During a flight today, I took a video of the propellers spinning and noticed this strange result: I was using a Samsung Vice cell phone's video camera. Now, it makes sense that the frame rate of the camera as compared to the rotational velocity could make for some weird effects, namely the slowing. The propellers were impossible to distinguish by eye; just look at the blur left by fan blades to get an idea. But what causes the outrageous appearance of bending? Is it the pressure gradient across the propeller blades, which results in a density gradient of the air and hence bends the light. My other guess is that the propeller was actually spinning in the opposite direction as it appears in the video. In this case, the parts furthest from the center are moving much faster than the parts of the propeller inside. I feel like this might, in combination with the finite (but short) shutter speed of the camera, possibly explain the bending. But I'm not sure how to complete this thought.