Weathervaning

Just a quick question...

During a crosswind landing, for instance a left crosswind, you'd lower
the left, upwind wing to counter the right drift induced by the
crosswind.

You'd also use some right rudder to keep the nose straight and prevent
it from "weathervaning".

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. The rightward crosswind
only displaces the airplane to the right. Only the relative motion of
the airplane with respect to that airmass would induce the
weathervaning effect. I presume that the airplane does not know,
aerodynamically, of the left crosswind.

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?

Alex

As far as the plane is concerned, there is no such thing as wind until the
wheels touch the ground. When you are in a hot air balloon, you don't feel
any wind at all because you are being carried along with it. Same with the
plane in a steady wind. If the wind is changing speed or direction quickly,
the plane will feel it momentarily because its inertial prevents it from
moving instantaneously. In the simple case of a steady crosswind, there is
no wind aerodynamically. The fact that the ground is sailing along sideways
is irrelevant, until the wheels touch that is.

You don't want the wheels to touch while you are moving sideways so you
bank. This angles the lift to the side which pulls the plane in that
direction. You bank until the plane is being pulled sideways by its wings
at the same speed as the wind. There is now a wind blowing sideways on the
rest of the plane, including the rudder. The rudder, having lots of
leverage way back there, tries to turn the plane into the wind. The effect
you are counteracting with the pedals is caused by the bank; not by the
wind.

--
Roger Long

"Roger Long" om writes:

As far as the plane is concerned, there is no such thing as wind until the
wheels touch the ground.

Unless the wind changes too fast (i.e. sudden gusts, wind shear, etc.).


All the best,


David

That's what I said. Did you read the whole thing?
--
Roger Long

David Megginson wrote in message
...
"Roger Long" om writes:

As far as the plane is concerned, there is no such thing as wind until
the
wheels touch the ground.

Unless the wind changes too fast (i.e. sudden gusts, wind shear, etc.).


All the best,


David

"Roger Long" om writes:

That's what I said. Did you read the whole thing?

I thought I had, but I missed that part. Apologies.


All the best,


David

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

Kobra


"Koopas Ly" wrote in message
m...
Just a quick question...

During a crosswind landing, for instance a left crosswind, you'd lower
the left, upwind wing to counter the right drift induced by the
crosswind.

You'd also use some right rudder to keep the nose straight and prevent
it from "weathervaning".

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. The rightward crosswind
only displaces the airplane to the right. Only the relative motion of
the airplane with respect to that airmass would induce the
weathervaning effect. I presume that the airplane does not know,
aerodynamically, of the left crosswind.

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?

Alex

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

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

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

"Roger Long" om wrote in
message ...
But there can't be a relative wind unless some other force is acting on
the
plane.

"Some other force". You mean, like the lift vector being tilted to one side
or the other, dragging the airplane sideways?

An airplane is not a weathervane.

No, you're right. An airplane is an airplane and a weathervane is a
weathervane. However, the airplane can behave a lot like a weathervane in a
variety of situations, including while in flight. All it takes is for the
relative wind to not be coming directly from the nose.

Pete