Drag count explained

A drag count is a dimensionless unit used by aerospace engineers. 1 drag count is equal to a

C _{d} of 0.0001.^{[1] [2]}

As the drag forces present on automotive vehicles are smaller than for aircraft, 1 drag count is commonly referred to as 0.0001 of

C _{d} .

Definition

A drag count

\Delta C _{d} is defined as:\Delta C _{d=} 10 ^{4} \dfrac{ 2 F ^{2} _{d}{\rho v} A} , ^[3]

where:

F _{d} is the drag force, which is by definition the force component in the direction of the flow velocity,\rho is the mass density of the fluid,v is the speed of the object relative to the fluid, andA 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 more in payload.^[5]

See also

• Drag coefficient
• Zero-lift drag coefficient

Notes and References

1. Book: Yechout, Thomas R.. Introduction to Aircraft Flight Mechanics. 2003. AIAA. 978-1-60086-078-2. 51.
2. Wassim A. . Drag Prediction in Transitional Flow over Airfoils . Ghaly . Wahid S. . Journal of Aircraft . Basha . 2007 . 44 . 3 . 824–832 . 10.2514/1.22939.
3. Book: Hucho, Wolf-Heinrich. Aerodynamik des Automobils: Eine Brücke von der Strömungsmechanik zur Fahrzeugtechnik. 2013. Springer-Verlag. de. 978-3-642-57903-5.
4. Web site: Ask Us – Drag Coefficient & Lifting Line Theory . Aerospaceweb.org . 2004-07-11 . 2019-10-26.
5. Book: van Dam, C. P. . Aircraft design and the importance of drag prediction . CFD-Based Aircraft Drag Prediction and Reduction . 2003 . 1–37 . 53098762.