Propeller artifacts in the video is a symptom of filming through the prop with a digital camera like the GoPro. The propeller blades can look quite horrible in the picture unless you do something about it. In high light situations, attaching a neutral density filter to the camera seems to do the trick. I’m currently getting the best results by using ND4 filters from Camkix
Filters like this, can all-but eliminate the propeller from the recorded image, but if you use a filter that’s too dark for the conditions, the picture quality can suffer significantly.