How do you eliminate the propeller effect?

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

Cinematic Filter Pack for GoPro HERO 4 / 3+

Cinematic ND Filter Pack for GoPro HERO 6 / 5

Cinematic Filter Pack for GoPro HERO 4 / 3+ – Waterproof Housing

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.