but as the tail engages  it will be the compete sidecut that creates the turn shape.  This is how they are marketing this ski. If the tail had no sidecut then the first half sidecut would be the determining factor of  turn shapes available without pivoting.

It does make a difference having sidecut variables between all the possibilities but that's what makes them fun to use as a quiver  or to find that ski that fits your desired feel and function.

The flex of these skis in the different parts would act also like sidecut differences when it shows  how they are shaped when bent
post #27 of 27

Question for the gurus and experts:

Regarding the dual radius found on the Progessor line, how is it possible to carve out a clean edge on a ski with more sidecut in the tip than the tail? Since the rear of the ski has a different sidecut, won't the tails start to drag along the snow instead of slice the same path as the tips, once the sidecut in the front engages? Likewise, if you engage the mid-section of the ski and the skis follows the longer sidecut of the tail, won't the tips smear instead of slice?

It obviously works as many seem to report carving clean; but physically, it doesn't seem possible unless the rear and front of the skis have totally different flex patterns and can change shape to adjust. Is this what's going on?

 

Reply: 

 

When you realize the function of sidecut in a ski the answer to your question is self evident. Turn a ski without sidecut on its edge - no space underneath. You can try to decamber these all you like on the mountain and you will either wear yourself out behaving like a human snowplow or catapult yourself into oblivion when the entire edge of the ski catches. With sidecut, the contact pressure of the ski at the tips and tails is greater than anwhere else along the edge, therefore you can decamber them much more easily (all that missing mass creates less resistance to a force applied near the center of the ski). With the ski decambered, the pressure of the snow on the tip cause the ski to turn - the more the ski is decambered the shorter the radius of the turn. The tail acts to stabilize the ski in much the same way as an airplane's vertical tail stabilizer. It holds the tail in the snow and allows a torque to be applied by the force of the snow on the tip allowing the ski to turn smoothly.

 

The radius of the sidecut(s) does not predetermine the radius that the ski will carve. (You already knew that!). But the more sidecut, the easier it will bend and the shorter the radius you can carve (and the less stable it will be at higher speeds). The more pronounced sidecut in the forward part of the Progressor simply concentrates the pressure in a smaller area at the tip allowing you better turning control. Note that skis for folks skiing both backwards and forwards have tips at both ends; therefore they can exert equal turning control going either backward or forward.  Note that the tail of your ski will stay in the groove cut by the tip until you apply significantly more pressure to the tail section. Under most conditions the snow will not be able to hold up and the tail of the ski will push itself out of the groove. The tail will then skid across the snow. About 50-75% of skiers on the slopes are skiing like this.

 

Your next question should be about the best way to apply force to the tips of your skis (and avoid applying pressure too much pressure to the tails) to make them turn. The answer is a lot longer!

 

 

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