Editing Lift (force) (section)

===Angle of attack===
{{main|Angle of attack}}
[[Image:Airfoil angle of attack.jpg|thumb|300px|Angle of attack of an airfoil]]
The [[angle of attack]] is the angle between the [[Chord (aeronautics)|chord line]] of an airfoil and the oncoming airflow. A symmetrical airfoil generates 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 generates a lift force roughly proportional to the angle of attack.<ref>"You can argue that the main lift comes from the fact that the wing is angled slightly upward so that air striking the underside of the wing is forced downward. The Newton's 3rd law reaction force upward on the wing provides the lift. Increasing the angle of attack can increase the lift, but it also increases drag so that you have to provide more thrust with the aircraft engines" ''Hyperphysics'' Georgia State University Dept. of Physics and Astronomy {{cite web|url=http://hyperphysics.phy-astr.gsu.edu/hbase/fluids/angatt.html|title=Angle of Attack for Airfoil|access-date=26 July 2012|url-status=dead|archive-url=https://web.archive.org/web/20121014185450/http://hyperphysics.phy-astr.gsu.edu/hbase/fluids/angatt.html|archive-date=October 14, 2012}}</ref><ref>"If we enlarge the angle of attack we enlarge the deflection of the airstream by the airfoil. This results in the enlargement of the vertical component of the velocity of the airstream... we may expect that the lifting force depends linearly on the angle of attack. This dependency is in complete agreement with the results of experiments..." Klaus Weltner ''A comparison of explanations of the aerodynamic lifting force'' Am. J. Phys. 55(1), January 1987 p. 52</ref>

As the angle of attack increases, the lift reaches a maximum at some angle; increasing the angle of attack beyond this [[Angle of attack#Critical angle of attack|critical angle of attack]] causes the upper-surface flow to separate from the wing; there is less deflection downward so the airfoil generates less lift. The airfoil is said to be [[Stall (flight)|stalled]].<ref>"The decrease[d lift] of angles exceeding 25° is plausible. For large angles of attack we get turbulence and thus less deflection downward." Klaus Weltner ''A comparison of explanations of the aerodynamic lifting force'' ''Am. J. Phys.'' 55(1), January 1987 p. 52</ref>