"Jay" wrote in message om...

I'm not sure its fair to compare a 10" 1/4 HP electric fan to a 150HP
propeller.

That 150HP propeller is developing some useful thrust as well. For efficiency
the last thing you want is a large amount of it impinging on some flat plate.
That 1/4HP fan is shrouded and delivers almost all of it's flow directly to the cooling fins
of the radiator.