Can anyone please point me to any existing multi blade (does not matter how many blades) air propellers under approx. 20mm in diameter.
Thank you for your help.
The smallest propeller Robotshop sells are 55mm in diameter, unfortunately.
You might research propellers at HobbyKing.
Here’s an example 1.3":
You might be able to carefully cut down the diameter of a small prop, but you would have to carefully balance it.