Engineering a Safer Snow Jump
Terrain parks, in which skiers and snowboarders can perform tricks, have become increasingly common since they first appeared on California slopes in the 1990s.
Their increased popularity has a flipside—an increase in injuries associated with tricks and jumps. Spinal injuries are a particular concern and more likely to occur when skiers or snowboarders land on their necks or heads or when the impact with the ground is great enough to damage the spine.
One way to tackle this problem is to wear protective clothing and teach jumpers safer technique. But another, arguably better approach, is to make terrain parks safer by design.
However, few ski resorts have embraced the idea of engineering terrain parks in a way that minimizes the chances of injury. This is partly because of concerns over liability but also because of practical questions: can jumps really be engineered to be safer?
Today we get an answer thanks to the work of Nicola Petrone at the University of Padova in Italy and a few pals. These guys have designed a jump that produces the same impact with the ground for the jumper, regardless of how far they jump. “There is no question that riders occasionally make mistakes that put them at risk; nevertheless an engineering approach could allow the construction of jumps that reduce the likelihood that a mistake will result in a catastrophic outcome,” they say.
Engineers compare jumps using their equivalent fall height, the distance the jumper would need to fall vertically onto a horizontal surface to experience the same impact with the ground. In general, a jumper’s legs can absorb the impact of drops of up to 1.5 meters. But in places where skiers or snowboarders have suffered severe spinal injuries, engineers have measured equivalent fall heights of up to 10 meters.
Of course, it is straightforward to design a landing area with a surface curvature that produces a constant equivalent fall height, regardless of how far is jumped. “The equivalent fall height can be made small, in general, by orienting the snow surface to be nearly parallel to the jumper velocity vector at landing,” say Petrone and co.
But building and comprehensively testing such a jump has never been done, which is where Petrone and pals come in. These guys designed a constant equivalent fall height jump and constructed it at the San Vito ski resort in San Vito di Cadore in Italy.
In addition to the special shape of the landing slope, the team also ensured that the take-off area was flat to reduce body rotation during the jump. This helps prevent jumpers landing incorrectly after a so-called back-edge catch that causes them to rotate in the air.
That resulted in a take-off angle of about 10 degrees and a landing area about 14 meters long with an equivalent fall height of 0.5 meters along its length. At the end of the landing slope, the surface was about 30 degrees to the horizontal.
Construction was straightforward. The team used a snowcat to bulldoze snow into the required shape, marked out by poles stuck into the snow. Resort staff constructed the basic jump landing shape in about 12 passes using a Prinoth snow groomer. “The entire jump was constructed in about three hours and comprised an approximate volume 100 cubic meters of snow above the parent surface,” say Petrone and co.
Next, the researchers attached accelerometers to the boards and bodies of various skiers and snowboarders asked them to try the jump with increasing run-up distances. They recorded each jump with a 50-frames-per-second camera.
Over the next two days, they recorded data for more than 20 jumps as they increased the run-up from 10 meters to 40 meters.
The results are clear. The data shows that the jumpers experience an equivalent fall height of about 0.5 meters, but there is some small variation along the length of the landing slope due to imperfections in the way it has been constructed.
“The accelerometer-determined equivalent fall height and the theoretical equivalent fall height expected from the measured jump profile agreed quite well over the entire range of distances jumped,” say the team.
That shows the approach is feasible. “The jump constructed and measured in this work clearly demonstrates that impact on landing can be controlled through design of the shape of the landing surface,” say Petrone and co.
This approach could easily be combined with other common sense approaches such as limiting the length of the run-up and so on. So there is really no excuse for terrain parks to offer jumps with excessive equivalent fall heights now that Petrone and co have shown that these features are straightforward to design and build.
Ref: arxiv.org/abs/1611.04448: Designing, Building, Measuring and Testing a Constant Equivalent Fall Height Terrain Park Jump
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