Many L1 and L2 instructors forget that many of the visual cues they are given to conduct their own D&C's are models that are simplified versions of reality.
The most common assumption that Examiners make for their junior instructors is the skiing can viewed in 2D. This greatly simplfies fore/aft balance assessements especially. This for the most part is a valid assumption, for beginner to intermediate skiers, skiing on groomed terrain, of moderate pitch at moderate speed, with moderate levels of performance. And since this is the teaching environment that many instructors find themselves 95% of the time, it is an simplfying assumption that is made regularly and without much consequence.
However instructors who do not realise this assumption is there, fall down when they try to apply this simplified view of fore/aft balance to advanced, or indeed expert skiing. In these cases the 2D assumption no longer holds true and skiing must be viewed in the 3D realm. This has profound implications on fore/aft balance. Moguls, crud, powder and even performance skiing on perfectly groomed terrain is not immune as the virtual bump becomes very real.
Cgeib's illustrations are is just one great example of this....
When looking at skiing in 3D fore/aft assements largley needs to be looking to see that the COM is supported by the BOS. Where it gets confusing is understanding that the resultant forces with the third dimension will sometimes mean that the skiers COM will need to be behind the BOS to actually be in balance. The bottom portion of a turn in a GS race course is a another great example.
Hence that "red line" cannot be simply drawn vertical, nor can it simply be perpendicular to the skis, it needs to reflect the resultant of all the forces acting on the skier. Hence why you can shots like the last image in this sequence that may at first "appear back" but in reality the skier is in perfect fore/aft balance.
Tons of other great examples out there...just look at the Sayto vid in Weem's "what do you think of these turns thread" or just about any other expert skiing vid
Edited by Skidude72 - 5/6/2009 at 03:18 am GMT