ISA - The Standard Atmosphere
In this video, you will learn about the International Standard Atmosphere and how it is used in the world of aerospace.
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Let's talk about ISA, specifically what is it and how do we use it? ISA is and abbreviation for the International Standard Atmosphere.This is a agreed upon model that we use to reliably describe how the atmosphere varies, in terms of temperature, pressure and density with altitude.
It is important for us because we need a way to describe how this parameters change so that we can calculate performance, for any altitude for any airplane.
The International Standard Atmosphere looks something like this. On the x-axis we have there ratio of the value on altitude to value at sea level; and on the y-axis we have altitude. As you can see, temperature varies linearly up to the tropopause at about 36,000 feet, then remains constant until well above the cruise altitude of most aircraft, and then increases and decreases again as you reach space. Density and pressure vary exponentially with altitude. As you can see, there is a huge difference between density and pressure at sea level, and the density and pressure at cruise altitude for jet aircraft.