Drag count

A drag count ${\displaystyle \Delta C_{\mathrm {d} }\,}$ is defined as:

${\displaystyle \Delta C_{\mathrm {d} }=10^{4}{\dfrac {2F_{\mathrm {d} }}{\rho v^{2}A}}\,,}$ [3]

where:

${\displaystyle F_{\mathrm {d} }\,}$ is the drag force, which is by definition the force component in the direction of the flow velocity,[lower-alpha 1]

${\displaystyle \rho \,}$ is the mass density of the fluid,[lower-alpha 2]

${\displaystyle v\,}$ is the speed of the object relative to the fluid, and

${\displaystyle A\,}$ is the reference area.

The drag coefficient is used to compare the solutions of different geometries by means of a dimensionless number. A drag count is more user-friendly than the drag coefficient, as the latter is usually much less than 1. A drag count of 200 to 400 is typical for an airplane at cruise.[4] A reduction of one drag count on a subsonic civil transport airplane means about 200 lb (91 kg) more in payload.[5]

• Drag coefficient
• Zero-lift drag coefficient