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| A '''drag count''' is dimensionless unit used by [[aerospace]] engineers where 1 drag count <math>\Rightarrow</math> a <math>C_d</math> of 0.0001.<ref>T. Yechout. Introduction to Aircraft Flight Mechanics: Performance, static stability, dynamic stability, and classical feedback control. AIAA Education Series. 2003. http://books.google.ca/books?id=a_c2V0zAFwcC&pg=PA51&lpg=PA51&dq=drag+count&source=bl&ots=ZE7-7RqzBf&sig=_zGTQQWXAuPaYLlgd-tReHT1pa4&hl=en#v=onepage&q=drag%20count&f=false</ref><ref>Basha, W. A. and Ghaly, W. S., “Drag Prediction in Transitional Flow over Airfoils,” Journal of Aircraft, Vol. 44, 2007,p. 824–32.</ref>
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| ==Definition==
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| A drag count <math>\Delta C_\mathrm d\,</math> is defined as:
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| :<math>\Delta C_\mathrm d = 10^{-4} \dfrac{2 F_\mathrm d}{\rho v^2 A}\, ,</math>
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| where: | |
| :<math>F_\mathrm d\,</math> is the [[drag (physics)|drag force]], which is by definition the force component in the direction of the flow velocity,<ref>See [[lift force]] and [[vortex induced vibration]] for a possible force components transverse to the flow direction.</ref>
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| :<math>\rho\,</math> is the [[mass density]] of the fluid,<ref>Note that for the [[Earth's atmosphere]], the air density can be found using the [[barometric formula]]. Air is 1.293 kg/m<sup>3</sup> at 0 °C and 1 [[atmosphere (unit)|atmosphere]]</ref>
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| :<math>v\,</math> is the [[speed]] of the object relative to the fluid and
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| :<math>A\,</math> is the reference [[area]].
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| The [[drag coefficient]] is used to compare the solutions of different geometries by means of a dimenionless number. A drag count is used as a more user-friendly measurement as the coefficient of drag is usually less than 1. A drag count of 200 to 400 is typical for an airplane at cruise.<ref>"Ask Us - Drag Coefficient & Lifting Line Theory". Aerospaceweb.org. 2004-07-11. http://www.aerospaceweb.org/question/aerodynamics/q0184.shtml. Retrieved 2010-12-07</ref> A reduction of one drag count on a subsonic civil transport airplane means about 200 lbs more in payload.<ref>Van Dam, C. P., Aircraft Design and the Importance of Drag Prediction, VKI Lecture Series 2003-2:CFD-Based Aircraft Drag. Prediction and Reduction, National Inst. of Aerospace, Hampton, VA,Nov. 2003.</ref>
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| ==References==
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| {{Reflist}}
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| ==See also==
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| * [[Drag coefficient]]
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| * [[Zero-lift drag coefficient]]
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| {{DEFAULTSORT:Drag Count}}
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| [[Category:Aerodynamics]]
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| [[Category:Equations]]
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| [[Category:Fluid dynamics]]
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| [[Category:Force]]
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| {{Fluiddynamics-stub}}
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