One rotating blade ( but rotated very, very slow). No sound.I saw an object moving 3,000 to 4,000 ft in the air moving 15-50 MPH To the NW. No wind at all at my location. Object appeared to have one revolving blade (like a helicopter). It rotated so slow that I could watch the blade rotate. It was not a helicopter. No noise, and it should have fallen straight down due to the slow speed. I was on top of a grain bin at the time I saw it.