On the subject of 3-blade props reducing noise... A few years back, Aviation Consumer ran a test with two different airplanes, and two different prop manufacturers. The "control" was using the same blade/hub manufacturer on the same airframe for the tests. (They tested a Bonanza, using two- and three-blade props from the same manufacturer for the tests. Ditto for the other airplane - which I think was a 182, but can't really remember.)
Anyway, they tried really hard to do a scientifically accurate, controlled test. But they also had a good number of pilots participate in the review to obtain some "subjective" feedback. The instrumented flight results were about what you'd expect: 2-blade props produced slightly faster cruise speeds, and 3-blade climbed slightly faster. But the differences were pretty negligible – something like ± 100 fpm and maybe 2-3 KTAS. And with both types dynamically balanced, the 3-blade props were slightly smoother in operation. (Keep in mind, this is with the same blade profile and construction - no "new tech here...)
The "interesting" part of the results (to me anyway) was that 100% of the pilots reported that the 3-blade props were significantly less noisy, both when they're flying the airplane and when they were observing from the ground as the airplane flew a low pass. The actual instrumented test results, however, showed that there was zero difference in the actual noise level as measured by a calibrated sound meter. The only real differences was the "pitch" (frequency) of the noise. Three-blade props produced their noise at a somewhat higher frequency than the 2-blade props. That seems logical, with 3 blades turning at the same RPM), and the report concluded that this upward shift in frequency made the 3-blade prop "seem" less noisy to both pilots inside the airplane and to observers on the ground.
The other theory (which makes more sense to me, given some studies on helicopter tail rotor noise signatures I was involved with while in the Army) is that the 3-blade prop "sound waves" are at least partially disrupted by the wave produced by the next blade. Obviously with 3 blades, there is a shorter interval between those sound waves. It's similar to the principle behind active noise-reduction headsets. Hughes Helicopter (now McDonnel-Douglas) was doing some R&D pursuing a "silent" tail rotor for the Army. They found that just offsetting a 2nd pair of blades (at about a 30º angle from the first pair), the noise signature of the tail rotor was reduced by something like 60%. It wasn't "silent" by any means, but it was far more "stealthy" than the original... But to observers on the ground, it definitely seemed to be significantly more quiet than the standard rotor –far more so than the instrumented test results reflected.
The other thing pretty much agreed upon by all participants (and even some casual observers who just happened to come by during the Aviation Consumer test) was that 3-blade props made the airplane look better – no contest whatsoever. And as we all know, airplanes fly pretty much how they look... (LOL)
