Question: What is an angle attack?
About the article "Beach volleyball", section "Common block signals".

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When the angle of attack is less than the stalling angle any increase in angle of attack causes an increase in lift coefficient that causes the wing to rise.
As the wing rises the angle of attack and lift coefficient decrease which tend to restore the wing to its original angle of attack.
Conversely any decrease in angle of attack causes a decrease in lift coefficient which causes the wing to descend.
As the wing descends, the angle of attack and lift coefficient increase which tends to restore the wing to its original angle of attack.
For this reason the angle of attack is stable when it is less than the stalling angle.
The aircraft displays damping in roll.
When the wing is stalled and the angle of attack is greater than the stalling angle any increase in angle of attack causes a decrease in lift coefficient that causes the wing to descend.
As the wing descends the angle of attack increases, which causes the lift coefficient to decrease and the angle of attack to increase.
Conversely any decrease in angle of attack causes an increase in lift coefficient that causes the wing to rise.
As the wing rises the angle of attack decreases and causes the lift coefficient to increase further towards the maximum lift coefficient.
For this reason the angle of attack is unstable when it is greater than the stalling angle.
Any disturbance of the angle of attack on one wing will cause the whole wing to roll spontaneously and continuously.
When the angle of attack on the wing of an aircraft reaches the stalling angle the aircraft is at risk of autorotation.
This will eventually develop into a spin if the pilot does not take corrective action. 
The angle of attack is the angle between an airfoil and the oncoming air.
A symmetrical airfoil will generate zero lift at zero angle of attack.
But as the angle of attack increases, the air is deflected through a larger angle and the vertical component of the airstream velocity increases, resulting in more lift.
For small angles a symmetrical airfoil will generate a lift force roughly proportional to the angle of attack.
As the angle of attack grows larger, the lift reaches a maximum at some angle; increasing the angle of attack beyond this critical angle of attack causes the air to become turbulent and separate from the wing; there is less deflection downward so the airfoil generates less lift.
The airfoil is said to be stalled.
Cambered airfoils will generate lift at zero angle of attack.
When the chordline is horizontal, the trailing edge has a downward direction and since the air follows the trailing edge it is deflected downward.
When a cambered airfoil is upside down, the angle of attack can be adjusted so that the lift force is upwards.
This explains how a plane can fly upside down. 
When an aircraft is in straight and level flight at cruise speed, the propeller disc is perpendicular to the relative wind.
Each of the propeller blades will contact the air at the same angle and speed and thus the thrust produced is evenly centered across the propeller.
As the aircraft's angle of attack increases and the propeller disc rotates toward the horizontal, the airflow will meet the propeller disc at an increasing angle.
The propeller blades moving down and forward (from the one o'clock to the six o'clock position when viewed from the front) will have a greater relative wind velocity and therefore will produce greater thrust, while propeller blades moving up and back (from the seven o'clock thru 12 o'clock position) will have a decreased relative wind velocity and therefore decreased thrust.
This asymmetry displaces the center of thrust of the propeller disc towards the blade with increased thrust.
In an aircraft with two or more propeller engines, P-Factor is what determines which engine is the critical engine.
-Factor is sometimes erroneously explained with the word "bite", as in "the descending blade has a bigger bite, or angle of attack, than the ascending blade".
This faulty explanation does not take into account the forward motion of the blades as aircraft's angle of attack increases.
In order to better understand this concept, imagine a propeller aircraft moving forward with a 90° angle of attack (vertical).
This situation is identical to what a helicopter experiences, but a helicopter can reduce or increase the angle of attack of individual blades of the rotor (decreasing the angle of attack on the advancing blade, while increasing the angle of attack on the retreating blade) in order to keep the lift of the rotor disc balanced.
Because the force of the air on the blades moving forwards through the arc is greater, they will produce more thrust than the blades that move backwards.
If the blades of the rotor were unable to independently change their angle of attack there would be a constant backwards rolling motion due to the increased lift on the side of the rotor disc with the advancing blade.
In a fixed-wing aircraft, there is usually no way to adjust the angle of attack of the individual blades of the propellers, therefore the pilot must contend with P-Factor and use the rudder to counteract the shift of thrust. 
 of fixed-wing aircraft.
The term can also be applied to horizontal surfaces in general (such as canards or horizontal stabilizers) for the angle they make relative the longitudinal axis of the fuselage.
The figure to the right shows a side view of an airplane.
The extended chord line of the wing root (red line) makes an angle with the longitudinal axis (roll axis) of the aircraft (blue line).
Wings are typically mounted at a small positive angle of incidence, to allow the fuselage to be have a low angle with the airflow in cruising flight.
Angles of incidence of about 6° are common on most general aviation designs.
Other terms for angle of incidence in this context are "rigging angle" and "rigger's angle of incidence".
It should not be confused with the angle of attack, which is the angle the wing chord presents to the airflow in flight.
Note that some ambiguity in this terminology exists, as some engineering texts that focus solely on the study of airfoils and their medium may use either term when referring to angle of attack.
The use of the term "angle of incidence" to refer to the angle of attack occurs chiefly in British usage. 
In sailing, the physical principles involved are the same as for aircraft.
A sail's angle of attack is the angle between the sail's chord line and the direction of the wind.
A boat's angle of attack is the angle between the boat's course and the wind direction.
See points of sail.