Stalls - Angle of Attack versus Vstall

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

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.

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

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.

"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 he
http://www.av8n.com/how/

--Gary

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

"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 he
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

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.

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.

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.