On Jul 21, 9:00*am, Home Guy wrote:
A flat blade angled at 45 degrees will probably get you the
most torque and rotational speed out of a given breeze of air (but it's
totally possible that optimal blade angle is a function of RPM), and the
more surface area your blade has, the more of that wind energy it can
convert into rotational energy.

If you look at the old stereotypical "prairie" style windmills, that's
how they are. A disk with pie-shaped blades angled at 45 degrees,
facing directly into the wind with the help of a fin.

All that surface area catches a lot of wind, but it also creates a lot
of aerodynamic drag which makes it require higher wind speeds to turn.
The air pushing through the "fan" creates rotational energy, but the
air AROUND the fan is creating drag as the tips of the blades contact
it.

The reality is that what makes a good propeller or helicopter rotor
also makes a good windmill blade. Maximum lift with minimum drag. THAT
is why we have thin blades. The cross-section of a modern wind turbine
blade is a high lift, low drag airfoil that will catch air and turn
the rotor at far lower wind speeds than a solid disk of 45 degree flat
plates.