A Level 1 AOA clarification

Ramapriya wrote:

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

I'll try to simplify it a bit. An angle of attack is the angle at which the wing
"attacks" the air. If the air is relatively stable and you raise the nose, you
have just increased the angle of attack. Lower the nose, the angle decreases.

Ok so far?

Now. The stall angle of attack is the angle at which the airflow over the wing
won't follow the curve of the wing anymore. The wing is tilted up too steeply
relative to the airflow. If I undrestand him correctly, Andrew is stating that
the angle of attack at which this occurs is the same regardless of airspeed. I
believe he is incorrect in this - definitely my aircraft will stall at a much
lower angle of attack at 50 mph than at 60 mph, and I've never been brave enough
to get the nose high enough to stall it at higher airspeeds.

Now, there *is* a misconception that stall airspeeds are constant, and this is
not true. The way the truth is usually phrased is "an airplane can stall at any
speed." You can exceed the stall angle of attack while flying perfectly level at
a pretty fair speed if you fly into a wind that is blowing up a steep slope.
There are also "high-speed" stalls caused by attempting to maneuver too rapidly
at high speed.

The true airspeed at which a stall occurs also increases with density altitude.
This is not usually a factor for light aircraft, since the indicated airspeed
for a given true airspeed decreases at the same rate. In other words, if your
plane has a pitot tube and stalls at 60 knots indicated, it will stall in that
configuration at that speed at any altitude it can reach. If the aircraft is
equipped with an indicator that reports true airspeed, however, stall speed is
not constant.

I do not know whether or not the stall angle of attack changes with weight, but
the stall airspeed in any configuration increases as weight increases. Paul's
points on the effects of loading and the downforce produced by the tail surfaces
are also good.

George Patterson
The desire for safety stands against every great and noble enterprise.