# Stall Aerodynamics

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Check out the video above to have a look at what actually happens to the airflow over the wing of an airplane when it stalls.

#### Lift and the Center of Pressure

Two important things to notice from the diagrams above.

More lift is generated at higher angles of attack. Note that with more lift, however, you generate substantially more drag, which will slow down the airplane, causing a reduction in lift, which will make you want to pitch up and increase angle of attack more to maintain altitude; but this just causes more drag, and you quickly find yourself having stalled the wing. This is why the airplane stalls at the point of maximum lift.

The CENTER OF PRESSURE moves forward with increasing angles of attack.  The low-pressure air begins to move further toward the leading edge of the wing (generally activating the stall warning device mounted on the leading edge of the wing if your aircraft happens to have one).

#### Stall Progression

The stall begins at the wing root and works its way out to the wingtips.  Most GA airplanes are designed this way to give you at least some aileron control to keep your wings level when you are approaching a stall.  While this is a nice design feature, don’t rely on it too much, as you can see how quickly the wing goes from flying to stalled, and ailerons can certainly be enough to push you past the edge of say 15 degrees Angle of Attack to 16 degrees Angle of Attack and be a cause of the stall when you are already flying at too high an Angle of Attack. Remember, this is because, by using aileron and making one wing rise while lowering the other, you are also increasing the Angle of Attack on the rising wing, and slowing it slightly if you are not using rudder to properly compensate for adverse yaw. Indicators of a stall can include:

Feel:

• The pilot will feel control pressures changes in the flight controls as airspeed diminishes. As less air is being pushed against control surfaces, larger control inputs are needed to get the desired aircraft response. There will be a noticeable increase in the time between the control movement and aircraft reaction. Right before the stall; buffeting, roll, or vibrations may begin to occur.

Hearing:

• As speed diminishes, you should notice a change in the sound of the airflow hitting the structure of the airplane.

Sensation:

• Referred to as “seat of the pants” sensations, changes in direction or speed can be detected by the trained and experienced pilot. This sense, if properly developed, can warn the pilot of an impending stall.

#### There is only one answer.

You can argue that increasing power, speeding up, and pitching nose down can all help you recover from a stall.  However, the ONLY one right answer that is totally correct when asked “How do you recover from a stall?” is to reduce the angle of attack.  There are many WAYS you can reduce the AOA, but the most surefire way on most GA airplanes is going to involve stop pulling back on the controls and possibly pushing forward on them.  The other minor details your CFI can fill in for you.