Have you ever wondered how fast you slide down a slope?

[Hacksaw]

This was on the NPS morning report this morning. The GPS information is interesting. Another reasone to practice self arrests with your ice axe.


Klondike Gold Rush National Historical Park (AK)
Hikers Rescued After Fall On Chilkoot Trail

On the morning of Monday, June 18th, two members of a family of four fell while ascending the Golden Stairs near the US/Canadian border on the Chilkoot Trail. The family consisted of an 80-year-old man, his two sons, and one of his grandsons. The weather was foggy at the time, with approximately 30 meters of visibility and winds of from 10 to 15 mph. A light rain and cool temperatures left the snow on the trail slick and icy. Two members of the party had hiked on ahead, leaving the 80-year-old man and his 50-year-old son behind. The older man thought that he was nearing the top of the first of two summits and stopped to look up to see how close he was. Due to the weight of his pack and the 60-degree slope, the action of looking upward set the man off balance and he began to slide downhill. The son attempted to stop his father by grabbing his foot as he slid past, but was unsuccessful. Both men slid about 70 to 80 meters down the slope. A GPS in their possession later revealed that they had traveled at a top speed of 39.8 mph before they came to rest in an exposed talus slope. Ranger Jeremy Prater responded from the summit and found both patients alert, sitting up, and calmly talking. The older man had lacerations to his forehead and eye which were bleeding profusely; the younger man had various lacerations, the worst of which was an avulsion on his left tibia, just below the knee, which went all the way to the bone. Despite the severity of the cut, it was not bleeding and there was no obvious deformity and he had full range of motion and sensation in his foot. A Parks Canada patrol person arrived on scene to assist with medical care. Both patients were stabilized, dressed in warmer clothes, and given hot food and drink while rangers and the patrol person assessed the possibility of evacuating the patients off the mountain. Due to the fog, the stability and willingness of the patients, and the potential for hypothermia while waiting for the weather to shift, a decision was made to move to a lower elevation where a helicopter landing zone could be established. During the slow descent, the fog began to lift and a closer LZ was established. A TEMSCO helicopter flew Skagway VFD chief Mark Kirko and firefighter/EMT Colin Aikman to the LZ, and the patients were transported to the Dahl Memorial Clinic in Skagway for treatment. The park extends its thanks to Parks Canada and the Skagway Volunteer Fire Department for their assistance during the incident. Ranger Dave Keltner was IC. [Submitted by Jacqueline Ashwell, Dyea Ranger]

[FiveLarge]

A friend had a GPS along for night skiing once this past winter at Keystone. I believe our top speed was right around 60mph. That was as fast as I felt comfortable with 180cm skis, on an open public run with snowplowing beginners sweeping across the entire fall line below blind rolls.

[rideit]

I know I hit 73 mph repeatedly on a carving deck this last winter at Targhee.
I could barely walk the next day.

[Pow4Brains]

Total JONG GPS question, does a GPS take in to account the angle of the slope when measuring speed?

[rideit]

I don't believe so, exactly. You can factor elevation loss X speed, and thereby roughly calculate slope angle.


Or I could be completely talking out of my ass.

[advres]

Or I could be completely talking out of my ass.

So what else is new?

[rideit]

Unlike many here, I readily admit it.

That is a good first step.

[StanWagon]

Great question as to whether GPS speeds use only the x-y coordinates, or include the change in altitude as well. My guess is that only the x-y are used. For a slope that averages 45 degrees (possible for the victim in the story) one would then multiply by 1.4 to get the actual speed with respect to the air. So the fellow's 38 mph becomes 53 mph. Possible. For the ski areas, as noted, it depends on the slope angle. If anyone knows for certain, it would be useful to know...

What about the sport of speed skiing? That would almost surely be measuring the skier's speed in the 3-dim direction he or she is traveling.

[mntlion]

don't GSP show elevation too?

so would the GSP show speed if you where in freefall.





and what if the GSP was on a plane that was on a treadmill?

[Toby]

Dunno how fast I've skied. Once I went on a speed skiing course on the Zugspitze. The speed skiers were going 175km/h from the top with all the right equipment and those rubber suits and foiled helmets. We went from 3/4, which missed the steepest section at the top and it felt pretty fast. But there was a slope in my local resort that we skied faster on. It was usually empty for a considerable distance (it was off the beaten track). Where it met up with another run there was a cat track coming down. If you got the angle right you could use the cat track to slow you down, because the slope kept going and got more dangerous at those speeds. If you got the angle wrong, as a female friend did one day, you went through a huge compression dip and then got shot off the cat track, through the air for about 30m and landed in a bump run. Hardcore chick, a bit shaken up but laughed about it. Good times. It was also funny passing people coming down the cat track while flying up it the wrong way. That required some dodging skills. A lookout came in handy to hold people up. You didn't want a whole bunch of people coming down the cat track while hitting it at ~80mph.

[Freuchen Icepick]

Speed skiing uses a "trap" method for measuring speed, and the result is something of an average top speed, rather than a top-speed spike. Skiers trigger two beams along the course and the time betwixt the two (divided by linear distance?) provides the calculatory necessities.

[StanWagon]

Yes, GPS's now show altitude, but that info is slower to get and generally not quite as accurate. That leads me to think that the speed is determined solely by the x-y coords. When I put my unit on my dashboard and compared its readings to my speedometer it was very accurate, and reacted very quickly. I was not driving on hills, which in any case would have been small, but my guess is still x-y only on this measurement.

[couloirman]

so would the GSP show speed if you where in freefall.

Ill let you know tommorow as Ill be making a few skydives in the morning and am looking for an excuse to play with my new garmin...

EDIT: on wind hold today, will try again tuesday

[ski_adk]

I've clocked myself at 57 one day at Whiteface. Scariest thing ever, especially since my skis (180 Atomic 9:18 - an intermediate carving ski ) at the time had cracks on all 4 edges. I stopped carrying the thing since then just b/c I don't need the temptation to keep breaking my personal speed records. I think I've actually been faster than that since then, but who cares.

Although, now that I kinda know how fast I'm going, I can't even begin to imagine what the World Cup guys are experiencing.

[GBB]

So what is average speed if you are absolutely maching down a run?

[Bennett]

and what if the GSP was on a plane that was on a treadmill?

It would take off.

[iceman]

So what is average speed if you are absolutely maching down a run?

For you, or for normal people?

[iceman]

BTW, that is one badass 80-year-old dude in the initial post. Props to him. Even though he fell over backwards he's still a badass.

[Ghost]

I have a Garmin 76CS. It tracks elevation, but the speeds logged are simple horizontal distance divided by time. Here's a link to a thread where I posted (post 31) some data from GPS track logs. http://forums.epicski.com/showthread...ght=png&page=2

[summit]

Ill let you know tommorow as Ill be making a few skydives in the morning and am looking for an excuse to play with my new garmin...

this post is the pinnacle of nerdyness combined with gravity sports... i love it!

[twodogs]

I straitlined "the Flying Goose" once.

really.

[GBB]

For you, or for normal people?

Let's just go with normal people for now.

[couloirman]

The speed reading is solely in the xy plane. While jumping, I got a 0mph reading in stable freefall while falling perfectly straight down, then a slow reading(20 mph) when tracking horizontally across the sky for several seconds. While in the plane it read in the 100's. This would mean to get your speed of skiing you'd have to factor in slope angle, which would be inaccurate on most slopes because most slopes are not the exact same pitch for really long distances(obviously), but could be done with a reasonable degree of accuracy on consistently pitched slopes.

this post is the pinnacle of nerdyness combined with gravity sports... i love it!

haha, well I am very nerdy about things I love.

Heres the ultra nerd part: your actual speed is v/cos(theta) where v is the speed reading from the GPS

[StanWagon]

Thanks for the definitive word, couloirman. So this means that using GPS for speeds when skiing is pretty much useless, except for people like me who like nordic skiing/skating, where the slopes are flat and the speeds low... For a slope of 20 degrees one would add 6%, 10 degrees, just 1%, or negligible. But at 40 degrees one adds 30%.

Stan Wagon

[maniloff]

A buddy once hit 68 mph on the groomers below Milli while drunk. Things were fine until he pulled a binding out of one of his Lines.