Rolling shutter artifacts Shutter speed test

Bombardier Q400 propeller while cruising as seen through a Canon 5D Mk II while varying the shutter speed from 1, 30 sec to 1, 4000 sec and back. (Interesting to note that, even at the low shutter speed end, there are resonance artifacts at most speeds, but not so much at 1, 40 sec and 1, 80 sec. I m guessing the rotation speed is a roughly a multiple of 15 but not 2 ) br, br,