Stalls - Angle of Attack versus Vstall

"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

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?"

"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.


--

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".

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

"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

"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

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.

In article . com,
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

"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.
--
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