Drag coefficient

[jim0940]

Understanding the various applications that is applied to an aircraft skin, film, etc, what is the conservative formula one uses to figure the drag coefficient?

[modest]

The drag coefficient is a term in the drag force equation:

[math]F_D = \frac{1}{2} C_D A \rho v^2[/math]

where,

• [imath]F_D[/imath] is the drag force in Newtons on a body moving through a medium
  
• [imath]C_D[/imath] is the drag coefficient, a dimensionless number
  
• [imath]A[/imath] is the reference area in [imath]m^2[/imath]
  
• [imath]\rho[/imath] is the mass density of the fluid in [imath]kg/m^3[/imath]
  
• [imath]v[/imath] the velocity of the medium relative to the body in [imath]m/s[/imath]
  

The drag coefficient is a function of several parameters such as; the shape of the body, the roughness of its surface, the velocity of the body, and the viscosity of the medium.

 

If the coefficient is known for a given velocity, it is possible to us the body's Reynolds number to approximate the coefficient at different velocities. However, finding the drag coefficient is typically a matter of wind tunnel measurements for unknown bodies and materials, and reference tables for known bodies and materials.

 

Some typical values are given here.