"Jay Honeck" wrote in message
news:6DIGf.756459$x96.534195@attbi_s72...
Interesting. So what we've always interpreted as an "updraft" is *really*
an increase in relative wind, which (in turn) increases (or decreases)
lift?

That's not an "either/or" proposition.

That makes a LOT more sense to me than the commonly labeled "UPdraft",
which implies a wind from below. True UPdrafts only make sense to me near
the ground, where wind over ground obstacles can create eddies and
currents, much like water in a stream burbles around rocks and other
obstructions.

For orographic uplift (updraft), your statement is true by definition.
However, it ignores convection, which can and does create updrafts that rise
tens of thousands of feet. In either case, what goes up must come down,
figuratively speaking.

A change in relative wind would also better explain the other common type
of turbulence, where the tail is "kicked" to one side or another, creating
that annoying "fishtail" feeling.

Since a change in relative wind and an up (or down) draft are not mutually
exclusive, I don't see how "a change in relative wind" can explain
turbulence-induced yaw better than any other description of turbulence.
They are part and parcel of the same thing.

I do agree that "a change in relative wind" provides a more clear
explanation of what's going on in turbulent air. But it's really just a
more general way of describing the various sources of turbulence that exist.
All turbulence involves a change in the relative wind, but that change can
result from a wide variety of causes.

The only part of turbulence I truly DON'T understand is the kind that tips
one wing up violently. How the heck a "parcel" of air can be so different
in the span of just 30 feet (our approximate wingspan) escapes me, but
I've had turbulence push one wing up so hard that it took nearly full
opposite aileron to remain level.

It's not necessarily the case that your airplane is "one foot in, one foot
out" so to speak. Since you already understand that the turbulence felt is
a result of a change in the relative wind, it should not take much for you
to understand this change can result in the dihedral (physical and design)
to induce a rolling force.

Just as the airplane will return to level flight in calm air if it's banked
a bit, due to dihedral, a change in relative wind can alter the point of
equilibrium, bank-wise. The resulting bank is simply the airplane trying to
follow this new point of equilibrium.

I'd say it's probably pretty rare for an airplane to actually be a little
bit in one parcel of air and a little bit in another (except for gliders,
the pilots of which go around intentionally doing this ).

Pete