The "car top wind tunnels" used by Rutan and others also worked pretty well. You can put a small scale version of a whole plane up there, or a full scale version of a small bit (wing section, cooling duct and radiator, etc). The car/truck/flatbed trailer provides a lot of real estate for manometer tubes, cameras (for tuft or dye drip testing), force sensors so you don't have to guess about what is going on, etc. And, it is unlikely to crash--unless you crash, too.
An RC model is good for a lot of things, but can require a lot of trial and error to determine the "why” that accompanies a "what.' If the "what" results in a crash, then another model will need to be built. So, computers, low budget wind tunnels, and RC models are complementary.