> Lostboy: "What I was refering to in my
> post above is that the deeper the sidecut
> (all other things being equal) the easier
> it is to bend the ski ..."
If I'm not mistaken, I think you are probably saying that with everything else held constant, specifically narrowing the waist of a ski should make it easier to flex. This is indeed true, but is not what is important or what happens when a mfgr designs and manufactures a particular model of ski.
By adjusting the thickness of the ski and method of construction (eg, torsion box, glass wrapped, wood / foam core, cap vs sidewall, etc.), the mfgr has essentially total and independent control of the flex without changing the sidecut or width of the ski by one iota. The designer usually decides on (among other things) the desired flex, sidecut and waist width first, and then adjusts parameters like the thickness and construction to achieve those goals simultaneously.
> "...with the result that more of the ski's
> total available edge is being engaged at a > given time throughout a turn."
I believe that what you are saying is that you think that if you make a ski more flexible, more of the edge will be in contact with the snow. Unfortunately, this is not generally true.
Lets first assume the simplest case of icy/hardpack conditions on an absolutely flat, smooth slope. In this case, what actually happens is that an edged ski with no force applied to it will be supported only at its tip and tail. (Try this at home, with a ski on a hard floor).
However, when you apply a modest force (say fifty pounds or less at any reasonable edge angle) perpendicular to this edged ski, the tip and tail of course stay in contact with the snow (floor), but now, the waist of the ski is also forced into contact with the floor. So, now you have three points of the ski in contact with the floor.
From this point on, no matter how much harder the boot presses down in the center of the ski, the fraction of the edge in contact with the floor never changes. Realizing this, I think it should be pretty easy to see that for the exact same reason, no matter how much you adjust the longitudinal flexibility of the ski, so long as the waist is touching the floor, you never change how much of the edge is in contact with the floor (snow) - it will always be the same three points.
No modern alpine ski is so stiff that the waist doesn't touch the floor (ie, snow) under the typical loadings applied by skiers (ie, his weight plus any centrifugal force he might be generating). Thus, in the case of hardpack, the overall flex of the ski almost nothing to do with how much of the edge is in contact with the snow.
Rather, what is critical to bringing as much of the edge as close to the floor (snow) as possible is the exact shape of the sidecut. If the sidecut is wrong in any way, only three points contact the floor. However, if the shape is correct, the whole edge can be arbitrarily close to the floor.
I should note that the distribution of flex along the length of the ski does determine the exact shape (in the other plane) of the fully reverse cambered ski, but the optimal flex distribution is essentially dictated by other design / performance goals (eg, soft forebody and stiff tail; soft tip and tail with a firm mid; etc. etc.), so getting as much of the edge in contact with the snow still boils down to the exact shape of the sidecut and not the overall flex.
> With a conventional sidecut ski more human
> effort, higher edge angles and more speed
> is required to cleanly carve a turn ...
This part of your statement is absolutely correct.
> ... because proportionatly less of the
> ski's total edge length is in contact with
> the snow at any given point in the turn.
> That is in large part what the shaped-
> short ski evolution is all about, at least
> I thought that was what it is about.
Unfortunately, the reason you hypothesize for the correct observatons in the first part of your sentence is not quite correct.
The main reason for less effort (say in terms of foot-twisting needed in skidded turns) is simply that the differences in angles of attack of the snow on the forebody uphill edge versus the aft uphill edge is so much larger with shaped skis, that these skis automatically generate a much larger twisting torque, so the skier doesn't have to apply so much manual foot steering.
The main reason for the ability to carve turns at lower speeds with shaped skis is simply that the arc formed by the decambered edge (as viewed perpendicular to the snow) has a much smaller radius than with old straight skis. Thus, to achieve a given centrifugal force (and indirectly, a given edge angle), a much lower speed can be employed.
The extra fraction of the edge in contact with the snow is a side benefit of care taken in modern ski design. It may account for part of the ability to go to shorter lengths, but is not the reason behind the major performance changes mentioned above (ie, less foot-steering, carving at lower speeds, etc.)
> I do however assume that a shorter wider
> ski will compensate to an extent for
> longer narrrower traditional skis. That is
> what Mid-Fats and Fats with their also
> wider waists are about I thought.
This is absolutely true in soft snow. In this case, the relevant issue is the pounds per square inch it takes to compact a specified type of snow by a given amount. To a good approximation, as long as the number of square inches is held constant, the depth to which you sink is independent of whether you get those square inches from a long skinny ski or a short wide one.
I hope my long winded explanations clarified things a bit. Unfortunately, sometimes I just can't figure out how to make my explanations any shorter.
Tom / PM