Learning to ski in the dark ages
Originally Posted by BillA
Have at it.
Turning on skis - from an old man’s perspective.
Many years ago, before the flying wedge, skiers progressed to arcing turns through a simple series of progressions from snow plow to stem Christie to parallel turns to arcing.
It might be useful to see how this worked.
First we appeal to Newton’s laws.
Turning requires acceleration which requires forces, a = F/M. You apply forces to the snow via the bottoms of your skis, and the snow pushes back on the skis.
Now let’s examine how we can get forces from skis using some simple models.
First consider the ski as a plank of wood, a stiff unbendable plank as a 1st approximation.
Most of us have used those snow shovels that are about 8 inches high and two feet wide. You can push them along in front of you as you scrape your driveway of snow. They push back. You can angle them so that one end is further ahead than the other. The snow will form a trail along one side and a noticeable sideways force must be applied to keep the shovel tracking straight. Like a snow plow pushing the snow to one side of the road, the snow pushes the snowplow towards the other side.
If you push a vertical plank of wood held across your direction of travel through the snow it will push straight back. If you angle that plank so that it’s top is tipped forward it will ride up over the snow. The closer to vertical it is the more it pushes back, the closer to horizontal it is the less it pushes back.
If you place one end of that plank further ahead than the other end, it will push snow to one side and be pushed to the other side by the snow. In effect it is trying to follow its edge while deflecting the snow one way and you the other.
This is the basic principle of the snow plow turn. Setting your two skis at an angle to each other and tipping them up on edge in effect produced two “snow plows”, one pushing you one way, and the other pushing you the other way. Giving one ski more weight or more edge angle caused it to win the battle and make you turn. Giving both skis a lot of edge angle and weight caused them to fight each other and end up not going forward very well at all.
Snow plows were and are hard on the legs and very inefficient. The stem christie is a slight step better. Basically accepting that skis like to go where they are pointed a developing skier would soon point his skis down the hill to go down the hill and only do a snow plow turn when he needed to turn. The skier would adopt the “snow-plow” position by concentrating on the ski that was to supply the turning force. First it would be placed out there at an angle to the current direction of travel, and then weighted and put on edge. The other ski, not needing to supply any force was neither edged nor put into a “plow” position. In fact it was brought back parallel to the ski that had been moved into the new direction as soon as possible. The problem with the stem christie is that a lot of people it seems spent too long at this stage and developed a permanent stemming habit, instead of moving on.
Knowing full well that the stem-christie was a stop-gap technique, designed solely for the purpose of getting skiers to feel the end of the turn when the non-stemmed ski was riding along side the ski providing the turning force, skiers soon discovered they could just adopt that inclined position with both skis parallel without needing to stick out a ski and then bring the skis back together, the parallel turn.
The parallel turn in its ultimate form had the skis doing what they did best, travelling along their edges and not across them, but there were and are other forms of it. As with the snow plow, a ski on edge moving across the snow will push back and sideways. The amount of sideways force will depend on a number of factors, including the angle at which it crosses the direction of travel. The angle at which a ski on edge crosses the direction of travel can be changed, easily by applying more weight to the front or back of the ski and letting the snow do the work, or not so easily by forcibly twisting it by applying torque through the ski boot. A ski not so much on edge can be more easily twisted, and is less affected by the snow. An unweighted ski is also easier to twist. Playing with fore aft weighting and torque was used to shape the turns.
Skis do bend.
Carving “arc to arc” turns implies that the skis are moving along the edges of a ski that is bent into a curve. On soft snow the bases and the platform of snow supporting them are bent with the tips higher than the mid section. Inclining the skis so that a skier skiing up this page is leaning to the right would turn the curved shape of two skis into something like this ((, and the skis would go forward cutting a nice turn with their bases. On hard snow the side cut of the ski would ensure the same curved shape. Any skier skiing fast enough would discover arcing.
With today’s highly shaped skis, it is much easier to weight the edges and let them do the work, unweighting the ski to provide an initial angle across the direction of travel with a twist, makes it harder to have the edges grab. Edges cannot grab when they are unweighted. You can have the edges grip or you can have the edges release, but not both at the same time.