What determined the number of prop blades?

[swampyankee]

Here is a tugboat with a Voith prop maneuvering. It weights many tens of tons.

Imagine if we could mount a Voith-type prop perpendicular to the airflow on an airplane!
I
Maybe it could hover! ... and VIFF ... ?


View: https://youtu.be/w6lg9GM5Ogs

Google cyclogiro or cyclocopter.