A Level 1 AOA clarification

"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.