Boncuk asked, "On the other hand, why does your propeller have to rotate at speeds making it look "transparent"?"
For a given blade diameter, you maximize power extraction from the wind by maximizing tip speed, but want to keep tip speed below sonic velocity to avoid excess noise. Additionally, if you have a gearbox, wear increases with rotor speed. Engineers try to balance the various tradeoffs for best return for the money invested in the machine.
tcmtech's tip speed is 783 ft./sec., about 70% of sonic velocity. The giant megawatt size utility wind turbines that look like they are lazing along actually are operating with tip speeds approaching sonic velocity.
Despite the invisibility of the blade disc, is it possible that an interrupted spiral painted on the blades would be visible, even if the blades themselves are not? Seems like I've seen that phenomenon somewhere - possibly in the "optical illusions" exhibit area at the Exploratorium science museum in San Francisco. The relatively slow apparent movement of the pattern is much more perceptible to the eye than the rapidly rotating blades alone.
Jerry In Maine, you must be in quite an isolated area to consider noise as a deterrent. (I did noise studies for wind farms in Altamont and San Gorgonio, CA because even isolated neighbors miles away complained about the noise. People who did not benefit from the energy production complained - those who did benefit from revenue or jobs, did not complain.)
I tried ultrasonic pest repellers to keep birds off my cherry trees. The birds couldn't care less, even from a foot or two away. Have you tried strobes?
awright