Reynald's number
lennyk,
I've thought a bit more about this, and I'm not too happy with my explanation of Reynold's number. The problem is that, unlike some of the results from fluid mechanics and aerodynamics, the Reynold's number is kind of a complicated concept. The bottom line is that the Reynold's number tells you whether you can expect similar behavior from aircraft ( or other objects affected by airflow ) of different sizes. If I want to compare my model airplane wing to a full scale airplane wing, and it turns out the the Reynold's numbers at which they operate are very different, then the comparison is suspect. Most of the references to Reynold's number are extremely simplified, usually as generalized design rules. For example, "laminar separation is more likely at low Reynold's number". You can kind of explain this in terms of the "energetic flow" or "inertial forces vs. viscous forces" ideas, but what it comes down to in most cases is trusting these design rules to be correct, and using them without necessarily having a complete understanding. I have quite a bit of background in fluid mechanics and aerodynamics, but I still find myself looking up "design rules" and other factoids in my old books, and just trusting them, even when I can't necessarily come up with a theoretical derivation of them.
To get back to your original question, I full scale wings fly "better" than small scale ones largely because, at high Reynold's number, the flow on the upper surface has a stronger tendency to stay "attached" to the surface, so that the wing has less tendency to stall. Now I am going to get a little bit wordy, so you can skip to the end if that bothers you. The reason has to do with what an aerodynamicist would call the "adverse pressure gradient". When a wing generates lift, it is because the pressure on the top is lower than on the bottom. If you look at the pressure on the upper surface of the wing ( or airfoil ), you will see that it reaches its lowest value at a point fairly near the leading edge. That means that from that point back, the pressure is increasing. This is kind of unnatural, since air wants to flow from high pressure to low pressure, and we are asking it to go from low pressure to high pressure ( hence, the name "adverse pressure gradient" ). Well, the air can do this, to a limited extent. If you make the low pressure peak at the front of the wing too extreme, then it can't make it, and you have stall. If the air is more "energetic", or if it is turbulent, which is related, then it is better able to make it through the adverse pressure gradient.
I personally don't like the often heard assertion that larger wings "fly better", because I think it oversimplifies the issue. It is definitely true that there is much more high quality data for higher Reynolds numbers though, so it is easier to design for.
banktoturn