The Pipistrel aircraft from Slovenia with a 80 hp Rotax 912 engine did very well in a CAFE test some Years ago. Propeller was 1.6 m diameter and turned 40 rev per second giving a tip speed of 200 m per second.This gives an acceptable flyover noise. American engines/props/aircrafts run 270 meter per second .Noise is not acceptable and is the reason/excuse why most hobby airports in Europe are closing. I have been dreaming of an opposed piston twin prop scheme since 1988 and still believe it is the rigth way,but a single prop driven by an inverted V2 two stroke is maybe smarter,and at least much more acceptable to old know it alls.Me for one.Let us play that You had some money and wanted to invest it in the shining future of personal aircrafts. We have already lost ground contact here. The twin scheme can be seen to a certain extent here http://archive.today/zHnXJ and http://archive.today/s7gTY and the picture shows a V2 twostroke with a 1.6 meter prop superimposed on a twin 1.2 meter prop scheme. Both will do the same job as the Rotax 912 and be ligther and more fuel efficient. Noise will be the same.