Weathervaning

I think we are in agreement, but talking about it differently. Here is the
original poster's question:

"say you're dead on centerline on landing, *and all of a sudden* a crosswind
from the left starts blowing."

And my answer to the *all of a sudden* we have a crosswind question and he
wanted to know what is it that would make the plane "weathervane" in an *all
of a sudden* wind...my answer was:

"It's from the wind striking the vertical stabilizer and pushing the nose
into the wind." Which is correct as an *all of a sudden wind* = GUST!

Kobra





"Roger Long" om wrote in
message ...
But there can't be a relative wind unless some other force is acting on
the
plane. It goes along with the wind just like a raisin in a cake.

If the wind changes speed or direction suddenly, the inertia of the plane
drags the raisin through the cake briefly creating relative wind until the
plane reaches the same speed as the wind. The inertia is acting briefly
like an outside force.

Take a look at the next weathervane you see. It has a pivot attached to
the
roof which is attached to the ground. Take a look at the next airplane
you
see...

An airplane is not a weathervane.

Let's say you are in a open cockpit airplane in no wind. You are hit from
the side by a sudden 75 knot gust that continues as a steady wind.
Because
of the inertia, the plane does not start moving sideways at 75 knots
instantly. You will experience a brief moment of 75 knots of wind on your
cheek which will rapidly diminish as the plane picks up sideways speed.
Because the vertical tail is well aft of the center of gravity, the plane
may well "weathervane" into the wind as you suggest. The inertia of the
plane, acting through the center of gravity, which is point bodies in
space
tend to rotate about, is briefly the pivot of the weathervane. The plane
will quickly accelerate to 75 knots sideways motion. When it reaches the
speed of the wind, there will be not further evidence of wind (and no
further weathervane tendency) except by looking at the ground.

If you were in a hot air balloon, you would also feel a sudden strong wind
that dropped of very quickly to zero after which you would be sailing
across
the landscape at 75 knots but able to light a candle in the basket and not
see if flicker a bit.

--
Roger Long

Kobra wrote in message
...
Do I fly?! Don't be a wise ass...why do you think they call it
"weathervaning"? What does a weathervane do? It turns the
"weathervane"
into the relative wind. An airplane is a weathervane too and the wind
can
and does turn an airplane into the relative wind. Definition:
"weathervaning".

Kobra

"CASK829" wrote in message
...
The tail does not know what direction the wind is blowing if the
airplane
is in
the air. So therefore it DOES NOT push the nose into the wind.
Do You fly?



It's from the wind striking the vertical stabilizer and pushing the
nose
into the wind.

Kobra