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Why are men racers faster than women? And factors influencing speed - Page 4

post #91 of 101
Quote:
Originally Posted by NordtheBarbarian View Post

Ghost

Drag on a skier in a tuck at 70 Mph is like 18 lbf.

Somewhere your drag calculation is off by a factor of 5.


Where did you get this?  Would be interesting to see more.
 

 

post #92 of 101
Quote:
Originally Posted by NordtheBarbarian View Post

Ghost

Drag on a skier in a tuck at 70 Mph is like 18 lbf.

Somewhere your drag calculation is off by a factor of 5.


This site seem to match my drag forces:  http://biomekanikk.nih.no/xchandbook/ski4.html

10 m/s => 40 N;  tiny Graph gives 135ish at 20 m/s.

 

You get 80 N at 70mph, I get 330 N  It would be interesting to see how I could lower my drag force by that much, (a tuck might cut  it in half, but don't try that at Jay Peak, unless you on a course).  Maybe air density; are you skiing at the top of mount everest?  That would reduce it to a third...not enough! Did you use 32.2 ft/s/s for g? I give up. Where did you get your numbers? th_dunno-1[1].gif

 

post #93 of 101



 

Quote:
Originally Posted by Ghost View Post




This site seem to match my drag forces:  http://biomekanikk.nih.no/xchandbook/ski4.html

10 m/s => 40 N;  tiny Graph gives 135ish at 20 m/s.

 

You get 80 N at 70mph, I get 330 N  It would be interesting to see how I could lower my drag force by that much, (a tuck might cut  it in half, but don't try that at Jay Peak, unless you on a course).  Maybe air density; are you skiing at the top of mount everest?  That would reduce it to a third...not enough! Did you use 32.2 ft/s/s for g? I give up. Where did you get your numbers? th_dunno-1%5B1%5D.gif

 

 

18 lbf is.  From article on US ski Team tests at CALSPAN Wind Tunnel.  

Article Below

 

 

Streamlining for the Slopes

Downhill racers improve their speed by skiing at a standstill.

There's no snow to be seen, but an anxious Olympic -- hopeful downhill racer is about to take a run through a rigorous training course complete with jumps, straightaways and tight tums. Instead of gliding to the starting gate through the crisp, crackling snow, the skier cautiously steps onto a gridded platform in a test cell. The wind begins to rush by, and he drops into a compact tuck.

The scene is the Calspan Corporation's wind tunnel in Buffaio, New York. NormalIy used to test the dispersion of pollutants and the airfiow around buildings, the tunnel is sometimes a training arena for members of the U.S. Olympic ski team. Mike Holden, a ski instructor and a principal engineer at Calspan, directs the program, helping both new and accomplished skiers to perfect their high-speed zigzags on treacherous downhill courses.

The training has already proved its worth. Bill Johnson -- who in 1984 became the first American man to take a gold medal in downhill racing -- mastered his incredible tuck in the wind tunnel. And the sleek, aerodynamic style of Doug Lewis, a hot new downhiller, is attributable to his wind-tunnel training. "There's no way a skier can effectively evaluate and improve his aerodynamics on a downhill course," Holden says. "But in the wind tunnel, we can help him learn how to diminish drag." As a 200-horsepower motor generates a 70-mile-per-hour wind, the racer either watches a video of a course, moving his body as if he were skiing, or experiments with different positions. Sensors in the platform measure the changes in drag caused by his movements; a digital readout on the floor displays drag figures and improved time. Another screen shows the skier himself so that he can correlate drag and position.

But just how much of a difference does the training make? "In a low-tuck position, with arms held tight in against the body, a skier generates a drag of about eighteen pounds," Holden explains. "But if he holds his arms along the outside of his legs, as some skiers do in approaching a jump, drag can increase to forty-three pounds."

Other countries have wind-tunnel training programs, but the American program's success at integrating the tunnel work into racing is unique. "You have to study what really works on.the slope and apply it in the tunnel -- not find something that works in the tunnel and try to apply it on the slope," Holden says. Stability is crucial: If a skier's position in the tunnel has low drag but he feels uncomfortable or can't hold it, it's no good.

Downhill racers aren't the only visitors to Calspan's tunnel. Skaters, ski jumpers and luge sleds have all come to improve their performance. "Jumping is an area with lots of potential, and it's never been studied in any great detail," says Holden. "Once a jumper leaves the ground, it's all aerodynamics."

He concedes that wind-tunnel ski jumping is far from perfect. "The technical equipment isn't fully developed. Also, it's difficult for the skier to get the feel of a real jump, because he must hold himself differently in the tunnel in order to simulate the correct angle between body and wind."

During the next year, Holden will take his testing to the slopes. He is just finishing a device that will fit into a ski binding and measure forces as a skier actuaily negotiates a course. A small backpack housing a portable computer records the readings, and after the skier completes the course, these are matched frame by frame with a video of the run. "We'll be able to tell in each instance how the forces are generated by the skier -- on which ski, on which edge, toward the front or toward the back," explains Holden. The measurements will be used to improve overail skiing technique. "A lot of people forget," he says, "that not only are top competitors mentally tough, they ski in a technically superior manner."

-Amy Wilbur, Science Digest, February, 1986.

post #94 of 101

Ghost

Your drag coefficient is wrong.

 

Wikipedia gives the drag Coefficient of a upright man as 1.0-1.3

Wikipedia gives the drag Coefficient of a skier as 1.0-1.1 which must be the range for a skier standing up

Wikipedia gives the drag Coefficient of a bicylist as 0.7 but a skiers tuck is more aerodynamically effiecient than a bicyclist so drag coeffiecient should be lower than that.

Drag Coeff also varies with Reynold numbers which include dimension of size and velocity.

Hand and elbow position greatly effects how good your tuck is as they streamline your torso and legs.  

 

 

http://en.wikipedia.org/wiki/Drag_coefficient

 

Quote:
Originally Posted by Ghost View Post




This site seem to match my drag forces:  http://biomekanikk.nih.no/xchandbook/ski4.html

10 m/s => 40 N;  tiny Graph gives 135ish at 20 m/s.

 

You get 80 N at 70mph, I get 330 N  It would be interesting to see how I could lower my drag force by that much, (a tuck might cut  it in half, but don't try that at Jay Peak, unless you on a course).  Maybe air density; are you skiing at the top of mount everest?  That would reduce it to a third...not enough! Did you use 32.2 ft/s/s for g? I give up. Where did you get your numbers? th_dunno-1%5B1%5D.gif

 



 

post #95 of 101
Quote:
Originally Posted by Tog View Post


So, you want to make the cars out of depleted uranium for max speed?

 



Given the difficulty in obtaining uranium and the expense of gold, lead would probably be the best option. But, I'm guessing they've got rules against that. smile.gif

 

post #96 of 101

OK.  43 lbs, double that for coming out of a tuck, and you get about 380 Newtons, but we were talking about racers in a tuck,  Even with the Cd yielding18 lbs at 70 mph, drag force is still significant above 45 mph.

 

If you look at skiers in a course with turns, I'm pretty sure that Cd is closer to my original Cd than the Cd for a tuck in a wind tunnel..

Originally Posted by NordtheBarbarian View Post

Ghost

Your drag coefficient is wrong.

 

Wikipedia gives the drag Coefficient of a upright man as 1.0-1.3

Wikipedia gives the drag Coefficient of a skier as 1.0-1.1 which must be the range for a skier standing up

Wikipedia gives the drag Coefficient of a bicylist as 0.7 but a skiers tuck is more aerodynamically effiecient than a bicyclist so drag coeffiecient should be lower than that.

Drag Coeff also varies with Reynold numbers which include dimension of size and velocity.

Hand and elbow position greatly effects how good your tuck is as they streamline your torso and legs.  

 

 

http://en.wikipedia.org/wiki/Drag_coefficient

 



 


 

 


Edited by Ghost - 3/28/11 at 4:28am
post #97 of 101

If skilled and strong you can stay in your tuck. Thus maintaining your speed. Breaking your tuck unecessarily is slow and considered a major mistake in SG or DH.

So skill and strength makes you fast.

 

Easier SG or DH can be run almost entirely in a tuck. The Masters SG I ran clast week could be done entirely in a low tuck.

Your calculations with CD =.9 and Frontal Area = .8 probably only apply to Slalom and upright GS positions (not high tuck). In the technical events skill and speed are the determining factors for speed. Moving into into a high tuck will drop the frontal area and lower drag coefficient.

 

Quote:
Originally Posted by Ghost View Post

OK.  43 lbs, double that for coming out of a tuck, and you get about 380 Newtons, but we were talking about racers in a tuck,  Even with the Cd yielding18 lbs at 70 mph, drag force is still significant above 45 mph.

 

If you look at skiers in a course with turns, I'm pretty sure that Cd is closer to my original Cd than the Cd for a tuck in a wind tunnel..


 

 



 

post #98 of 101
Quote:
Originally Posted by CerebralVortex View Post

Given the difficulty in obtaining uranium and the expense of gold, lead would probably be the best option. But, I'm guessing they've got rules against that. smile.gif


How about Tungsen, Ni, Fe composite.? 18.5 gms/cc Pretty dense, available. Lead is 11.4 gms/cc, gold 19.3.

http://www.mi-techmetals.com/documents/Tungsten-Typical-Properties.pdf

 

http://www.cmwinc.com/tungsten-alloys.php#1000  the 2000 series is 18 gms/cc

 

There is similar commonly availabe as crankshaft counterweights. So called "Mallory Metal". About 17gms/cc

Depleted Uranium available perhaps if not burned up, on battlefields of Iraq, Afghanistan, Bosnia, Kosovo. Now Libya.

Depl. Ur. also used as counterweights in some aircraft.

All this for a pinewood derby on a ski site...

Apparently tungsten is used in the pinewood cars, but overall weight is restricted.


 

 

post #99 of 101

This thread was interesting but silly. All the math is fun, but somehow obscures the obvious.

 

Biology: Men have more muscular strength per unit of mass (testosterone). That men tend to weigh more only magnifies this advantage.

 

Physics: Greater mass helps overcome ski/snow friction. Not a factor when comparing men/women of equal weight.

 

Probability theory: "Mental" differences may be small when comparing elite athletes, but probably play a huge role in determining the size of the pools from which elite athletes are drawn. Simply put, more men participate in competitive skiing. More participants = more high-performance "outliers" aka elite athletes. For the extreme example, if only 10 men skied, but 100,000 women did, I bet women would set the records.

 

IMO, other factors pale in comparison to the big three above.

post #100 of 101
Quote:
Originally Posted by hoody View Post

This thread was interesting but silly. All the math is fun, but somehow obscures the obvious.

 

How do you feel about helmet threads? smile.gif 

post #101 of 101
Quote:
Originally Posted by hoody View Post

This thread was interesting but silly. All the math is fun, but somehow obscures the obvious.

 

Biology: Men have more muscular strength per unit of mass (testosterone). That men tend to weigh more only magnifies this advantage.

 

Physics: Greater mass helps overcome ski/snow friction. Not a factor when comparing men/women of equal weight.

 

Probability theory: "Mental" differences may be small when comparing elite athletes, but probably play a huge role in determining the size of the pools from which elite athletes are drawn. Simply put, more men participate in competitive skiing. More participants = more high-performance "outliers" aka elite athletes. For the extreme example, if only 10 men skied, but 100,000 women did, I bet women would set the records.

 

IMO, other factors pale in comparison to the big three above.



It is not silly when you consider everyone is missing another obvious factor: speed events are often times won or lost at one or two critical points in the course. If a skier can't hold the fastest line skied by another and the race could be over well before the finish line.  Those with the most strength to carve an optimal line, experience, and speed (and that includes weight, wax, etc.) coming out of the critical sections of the course will have a good chance at winning.  When no such critical section exists that favors the strongest handful of competitors, the times will be close and anyone can win (e.g., the Vancouver Olympics).  So having strength is a difference, but having the necessary strength when others don't have it makes the most difference.  That is why women should be able to extreme ski as well as men (assuming they are just as insane), but should not be as fast as men on the race course.

 

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