A dumb doubt on stalls

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

Jim Macklin wrote:
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.

I've never seen this discussed in any book on aerodynamics that I've
ever read. Do you have even one credible reference to support your claims?

Matt

No, do I need a credible reference?



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

"Matt Whiting" wrote in message
...
| Jim Macklin wrote:
| 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.
|
| I've never seen this discussed in any book on aerodynamics
that I've
| ever read. Do you have even one credible reference to
support your claims?
|
| Matt

Jim Macklin wrote:
No, do I need a credible reference?

Only if you want us to believe you as what you are saying goes against
everything most of us have seen published in the literature.

Matt

I don't care what you believe. Maybe I just wanted a heated
discussion to start, or maybe there is another reason.
Factors to consider...
CG range approved
Actual operational CG
condition of the airfoils
pilot technique


Let see what this logic shows...
aircraft is slowed to near stalling speed by the application
of back pressure on the elevator which increases the down
force on the aircraft tail cone which levers the nose upward
by dynamically shifting the CG to a point behind the CP
which is the moment arm of the tail times the force produced
by the tail in an algebraic balance with the arm of the CG
and CP.

If the tail does not stall, to some degree, what tail down
force ceases to exist to maintain the nose up attitude? If
the wing is stalled does the lift not decrease and thus the
CP force decrease? Would that not reduce the moment needed
to rotate the nose downward to regain flying speed reduce
the angle of attack)?

FAR 23 has design limits for control degradation, the rudder
must be able to yaw the aircraft at a speed less than
lift-off speed, the elevator must be able to apply forces
and even the ailerons have limits. But when the aircraft is
stalled, out of ground effect, what force or forces change
that cause the nose to pitch downward? The wing is
producing less lift which means that the moment produced by
wing lift also decreases, reducing the nose down force. The
tail was supplying the force needed to establish the
attitude and what would cause THAT forced to be reduced if
it is not at least a stall (partial or complete) of the
elevator?

If the aircraft is held in a stalled condition, with the
elevator full back and the aircraft has a stall break, the
nose drops and then the nose pitches back up and the stall
break happens again and again in a cycle, the pilot keeping
the elevator full back and the wings level with rudder and
some aileron if the ailerons still function, what change in
forces on the aircraft is causing the cycle? Did the wing
regain lift or did the tail regain down-force?


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




"Matt Whiting" wrote in message
...
| Jim Macklin wrote:
| No, do I need a credible reference?
|
| Only if you want us to believe you as what you are saying
goes against
| everything most of us have seen published in the
literature.
|
| Matt

Jim Macklin wrote:

I don't care what you believe.

Confirms my suspicion. You don't care about being correct either so no
need for further discussion. Ignorance is bliss.


Matt

"Jim Macklin" wrote in message
news:Z6vmg.49402$ZW3.30156@dukeread04...
"Matt Whiting" wrote:
Jim Macklin wrote:
No, do I need a credible reference?

Only if you want us to believe you as what you are saying goes against
everything most of us have seen published in the literature.

I don't care what you believe.

You're a CFI, so we care what your students are led to believe.

Maybe I just wanted a heated discussion to start,

Uh, sure Jim. But there's been little heated discussion. Several of us have
just been patiently explaining to you an elementary aspect of aviation.

If the tail does not stall, to some degree, what tail down
force ceases to exist to maintain the nose up attitude?

That's a perfectly reasonable question, and it's been answered for you at
least five times in this thread. (Hint: search for "relative wind".) Each
time, you've simply *ignored* the answer without even *trying* to point out
any flaw in it.

Your approach to discussing aviation is the same as your approach to
discussing politics. In both domains, you're willing to engage in debate *as
long as it just rehashes material that's already familiar to you*. But as
soon as anyone raises an objection that you hadn't previously considered,
you just ignore it and retreat to familiar ground, repeating the claims that
the objection already defeated, making no attempt to refute the objection.

Unfortunately, that approach completely defeats the purpose of rational
discourse, because it renders your beliefs incorrigible. Perversely, you're
left with the illusion that you've sustained your position; but the reality
is that you merely went through the motions of rational discourse until just
before the point where a meaningful exchange of ideas would begin.

--Gary

Gary Drescher wrote:

That's a perfectly reasonable question, and it's been answered for you at
least five times in this thread. (Hint: search for "relative wind".) Each
time, you've simply *ignored* the answer without even *trying* to point out
any flaw in it.

It is pretty clear that he doesn't want to know the correct answer.
Yes, it is sad that he's a CFI and propogating these OWTs to his
students. It is even scarier than the system let him get to the ATP
level with this erroneous thinking.

Maybe I'll try to get a note to Barnaby Wainfan and see if he'll address
it in one of his future columns. I know he's dicussed stalls before,
but I'm not sure from this perspective of level of detail.

Matt

Sorry, I've been attempting to emulate the mental processes
of a Democrat.


"Gary Drescher" wrote in message
. ..
| "Jim Macklin" wrote
in message
| news:Z6vmg.49402$ZW3.30156@dukeread04...
| "Matt Whiting" wrote:
| Jim Macklin wrote:
| No, do I need a credible reference?
|
| Only if you want us to believe you as what you are
saying goes against
| everything most of us have seen published in the
literature.
|
| I don't care what you believe.
|
| You're a CFI, so we care what your students are led to
believe.
|
| Maybe I just wanted a heated discussion to start,
|
| Uh, sure Jim. But there's been little heated discussion.
Several of us have
| just been patiently explaining to you an elementary aspect
of aviation.
|
| If the tail does not stall, to some degree, what tail
down
| force ceases to exist to maintain the nose up attitude?
|
| That's a perfectly reasonable question, and it's been
answered for you at
| least five times in this thread. (Hint: search for
"relative wind".) Each
| time, you've simply *ignored* the answer without even
*trying* to point out
| any flaw in it.
|
| Your approach to discussing aviation is the same as your
approach to
| discussing politics. In both domains, you're willing to
engage in debate *as
| long as it just rehashes material that's already familiar
to you*. But as
| soon as anyone raises an objection that you hadn't
previously considered,
| you just ignore it and retreat to familiar ground,
repeating the claims that
| the objection already defeated, making no attempt to
refute the objection.
|
| Unfortunately, that approach completely defeats the
purpose of rational
| discourse, because it renders your beliefs incorrigible.
Perversely, you're
| left with the illusion that you've sustained your
position; but the reality
| is that you merely went through the motions of rational
discourse until just
| before the point where a meaningful exchange of ideas
would begin.
|
| --Gary
|
|

"Jim Macklin" wrote:
I don't care what you believe. Maybe I just wanted a heated
discussion to start

This is called being a troll, and is generally not something which most
people appreciate.

aircraft is slowed to near stalling speed by the application
of back pressure on the elevator which increases the down
force on the aircraft tail cone which levers the nose upward
by dynamically shifting the CG to a point behind the CP
which is the moment arm of the tail times the force produced
by the tail in an algebraic balance with the arm of the CG
and CP.

This is gibberish. The CG doesn't shift unless stuff moves around in the
airplane. A study of shifting loads (such as fuel sloshing around in
half-full tanks) would be a fascinating but very complicated endeavor, and
not particularly germane to this discussion.

If the tail does not stall, to some degree, what tail down
force ceases to exist to maintain the nose up attitude?

OK, I explained this once, but I'll do it again, slowly, and more carefully.

Let's invent a hypothetical airplane where the main wing stalls at an alpha
(angle of attack, AOA) of 18 degrees, which happens to be a fairly typical
number for the kinds of wings most of us fly. Let's also imagine that it's
got a symmetric one-piece stabilator (such as found on an Archer), which
also stalls at 18 degrees (positive or negative). Vso for this plane is 60
kts (that's a pretty high value, but it makes the math easier

Now, let's put the plane at the edge of stall in a typical power-off stall
demonstration. The main wing AOA is 17.9 degrees. The yoke is almost all
the way back, and the stabilator is set at an AOA of -15 degrees. Power is
at idle, true airspeed is 50 kts, and you're maintaining altitude.

Now, pull back on the yoke just a bit more. The AOA increases to 18.1
degrees, and the main wing is now stalled. The wing is now producing less
lift than the airplane weighs, so it starts to accelerate downward. After
a short time, it's in a 100 fpm descent, but we're still holding the same
pitch attitude.

If you work the math, 60 KTAS and 100 fpm down works out to a glide slope
of just about -1 degree, which means the relative wind is now coming from 1
degree below the horizontal. Since the pitch angle hasn't changed, the AOA
of both the main wing and the tail will change by this same 1 degree. For
the main wing, that means the AOA has been driven from 18.1 degrees to 19.1
degrees; further into stall, and further reducing the amount of lift being
generated (increasing drag too, but that's a secondary issue).

Now, here's the interesting part. The tail has gone from -15 to -14. It's
moved further away from stall. But, it too, is producing less (downward)
lift because the AOA is reduced. Less downforce from the tail means the
nose will start to drop. No tail stall, just reduced downwards lift from
the tail due to decreased tail AOA caused by the downward motion of the
aircraft.

That's it, I'm done. If you really want to be a troll, enjoy yourself.





If
the wing is stalled does the lift not decrease and thus the
CP force decrease? Would that not reduce the moment needed
to rotate the nose downward to regain flying speed reduce
the angle of attack)?

FAR 23 has design limits for control degradation, the rudder
must be able to yaw the aircraft at a speed less than
lift-off speed, the elevator must be able to apply forces
and even the ailerons have limits. But when the aircraft is
stalled, out of ground effect, what force or forces change
that cause the nose to pitch downward? The wing is
producing less lift which means that the moment produced by
wing lift also decreases, reducing the nose down force. The
tail was supplying the force needed to establish the
attitude and what would cause THAT forced to be reduced if
it is not at least a stall (partial or complete) of the
elevator?

If the aircraft is held in a stalled condition, with the
elevator full back and the aircraft has a stall break, the
nose drops and then the nose pitches back up and the stall
break happens again and again in a cycle, the pilot keeping
the elevator full back and the wings level with rudder and
some aileron if the ailerons still function, what change in
forces on the aircraft is causing the cycle? Did the wing
regain lift or did the tail regain down-force?