I had something happen today that has me confused. Maybe the more technical minded can explain. I switched from an 11.5 x 6 APC 2 balded prop to a Master Airscrew 11 x 7 three blade. It was electric , runs the wrong direction and I did not change rpm (9,550) I was expecting faster laps - they were slower by .1. I was expecting to use more battery - it used less. What I got was vastly improved overhead tension, smoother rounds and greatly improved exits from corners. What I don't understand is why?
I don't know enough about the rest of the system to say, but it is pretty obvious that if you are flying slower, you have less drag, so less energy is required, so the battery lasts longer. I presume that this is a bigger effect than the loss of efficiency (maybe) that caused you to lose speed. Reducing the diameter generally makes the cornering better so that is no surprise. It may also be that it was a touch tail-heavy and that adding nose weight helped - it is certainly suggested when it made the rounds smoother.
We don't know the actual effective pitch, it may have been more, less, or have a different pitch distribution. Usually reducing the diameter reduces efficiency, that would potentially explain why it slowed down.
The other conditions matter, too, so I can't tell you why the overhead tension went up, maybe because your backwards-operating prop caused you to yaw outboard more than you would have otherwise in the top of the hourglass, and you needed that from a trim perspective. Sometimes, the effects of a lower-pitched prop also has the effect of increasing the airspeed stability, that can easily reduce the tension as the airplane slows down in groundspeed More pitch sometimes permits you to take advantage of the whip-up to get more groundspeed and thus more line tension.
A lot of people have done these sorts of uncontrolled experiments and then jumped to wrong conclusions, so beware of that. This really tells you very little about 2-blade VS 3-blade per se. You changed far more than just the number of blades - you changed the diameter, the pitch, the pitch distribution, the blade shape, the airfoil, the mass, the moment of inertia, blade surface finish, and the speed. File it away as part of your trimming and setup knowledge, but it would be easy to over-interpret the results.
Brett