Quote Originally Posted by wumpus View Post
...
The Wright brothers invented the wind tunnel but didn't understand how badly it scaled. Thus the famous "Wright Flyer" (first airplane) was designed assuming that air had the viscosity of molasses (I'm assuming this is a wild exaggeration, but it is in all the books). This was still "good enough" and the airplane flew. Eventually they figured out the problem and had to build larger and larger wind tunnels....
Mostly this was due to lacking the understanding of scale and how we now use the REynolds Number and Nusselt Numbers to predict actual performance from scaled performance. As an interesting aside, if you look at older movies that used scaled models for cities or boats that were either on fire or in waves it's how/why they behavior of the flames and waves don't "look real" to us.