or Connect
EpicSki › The Barking Bear Forums › Ski Training and Pro Forums › Ski Instruction & Coaching › "NEW School" v "OLD School"???
New Posts  All Forums:Forum Nav:

# "NEW School" v "OLD School"??? - Page 3

Quote:
 Originally Posted by timvwcom ...I wonder what those tip/waist/tail measurements at a 7.5 meter radius would equate to???
Got me, but try searching. I think PhysicsMan posted a link to a spreadsheet that lets you enter dimensions and it will calculate the skis radius.

Here's a link to a discussion about calculating turning radius of a ski on edge you might be interested in: http://forums.epicski.com/showthread...ghlight=radius
Suppose we were to think outside the box and differenciate between (body) weight distribution and (dynamic) pressure distribution?

If we stood with on our skis with 50/50 weight distribution and started a carved turn, wouldn't the dynamic forces generate an increase of pressure to our outside foot, in addition to that 50% of our body weight? So couldn't we concievably ski 50/50 weight distribution with 60/40 (or whatever) pressure distribution when we are arc'n and pulling G's?
Quote:
 Originally Posted by cgeib Got me, but try searching. I think PhysicsMan posted a link to a spreadsheet that lets you enter dimensions and it will calculate the skis radius. Here's a link to a discussion about calculating turning radius of a ski on edge you might be interested in: http://forums.epicski.com/showthread...ghlight=radius
Hey Chris,

GREAT lead!!! I had to trace to an earlier thread via PM's link, but it worked. Not that this really answers anything other than the obtuse question I asked... Which was what would the tip/waist/tail measurements be to equal a 7.5 meter radius ski. I started with MY current 163 ski and it's listed tip/waist/tail measurements. PM's calc was within .5 meter radius or so of the "marketed" radius. If I only widened tip and tail, leaving waist alone, I arrived at exactly 7.5 meter turn radius with measurements of... Taaa Daaa...

140-65-127 Quite an hourglass figure, huh? Not that it means anything I guess??

But it was interesting to note, based on the "claims" at that and the linked thread, that the turning radius under a bend is related to the cosine of the edge angle... snore... sigh... Actually, I find this interesting, sorry! BUT, and a HUGE BUT... based on that theory, wouldn't a ski of any radius, when tipped progressively on edge have a shorter and shorter turning radius until that radius equalled "zero" at a full 90 degree edge angle??? Either that means that the ski has "bent in half" -OR- the claim is incorrect. I'd argue that a ski on a 90 degree edge had an infinite radius??? In other words, at a FULL 90 degrees angle to the surface of the snow, with the tip pointed straight downhill, the tail would follow staight behind it no matter what the "arc" or turning radius of the ski. I know, I know, who cares??? You're right, but just a quick reminder... "Physics Club" meets after 6th hour today... and we don't meet in the gym any longer since the "incident".

Tim
Quote:
 Originally Posted by Arcmeister So couldn't we concievably ski 50/50 weight distribution with 60/40 (or whatever) pressure distribution when we are arc'n and pulling G's?
My amateur answer... "no". The "weight" would shift to CAUSE the "pressure".

Tim

"That's what I think, but who cares what I think!"
Quote:
 Originally Posted by timvwcom ...Actually, I find this interesting, sorry! BUT, and a HUGE BUT... based on that theory, wouldn't a ski of any radius, when tipped progressively on edge have a shorter and shorter turning radius until that radius equalled "zero" at a full 90 degree edge angle??? Either that means that the ski has "bent in half" -OR- the claim is incorrect. I'd argue that a ski on a 90 degree edge had an infinite radius??? In other words, at a FULL 90 degrees angle to the surface of the snow, with the tip pointed straight downhill, the tail would follow staight behind it no matter what the "arc" or turning radius of the ski...
This brings to mind an expression I once heard that went something along the lines of: Any concept taken to its ultimate conclusion, is utterly ridiculous.

I suppose if your theory were correct, there would only be one ski and we'd all be skiing on it to make any size carved turn we wanted. This is not the case, so there must be some practical limitations relating to things other than just the shape of a ski.

I believe that decambering a ski on edge will shorten the turning radius to a point, but I hope I never fold one in half!
Quote:
 Originally Posted by cgeib I suppose if your theory were correct, there would only be one ski and we'd all be skiing on it to make any size carved turn we wanted...
First, what you still doing up at 1:30am??? Like I should talk?

Then, actually... there was a claim on one of those threads that a 12m radius ski would when: tipped 30 degrees have a 8m radius. When tipped 60 degrees would have a 4m radius.

As you can see, this person (I don't remember who) was obviously using a linear rather than "cosineular" calculation. (Actually, I am MORE than quite proud of the "cosineular" comment, did i just "quoin/coin" cosineular??? My delusions of grandeur will be gone by the time I wake up, I think?)

Tim

ps. It's funny you commented on the "one ski" idea... I had been "spazzing" mentally the last half hour about a "multi-radus" ski. Either using a curved base, or a multi-edged ski??? Will post new thread when I'm somewhat cogent on it?
Quote:
 Originally Posted by timvwcom ... but just a quick reminder... "Physics Club" meets after 6th hour today... and we don't meet in the gym any longer since the "incident".

That was absolutely hillarious!

Sheesh, I haven't popped in here for at least a couple of weeks, and what do I find when I come back ... :

BTW, thanks for reminding people about the new location - please feel free to swing by the executive dining room every other Wednesday. When Tony No Neck answers the door (you remember ... the kid from gym class) tell him that I said it was OK.

Tom / PM
Tim, the mathematical radius limit at which any ski could theoretically carve a turn is it's length divided by 3.14. Beyond that, the curvature of the ski would become irregular, and the ski would not be able to carve.

- Circumference = Pi(D)
- Ski length = circumference divided by 2
- Ski length = Pi(D) divided by 2
- Ski length = Pi(R)
- Ski length divided by Pi = Pi(R) divided by Pi
- Ski length divided by 3.14 = Radius

******************************************

Now Tim, here's another one for you. At a speed of 30 mph, and an edge angle of 45 degrees, at what sidecut radius threshold will a skier begin needing to employ reverse angulation to remain balanced on his outside ski?

Have fun.
Quote:
 Originally Posted by Rick Tim, the mathematical radius limit at which any ski could theoretically carve a turn is it's length divided by 3.14. Beyond that, the curvature of the ski would become irregular, and the ski would not be able to carve. - Circumference = Pi(D) - Ski length = circumference divided by 2 - Ski length = Pi(D) divided by 2 - Ski length = Pi(R) - Ski length divided by Pi = Pi(R) divided by Pi - Ski length divided by 3.14 = Radius ****************************************** Now Tim, here's another one for you. At a speed of 30 mph, and an edge angle of 45 degrees, at what sidecut radius threshold will a skier begin needing to employ reverse angulation to remain balanced on his outside ski? Have fun.
My brain hurts...

I just posted a new "quantum theory" on the main skiing discussion thread... whatdya think???

Tim

ps. My answer: The train leaving from the west passes the east bound train after 20.5 minutes??? huh???
Quote:
 Originally Posted by PhysicsMan That was absolutely hillarious!
Hey... I laughed for 5 minutes straight after I posted it... but wasn't sure anyone else would notice. GOOD timing, welcome back!

Tim
Quote:
 Originally Posted by Rick Ski length = Pi(D) divided by 2
OK, my brain just skidded... without figuring the rest of that... this stood out??? Too late to even work out the logic of the multiple equililant statements. But looks like a "proof"... now mind you... it's been 20+ long years since I've been "schooled" and that could really be a "poof" instead???

If my "Ski length" = 163 cm and their turning radius is 14 meters... Then
Ski length (163 cm) = ( 3.14159 * 28 meters ) / 2 ???
or 163 cm = ( 87.96 [m?] ) / 2
or 163 cm = 43.98 something ???
Huh????

NOTE: Tim is NOT a nuclear scientist (I probably didn't spell nuclear right)

Tim
Quote:
 Originally Posted by Rick Ski length divided by Pi = Pi(R) divided by Pi
No wait... I get it!!!

You are saying the "downhillers" get all the chicks?

You know, "ski length gets the pi"???
Tim, the diameter in the formula is of the theoretically smallest circle you could carve with any ski of a particular length. It's not referring the the sidecut radius of the ski. That represents the largest radius turn that can be carved. In the formula it's assumed the ski is bent into a semi circle,,, and represents half the circumference of that smallest possible circle that can be carved.

D and R are unknowns.
Quote:
 Originally Posted by timvwcom You know, "ski length gets the pi"???
I'll take the 5th.
Quote:
 Originally Posted by Rick Tim, the diameter in the formula is of the theoretically smallest circle you could carve with any ski of a particular length. It's not referring the the sidecut radius of the ski. That represents the largest radius turn that can be carved. In the formula it's assumed the ski is bent into a semi circle,,, and represents half the circumference of that smallest possible circle that can be carved. D and R are unknowns.
Still standing in a fog... my arms are flailing trying to keep me from smacking my face on something!!! Have I meet D and R before, are they those cute twins from the east side?

But? Do you mean, that at it's shortest turning radius the ski is bent from tip to tail 180 degrees??? Or half-a-circle ???

Huh? Sounds like that would mean a ski could "theoretically" (sp?) turn in only a fraction of it's actual length??? Huh? Me dumb!

Tim
Yea, you got it.

Like I said, only theoretical. The forces it would take to bend a ski in that manner would be hard to come by. And the resultant lateral turn forces such an arc would produce would surely overpower the integrity of the edge hold availabe on such a sharp tangent angle to the snow surface.

Anyway, it makes for interesting conversation. Now,,, get to work on that reverse angulation problem, would ya!! That represents a true limitation factor in evolution of sidecut radius reduction.
Quote:
 Originally Posted by Rick Tim, the mathematical radius limit at which any ski could theoretically carve a turn is it's length divided by 3.14. Beyond that, the curvature of the ski would become irregular, and the ski would not be able to carve. - Circumference = Pi(D) - Ski length = circumference divided by 2 - Ski length = Pi(D) divided by 2 - Ski length = Pi(R) - Ski length divided by Pi = Pi(R) divided by Pi - Ski length divided by 3.14 = Radius ****************************************** Now Tim, here's another one for you. At a speed of 30 mph, and an edge angle of 45 degrees, at what sidecut radius threshold will a skier begin needing to employ reverse angulation to remain balanced on his outside ski? Have fun.
OK start saving these & you will have the damn book half written!!!!
That's funny!

C = circumference.
pi = 3.1415.....
L = ski length

We all know that C = 2 x pi x r right?

so r = C / ( 2 x pi)

Which means that of L = C the ski is bent into a complete circle.

But if you only allow the ski to go half way around, then the circumference C = 2 x L

so, r = (2 x L)/(2 x pi) or r=L/pi.

Which means a 157 cm ski would have a theoretical minimum turn radius of 0.5 m.

Maybe HighwayStar is right! :

Somewhere, someone was really arcing their ski(s) hard... and someone else took a picture of it. I wonder what the most (change in camber/largest bend?) is in reality? Who has or can find a pic of a REALLY bent ski in action??? Post it here or list a link to it.

Tim
Really bent ski in action...

Page 74, "Ski The Whole Mountain" by Eric and Rob DesLauriers

Also probably my favorite skiing action picture.
The thing to take away from the radius discusion is that the sidecut radius is the radius of the arc traced by the skis edge on a flat surface when the ski is parallel to that surface, and sidecut radius * cosine(tipping angle) is the radius of the arc that would be traced on that flat surface if the ski were decambered enough to keep the entire edge in contact with the surface. If you angle your 15-m ski at 60 degrees on hard ice, and the tip and tail do not dig in more than the middle and the the entire ski is touching that flat surface, you get a 7.5 m radius scribed on the ice.

It is a simple model. The snow surface isn't really flat. It is also possible to bend skis more than the turn radius given by that formula, but it takes skills; straight skis can be bent into a curve. In soft snow a ski is already decambered when you are going straight. The turn radius depends more on flex than sidecut in soft snow.

(keep it quiet, but I think it was the resort ski instructors who taught that tail swishing feet together skiing)
Quote:
 Originally Posted by timvwcom Steve, I've "skimmed" much of the first two...
Tim, it's important to understand that there's nothing sacred about the turns Bob describes, so please do your best to avoid that mindset. I think a better term for the turn might be "optimal" or "effective".

The concepts that I think may help you in your exploration of the changes in technique are those that suggest that effort added for no necessary reason are superfluous and inefficient. That's not to say that they are "wrong" or "bad"! I love doing stuff that's superfluous! But, only that when we consider the optimal or most effective turn in a safe and simple terrain environment, Bob does a pretty good job describing it, in my opinion. No forcing, no sudden movements, no extra muscle used. Instead, only the energy that's needed is expended, the skis mostly turn themselves ("allowing" the skis to turn rather than "making" the skis turn). This is a fundamental difference in modern skiing for me.

FWIW, I was a rebound guy. I'd slam the edge, "build a platform", and launch into the next turn. I did it for years. I've been "unlearning" a lot of stuff in the past couple of years. My skiing is much smoother than it was, and much more efficient (which is great for me, since I'm getting older!).
Quote:
 Originally Posted by ssh Here is a better start:http://forums.epicski.com/showthread.php?t=8328 especially starting at post 11.http://forums.epicski.com/showthread.php?t=8972 starting at post 2. and, perhaps best for understanding:http://forums.epicski.com/showthread.php?t=7969
This is great stuff from where I sit. These links hit every point and question I have been looking for info on since browsing this forum. Thanks, ssh. I'm hoping to be up at Copper on Sunday.
Quote:
 Originally Posted by janesdad This is great stuff from where I sit. These links hit every point and question I have been looking for info on since browsing this forum. Thanks, ssh. I'm hoping to be up at Copper on Sunday.
Good deal! I think that they are "must read" posts.

I'll miss you, I'm up Monday/Tuesday. I hope the Metrons get here before then! :
Sidecut,

Quote:
 This cannot be true...please explain.
Take a bump or a rounded mound of snow that is let's say 2 meters across. It is possible (and I do it all of the time) to carve a turn around it until you are facing back up the hill. The radius of that carved turn might be 1 meter. This a trick by carving on a round feature, but terrain does play a role in turn radius such as carving from a flatter area over a drop-off. The terrain there is rounded, so the radius is shortened.

RW
Tim,

Quote:
 Quote: Originally Posted by timvwcom...Actually, I find this interesting, sorry! BUT, and a HUGE BUT... based on that theory, wouldn't a ski of any radius, when tipped progressively on edge have a shorter and shorter turning radius until that radius equalled "zero" at a full 90 degree edge angle??? Either that means that the ski has "bent in half" -OR- the claim is incorrect. I'd argue that a ski on a 90 degree edge had an infinite radius??? In other words, at a FULL 90 degrees angle to the surface of the snow, with the tip pointed straight downhill, the tail would follow staight behind it no matter what the "arc" or turning radius of the ski... This brings to mind an expression I once heard that went something along the lines of: Any concept taken to its ultimate conclusion, is utterly ridiculous.I suppose if your theory were correct, there would only be one ski and we'd all be skiing on it to make any size carved turn we wanted. This is not the case, so there must be some practical limitations relating to things other than just the shape of a ski. I believe that decambering a ski on edge will shorten the turning radius to a point, but I hope I never fold one in half!
The sidecut defindes the shape of the ski, but the actual arc the ski will carve on edge is determined by resistance. As the ski decamberes on edge, the tip of the ski climbs the snow as long as enough force is exerted to keep it decambered. The stiffer the flex of the ski, the more resistance, or climbing power the ski has. The 3 varyables on the same snow and speed are, shape of the ski, flex of the ski and edge angle.

RW
Quote:
 Originally Posted by Rick ... At a speed of 30 mph, and an edge angle of 45 degrees, at what sidecut radius threshold will a skier begin needing to employ reverse angulation to remain balanced on his outside ski?
Assuming a 'flat' & firm surface on Earth with no slope angle to consider...

A skier tipped 45-degrees to the Inside of an 85-foot Turn-Radius could stand "In Balance" if their CM were held exactly 45-degrees "over" the ski-edge, also tipped to a 45-degree angle - when traveling at 30.0 mph.

If the skier wished to ski a tighter Radius turn - and yet keep their speed at 30.0 mph and their edge-angle at 45-degrees, they'd either have to create some 'reverse angulation' (to get their CM lower while not reducing edge-angle) or they would gradually fall-over to the outside of the turn.

Since I don't believe a ski's 'sidecut & tilt' are the only determinant of that ski's turn radius I'm unwilling to specify a particular sidecut that will achieve the 85-foot radius turn...

.ma

EditPS: Probably should add that the skier's skis will quickly begin to slide up and out of their carve track once the CM gets below the 'rise-line' perpendicular to the base of the ski...
Hey MichaelA, can you share the calculation process you used to come up with that? :

The result you came up with doesn't seem right. 85 feet seems like a pretty big radius turn to be able to stand completely inclinated on a 45 degree angle (perpendicular to the ski base), at slalom racing speed, and not fall over to the inside. :

Most skis used today won't even carve a radius that large when tipped at 45 degrees. So by these calculations, everyone on the slopes would need to reverse angulate to remain in balance when making the type of turn I described because they'd be carving a much smaller radius, and would therefore exceed your inclination threshold. Something must have gone astray in the calculations, don't you think?
Hmmm, could be... I just grabbed up a spreadsheet I did a few years ago and popped in some numbers. You're right though, 30 mph @ 45 degree incline does seem off for 85 feet...

I was more concerned with trying to figure out a way to keep the skis from de-trenching once the CM got below the base angle. I'll go read the formulas and make sure I didn't screw up feet to meters or degrees and radians.
Not like I've not done that before.

.ma
oops, false start... problem with the antimatter... horizontal rate vs tangential stuff...

.ma
New Posts  All Forums:Forum Nav:
Return Home
Back to Forum: Ski Instruction & Coaching
EpicSki › The Barking Bear Forums › Ski Training and Pro Forums › Ski Instruction & Coaching › "NEW School" v "OLD School"???