View source for Downwash

{{Short description|Change in direction of air by rotor blade}}
[[File:US Navy 050419-N-5313A-414 Search and Rescue (SAR) swimmers attached to the Kearsarge Expeditionary Strike Group conduct search and rescue training during routine helicopter operations.jpg|thumb|upright=1.14|The effect of downwash from a hovering [[Sikorsky Seahawk]] is clearly visible on the surface of water below.]]

In aeronautics, '''downwash''' is the change in direction of air deflected by the aerodynamic action of an [[airfoil]], [[wing]], or [[helicopter rotor]] blade in motion, as part of the process of producing [[lift (force)|lift]].<ref name="Crane">Crane, Dale: ''Dictionary of Aeronautical Terms, third edition'', page 172. Aviation Supplies & Academics, 1997. {{ISBN|1-56027-287-2}}</ref> In helicopter aerodynamics discussions, it may be referred to as '''induced flow'''.<ref name="ALC104">{{cite web |title=ALC-104: Helicopter - General and Flight Aerodynamics |url=https://www.faasafety.gov/gslac/alc/course_content_popup.aspx?cID=104&sID=451 |website=www.faasafety.gov |publisher=Federal Aviation Authority |access-date=18 January 2022}}</ref>

Lift on an airfoil is an example of the application of [[Newton's laws of motion#Newton's third law|Newton's third law of motion]] – the force required to deflect the air in the downwards direction is equal in magnitude and opposite in direction to the lift force on the airfoil. Lift on an airfoil is also an example of the [[Kutta-Joukowski theorem]]. The [[Kutta condition]] explains the existence of downwash at the [[trailing edge]] of the wing.<ref name="Crane" /><ref name="Anderson_Flight_5.19">{{citation
| last=Anderson
| first=John D.
| title=Introduction to Flight
| year=2004
| edition=5th
| publisher=McGraw-Hill
| isbn=0-07-282569-3
| pages=352–361, §5.19
}}</ref><ref name=Langewiesche_6_10>"The main fact of all heavier-than-air flight is this: ''the wing keeps the airplane up by pushing the air down.''" In: {{citation
| first1=Wolfgang
| last1=Langewiesche
| title=Stick and Rudder: An Explanation of the Art of Flying
| publisher=McGraw-Hill
| year=1990
| isbn=0-07-036240-8
| pages=[https://archive.org/details/stickrudderexp00lang/page/6 6–10]
| url-access=registration
| url=https://archive.org/details/stickrudderexp00lang/page/6
}}</ref><ref>{{cite web |url=https://www1.grc.nasa.gov/beginners-guide-to-aeronautics/downwash-effects-on-lift/ |title=Downwash Effects on Lift |work=nasa.gov |accessdate=9 February 2023}}</ref>

==See also==
*[[Brownout (aeronautics)]]
*[[Jet blast]]
*[[Slipstream]]
*[[Wake turbulence]]
*[[Wingtip vortices]]

==References==
{{Commons category|Downwash (fluid dynamics)}}
{{Reflist}}

{{Authority control}}

[[Category:Aerodynamics]]
[[Category:Vortices]]