da Rock,

You are right, area, density, angle of attack, are all constant from the values he has given me. If any of those items change, then his answer will be wrong.

He asked what his downforce would be per a given velocity. My equation has all the constants included, and fixed. The actual equation is for approximating drag of flat plate, from about 12 deg to 90 deg aoa. Around 8-12 degrees aoa, seaparation is occuring, and the equation shouldn't be used.

Another assumption is that it shouldn't be used at velocities where compressibility effects raise their head.