[ODE] more air friction

[Don Burns]

I've not been following this thread, so forgive me if this has been said 
or is irrelevant.

On Thu, 22 Apr 2004 barbara.yersin at urbanet.ch wrote:

> Ok guys. As you told me, I've added a force computed like this:
> damping coeff * velocity.
> 

I recently wrote a Hot Air Balloon simulator and applied this force for 
aerodynamic drag:

    _dragForce = 0.5 * rho * sqr(_velocity) * _area * _CD0;

Where:

    rho  = air density ( 1.225571 Kg/Meter^3 at sea level)
    area = profile area of the object (pi * sqr(radius) for the balloon).
    _CD0 = Drag coefficient.  This number depends on the properties
           of the moving vehicle.  I used 0.05.

Note that velocity must be squared.

Cheers,

-don

PS. as a personal plug and if you want to see interesting things ODE is 
used for, check about half way down the page for the Hot Air Balloon sim 
here:

    http://museum.eaa.org/activities/events.asp