Reynolds number is important in fluid mechanics but it is not the defining equation, for drag modeling, derived using similitude techniques.
If you are familiar with Similitude and Buckingham Pi then this equation is trivial to develop (if you would like me to derive it, I shall):
Drag = (w/w_m)^2([rho]/[rho]_m)(V/V_m)^2 [Drag]_m
What this tells us is that the characteristics of a model scale using those terms - no more and no fewer. So if you know the operating air density, width (component), and velocity of the airplane and your vehicle, you can scale the drag of an airplane (component) using that equation, to find the drag it will apply on your car. A side effect of this shows that shapes and components developed for airplanes DO scale to lower speeds.
I hope this makes sense
