Stalls - Angle of Attack versus Vstall

"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

"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

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.

"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

"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 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.