interesting web page describing how foiling a c-fan blade raises energy efficiency…nice side to side comparison photos showing flow seperation…
It’s funny, I’ve thought about that for a while now, as my parents live in the tropics where there are thousands of ceiling fans.
I think the reason most of those fan blades are flat pressed metal is the same reason for flat sided side fins…economy, not performance.
edit…economy of manufacture that is.
They carry them at Home Depot, but they are a bit pricey. They were developed in Cocoa, FL at the Florida Solar Energy Center. It would be really easy to make your own, the only problem would be balancing them so your fan didn’t wobble. You’d have to be pretty strict on your quality control. They should sell just the blades as a retrofit for existing fans.
Lots of other really interesting stuff on their site as far as energy conservation and solar implementation.