A drag count is a dimensionless unit used by aerospace engineers where 1 drag count is equal to a of 0.0001.[1][2]
Definition
A drag count is defined as:
where:
- is the drag force, which is by definition the force component in the direction of the flow velocity,[a]
- is the mass density of the fluid,[b]
- is the speed of the object relative to the fluid and
- 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 used as a more user-friendly measurement as the coefficient of drag 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]
Notes
- ^ See lift force and vortex induced vibration for a possible force components transverse to the flow direction.
- ^ Note that for the Earth's atmosphere, the air density can be found using the barometric formula. Air is 1.293 kg/m3 at 0 °C and 1 atmosphere
References
- ^ Yechout, Thomas R. (2003). Introduction to Aircraft Flight Mechanics. AIAA. p. 51. ISBN 978-1-60086-078-2.
- ^ Basha, Wassim A.; Ghaly, Wahid S. (2007). "Drag Prediction in Transitional Flow over Airfoils". Journal of Aircraft. 44 (3): 824–832. doi:10.2514/1.22939.
- ^ Hucho, Wolf-Heinrich (2013). Aerodynamik des Automobils: Eine Brücke von der Strömungsmechanik zur Fahrzeugtechnik (in German). Springer-Verlag. ISBN 978-3-642-57903-5.
- ^ "Ask Us – Drag Coefficient & Lifting Line Theory". Aerospaceweb.org. 2004-07-11. Retrieved 2019-10-26.
- ^ van Dam, C. P. (2003). "Aircraft design and the importance of drag prediction". CFD-Based Aircraft Drag Prediction and Reduction. pp. 1–37. OCLC 53098762.
See also