Currently, adding more blades to a propeller adds efficiency, but no thrust, meaning that you want as many blades as possible to have the best fuel efficiency. In real life, adding more blades decreases the efficiency as there's more propeller to spin, but it adds thrust because there are more blades, meaning that the most efficient propeller would be 1 bladed (which does exist, Google it). Possible to change, or too hard?

Went and checked the physics system, and I cannot find really anything that seems amiss with propeller physics. If you wish to see a change, you are welcome to submit a Pull Request with the code changes. Other that that, I'm keeping things as they are.

Possible for sure. I agree that the number of blades does define how much thrust you generate IRL. However, that number isn't necessarily linear. For example, two blades does not mean twice the thrust of one blade. Still, I should be able to take a look at the propeller thrust equation again to see if I'm missing something. I do know the number of blades is factored in, but I forget how at the moment...