Weathervaning

concensus.

Note that the word is consensus.

The answer should make SENSE.

It does not suffice to ake a vote (i.e., a CENSUS).

This is a serious matter and could lead to the death of democracy.

all the best -- Dan Ford
email: (put CUB in subject line)

see the Warbird's Forum at www.warbirdforum.com
and the Piper Cub Forum at www.pipercubforum.com

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 also want to prevent the wind getting under the wing and flipping
the plane.

all the best -- Dan Ford
email: (put CUB in subject line)

see the Warbird's Forum at www.warbirdforum.com
and the Piper Cub Forum at www.pipercubforum.com

Is this "weathervaning effect" caused by your leftward relative motion
due to the left bank OR by the rightward crosswind ITSELF?

I vote for the crosswind. On a taildragger, where the CG is behind the
mainwheels, you are always concerned about the effect of a crosswind
on the fuse and tail. This is as true on takeoff as it is on landing,
and it is true when there is no relative motion (because the tires are
still on the ground).

all the best -- Dan Ford
email: (put CUB in subject line)

see the Warbird's Forum at www.warbirdforum.com
and the Piper Cub Forum at www.pipercubforum.com

"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

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

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

ken wrote:
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.

Well, you could look at as you describe, or just say that the plane doesn't
like slips/skids (as a result of its inherent stability) which is the way I
think of it.


Koopas Ly wrote:
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?

What's the difference? Remember, we always think about 'relative' motion.


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, due to the aircraft's stability, it would yaw to the left.

Hilton