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Old 12-13-2008, 03:31 PM   #35 (permalink)
aerohead
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Air Density (rho) defining and using

Hello all.As we move into the colder weather,and later as we move back into warmer times,the density of the air will be affecting our air drag.--------- For those who'd like to contemplate the implications of changing air density,the following is offered.------------------ Air density,designated by the Greek letter rho,and used in aerodynamic drag calculations is defined as the ratio of the air's specific weight,divided by the local acceleration due to gravity (g).-------------------- A sling-psychrometer can be used to measure accurate dry and wet-bulb temperatures,and using a Psychrometric chart (available from air conditioning contractors) one can determine current specific weight of air.------------ Standard air is measured around 59-degrees F and has a specific weight of 0.07651 pounds per cubic foot.------------------- (g) as measured at sea-level,is 32.2 ft/second/second.------------------ running the numbers,for standard air, 0.07651/ 32.2 = 0.002376.------------ Rho is commonly stated at 0.00238 at standard conditions.------------ Anyone with a psychrometer,or access to local weather conditions,a chart,and a calculator can calculate current air density to determine what cold winter /or hot summer air means to there drag.
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