Weathervaning

"Koopas Ly" wrote in message
m...
Is this "weathervaning effect" caused by your leftward relative motion
due to the left bank OR by the rightward crosswind ITSELF?
Personally, I think that the former applies.

Yes, the former applies. It doesn't have anything to do with the crosswind,
and has everything to do with the airplane's sideways motion through the
airmass. The vertical stabilizer tends to orient the airplane into the
relative wind, and in a slip, you are trying to maintain an orientation at
an angle to the relative wind. Rudder is necessary to counteract the
vertical stabilizer's normal force.

(Oversimplifying, of course, since there are other forces involved that act
in a variety of directions, including both with and against your rudder
input).

Next thing I was wondering, which is related to the above: say you're
dead on centerline on landing, and all of a sudden a crosswind from
the left starts blowing. The effect would be that you should only be
displaced to the right of runway centerline. Your airplane nose would
still be parallel to the centerline. Do you agree?

I disagree. Because of inertia, a change in the air mass's momentum will
momentarily not be compensated for by the airplane's configuration. Until
the airplane "catches up" with the air mass, the relative wind is from the
left, and will cause a temporary yaw force turning the airplane to the left.
The force will gradually diminish as the airplane accelerates in the
direction of the new movement of the airmass. The airplane will remain in
this orientation unless the pilot adjust for it (and of course, the pilot
most likely will).

Pete