On Jul 20, 5:40*pm, Home Guy wrote:
jamesgangnc wrote:
If a fan has fan blades that are designed to *efficiently move
air*, *then why won't that same basic blade design also be
*efficiently moved by air* ?

That's not true. *Look at a propeller airplane. *It's blades
move air and they are long and thin.

The cross-sectional area of a plane's propellers are a hindrance (drag)
to forward motion. * So while a fatter blade can provide more thrust at
a lower rpm or with a lower swept area, a fatter blade will present more
drag to counter a plane's forward movement. *The slower a plane is
designed to fly, the slower a plane's engine is designed to operate, the
more sense it makes to use a fatter blade, or more blades (3 or 4 vs 2).

A helicopter develops lift because it's blades are really air foils that
just like wings develop a low pressure area on their upper surface as
they are moved forward (ie - as they are rotated).

When you look at the constraints of a typical house fan (low speed,
inefficient motor, small design envelope or package) what you get are
wide, fat blades. *If wide fat blades are best at being turned by motors
of low power to generate a breeze that consumers demand out of a small
package size, then I'd have to assume that wide, fat blades would also
be most easily and efficiently rotated by a breeze or flow of air
passing through them.

If it doesn't take much motor force or motor power to turn wide/fat
blades to generate an acceptible air flow, then the converse must also
be true - that wide/fat blades are more easily turned by a given breeze
vs long/narrow blades.

The energy potential in a wind field is measured in terms of the swept
area of the blades.

So how can you capture a respectible fraction of this energy by using
thin blades that "see" or experience only a small fraction of this swept
area, vs using fatter blades that expose themselves to a greater
percentage of this wind field?

Fat and thin. They are all airfoils. Do you think they woudn't use
fat blades if they worked better? You think engineers didn't design
the blades on wind turbines?