Redid the experiment with similar results--except I found I was missing a
conversion factor so that my wind speeds are actual higher. Here is the
data 5.0 m/s--1.22 mW, 4.5 m/s---1.05 mW, 3.4 m/s--.74 mW. (Took the
equipment outside in a mild breeze and measured about 1-2 m/s.) If one
includes a (0,0) point, the linear fit is not bad--but of course the blades
won't turn at all at very low speed so I don't think we are in danger of
having created the perpetual motion machine that John Denker worried about .
Power Law fit gives a 1.2 exponent.
Again, a simple plastic fan blade on what can be seen above to be a pretty
inefficient generator that operates with a fixed 100 ohm load (so that the
software will work). One factor that comes to mind here is that our fans
(straight from Wall-Mart) have a fairly narrow stream of air. I think I am
completely 'painting' the rotor blades with the air--adjusting the
orientation of the fan for maximum power output. Anyway, since the lab
starts Tuesday, we will go with the results obtained in lab and make some
comparisons to the theoretical max which would be the cubic dependency.