A dumb doubt on stalls

Roy Smith wrote:

Skywise wrote:


I've been seriously thinking of getting an account [on Wikipedia] so I
can make changes as I see the need.


In about the same amount of time it took you to write that sentence, you
could have made your account. Just got to http://tinyurl.com/6fvtg, type
in a user name and a password, and you're done.

Wikipedia and usenet are similar in many ways. On both, there are experts
and idiots and everything in between. The difference is that on Wikipedia,
articles have a decent chance of evolving towards containing better and
more correct information. On usenet, the same crap just gets recycled.

What causes it to evolve towards more accuracy? I haven't used it, but
I thought most anyone could add to or change the definitions contained
therein. Is this not how it works? Is there some sort of review and
approval process?


Matt

Jim Macklin wrote:

Unless the wing is producing lift, there is no rotation to
reduce the angle of attack. If the wing was really stalled,
the airplane would fall flat, if it was spinning it would be
a flat spin, but if was fully stalled, it would be a deep
stall and would not rotate the nose down and it would stay
in the stall.

The lift from the wing doesn't go to zero during a stall.


Under normal conditions, neither the wing or the tail fully
stalls. Stall strips, wing twist or air foil changes along
the span keep the wing from reaching the critical angle of
attack at one moment in time. Also the tailplane is usually
a different airfoil and more heavily loaded and is designed
to begin shedding lift [down-force] before the wing. The CG
range is set so that a certified airplane will have that
stable pattern.

I'm now really curious to hear your definition of what stall means.


The weight of the airplane does not cause the stall break
rotation, it is the lift moment. If it was not for the wing
lift, the airplane's mass as concentrated on the CG would
simply fall as a unit in the same attitude as it was in at
the moment.

No it won't because there is still some lift from the wing, however, it
is now less than the weight of the airplane so the imbalance in forces
causes the airplane to both descend and rotate. It would only fall
downward in a flat attitude of the lift (and drag) of the wing and tail
and fuselage went either completely to zero or remained perfectly equal
forward and rearward of the CG.



If the center of pressure was located at the same location
as the CG, there would be no moment or force to cause
rotation.

Sure, there is still the force from the tail.

Are you really a CFI and ATP as your .sig advertises?

Matt

T o d d P a t t i s t wrote:

"Jim Macklin" wrote:


Unless the wing is producing lift, there is no rotation to
reduce the angle of attack.


If you simply drop an aircraft flat, it will rotate nose
down. The wing is fully stalled (AOA=90) and the CP is well
behind the CG producing the rotation. When the main wing
stalls, lift is reduced and the same thing happens.


If the wing was really stalled, the airplane would fall flat,


Why do you think so? A stalled wing is still producing
lift, and unless the CP and CG are aligned the plane will
rotate. Planes are designed to rotate nose down in this
situation.

And it still produces drag in any event. It doesn't matter if the force
applied is due to lift or drag, it will still cause a rotation about the
CG if the forces are unbalanced.


Matt

wrote:
Hi Marty,

Rallyes are really fun, I miss mine from time to time. :-(

Great short field performance especially the 885

"Matt Whiting" wrote in message
...
Jim Macklin wrote:

If the center of pressure was located at the same location as the CG,
there would be no moment or force to cause rotation.

Sure, there is still the force from the tail.

No, Jim is right if he's referring here to the plane's CP (not just the
wings' CP).

--Gary

"Matt Whiting" wrote in message
...
T o d d P a t t i s t wrote:
A stalled wing is still producing
lift, and unless the CP and CG are aligned the plane will
rotate. Planes are designed to rotate nose down in this
situation.

And it still produces drag in any event. It doesn't matter if the force
applied is due to lift or drag, it will still cause a rotation about the
CG if the forces are unbalanced.

No, not necessarily. Even if the forces are unbalanced (which just means
there's nonzero acceleration), there's still no rotation if the plane's CP
coincides with its CG (as Jim pointed out).

Moreover, at least for a high-wing plane, rotation caused by drag upon the
wing would be nose-up rotation, not nose-down, and thus would not account
for the nose-down pitch at the stall onset, which is what's under
discussion.

--Gary

Gary Drescher wrote:
"Matt Whiting" wrote in message
...

Jim Macklin wrote:


If the center of pressure was located at the same location as the CG,
there would be no moment or force to cause rotation.

Sure, there is still the force from the tail.


No, Jim is right if he's referring here to the plane's CP (not just the
wings' CP).

True, and the odds of that happening are infinitesimal.

Matt

"Matt Whiting" wrote in message
...
Gary Drescher wrote:
"Matt Whiting" wrote in message
...

Jim Macklin wrote:
If the center of pressure was located at the same location as the CG,
there would be no moment or force to cause rotation.

Sure, there is still the force from the tail.

No, Jim is right if he's referring here to the plane's CP (not just the
wings' CP).

True, and the odds of that happening are infinitesimal.

You're referring to the odds of the plane's CP and CG coinciding? There's
nothing unlikely about that--it's what happens whenever the plane is *not*
changing pitch.

--Gary

Gary Drescher wrote:
"Matt Whiting" wrote in message
...

Gary Drescher wrote:

"Matt Whiting" wrote in message
...


Jim Macklin wrote:

If the center of pressure was located at the same location as the CG,
there would be no moment or force to cause rotation.

Sure, there is still the force from the tail.

No, Jim is right if he's referring here to the plane's CP (not just the
wings' CP).

True, and the odds of that happening are infinitesimal.


You're referring to the odds of the plane's CP and CG coinciding? There's
nothing unlikely about that--it's what happens whenever the plane is *not*
changing pitch.

The topic is stalling the airplane. That isn't a steady-state situation
as is straight and level and unaccelerated flight.

Matt

Feel free to look me up on the FAA web. Certificated
airplanes are designed to not fully stall the wing or the
tail for that matter. But within the limits of what does
happen, and without discussing wash-in, wash-out, twist,
airfoil section changes, control stops, stick shaker and
pullers, gust loading, accelerated stalls, mushing, getting
a useable idea of what happens when the controls are applied
smoothly, violently or the airplane breaks apart in flight.

If the nose would always go down from a stall, spin chutes
would not be required. If the airplane is abused in flight,
it will do some pretty remarkable things. I know a Beech
test pilot who wondered about what would happen in an E90 at
cruise if you put the props into reverse. The airplane did
not break, but they were reported to have changed their
clothes after the flight. Same pilot tried the same thing
in an F90 with the T-tail and nothing really uncontrollable
happened.

It is possible to design a wing that will stall, 100% across
the entire span, but it won't be certified for civil use.

If the tail surface reaches max lift (down-force) and you
try to go slower, it will begin the stall as air flow
reaches the critical angle of attack on the tail
PROGRESSIVELY and the nose will drop because the moment
between the CP and CG will not be countered by the tail
forces. Do it slowly and the nose pitches down slowly.
Pull a few Gs and the reaction is faster and the degree to
which the stall progresses on the tail and wing is much
faster because inertia will carry the aircraft past the
critical angles at a higher kinetic energy level.


--
James H. Macklin
ATP,CFI,A&P

"Matt Whiting" wrote in message
...
| Jim Macklin wrote:
|
| Unless the wing is producing lift, there is no rotation
to
| reduce the angle of attack. If the wing was really
stalled,
| the airplane would fall flat, if it was spinning it
would be
| a flat spin, but if was fully stalled, it would be a
deep
| stall and would not rotate the nose down and it would
stay
| in the stall.
|
| The lift from the wing doesn't go to zero during a stall.
|
|
| Under normal conditions, neither the wing or the tail
fully
| stalls. Stall strips, wing twist or air foil changes
along
| the span keep the wing from reaching the critical angle
of
| attack at one moment in time. Also the tailplane is
usually
| a different airfoil and more heavily loaded and is
designed
| to begin shedding lift [down-force] before the wing.
The CG
| range is set so that a certified airplane will have that
| stable pattern.
|
| I'm now really curious to hear your definition of what
stall means.
|
|
| The weight of the airplane does not cause the stall
break
| rotation, it is the lift moment. If it was not for the
wing
| lift, the airplane's mass as concentrated on the CG
would
| simply fall as a unit in the same attitude as it was in
at
| the moment.
|
| No it won't because there is still some lift from the
wing, however, it
| is now less than the weight of the airplane so the
imbalance in forces
| causes the airplane to both descend and rotate. It would
only fall
| downward in a flat attitude of the lift (and drag) of the
wing and tail
| and fuselage went either completely to zero or remained
perfectly equal
| forward and rearward of the CG.
|
|
|
| If the center of pressure was located at the same
location
| as the CG, there would be no moment or force to cause
| rotation.
|
| Sure, there is still the force from the tail.
|
| Are you really a CFI and ATP as your .sig advertises?
|
| Matt