Editing Stall (fluid dynamics) (section)

==Spoilers==
{{Main|Spoiler (aeronautics)}}
Except for flight training, airplane testing, and [[aerobatics]], a stall is usually an undesirable event. [[spoiler (aeronautics)|Spoilers]] (sometimes called lift dumpers), however, are devices that are intentionally deployed to create a carefully controlled [[flow separation]] over part of an aircraft's wing to reduce the lift it generates, increase the drag, and allow the aircraft to descend more rapidly without gaining speed.<ref>{{cite web|title=Spoilers|url=http://www.grc.nasa.gov/WWW/K-12/airplane/spoil.html|publisher=NASA, [[Glenn Research Center]]}}</ref> Spoilers are also deployed asymmetrically (one wing only) to enhance roll control. Spoilers can also be used on aborted take-offs and after main wheel contact on landing to increase the aircraft's weight on its wheels for better braking action.

Unlike powered airplanes, which can control descent by increasing or decreasing thrust, gliders have to increase drag to increase the rate of descent. In high-performance gliders, spoiler deployment is extensively used to control the approach to landing.

Spoilers can also be thought of as  "lift reducers" because they reduce the lift of the wing in which the spoiler resides. For example, an uncommanded roll to the left could be reversed by raising the right wing spoiler (or only a few of the spoilers present in large airliner wings). This has the advantage of avoiding the need to increase lift in the wing that is dropping (which may bring that wing closer to stalling).