A Level 1 AOA clarification

Andrew Sarangan wrote:

a. is dependent on its airspeed, and is independent of its weight
and
weight distribution, and

No, the stall AOA is independent of both airspeed and weight.

Too confusing

Getting back to basics, wings produce lift only when wind hits them,
i.e. when the aircraft starts moving. This keeps increasing until the
airspeed is adequate enough to produce a total lift that can levitate
the aircraft. Since the angle of the wings can't be varied, ignoring
flaps momentarily, I can't see how the stall AOA can be independent of
airspeed. What then is 'stall speed' of an airplane?

If stalling AOA is reached, adding engine power before the plane goes
into a stall will prevent the stall by increasing airspeed, right?

b. varies, for a given airspeed, with the air density (altitude)

No the stall AOA does not vary with density.

The stall AOA is determined by the shape of the wing. It is
independent of
weight and airspeed. However, the airspeed vs AOA relationship
depends on a
variety of factors, such as weight and density. This is why stall
speed is
somewhat a misleading quantity. AOA would be a better quantity.
Unfortunately there is no direct way to measure the AOA in most
aircraft,
so we use the airspeed as an indirect indication of the AOA.

Don't know much yet about this but I'm sure I saw the AOA indicated in
an A320 cockpit recently. I thought the pitch itself indicated AOA but
when the captain showed me the actual AOA reading, it varied by a wee
from the aircraft's pitch. He had to punch some buttons into the flight
computer to get the AOA reading.

Need to read up John Denker's book and the FAA material a lotttt more,
I guess :\

Ramapriya

"Ramapriya" wrote in
ups.com:

Andrew Sarangan wrote:

a. is dependent on its airspeed, and is independent of its weight
and
weight distribution, and

No, the stall AOA is independent of both airspeed and weight.

Too confusing

Getting back to basics, wings produce lift only when wind hits them,
i.e. when the aircraft starts moving. This keeps increasing until the
airspeed is adequate enough to produce a total lift that can levitate
the aircraft. Since the angle of the wings can't be varied, ignoring
flaps momentarily, I can't see how the stall AOA can be independent of
airspeed. What then is 'stall speed' of an airplane?

I see where you are getting the misconceptions from. You are thinking of
the takeoff and landing as the start and end of flight. Just because an
aircraft is on the ground does not mean it is stalled. Instead, picture
an aircraft in mid flight. Then imagine what happens if you increase the
angle of attack. The airflow over the wings will start to break up. This
is the start of stall.This point is only related to the angle at which
the airstream strikes the wing.

Think of the AOA as the difference between the angle where the aircraft
is pointing and where it is going.




If stalling AOA is reached, adding engine power before the plane goes
into a stall will prevent the stall by increasing airspeed, right?

b. varies, for a given airspeed, with the air density (altitude)

No the stall AOA does not vary with density.

The stall AOA is determined by the shape of the wing. It is
independent of
weight and airspeed. However, the airspeed vs AOA relationship
depends on a
variety of factors, such as weight and density. This is why stall
speed is
somewhat a misleading quantity. AOA would be a better quantity.
Unfortunately there is no direct way to measure the AOA in most
aircraft,
so we use the airspeed as an indirect indication of the AOA.

Don't know much yet about this but I'm sure I saw the AOA indicated in
an A320 cockpit recently. I thought the pitch itself indicated AOA but
when the captain showed me the actual AOA reading, it varied by a wee
from the aircraft's pitch. He had to punch some buttons into the
flight computer to get the AOA reading.

True, some of the larger aircraft and military jets have an AOA
indicator. Most small aircraft do not have an AOA indicator. There is a
good reason for this. In a large aircraft, the weight can vary
substantially over its flight envelope. This will result in a large
variation in stall speed. In a small aircraft, the stall speed variation
is rather small, and a single stall speed can be used safely.





Need to read up John Denker's book and the FAA material a lotttt more,
I guess :\


No, you need to take a couple of flying lessons.

Andrew Sarangan wrote:
True, some of the larger aircraft and military jets have an AOA
indicator. Most small aircraft do not have an AOA indicator. There is a
good reason for this. In a large aircraft, the weight can vary
substantially over its flight envelope. This will result in a large
variation in stall speed. In a small aircraft, the stall speed variation
is rather small, and a single stall speed can be used safely.

IMHO, there is no good reason for not having an AOA indicator on GA
aircraft. Stall/spin is a leading cause of death among GA pilots and
passengers. Best glide (potential emergency situation) is determined by
AOA. Put an AOA sensor on GA planes with a hand that smacks the pilot on
the head when the AOA approaches the critical AOA and a lot fewer people
will die while having fun on the weekends.

Hilton

"Hilton" wrote in message
link.net...
Andrew Sarangan wrote:
True, some of the larger aircraft and military jets have an AOA
indicator. Most small aircraft do not have an AOA indicator. There is a
good reason for this. In a large aircraft, the weight can vary
substantially over its flight envelope. This will result in a large
variation in stall speed. In a small aircraft, the stall speed variation
is rather small, and a single stall speed can be used safely.

IMHO, there is no good reason for not having an AOA indicator on GA
aircraft. Stall/spin is a leading cause of death among GA pilots and
passengers. Best glide (potential emergency situation) is determined by
AOA. Put an AOA sensor on GA planes with a hand that smacks the pilot on
the head when the AOA approaches the critical AOA and a lot fewer people
will die while having fun on the weekends.

Hilton


The April, 1973 (yeah, that's a while ago) issue of FLYING had a great
article about Safe Flight's AOA indicator. Peter Garrison described it as
"phenomenally useful", after flying a Beech Sierra equipped with one.

Stall/spin is a leading cause of death among GA pilots and
passengers.

Caused by the pilot not paying attention. Will having another
instrument that he's not paying attention to really help?

Best glide (potential emergency situation) is determined by AOA.

A few knots either way isn't going to make much difference. Plus, how
often is maximum glide range critical in an engine out situation? How
closely is the pilot really maintaining one airspeed (or AOA) during
an emergency?

Put an AOA sensor on GA planes with a hand that smacks the pilot on
the head

Some studies I've seen have shown that pilots are often oblivious to
warning horns and lights, though stick shakers are effective.

My prediction: put an AOA indicator on every airplane in the fleet
and you won't see much change in the accident rate due to stall spin.

Greg Esres wrote:
Stall/spin is a leading cause of death among GA pilots and
passengers.

Caused by the pilot not paying attention. Will having another
instrument that he's not paying attention to really help?

Yes, *if* the AOA is effectively communicated to the pilot. I'm not
suggesting we just stick a few LEDs on the panel. I would want to see some
audio piped into the headset, and/or a stick-shaker etc. I find it amazing
that everyone jumps all over this new GPS whizbang stuff - is it going to
increase or decrease the accident rate? I don't know. But a simple AOA
detector that will directly reduce the number of accidents and fatalities
goes completely ignored.


Best glide (potential emergency situation) is determined by AOA.

A few knots either way isn't going to make much difference. Plus, how
often is maximum glide range critical in an engine out situation?

Take a look at the fuel exhaustion/starvation accidents - they always seem
to 'land' a mile or two from their destination.



How
closely is the pilot really maintaining one airspeed (or AOA) during
an emergency?

I don't know - I haven't seen any research on this one.


Put an AOA sensor on GA planes with a hand that smacks the pilot on
the head

Some studies I've seen have shown that pilots are often oblivious to
warning horns and lights, though stick shakers are effective.

Lights are useless - the Arrow's stall light is embarrasing. Stall
'buzzers' are OK. So, let's figure out something new, or how about stick
shakers on GA aircraft. Just throwing up our arms while people continue to
die is not good enough.


My prediction: put an AOA indicator on every airplane in the fleet
and you won't see much change in the accident rate due to stall spin.

I completely disagree (if done correctly - see above).

Hilton

Yes, *if* the AOA is effectively communicated to the pilot.

You're really just talking about a more effective stall warning
system. Fine.

But a simple AOA detector that will directly reduce

Hypothesis. Skydivers point out that in spite of all the new safety
equipment they have these days, the fatality rate stays about the
same. People will always push the limits to achieve what they
consider an "acceptable" risk.

Consider that the unstallable airplanes such as the Ercoupe didn't
show any improvement in accident rates.

Just throwing up our arms while people continue to
die is not good enough.

The sure-fire way to reduce the fatality rate is to add ballistic
parachutes to our aircraft....no, wait, that hasn't worked either.
;-)

I don't know the solution to the problem. It may be an unavoidable
aspect of our freedom to fly.

Greg Esres wrote:
Yes, *if* the AOA is effectively communicated to the pilot.

You're really just talking about a more effective stall warning
system. Fine.

Both really (indicator and stall warning), but yes, a more effective stall
warning system would literally be the life saver.


But a simple AOA detector that will directly reduce

Hypothesis.

Are you contradicting your previous comment: "Some studies I've seen have
shown that pilots are often oblivious to warning horns and lights, though
stick shakers are effective."?


The sure-fire way to reduce the fatality rate is to add ballistic
parachutes to our aircraft....no, wait, that hasn't worked either. ;-)

I see the parachute guys got a mention on CNN. I wonder if/when the
research will start about the effect they have on a pilot's thinking,
decision making, and risk assesment. I know one was 'fired' when an aileron
became detached - was the plane really uncontrollable? Maybe, I'm not going
to doubt the pilot's remarks. But what about the other ones, and the
accidents where a pilot *perhaps* fly into 'unsuitable' conditions. BTW:
I'm also writing this in future tense.


I don't know the solution to the problem. It may be an unavoidable
aspect of our freedom to fly.

I'd like to think it's a solvable problem, or at least reducable.

Hilton

I agree that AOA is a nice instrument to have, but I am not convinced if
that is going to reduce the number of stall spin accidents. Most stall spin
accidents despite all stall indications, such as low airspeed, buffet and
descent rate. Having another instrument on the panel is not going to change
the situation.



"Hilton" wrote in news:5_Azd.10136$9j5.3520
@newsread3.news.pas.earthlink.net:

Andrew Sarangan wrote:
True, some of the larger aircraft and military jets have an AOA
indicator. Most small aircraft do not have an AOA indicator. There is a
good reason for this. In a large aircraft, the weight can vary
substantially over its flight envelope. This will result in a large
variation in stall speed. In a small aircraft, the stall speed variation
is rather small, and a single stall speed can be used safely.

IMHO, there is no good reason for not having an AOA indicator on GA
aircraft. Stall/spin is a leading cause of death among GA pilots and
passengers. Best glide (potential emergency situation) is determined by
AOA. Put an AOA sensor on GA planes with a hand that smacks the pilot on
the head when the AOA approaches the critical AOA and a lot fewer people
will die while having fun on the weekends.

Hilton

Well, not to dispute the thrust of your argument, but your statistics
are wrong... CFIT is the leading cause of injury and death in GA...
Stall/spin crashes in vfr flight are down the list a ways..

Now, if the pilot is incapable of noticing the air speed indicator well
down into the white arc, or is incapable of noticing that the nose is
well up, or that he is pulling G's while stomping top rudder, what
makes us suspect that he will notice the AOA needle in the red?

Denny