# Thread: Quick "Standard Atmosphere" Question

1. ## Quick "Standard Atmosphere" Question

I realize that scientifically in the real world, a theoretical "standard atmosphere" is defined as having a temperature of 59-deg F and an air pressure of 29.92" at sea level.

When I run clear skies in FS2004, and then open up the user weather settings to change the values, these are what it will start at... so I know that simulator program recognizes this as a standard too.

However, the simulator also will display 41-deg F as the dew point temperature, when going into the user adjust weather menu for temp/pressure.

So am I to take this to mean that 41-deg F is also recognized in the scientific world as the "standard dew point" in a "standard atmosphere"? Or is that simply an arbitrary number that the makers of FS2004 placed in the pull down menu?

Is dew point temperature even taken into consideration as piece of data, when defining a "standard atmosphere"?

Thanks.
Last edited by b3burner; 06-16-2012 at 05:42 PM.

2. That's an interesting question. A temperature 59F and dewpoint of 41F yields a relative humidity of about 50%, a generally comfortable level. Perhaps that's where the number comes from. Or maybe MS pulled that number out of a thin standard atmosphere

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Dew point is not part of the International Standard Atmosphere (ISA). ISA is based on a base temp/pressure at Sea Level, a standard temperature lapse rate to the stratosphere (about 33000 ft), then constant temp up to top of the stratosphere (about 60,000 ft); it is simply an internationally agreed upon model so as to define other parameters such as standard density, for aeronautical engineering and meteorology.

Look up the ISA on the web - you will normally find tables, even calculators to examine the various pieces of the model.

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The humidity is not included in the "standard atmosphere" calculations. The air is assumed to be dry and of a certain makeup. AKA: X percent Nitrogen, X percent oxygen etc...

The 41 degrees is as a result of there being a model that does assign a value for the humidity factor.
Look up "Standard Atmosphere" and read up on the subject.

"Standard Atmosphere" is a base line to work from, not the be all, end all for aerodynamic calculations.
I have seen models that will give a base line of humidity of 50 %.

Clay