I had made the swap to an RX-8 fan and it was better than the stock FD fan but not by much. In my past was was into RC things before and after the change to brushless and the near death of nitro. Got to thinking....maybe I can brushless overpower the fan.
I know there will be diminishing returns with how much the box can flow but I figure...why not force it.
The RX-8 fan pulls 8.5A at 13.1v with a sustained RPM of 3500. That comes out to about an 270kv motor and "only" 110W. My mind goes to racing drones where a 5" quad can pull in excess of 1600W at full tilt.
I think a 5-8mm shaft will be sufficient. Anything over 600w capable will be enough. I'm looking in the 500kv range. Will theoretically give me double the RPM for the same current since brushless is almost always double the efficiency.
Looking in the 5050 size motors at 500kv and a speed controller in the 60A range. Overkill will hopefully mean longevity.
The only thing I'm not sure on is the shaft to the fan. It's rather offset to the top making vibration management very difficult without upper support. May use a pair of bearings and flex joint to support the whole thing mounted to a laser cut mounting plate.
Teaser testing
First test will probably run a cheaper china motor similar to this one in spec.
https://www.horizonhobby.com/product/avian-5055-500kv-outrunner-brushless-motor/SPMXAM4740.html