Why are the blades on today's household fans scoop shaped?

It would appear that fans with more helicoid blades would put out a much smoother, higher velocity airflow than blades that are scoop shaped which appear to cause a turbulent, reduced speed flow of air.  Even the blades on a ship's propellers are not scoop shaped as otherwise there would be less efficient propulsion.  For example, think of the propellers on the U-505 submarine.  Anyone who has visited Chicago's Museum of Science and Industry surely would have seen the U-505 submarine and noticed how the huge bronze propellers at the stern have a helix shape in the blades, sort of like the threads on a screw.  At the same time, the blades on a few older, 80s era plastic bladed box fans such as ones made by Edison, General Electric, Wards Signature, and Toastmaster in the 1970s and early 80s have that same helix or "screw" shape in the blades, and they really move a lot of air.

So why do they make today's fans with scoop shaped blades?  It doesn't really make a lot of sense if you're going to design a fan to move air with a minimum amount of power and effort.  As far as I can tell, a screw shaped fan blade would move a lot more air at typical household spin speeds than one with scoop shaped blades.

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  • 4 weeks ago

    I suspect it's down to newer designs intended to run at lower speeds, to reduce the noise levels.

    As a parallel, think of an aircraft extending the flaps to maintain proper airflow at lower speeds. The wing section is then definitely "scooped".

    https://history.nasa.gov/SP-468/p274a.jpg

  • 4 weeks ago

    Its all about the money.  Look at the price of a typical  box fan or standing fan.  A screw fan would cost more to make.

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