Downhill and slalom skiers, although part of different disciplines, share a common goal: to keep control of their skis, not only to prevent a fall but also, and especially, to gain those precious few hundredths of seconds that will make all the difference at the finishing line. Competitors often reach speeds of 150km/h and each competitive skier knows they can rely on their shoes: the "transmission belt" between legs and skis. And constraints are far more numerous than might seem at first glance. Like all ski boots, a competition-level boot is made up of a shell, liner and tongue, all manufactured from plastics, as well as plastic or metal hooks. The difference between an ordinary boot and that of a champion may not be immediately apparent and yet...
Cutting it fine
Each skier faces the same dilemma: precision or comfort. We have yet to find the perfect answer to this age-old riddle! The reason for this is as follows: the foot, ankle and lower shin need to be encased in a rigid envelope in order to accurately transmit pressure to the skis without deforming the boot. The boot is a real straitjacket! "Pro" shells are made out of polyether, a high-performance and very rigid polymer which hardly deforms under pressure and is cold-resistant. The shell is composed of two parts: the shoe which covers the foot and the collar which surrounds the ankle and lower leg. They are articulated at the ankle bone in order for the user to be able to perform bending movements. The degree of articulation is a characteristic which defines shoes. The "flex" index is used to gauge a shoe's rigidity; the higher the index, the more rigid the shoe. The index can vary according to the type of boot and the higher the index, the better the boot is adapted for use in sports.
A snug fit?
Not really, at least concerning those shoes designed for athletes. The liner's purpose is generally the opposite of that of the shell. Good heat insulation and an acceptable level of comfort require a certain thickness of foam to be used. Although soft, foam has the drawback of being less efficient for transmitting movements. Some progress has been made recently thanks to Arpro®, a new expanded polypropylene which provides better insulation, is much lighter and perfectly adapts itself to the shape of the foot. A competition-level liner consists of several superimposed layers of breathable foam. They are generally made of polyethylene and their density increases as they move away from the foot and therefore combine comfort and rigidity.
Much more than a simple board
In their jargon, skiers call their skis "boards". Fortunately, they use it as an affectionate term because it could be construed as a dig at manufacturers who expend considerable efforts to develop marvels of technology which enable athletes to gain the infinitesimal fractions of seconds that make all the difference. Modern skis consist of a dozen different materials with distinct mechanical properties. Indeed, the ideal material for manufacturing a ski has yet to be invented. It must have sufficient stiffness - bending, torsion - a relatively low mass and a high threshold of deformation in order to always be in contact with the ground, whatever its configuration. In the absence of such a revolutionary material, manufacturers superimpose and assemble various materials in a homogeneous and compact block.
A ski is first, and above all, a core - the basic element that occupies a significant portion of the total volume. All of the various other components, such as the sidewalls, the sides of the skis etc, are assembled around the core. They help fasten together the various elements which make up the ski. Among these are also the effective edge, the part which is in contact with and grips the ice, and the base which enables the ski to slide. This sandwich is then encapsulated in a plastic structure - often a polyamide or a fibre-reinforced epoxy composite - to hold it in place and to protect it from the effects of snow and sun.
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Wood and metal still feature heavily in the manufacture of racing skis. Only the composite shell and the base are made of plastic. Contrary to popular belief, the base of alpine ski is not smooth. Its surface is covered in micro-grooves whose function is to warm the snow and turn it into the water. The ski does not slide on snow; it slides on water! This is where things get difficult: each type of snow reacts differently. The configuration of the grooves in the polyethylene base of "pro" skis is based upon the geographical location of the race.
It's not all downhill racing
Cross country skiing, ski touring, jumps, freestyle...There are many different disciplines, and each requires very specific equipment. However, with the exception of Nordic skiing (see interview with Thomas Saillet in the "Plastics as seen by" section), the main differences between the other types of skis lie in their various widths and degrees of streamlining. Weight is an important factor, especially for touring skis, given that athletes wear them for steep climbs. Finally, and for the sake of being as comprehensive as possible, the components used in surfboards are roughly similar to those used in skis, depending on the chosen discipline - freeride, speed, jumps...
They fly through the air
Bobsleighing, luging, skeletoning...quintessential winter sports which take place on courses made of ice (not snow). Contrary to popular belief, it is not simply a matter of clambering into the vehicle as quickly as possible and then letting yourself slide down to the finish line. It is actually much more complex than that! The pilot must always be in control of their vehicle in order to take the most accurate trajectories possible. We can well imagine the requirements when we take into account the infernal vibrations and the fact that the bobsleigh can approach speeds of 200km/h. These modern vehicles manufactured from composite materials aim to achieve fewer vibrations and provide more control. Recently, the more sophisticated models have been equipped with small parts made of a thermoplastic elastomer - which is resistant to temperatures approaching -30 ° - which are interposed between the housing and the pads and serve as shock absorbers.
According to the crews, these tiny pieces of plastic, barely a few millimetres in size, make all the difference. New records are about to be made in Russia!
Research isn't stopping there. Reducing weight and designing the most aerodynamic profile are on top of the list of priorities. BMW, best known for its "Efficient Dynamics" concept, has signed a partnership agreement with the North American Bobsleigh Federation to design a bobsleigh for the team that will be competing in the upcoming Winter Games. After undergoing many hours of wind tunnel tests, the new vehicle was recently presented to the press. Its particularly aerodynamic design, and construction based entirely on carbon fibre, affords it a great deal of rigidity for an unbeatable weight.
Suits you, sir
Skiers taking on the Flying Kilometre have a single aim: to make a human being the most aerodynamic thing alive. The discipline involves descending a particularly steep track at the highest possible speed. The best reach speeds of over 250km/h! Such achievements are partly due to their equipment, namely the suits made from vinyl plastic and latex. Breathable fabrics are completely out of the equation; these suits are completely waterproof and smooth in order to allow the air to slide around the skiers as they adopt the position for speed. Man becomes machine; the suits are made to measure and are intended to accommodate various fins, also made from plastic, which serve to increase stability. Finally, for the record, it takes a downhill skier upwards of forty minutes to put on the suit...
Aerodynamics are also crucial in ski jumping. The suits used in this discipline are so important that they are subject to draconian regulations: each suit must be made of a single piece of a single material. The various teams invest heavily into the research of new materials aimed at optimising lift during flight. The Austrian team, for instance, will be taking on the next Olympics with a unique suit whose "formula" is obviously, kept secret. Apparently, this suit could ensure a larger air intake thanks to its innovative seams and an optimised weft based on synthetic fibres which help to reduce air flows on the back. These improvements could help increase lift in a remarkable way.
When life hangs by a thread
Mountains aren't just for sliding around on! There is also mountaineering and the desire to climb ever higher. Mountain climbers, conquerors of the useless as they like to call themselves, know wellthat they practice a dangerous sport. Falling seracs and avalanches are just some of the natural hazards against which they are all too often powerless. All the more reason to optimise their equipment, namely the ropes that are so crucial to their survival. In mountaineering, the ropes are dynamic because they have a capacity for elongation of between 8 and 10% and even up to 20% in a fall. Why is this important? Simply because the rope will stretch and cushion shock in the event of a fall. This may not seem like much, but many lives have been saved since the advent of synthetic textile ropes.
During a large portion of the ascent, climbers are connected by a rope attached to a mooring located below them. If a climber happens to fall, they are caught by the rope. If the rope has no elongation capacity, the climber could dislocate any number of limbs due to the stress that their limbs, and especially their spine, will suffer when the rope is pulled taut. Worse, they could be dashed to the bottom of the cliff as the anchor points are pulled out of the rock by the pressure of the shock. Although all ropes have a nylon sheaf, their cores differ depending on the desired elasticity. They are most often made of polyethylene or polyamide.