Faster and Greener-- Pocket Airports - CAFE Foundation

42 Extreme noise reduction for propellers presents a somewhat new quest in civil aviationbecause of the availability of near-silent electric motors as replacements for thepreviously difficult-to-quiet internal combustion engine. The new Benchmark softwareprogram enables one to pre-compute the noise footprint of a propeller. From thatprogram, we can see that quiet propellers of good efficiency that offer the necessary lowtip speeds can be created. Expert consensus is that the propeller blade tip speeds need tobe kept below 400 fps. The graph below shows the convergence of ideal climb and cruiseefficiency for a sample low power GQ aircraft to occur with a slow-turning propellerdiameter of between 9 and 11 feet.