Or to put it yet another way, the way to scale up from the model forces to derive the full size ones is to scale up the reference area from the model’s wing area to the full size aircrafts wing area, keeping everything else in the equation (including Cd) the same. I have arrived at what I was trying to say at last – sorry it was a bit ’round the houses’ if only to get to something you already knew!

I am aware that there are slight qualifications to this.