I made a little fan for the not-quite-50mm flywheel on the Stirling engine I bought. It's to help move the air laterally not just vertically, during power outages when I want to dissipate the heat.
It works OK, there's probably lots of room for improvement! (Update: I made another one with fancier shaping. Untested, try it out!)
https://www.youtube.com/watch?v=_hSURbqQ_qw