Weathervaning

"Peter" wrote in message
news:dAYrb.121381$9E1.602249@attbi_s52...
Gary Mishler wrote:

Think about it, if airplanes "weathervaned" in flight every
plane in the sky would want to turn into the wind instead of going where
you
wanted it to.

When I wrote the above I was referring to actual wind because I thought
(right or wrong) that was what the post I was replying to was referring to.

With the rare exception of a few planes doing acrobatic maneuvers, all the
ones I've seen flying are in fact pointing into their relative wind (or at
least within a few degrees of it).

Absolutly correct when you are talking about relative wind rather than
actual winds.
Again, I was talking actual winds and you were talking relative wind.

This thread got very confusing because posts and replies were mixing
relative vs. actual wind and some were confusing coordinated turns vs side
slips.

I think if everyone goes back through the thread we would find that we all
would agree *IF* we were all on the same page using the same assumptions of
actual/relative wind and turn/slip.

David Megginson wrote:

That's interesting. Have you ever tested it formally and recorded the
results, i.e. write down your starting heading, hold a 15 degree bank,
set a timer for two minutes, write down your ending heading, and then
level out again?

Nope. I've just regarded it as a "circus trick". If I'm taking another pilot
up for his first flight in a Maule, I may demonstrate the phenomenum just for
laughs.

George Patterson
If you're not part of the solution, you can make a lot of money prolonging
the problem.

"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


Yes, but a weather vane's COG, if you will, is affixed to terra firma,
unlike an airplane in flight.

"Gary Mishler" wrote in message news:fBXrb.164593$HS4.1334282@attbi_s01...
"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".


As others have pointed out, it's only "weathervaning" if the aircraft is in
contact with the ground the same as a weathervane on a building. If the
airplane is airborne it is in a moving air mass and by definition can not
"weathervane". Think about it, if airplanes "weathervaned" in flight every
plane in the sky would want to turn into the wind instead of going where you
wanted it to. Relative wind in flight is airflow opposite the direction of
aircraft movement through the air mass, it is not defined as a headwind,
crosswind or tailwind.

The aircraft I primarily fly is a b*#&h on the ground in a crosswind due to
the large vertical stab area and the arm from the vertical to the center of
pressure. But, once airborne she's a beauty.

Regards,
Mish

....hence the difference between "course over ground" and heading.

"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.

From the point of view of the aerodynamics, the only thing the airplane
"knows" is the sideslip angle. It doesn't matter if you perceive this as a
forward slip (nil wind, tracking 270, heading 280) or a side slip (S'ly wind
causing 10 knots right drift, tracking 270, heading 270). In both cases
there's a sideslip angle of 10 degrees.

Is the sideslip angle because of the left bank or the rightward (from the
left?) crosswind? Is my mousemat compressed because the mouse presses down
on it or because the table presses up on it? :-)

If there is a sideslip angle there is a yawing moment, because of the
lateral lift from the fin. You can counter this with rudder, or let the
airplane yaw at a rate that increases until the natural yaw damping moment
balances it, as it does in a turn if you don't use rudder.

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?

No, not if you make no change in control inputs. You've introduced a
sideslip angle, so the airplane yaws.

Julian Scarfe

Read the original poster's question. He asked, "...say you're dead on
centerline on landing, *and all of a sudden* a crosswind
from the left starts blowing..." That's a gust and he wanted to know what
force was turning the plane into the wind. An "all of a sudden wind" will
"weathervane" the plane. That was the question, that is the answer...we've
been splitting hairs for 50 posts now.

Kobra




"Verbs Under My Gel" wrote in message
om...
"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


Yes, but a weather vane's COG, if you will, is affixed to terra firma,
unlike an airplane in flight.

On Mon, 10 Nov 2003 at 13:40:27 in message
, Koopas Ly
wrote:

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?

If the cross wind _suddenly_ started blowing then it would be a sideways
gust. An aircraft does not respond instantly to a sharp edged gust ,so
for a short time the aircraft is now yawed. Its natural yaw stability
and its inertia would then cause it to rotate in yaw until it is left
slightly turned and heading in a slightly different direction. So in
that case unless you put in control inputs you will not be just
displaced parallel to your original course. The amount depends on the
size and sharpness of the gust and the aerodynamic and mass
characteristics of the aircraft.

Gusts and flying in a steadily moving mass of air are not the same
thing.
--
David CL Francis

On Mon, 10 Nov 2003 at 18:05:54 in message
, Kobra
wrote:

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".

The centre of a weathervane is fixed to the ground - a different
situation from a free flying aircraft. Only gusts can have that effect,
steady winds cannot. With the wheels on the ground an aircraft does
become susceptible to a 'weathervane' effect.
--
David CL Francis

Keep me the hell away from your area of flight you don't know a damn thing now
do you. You probably think that down wind turns will cause you to crash.
At least have some knowledge of how and airplane works before you try and fly
the damn thing

John
CFII
ATP
PHD aeonautical engineering UT Austin.

do I fly?! Don't be a wise ass...why do you think they call it
"weathervaning"?

both - you will get secondary effects from the aileron bank causing yaw and
the aircraft will "weathercock" into wind. For those sceptics who don't
believe the aircraft will weathercock fly hands off with no rudder trim/bias
(and reduced power so there is no slipstream effect) and see what happens,
it will turn into wind.

--


KB

"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