Actually a 4 bladed prop is not that much less efficient, but ill suited for our purposes. The time between blades has nothing to do with it. For high speed planes a four bladed prop is often more efficient because moving a smaller air stream at a higher speed is an advantage when moving at a high rate of speed. I am afraid that using even a two bladed prop scale sized prop is a problem. I would consider trying the RCV engine if a scale prop is a must.