Angle of Attack - A Simple, Non-technical Explanation

A Simple, Non-technical Explanation

The angle of attack can be simply described as "the angle at which relative wind meets an airfoil. It is the angle that is formed by the chord of the airfoil and the direction of the relative wind or between the chord line and the flight path."

While a wing's angle of attack is less than its critical angle (which will vary for different wings depending on the shape of the aerofoil) there will not be enough lift generated for flight. If the critical angle is exceeded, the wing will stall. This can happen at any speed above the so-called ‘slow stall speed.’ A wing does NOT stall because it is going at, or less, than what is called the ‘slow stall speed.’ When the wing is moving into the relative wind at that speed or less, it does not generate sufficient lift, resulting in the critical angle of attack being exceeded because of gravity. The wing may be pointing parallel to the ground but gravity is pulling it down so the difference between where it is pointing and where it is going exceeds the critical angle and the wing stalls. In the event the aircraft is rotating about its yaw axis, the aircraft is said to be in a flat spin.

High Speed Stalls. A wing can stall at any speed above the ‘slow stall speed’ for the same reason. For example, an aircraft may go into a steep dive. At the bottom of the dive the pilot may pull back on the stick to make the aircraft flatten out and then climb. If done too quickly, or because of poor aircraft design, the wings can be pointing up but momentum i.e. gravity, continues to make the aircraft go down. If the wings are pointing up but the direction of travel is down the critical angle is exceeded and a high speed stall occurs.

To counter a stall the pilot pushes the stick forward, or applies power, or does both. Pushing the stick forward makes the direction of pointing and travel go below the critical angle and gravity accelerates the aircraft so the wing starts producing lift and therefore goes into an unstalled condition. That is, the direction of travel and pointing direction come in to harmony. Adding power can prevent the aircraft dropping very far because of gravity (which is very useful if near the ground) but the nose still needs to be lowered which again reduces the angle of attack below the critical level. See washout (aviation) for details.