In article ,
says...
An interesting effect with the prop. I suppose it is some digital version of
the frame rate vs prop RPM stroboscope effect that we are used to seeing,
but modified because of the digital camera thing.

Anybody got a better explaination?

Close. Most cheap cameras that use CMOS sensors and cheaper CCDs don't
expose the full frame all at once like if you took a photograph. They
expose one line at a time, so something that moves as fast as a prop
will move visibly between the time it takes to expose one line an move
to the next. The technical terms are "Full frame integration" versus
"Electronic Rolling Shutter".

So instead of a blur, you'll get a skewed image like you see in these
videos.

Its only in the last couple of years have CMOS imagers been developed
that do full frame integration. CCDs have been doing it for ages.

--Carlos V.