Keep in mind that on full scale planes, it was easier to put a three, four or more bladed propeller to develop the necessary thrust, rather than th have a much longer two bladed prop, which would be impractical due to the length the landing gear struts would have to be. Look at a WW II Corsair. The gull wing and multi blade prop allowed a larger total area for the prop blades to swing through the air ( the gull wing elevated the nose to clear a longer prop). keep in mind the RPMs those engines delivered compared to ours, and the fact that these blades were huge, compared to our tiny ones, so there was ample time for the air stream to clear before the next blade swept past. That's why you seldom see more than a two blade on our models. The Alpha trainer's three blade actually slows the plane, and is quieter than a two blade prop, but it is not as efficient. That was what the design accomplished though, as these planes do fly on the slow side with these props and are quieter, especially at low RPMS.