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Hi Aerohead,
Thanks for posting your chart about air drag versus temperature!
I'm not questioning the presented data, but simply pointing out that there must be other factors in the ISO table besides absolute temperature ratios.
For example, I work allot with air flow at work, and have to compensate for temperatures and barometric effects of the air, and the resultant mass flow rates of various flow meters we have.
Fortunately, barometric pressure is already in absolute numbers, i.e. inHg, kPa, or psi, which ever units you prefer. As the barometric pressure goes up on a given day, the air drag on our cars goes up by the same amount, just based on air density due to barometric pressure.
When working with baro readings from radio stations or TV, make sure to convert their reported number to the true barometric pressure at your specific elevation, otherwise you can be easily 2% off in your calculated numbers.
And air temperature has the same affect, except as the temperature goes up, and air density goes down. And we have to deal with air temperature in absolute units, rather than relative. Absolute units are typically Rankin or Kelvin, whereas relative units are Centigrade or Fahrenheit.
To get the absolute outside temperature in Rankin, just add 460°R + the relative temperature in °F, so room temperature is 460°R + 70°F = 530°R
Then if you want to know how a change in temperature affects air drag, just calculate the ratio between the temperatures to find the effect on air drag.
Such as other things in life, the ISO paper most likely has other factors that affect air drag that I don't know about or haven't considered. There is the z-factor compressibility of air, that is used when dealing with the true density of the air at pressures higher than 100 psig or so, but that factor is typically so small for our purposes here, that it does not need to be considered.
Again Aerohead, thanks for posting your info. It's a useful tool for those who are interested.
Jim.
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