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Member Since 02 Sep 2013
Offline Last Active Jan 09 2014 07:25 AM

#5121670 Air Resistance approximation re-entry

Posted by Mizmoon on 06 January 2014 - 11:40 AM

Here is the basic formula for air drag:


Fd = 0.5 * Cd * Rho * Velocity^2 * A




*Fd is the drag force in newtons, applied to the opposite direction of the velocity.


*Cd is the coefficient of drag - this is determined in wind tunnel test. It is a constant which you can tweak to your preference, but there are some examples of the Cd of different primitives to be found here: http://en.wikipedia.org/wiki/File:14ilf1l.svg


*Rho is the density of air. This can be tricky since it changes with temperature, and temperature drops at higher altitudes. Air humidity also affects density. I don't know the exact equation for this, but i suggest you use a constant air humidity, and then sample data from this calculator (http://www.denysschen.com/catalogue/density.aspx) and then make a function out of these points. You might have to find samples of air temerature at different altitudes aswell, but that should not be hard.


*Velocity relative to the airflow.


*A is the reference area in square meters.