Quote Originally Posted by Llwyd View Post
The trailing edge of the fan blade has a small vacuum behind it which creates a sort of swirling effect with the air, which creates part of the 'whooshing' noise a fan makes. The notches spread and break up this effect over a bigger area, lowering the pitch of the 'whoosh' and making life easier for the blade behind.

Apologies for the lack of airflow and static pressure testing. Official release was two days after I got the fan so just wanted to get some real world figures done. Might get hold of another two and do a radiator comparison with some other sets of fans in the near future but got a lot on at the moment
Owls fly silenty because they have millions of these tiny air distributers in their feathers.