View Single Post
  #25  
Old February 22nd 05, 01:51 PM
external usenet poster
 
Posts: n/a
Default

As often happens, the discussion is digressing into the particulars of
landing in a crosswind, and I couldn't be happier. Watching pilots
wrangle through the explanation of why they do what they do is
fascinating, especially since the inference chain gets all kinds of
twisted as they work their way back up to the model.

The trick, I'm convinced, is to completely divorce the slip/skid
alignment maneuvers from the maneuver required to establish a track
down the runway. Once we've determined that there is a crosswind, the
only way to establish a proper track is to change our direction through
the airmass. The problem arises when pilots confuse the alignment
maneuver with the turn. We've discovered this slick maneuver where we
can turn base to final and initiate the slip all in one motion. Which
leads to a false perception that we only turned 90 degrees, then used
the wing to compensate for crosswind. But we have in fact changed our
direction by more than 90 degrees and inserted our alignment slip early
on final. But whether your turn is coordinated throughout, or slipped,
the means by which we change direction is exactly the same. Remove the
slip, and you'll point upwind, put the slip back in and you'll point
down the runway. The forces produced by the glider remain balanced
throughout.

Maybe it is easier to conceptualize this if you simply ignore the
direction the nose is pointing and think of it in terms of the glider's
path through the air. Because in a side slip the nose is pointing down
the runway, there is an illusion that the lowered wing is dragging the
glider sideways, compensating for the "force" of the wind. But in a
side slip (as in a foward slip), the horizontal component of lift is
exactly balanced by the force created by sideways motion of the
fuselage. There is no extra force to compensate for an external force.
Which is a good thing since there is no external force from the wind.

That said, an unbalanced force is required to establish a new direction
through the air that will produce a desired ground track. And this is
only accomplished by turning. Whether the turn is slipped or skidded or
coordinated is a matter of pilot choice. It is nonetheless a turn since
the direction of the glider changes. When the new direction is
achieved, the turn ceases. Whether this is accomplished by rolling the
wings level or increasing beta to balance the wing turning force is a
matter of pilot choice.