Stalls - Angle of Attack versus Vstall

[[email protected]]

Hi,

I'm a student pilot, learning in Piper Warrior II's.

I'm hoping that someone can shed some light on stalls for me.

I understand that an aerofoil doesn't stall becauase of speed, it
stalls because it has exceeded it's critical angle of attack. It can be
stalled therefore at 100 kts (an accellerated stall?) just as it can at
20kts.

If this is the case, then why do they quote 'stall speeds' in aircraft
specs? For example (from Wikipedia), for the PA28 VS (stall, clean) =
50 kias. Is 50 kts the speed at which you would be unable to maintain
LEVEL flight? ie, at 50kts, in level flights, you would have an AOA of
16 degrees, therefore, any slower and you'd have to pitch back past the
critical angle?


Thanks very much in advance to anyone who can shed light on this for me
:-)



Damien Sawyer

[Jose[_1_]]

> If this is the case, then why do they quote 'stall speeds' in aircraft
> specs?

To first order, it's the stall speed in level flight at 1 g at a given
weight.

You can stall at the critical AOA. When you get to the critical angle
of attack, the wing is producing a certain amount of force (lift). If
you reach that AOA at a higher speed, it is producing more force,
presumably to accelerate you upwards (start a climb or arrest a
descent), sideways (when banked, in a turn), or to just hold altitude
(if overloaded).

> Is 50 kts the speed at which you would be unable to maintain
> LEVEL flight?

Well, sort of, and no. It's complicated by the fact that the engine is
also producing up force (you are, to some extent, hanging on the prop)
when pitched up.

To first order, it's the speed at which, in unaccelerated flight (you
can be descending at a constant velocity), if you pitch up further, you
will start to stall, because you are already pitched up as far as you
can be without stalling.

Jose
--
"Never trust anything that can think for itself, if you can't see where
it keeps its brain." (chapter 10 of book 3 - Harry Potter).
for Email, make the obvious change in the address.

[d&tm]

> wrote in message
ups.com...
> Hi,
>
> I'm a student pilot, learning in Piper Warrior II's.
>
> I'm hoping that someone can shed some light on stalls for me.
>
> I understand that an aerofoil doesn't stall becauase of speed, it
> stalls because it has exceeded it's critical angle of attack. It can be
> stalled therefore at 100 kts (an accellerated stall?) just as it can at
> 20kts.
>
> If this is the case, then why do they quote 'stall speeds' in aircraft
> specs? For example (from Wikipedia), for the PA28 VS (stall, clean) =
> 50 kias. Is 50 kts the speed at which you would be unable to maintain
> LEVEL flight? ie, at 50kts, in level flights, you would have an AOA of
> 16 degrees, therefore, any slower and you'd have to pitch back past the
> critical angle?
>
basically yes, the stall speeds quoted are for level flight at maximum wt.
As a student you will not be anywhere near max wt. if you want, you can
calculate what your stall speed will be at the wt you fly at by multiplying
the full wt stall speed in the book by the square root of the (actual wt
divided by the maximum wt). Same applies for best glide speed which is
quoted at 73 kts in the book for maximum wt of 2325 lbs. If you are flying
solo you may find the best glide speed might be only 65 kts. but discuss
this with your instuctor , mine preferred to use the book figure regardless
of wt.
terry >

[Stubby]

wrote:
> Hi,
>
> I'm a student pilot, learning in Piper Warrior II's.
>
> I'm hoping that someone can shed some light on stalls for me.
>
> I understand that an aerofoil doesn't stall becauase of speed, it
> stalls because it has exceeded it's critical angle of attack. It can be
> stalled therefore at 100 kts (an accellerated stall?) just as it can at
> 20kts.
>
> If this is the case, then why do they quote 'stall speeds' in aircraft
> specs? For example (from Wikipedia), for the PA28 VS (stall, clean) =
> 50 kias. Is 50 kts the speed at which you would be unable to maintain
> LEVEL flight? ie, at 50kts, in level flights, you would have an AOA of
> 16 degrees, therefore, any slower and you'd have to pitch back past the
> critical angle?
>
>
> Thanks very much in advance to anyone who can shed light on this for me

Don't forget the stall is caused by the elevator losing lift. That's
why the nose drops.

[Gary Drescher]

"Stubby" > wrote in message
. ..
> Don't forget the stall is caused by the elevator losing lift.

No, that's incorrect. There is such a thing as an elevator stall, but it's
very different from a normal stall. In typical small planes, an elevator
stall does not occur unless there is tail icing, or else a CG that's too far
forward when you apply substantial up elevator.

If you have an elevator stall during a landing flare, the nose snaps
abruptly downward, potentially damaging the nose gear.

> That's why the nose drops.

No, not in a normal stall. Rather, the wings produce insufficient lift and
so the plane accelerates downward. The plane weathervanes into the new
relative wind, dropping the nose.

You can find an excellent discussion of the physics of stalling here:
http://www.av8n.com/how/

--Gary

[Bob Gardner]

Bottom line is that you do not have an angle of attack indicator in the
airplane, so publishing an AOA in the manual would be useless.

For reasons given by others, airspeed is the next best thing.

Bob Gardner

> wrote in message
ups.com...
> Hi,
>
> I'm a student pilot, learning in Piper Warrior II's.
>
> I'm hoping that someone can shed some light on stalls for me.
>
> I understand that an aerofoil doesn't stall becauase of speed, it
> stalls because it has exceeded it's critical angle of attack. It can be
> stalled therefore at 100 kts (an accellerated stall?) just as it can at
> 20kts.
>
> If this is the case, then why do they quote 'stall speeds' in aircraft
> specs? For example (from Wikipedia), for the PA28 VS (stall, clean) =
> 50 kias. Is 50 kts the speed at which you would be unable to maintain
> LEVEL flight? ie, at 50kts, in level flights, you would have an AOA of
> 16 degrees, therefore, any slower and you'd have to pitch back past the
> critical angle?
>
>
> Thanks very much in advance to anyone who can shed light on this for me
> :-)
>
>
>
> Damien Sawyer
>

[Allen[_1_]]

"Gary Drescher" > wrote in message
. ..
> "Stubby" > wrote in message
> . ..
>> Don't forget the stall is caused by the elevator losing lift.
>
> No, that's incorrect. There is such a thing as an elevator stall, but it's
> very different from a normal stall. In typical small planes, an elevator
> stall does not occur unless there is tail icing, or else a CG that's too
> far forward when you apply substantial up elevator.
>
> If you have an elevator stall during a landing flare, the nose snaps
> abruptly downward, potentially damaging the nose gear.
>
>> That's why the nose drops.
>
> No, not in a normal stall. Rather, the wings produce insufficient lift and
> so the plane accelerates downward. The plane weathervanes into the new
> relative wind, dropping the nose.
>
> You can find an excellent discussion of the physics of stalling here:
> http://www.av8n.com/how/
>
> --Gary

I did not reply to him because even with the lack of a smiley I thought he
said that in jest. If he is serious then....?

Allen

[Ron Natalie]

Stubby wrote:

>
> Don't forget the stall is caused by the elevator losing lift. That's
> why the nose drops.

Say what? The stall has nothing to do with the elevator losing lift.
It occurs because the main wing has exceeded the critical angle of
attack. The reason the nose drops is that the elevator is NOT losing
lift while the main wing is, which pivots the aircraft nose down.

[Jose[_1_]]

> The reason the nose drops is that the elevator is NOT losing
> lift while the main wing is, which pivots the aircraft nose down.

Not that either. Remember, in a conventional airplane, the tail is
pushing down. The center of mass is ahead of the wing's center of lift,
so the tail pushes down to keep the nose up. (think "big heavy engine
trying to tip the airplane forward").

When the wings stall, the nose drops because nothing is holding it up
(anywhere near as effectively as when the wing is not stalled).

Jose
--
"Never trust anything that can think for itself, if you can't see where
it keeps its brain." (chapter 10 of book 3 - Harry Potter).
for Email, make the obvious change in the address.

[Aluckyguess]

Bottom line the wing needs airspeed to fly. At a certain speed the wing
starts to lift, when it loses this speed, losing lift it stalls. Stick your
hand out the window of your car shape it like a wing at a certain speed it
will lift all by itself and basically be weightless.

[Peter Duniho]

"Aluckyguess" > wrote in message
...
> Bottom line the wing needs airspeed to fly. At a certain speed the wing
> starts to lift, when it loses this speed, losing lift it stalls.

IMHO, this is a misleading description of stalling, and in fact will lead to
just the confusion the original poster describes.

Specifically, the wing's speed is really not directly related to stalling at
all. As others have explained, the reason a stall speed is published is
that it is true that at a given weight and load factor (eg max gross and
1g), there is a specific amount of lift required, and there is a specific
speed associated with the angle of attack that can produce that lift.

The published stalling speed is simply a speed at which the angle of attack
required to achieve the necessary lift at that speed is the same as the
critical (stalling) angle of attack. It is not true that under all
conditions, at that speed, the wing is stalled (or "when it loses this
speed, losing lift it stalls"). The wing loses lift because it stalls, not
the other way around. And the wing will only stall at a given airspeed if
its angle of attack exceeds the critical angle of attack. This is true of
any airspeed, above or below the published stall speed(s).

> Stick your hand out the window of your car shape it like a wing at a
> certain speed it will lift all by itself and basically be weightless.

However, as long as you keep your "hand wing" angle of attack below the
critical angle of attack, it will generate lift at ANY speed above 0. There
is no "stalling speed" for your hand in that scenario, as your hand is not
required to support itself with lift, and so there is no speed at which the
required angle of attack equals or exceeds the critical angle of attack.
(That is, there's not even a concept of "the required angle of attack" in
that case...your hand will fly along quite happily at any amount of lift, or
even zero lift).

Pete

[Roy Smith]

In article >,
"Peter Duniho" > wrote:

> Specifically, the wing's speed is really not directly related to stalling at
> all. As others have explained, the reason a stall speed is published is
> that it is true that at a given weight and load factor (eg max gross and
> 1g), there is a specific amount of lift required, and there is a specific
> speed associated with the angle of attack that can produce that lift.

Not to mention that most small planes do not have any direct way of
measuring AOA and displaying it to the pilot. If they did have AOA vanes
(as most larger planes do), there would be less attention paid to "stall
speed", and student pilots the world over would be less confused.

"Now, pay attention Mr. student pilot. A wing stalls when the AOA reaches
some magic value, not at any particular airspeed. But, we're not going to
let you know what your AOA is. Instead, we're going to talk about 'stall
speed', which I've already explained to you is a meaningless term. Are we
having fun yet?"

[John Godwin]

"Aluckyguess" > wrote in
:

> Bottom line the wing needs airspeed to fly. At a certain speed the
> wing starts to lift, when it loses this speed, losing lift it
> stalls.
>
That doesn't explain an accelerated stall.


--

[Andrew Sarangan[_1_]]

wrote:
> Hi,
>
> I'm a student pilot, learning in Piper Warrior II's.
>
> I'm hoping that someone can shed some light on stalls for me.
>
> I understand that an aerofoil doesn't stall becauase of speed, it
> stalls because it has exceeded it's critical angle of attack. It can be
> stalled therefore at 100 kts (an accellerated stall?) just as it can at
> 20kts.
>
> If this is the case, then why do they quote 'stall speeds' in aircraft
> specs? For example (from Wikipedia), for the PA28 VS (stall, clean) =
> 50 kias. Is 50 kts the speed at which you would be unable to maintain
> LEVEL flight? ie, at 50kts, in level flights, you would have an AOA of
> 16 degrees, therefore, any slower and you'd have to pitch back past the
> critical angle?
>
>



If the normal stall speed is 50 knots, you can make it stall at 100
knots if you pull some positive g's, or you can make it stall at 25
knots if you pull some negative g's. On the same token, you can stall
the airplane at higher or lower airspeeds depending on the aircraft
weight.


I don't know why all primary aviation texts focus so much on AOA when
nearly all of the airplanes we fly do not have an instrument to measure
it. Perhaps it is an attempt to make the description more
scientifically rigorous. But things would be a lot easier if they just
said "stall speed changes with load factor".

[Dave Doe]

In article . com>,
says...
>
> wrote:
> > Hi,
> >
> > I'm a student pilot, learning in Piper Warrior II's.
> >
> > I'm hoping that someone can shed some light on stalls for me.
> >
> > I understand that an aerofoil doesn't stall becauase of speed, it
> > stalls because it has exceeded it's critical angle of attack. It can be
> > stalled therefore at 100 kts (an accellerated stall?) just as it can at
> > 20kts.
> >
> > If this is the case, then why do they quote 'stall speeds' in aircraft
> > specs? For example (from Wikipedia), for the PA28 VS (stall, clean) =
> > 50 kias. Is 50 kts the speed at which you would be unable to maintain
> > LEVEL flight? ie, at 50kts, in level flights, you would have an AOA of
> > 16 degrees, therefore, any slower and you'd have to pitch back past the
> > critical angle?
> >
> >
>
>
>
> If the normal stall speed is 50 knots, you can make it stall at 100
> knots if you pull some positive g's, or you can make it stall at 25
> knots if you pull some negative g's. On the same token, you can stall
> the airplane at higher or lower airspeeds depending on the aircraft
> weight.
>
>
> I don't know why all primary aviation texts focus so much on AOA when
> nearly all of the airplanes we fly do not have an instrument to measure
> it.

??? - Stall warning buzzer - fairly common on most planes methinks.
(Next time yer up try a cruise speed max rate turn and pull back a bit
more - you'll hear it :)

--
Duncan

[Peter Duniho]

"Andrew Sarangan" > wrote in message
oups.com...
> If the normal stall speed is 50 knots, you can make it stall at 100
> knots if you pull some positive g's, or you can make it stall at 25
> knots if you pull some negative g's. On the same token, you can stall
> the airplane at higher or lower airspeeds depending on the aircraft
> weight.

Minor nit:

Replace "some negative g's" with "less than 1g". Or "between -1 and +1 g",
if you want to get really particular. :)

Most wings aren't symmetrical, so it's not strictly correct to mirror the
positive and negative g numbers, but it would be more correct than the above
to say that the stall speed depends on the absolute value of the load
factor, with absolute values above 1.0 increasing the stall speed above the
published 1g number, and absolute values below 1.0 decreasing the stall
speed below the published 1g number.

Pete

[Peter Duniho]

"Dave Doe" > wrote in message
. nz...
> [...]
>> I don't know why all primary aviation texts focus so much on AOA when
>> nearly all of the airplanes we fly do not have an instrument to measure
>> it.
>
> ??? - Stall warning buzzer - fairly common on most planes methinks.

The stall warning horn is an AOA indicator. But I wouldn't say that it
actually *measures* AOA. That is, the warning horn (or other device) can't
tell you what the AOA actually is...it just tells you what side of the
critical AOA you're on.

Pete

[Andrew Sarangan[_1_]]

Dave Doe wrote:

> >
> >
> > I don't know why all primary aviation texts focus so much on AOA when
> > nearly all of the airplanes we fly do not have an instrument to measure
> > it.
>
> ??? - Stall warning buzzer - fairly common on most planes methinks.
> (Next time yer up try a cruise speed max rate turn and pull back a bit
> more - you'll hear it :)
>

The stall horn is preset to go off at a specific AOA. It does not give
the pilot any indication of the actual AOA being flown. AOA indicator
is typically used in large transport airplanes and military jets where
the operating envelope is large. For typical GA airplanes, the envelope
is so small that the airspeed indicator is a good indication of AOA
under normal operating conditions.

[Dave Doe]

In article om>,
says...
>
> Dave Doe wrote:
>
> > >
> > >
> > > I don't know why all primary aviation texts focus so much on AOA when
> > > nearly all of the airplanes we fly do not have an instrument to measure
> > > it.
> >
> > ??? - Stall warning buzzer - fairly common on most planes methinks.
> > (Next time yer up try a cruise speed max rate turn and pull back a bit
> > more - you'll hear it :)
> >
>
> The stall horn is preset to go off at a specific AOA. It does not give
> the pilot any indication of the actual AOA being flown. AOA indicator
> is typically used in large transport airplanes and military jets where
> the operating envelope is large. For typical GA airplanes, the envelope
> is so small that the airspeed indicator is a good indication of AOA
> under normal operating conditions.

Isn't the texts on AOA about *critical* AOA? - the rest of it, is surely
the other angle - within the load envelope. The stall warning provides
a fixed measurement of the imminent critical AOA - what else does a
pilot need?

Is Fenwicks (sp?) one of your primary texts?

--
Duncan

[alexy]

"Andrew Sarangan" > wrote:


>If the normal stall speed is 50 knots, you can make it stall at 100
>knots if you pull some positive g's, or you can make it stall at 25
>knots if you pull some negative g's.
Or less than .25 positive g's. I suspect that the stall speeds in
negative g flight are very different, at least with a usual asymmetric
airfoil.
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.

[[email protected]]

Gary Drescher wrote:
> "Stubby" > wrote in message
> . ..
> > Don't forget the stall is caused by the elevator losing lift.
>
> No, that's incorrect. There is such a thing as an elevator stall, but it's
> very different from a normal stall. In typical small planes, an elevator
> stall does not occur unless there is tail icing, or else a CG that's too far
> forward when you apply substantial up elevator.
>
> If you have an elevator stall during a landing flare, the nose snaps
> abruptly downward, potentially damaging the nose gear.
>
> > That's why the nose drops.
>
> No, not in a normal stall. Rather, the wings produce insufficient lift and
> so the plane accelerates downward. The plane weathervanes into the new
> relative wind, dropping the nose.


There's more to it than that. The centre of pressure is
well behind the centre of gravity in normal flight, and as the AOA is
increased and the boundary layer begins to break up toward the aft wing
surface, the centre of pressure moves forward somewhat, helping to
raise the nose further. At the stall break, where the airflow over the
wing more or less completely breaks down, the CP moves aft again, the
stab/elevator can't hold the nose up against the suddenly increased
nose-down force, and the nose drops. That's not to say the elevator
stalled; it didn't, and elevators don't stall except under unusual
circumstances such as airframe icing or poor design such as the early
Cardinal's stabilator, where the thing would stall in the flare and
drop the nosewheel hard on the runway, sometimes breaking it. Cessna
added slots to the stab to fix that by preventing stab stall.
A stalled elevator would result in the airplane nosing
completely over onto its back in flight, since the stab/elevator's AOA
would increase as it came up, stalling it further, and control would be
totally lost. You'd never get that airplane certified.

Dan

[Andrew Sarangan[_1_]]

Peter Duniho wrote:
> "Andrew Sarangan" > wrote in message
> oups.com...
> > If the normal stall speed is 50 knots, you can make it stall at 100
> > knots if you pull some positive g's, or you can make it stall at 25
> > knots if you pull some negative g's. On the same token, you can stall
> > the airplane at higher or lower airspeeds depending on the aircraft
> > weight.
>
> Minor nit:
>
> Replace "some negative g's" with "less than 1g". Or "between -1 and +1 g",
> if you want to get really particular. :)

You are right. It is not negative g, but less than plus one g.

[Andrew Sarangan[_1_]]

Dave Doe wrote:
> > >
> >
> > The stall horn is preset to go off at a specific AOA. It does not give
> > the pilot any indication of the actual AOA being flown. AOA indicator
> > is typically used in large transport airplanes and military jets where
> > the operating envelope is large. For typical GA airplanes, the envelope
> > is so small that the airspeed indicator is a good indication of AOA
> > under normal operating conditions.
>
> Isn't the texts on AOA about *critical* AOA? - the rest of it, is surely
> the other angle - within the load envelope. The stall warning provides
> a fixed measurement of the imminent critical AOA - what else does a
> pilot need?

The only minor difference is that the stall warning does not tell you
where the critical AOA is. It just goes off at some predetermined angle
before reaching the critical AOA. However, as you say, a pilot of a GA
airplane does not need to know the exact AOA. This is why we don't have
AOA gauges in small airplanes. In fact, one could argue that you don't
even need the stall warning horn. As long as you are not doing any
high-g maneuvers, the ASI tells you how close you are to stall. The
dilemma is the lengthy discussions about AOA in texts that deal with
small airplanes. This causes all kinds of confusions that is not
helpful for the beginning pilot. You can read the archives from this
newsgroup and find how many people have been confused by this. We teach
them about AOA in the classroom, and then use the airspeed indicator in
the cockpit.

[[email protected]]

Andrew Sarangan wrote:
> Dave Doe wrote:
> > > >
> > >
> > > The stall horn is preset to go off at a specific AOA. It does not give
> > > the pilot any indication of the actual AOA being flown. AOA indicator
> > > is typically used in large transport airplanes and military jets where
> > > the operating envelope is large. For typical GA airplanes, the envelope
> > > is so small that the airspeed indicator is a good indication of AOA
> > > under normal operating conditions.
> >
> > Isn't the texts on AOA about *critical* AOA? - the rest of it, is surely
> > the other angle - within the load envelope. The stall warning provides
> > a fixed measurement of the imminent critical AOA - what else does a
> > pilot need?
>
> The only minor difference is that the stall warning does not tell you
> where the critical AOA is. It just goes off at some predetermined angle
> before reaching the critical AOA. However, as you say, a pilot of a GA
> airplane does not need to know the exact AOA. This is why we don't have
> AOA gauges in small airplanes. In fact, one could argue that you don't
> even need the stall warning horn. As long as you are not doing any
> high-g maneuvers, the ASI tells you how close you are to stall. The
> dilemma is the lengthy discussions about AOA in texts that deal with
> small airplanes. This causes all kinds of confusions that is not
> helpful for the beginning pilot. You can read the archives from this
> newsgroup and find how many people have been confused by this. We teach
> them about AOA in the classroom, and then use the airspeed indicator in
> the cockpit.

And too many students aren't taught that sudden pullups are
deadly because of the load factor. They'll buzz a friend, or take off
and hold the airplane low until they've got some "safe" airspeed, then
yank back on the elevator to get the G rush or to impress someone. Once
in a while the airplane will snap-roll right into the ground and the
guy never knew what hit him. He thought he was well above the stall
speed.

Dan

[Stefan]

Andrew Sarangan schrieb:

> dilemma is the lengthy discussions about AOA in texts that deal with
> small airplanes. This causes all kinds of confusions that is not
> helpful for the beginning pilot.

One of the most difficult things in teaching is to explain things an a
simple, but nonetheless correct way. Probably because this requires a
really profound understanding which most teachers or writers don't have.

Stefan

[Stubby]

wrote:
> Andrew Sarangan wrote:
>> Dave Doe wrote:
>>>> The stall horn is preset to go off at a specific AOA. It does not give
>>>> the pilot any indication of the actual AOA being flown. AOA indicator
>>>> is typically used in large transport airplanes and military jets where
>>>> the operating envelope is large. For typical GA airplanes, the envelope
>>>> is so small that the airspeed indicator is a good indication of AOA
>>>> under normal operating conditions.
>>> Isn't the texts on AOA about *critical* AOA? - the rest of it, is surely
>>> the other angle - within the load envelope. The stall warning provides
>>> a fixed measurement of the imminent critical AOA - what else does a
>>> pilot need?
>> The only minor difference is that the stall warning does not tell you
>> where the critical AOA is. It just goes off at some predetermined angle
>> before reaching the critical AOA. However, as you say, a pilot of a GA
>> airplane does not need to know the exact AOA. This is why we don't have
>> AOA gauges in small airplanes. In fact, one could argue that you don't
>> even need the stall warning horn. As long as you are not doing any
>> high-g maneuvers, the ASI tells you how close you are to stall. The
>> dilemma is the lengthy discussions about AOA in texts that deal with
>> small airplanes. This causes all kinds of confusions that is not
>> helpful for the beginning pilot. You can read the archives from this
>> newsgroup and find how many people have been confused by this. We teach
>> them about AOA in the classroom, and then use the airspeed indicator in
>> the cockpit.
>
> And too many students aren't taught that sudden pullups are
> deadly because of the load factor. They'll buzz a friend, or take off
> and hold the airplane low until they've got some "safe" airspeed, then
> yank back on the elevator to get the G rush or to impress someone. Once
> in a while the airplane will snap-roll right into the ground and the
> guy never knew what hit him. He thought he was well above the stall
> speed.
>

I have a video taken over the shoulder of a acrobatic pilot. He made
it through about 7/8 of a loop. I'm sure he was going quite fast and
pulling back hard to stay off the ground, but it didn't work.

[Andrew Sarangan[_1_]]

Stefan wrote:
> Andrew Sarangan schrieb:
>
> > dilemma is the lengthy discussions about AOA in texts that deal with
> > small airplanes. This causes all kinds of confusions that is not
> > helpful for the beginning pilot.
>
> One of the most difficult things in teaching is to explain things an a
> simple, but nonetheless correct way. Probably because this requires a
> really profound understanding which most teachers or writers don't have.
>
> Stefan

The problem is not the method of teaching, but the relevance of the
material being taught. We can talk at length about AOA, but we cannot
show the student how to measure it or control it in the cockpit. You
can fly the airplane just fine even if you knew nothing about AOA. It
is important for understanding of the aerodynamics of an airfoil, but
it does not help a presolo student fly an airplane. It is a concept
best introduced after mastering the basics of airplane control.

[Stefan]

Andrew Sarangan schrieb:

> The problem is not the method of teaching, but the relevance of the
> material being taught. We can talk at length about AOA, but we cannot
> show the student how to measure it or control it in the cockpit. You
> can fly the airplane just fine even if you knew nothing about AOA. It
> is important for understanding of the aerodynamics of an airfoil, but
> it does not help a presolo student fly an airplane. It is a concept
> best introduced after mastering the basics of airplane control.

Of course. But it must be taught at a later stage, because a pilot must
understand understand that stall speed depends on weight and g-load.
And, especially with laminar profiles, a lot on surface cleanness. No
scientific details needed, but this dependence must be taught and
understood.

Stefan

[Peter Duniho]

"Dave Doe" > wrote in message
. nz...
> Isn't the texts on AOA about *critical* AOA? - the rest of it, is surely
> the other angle - within the load envelope. The stall warning provides
> a fixed measurement of the imminent critical AOA - what else does a
> pilot need?

Calibrated correctly, an AOA indicator could be useful for a variety of
flight regimes, particularly when it comes to maximizing performance (best
glide, for example).

It's true that the usual student aviation texts don't discuss these things.
But that may be more about the lack of a suitable indicator in the airplane
than anything else.

Pete

[Aluckyguess]

"Peter Duniho" > wrote in message
...
> "Aluckyguess" > wrote in message
> ...
>> Bottom line the wing needs airspeed to fly. At a certain speed the wing
>> starts to lift, when it loses this speed, losing lift it stalls.
>
> IMHO, this is a misleading description of stalling, and in fact will lead
> to just the confusion the original poster describes.
>
> Specifically, the wing's speed is really not directly related to stalling
> at all. As others have explained, the reason a stall speed is published
> is that it is true that at a given weight and load factor (eg max gross
> and 1g), there is a specific amount of lift required, and there is a
> specific speed associated with the angle of attack that can produce that
> lift.
>
> The published stalling speed is simply a speed at which the angle of
> attack required to achieve the necessary lift at that speed is the same as
> the critical (stalling) angle of attack. It is not true that under all
> conditions, at that speed, the wing is stalled (or "when it loses this
> speed, losing lift it stalls"). The wing loses lift because it stalls,
> not the other way around. And the wing will only stall at a given
> airspeed if its angle of attack exceeds the critical angle of attack.
> This is true of any airspeed, above or below the published stall speed(s).
>
>> Stick your hand out the window of your car shape it like a wing at a
>> certain speed it will lift all by itself and basically be weightless.
>
> However, as long as you keep your "hand wing" angle of attack below the
> critical angle of attack, it will generate lift at ANY speed above 0.
> There is no "stalling speed" for your hand in that scenario, as your hand
> is not required to support itself with lift, and so there is no speed at
> which the required angle of attack equals or exceeds the critical angle of
> attack. (That is, there's not even a concept of "the required angle of
> attack" in that case...your hand will fly along quite happily at any
> amount of lift, or even zero lift).
>
> Pete
Try it. It wont lift until you have enough airspeed. At 0 it doesnot lift.
The higher the airspeed the higher angle of attack you can have.
>
>

[Jose[_1_]]

> As long as you are not doing any high-g maneuvers,
> the ASI tells you how close you are to stall.

Not at all.

Stall speed varies with g load. As long as you are not doing ANY
g-maneuvers (high or low or medium or "a little bit" the ASI will give
an indication of how close you are to stall. But if you are "close but
not that close" to stall, and you pull "some, but not very much"
g-force, you will come "that close" to stall.

Jose
--
"Never trust anything that can think for itself, if you can't see where
it keeps its brain." (chapter 10 of book 3 - Harry Potter).
for Email, make the obvious change in the address.

[Peter Duniho]

"Aluckyguess" > wrote in message
...
> Try it. It wont lift until you have enough airspeed. At 0 it doesnot lift.

Try what? At 0 whats, what does not lift?

If you believe that your hand, stuck out a car window, doesn't generate ANY
lift until you reach some magical airspeed, you need to educate yourself on
the topic (and please stop trying to educate others on it until you've done
so).

Lift is a direct consequence of airspeed, at any angle of attack. Whether
there is enough lift for you to feel it, or to keep an airplane aloft, that
does depend on sufficient airspeed. But lift is there, regardless, and as
long as the wing's AOA is below the critical AOA, the lift follows the
standard mathematical behavior given by the standard lift equation. That
is, it's proportional to the square of the velocity and to the angle of
attack...positive non-zero values for both of those result in a positive
non-zero value for lift, no matter how small those values.

> The higher the airspeed the higher angle of attack you can have.

Wrong. A given angle of attack will stall the wing regardless of airspeed.
If you are traveling at 1 knot, but the AOA is below the critical angle of
attack, the wing is not stalled, and *is* generating lift according to the
standard formula. Conversely, if the AOA is above the critical angle of
attack, no amount of airspeed will change the fact that the wing is stalled
(and not generating nearly as much lift as the standard formula would
indicate).

Pete

[Aluckyguess]

"Peter Duniho" > wrote in message
...
> "Aluckyguess" > wrote in message
> ...
>> Try it. It wont lift until you have enough airspeed. At 0 it doesnot
>> lift.
>
> Try what? At 0 whats, what does not lift?
>
> If you believe that your hand, stuck out a car window, doesn't generate
> ANY lift until you reach some magical airspeed, you need to educate
> yourself on the topic (and please stop trying to educate others on it
> until you've done so).
>
> Lift is a direct consequence of airspeed, at any angle of attack.
Isnt that what I said.

Whether there is enough lift for you to feel it, or to keep an airplane
aloft, that
> does depend on sufficient airspeed. So if you dont have enough airspeed
> it will still lift?
But lift is there, Where is it behind you in front of you?
>

[Peter Duniho]

"Aluckyguess" > wrote in message
...
>> Lift is a direct consequence of airspeed, at any angle of attack.
>
> Isnt that what I said.

No, it's not. You said no lift would exist below some minimum speed (that
is, the stall speed). Those are two completely different statements.

>> Whether there is enough lift for you to feel it, or to keep an airplane
>> aloft, that does depend on sufficient airspeed.
>
> So if you dont have enough airspeed it will still lift?

Yes. As I said, at any airspeed above zero, with any angle of attack above
zero, there is lift. It may be less lift than you have weight, but there is
still lift.

If your airplane is at max gross and you are flying below the stall speed
for that configuration, you won't be able to increase the angle of attack of
the wing enough to generate enough lift to keep the airplane from
accelerating toward the ground. The angle of attack required at that
airspeed in order to get as much lift as you have weight is higher than the
critical angle of attack. But as long as you keep the angle of attack low
enough, the wing still generates lift.

(And to further complicate things, the wing still generates lift even above
the critical angle of attack...it's just that the lift generated is a small
fraction of that generated when below the critical angle of attack).

> But lift is there, Where is it behind you in front of you?

I have no idea what you're asking. The lift is always perpendicular to the
relative wind. It's not "behind" or "in front".

Pete

[Andrew Sarangan[_1_]]

Aluckyguess wrote:
> >
> > Pete
> Try it. It wont lift until you have enough airspeed. At 0 it doesnot lift.
> The higher the airspeed the higher angle of attack you can have.


Not true. You can have lift even at 1 knot airspeed. It may not be
enough to lift the whole airplane, but it is still aerodynamic lift.
Even at 1 knot, the wing may not be stalled. It all depends on the
angle of attack, not the airspeed.

The higher the airspeed the higher the lift at a given angle of attack.
But airspeed does not have anything to do with the maximum angle of
attack you can have.

[Ron Natalie]

Andrew Sarangan wrote:
> Aluckyguess wrote:
>>> Pete
>> Try it. It wont lift until you have enough airspeed. At 0 it doesnot lift.
>> The higher the airspeed the higher angle of attack you can have.
>
>
> Not true. You can have lift even at 1 knot airspeed. It may not be
> enough to lift the whole airplane, but it is still aerodynamic lift.
> Even at 1 knot, the wing may not be stalled. It all depends on the
> angle of attack, not the airspeed.

And mechanics and homebuilders need to be aware of this when weighing
their aircraft. Even a slight breeze can lighten the load on the scales.

[Aluckyguess]

"Andrew Sarangan" > wrote in message
oups.com...
>
> Aluckyguess wrote:
>> >
>> > Pete
>> Try it. It wont lift until you have enough airspeed. At 0 it doesnot
>> lift.
>> The higher the airspeed the higher angle of attack you can have.
>
>
> Not true. You can have lift even at 1 knot airspeed.
Im not saying you wont.
It may not be
> enough to lift the whole airplane,
Exacty what I said. Or you hand.

but it is still aerodynamic lift.
i agreee
> Even at 1 knot, the wing may not be stalled. It wont be generating enough
> lift to carry the plane, I may be wrong but when a wing isnt flying
> anymore it is stalled.
It all depends on the
> angle of attack,not the airspeed. Not true.
>
> The higher the airspeed the higher the lift at a given angle of attack.
Now you get it.
> But airspeed does not have anything to do with the maximum angle of
> attack you can have.
No that would depend on a number of other things.
>

[mike regish]

Consider vertical flight. You can have 0 airspeed and not be stalled. Hope
the plane's built for tailslides, though.

mike

"Andrew Sarangan" > wrote in message
oups.com...
>
> Aluckyguess wrote:
>> >
>> > Pete
>> Try it. It wont lift until you have enough airspeed. At 0 it doesnot
>> lift.
>> The higher the airspeed the higher angle of attack you can have.
>
>
> Not true. You can have lift even at 1 knot airspeed. It may not be
> enough to lift the whole airplane, but it is still aerodynamic lift.
> Even at 1 knot, the wing may not be stalled. It all depends on the
> angle of attack, not the airspeed.
>
> The higher the airspeed the higher the lift at a given angle of attack.
> But airspeed does not have anything to do with the maximum angle of
> attack you can have.
>

[Andrew Sarangan[_1_]]

Aluckyguess wrote:

> >
> > The higher the airspeed the higher the lift at a given angle of attack.
> Now you get it.

> > But airspeed does not have anything to do with the maximum angle of
> > attack you can have.
> No that would depend on a number of other things.


I am not sure what you mean by this. This is what you said in your
post:
"The higher the airspeed the higher angle of attack you can have."
which is clearly not the case.

[Aluckyguess]

"mike regish" > wrote in message
. ..
> Consider vertical flight. You can have 0 airspeed and not be stalled. Hope
> the plane's built for tailslides, though.

So then your not flying on the wing your flying on the prop. This is more
like a rocket.
>
> mike
>
> "Andrew Sarangan" > wrote in message
> oups.com...
>>
>> Aluckyguess wrote:
>>> >
>>> > Pete
>>> Try it. It wont lift until you have enough airspeed. At 0 it doesnot
>>> lift.
>>> The higher the airspeed the higher angle of attack you can have.
>>
>>
>> Not true. You can have lift even at 1 knot airspeed. It may not be
>> enough to lift the whole airplane, but it is still aerodynamic lift.
>> Even at 1 knot, the wing may not be stalled. It all depends on the
>> angle of attack, not the airspeed.
>>
>> The higher the airspeed the higher the lift at a given angle of attack.
>> But airspeed does not have anything to do with the maximum angle of
>> attack you can have.
>>
>
>

[mike regish]

Not really. You're flying on inertia and prop thrust. You wing will provide
lift with the lift vector horizontal, but when your speed decays to zero,
even though at that point the wing is not providing any lift, it is not
stalled nor has it stalled at any point.

mike

"Aluckyguess" > wrote in message
...
>
> "mike regish" > wrote in message
> . ..
>> Consider vertical flight. You can have 0 airspeed and not be stalled.
>> Hope the plane's built for tailslides, though.
>
> So then your not flying on the wing your flying on the prop. This is more
> like a rocket.
>>
>> mike

[Peter Duniho]

"Aluckyguess" > wrote in message
...
>> Consider vertical flight. You can have 0 airspeed and not be stalled.
>> Hope the plane's built for tailslides, though.
>
> So then your not flying on the wing your flying on the prop. This is more
> like a rocket.

IMHO, it was a well-intended but poor example. At 0 airspeed, there is 0
pounds of lift.

The reason the example was well-intended is that it's a scenario in which
you could be moving, but in which the airplane is supported by something
other than the wing, and so the wing need not generate lift equal to weight
(as it normally would). In this case, some airspeed below the stalling
speed is fine, and the wing is not stalled. As Mike says, even if the
airspeed falls to 0, the wing never stalls.

Pete

[Doug[_1_]]

But the airspeed is NOT zero. The propeller is causing moving air to be
pushed over the surface of the wings!!

Peter Duniho wrote:
> "Aluckyguess" > wrote in message
> ...
> >> Consider vertical flight. You can have 0 airspeed and not be stalled.
> >> Hope the plane's built for tailslides, though.
> >
> > So then your not flying on the wing your flying on the prop. This is more
> > like a rocket.
>
> IMHO, it was a well-intended but poor example. At 0 airspeed, there is 0
> pounds of lift.
>
> The reason the example was well-intended is that it's a scenario in which
> you could be moving, but in which the airplane is supported by something
> other than the wing, and so the wing need not generate lift equal to weight
> (as it normally would). In this case, some airspeed below the stalling
> speed is fine, and the wing is not stalled. As Mike says, even if the
> airspeed falls to 0, the wing never stalls.
>
> Pete

[mike regish]

That was meant to be my point.

Maybe not perfectly stated.

mike

"Peter Duniho" > wrote in message

> As Mike says, even if the airspeed falls to 0, the wing never stalls.
>
> Pete
>

[Peter Duniho]

"Doug" > wrote in message
oups.com...
> But the airspeed is NOT zero. The propeller is causing moving air to be
> pushed over the surface of the wings!!

It may or may not be. But there's no reason to assume that it is. An
airplane with a pusher propeller, or a jet, or a sailplane, or whatever,
would behave in exactly the same way.