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. There are two causes of aerodynamic force: : §4.10 : 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 integrated over the body's total exposed area.
When an airfoil (such as a wing) moves relative to the air, it generates an aerodynamic force in a rearward direction, at an angle determined by the direction of relative motion. This aerodynamic force is commonly resolved into two components, both acting through the center of pressure:: 14 : § 5.3
- drag is the force component parallel to the direction of relative motion,
- lift is the force component perpendicular to the direction of relative motion.
In addition to these two forces, the body may experience an aerodynamic moment.
The force created by propellers and jet engines 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 vectors: thrust, lift and drag.: 151 : § 14.2
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