View source for Aerodynamic force

{{Short description|Force exerted on a body as it moves through a fluid}}
[[File:Airfoil lift and drag.svg|thumb|right|300px|The aerodynamic force is the resultant [[Euclidean vector|vector]] from adding the lift vector, perpendicular to the flow direction, and the drag vector, parallel to the flow direction.]]
[[Image:aeroforces.svg|thumb|Forces on an [[aerofoil]].]]

In [[fluid mechanics]], an '''aerodynamic force''' is a [[force]] exerted on a body by the [[air]] (or other [[gas]]) in which the body is immersed, and is due to the [[relative motion]] between the body and the gas.

==Force==
There are two causes of [[aerodynamics|aerodynamic]] force:
<ref name=":0">{{Cite book|last=Clancy|first=L.J.|title=Aerodynamics|date=1978|publisher=Wiley|isbn=0-273-01120-0|location=New York|oclc=16420565}}</ref>{{rp|§4.10}}<ref>{{Cite book|last=Massey, B. S. (Bernard Stanford)|title=Mechanics of fluids|date=1998|publisher=S. Thornes|others=Ward-Smith, A. J. (Alfred John)|isbn=0-7487-4043-0|edition=7th|volume=2|location=Cheltenham, England|chapter=10.8.2|oclc=40928151}}</ref><ref name=":1">{{Cite book|last=Hurt|first=H.H. Jr.|url=https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/00-80T-80.pdf|title=Aerodynamics for Naval Aviators NAVAIR 00-80T-80|publisher=U.S. Navy|year=1965|pages=14, 29, 151}}</ref>{{rp|29}}

*the [[normal force]] due to the [[pressure]] on the surface of the body 
*the [[shear force]] due to the [[viscosity]] of the gas, also known as [[skin friction]].

Pressure acts normal to the surface, and shear force acts parallel to the surface. Both forces act locally. The net aerodynamic force on the body is equal to the pressure and shear forces [[integral|integrated]] over the body's total exposed area.<ref>{{Cite book|last=Anderson, John D., Jr. (John David), 1937-|title=Aircraft performance and design|date=1999|publisher=WCB/McGraw-Hill|isbn=0-07-001971-1|location=Boston|chapter=2.2|oclc=40076736}}</ref>

When an [[airfoil]] moves relative to the air, it generates an aerodynamic force determined by the velocity of relative motion, and the [[angle of attack]]. This aerodynamic force is commonly resolved into two [[vector component|components]], both acting through the [[center of pressure (fluid mechanics)|center of pressure]]:<ref name=":1" />{{rp|14}}<ref name=":0" />{{rp|§ 5.3}}

*''[[Drag (force)|drag]]'' is the force component parallel to the direction of relative motion,
*''[[Lift (force)|lift]]'' is the force component perpendicular to the direction of relative motion.

In addition to these two forces, the body may experience an aerodynamic [[Principle of moments|moment]].

The force created by [[propeller (aircraft)|propellers]] and [[jet engine]]s is called ''[[thrust]]'', and is also an aerodynamic force (since it acts on the surrounding air).  The aerodynamic force on a powered airplane is commonly represented by three [[Euclidean_vector|vectors]]: thrust, lift and drag.<ref name=":1" />{{rp|151}}<ref name=":0" />{{rp|§ 14.2}}

The other force acting on an aircraft during flight is its [[weight]], which is a [[body force]] and not an aerodynamic force.

== See also ==
* [[Fluid dynamics]]

== References ==
{{Reflist}}

[[Category:Aerodynamics|Force]]
{{Fluid Mechanics}}