The Savonius Super Rotor !
(Page 2 of 4)
March/April 1974
By Michael Hackleman
Energy winds come mainly in the form of gusts which "ride on" a prevalent breeze but usually deviate from it in direction by 15-70 degrees. The practical importance of this fact can be demonstrated by placing a Stuart mill and an S-rotor side by side in a steady wind. Suddenly there's a gust, and the propeller-driven unit swings into it. Then, as the puff dies, the wind plant's tail slowly moves the fan back into the prevalent wind. The S-rotor, meanwhile, just speeds up in the rush of air and slows as the velocity drops.
RELATED CONTENT
The U.S. Department of Energy's work with the city of Greensburg, Kan., over the past year is beari...
. . . ENERGY FLASHES...... ENERGY FLASHES...... ENERGY FLASHES. . . September/October 1982 POPEYE W...
A new study predicts we could have one quarter of our energy needs from renewable sources by 2025, ...
Which renewable energy technology has the best potential to combat global warming and power our fut...
Rock Port, Mo., took advantage of the power generated from the nearby Loess Hills Wind Farm in a bi...
Here's the point: The Stuart mill needed time to align itself first with the gust and then with the steady wind and as a result could not take advantage of much of their force. The S-rotor which didn't have to swing or "track"-was able to absorb the full power of both. One of the Savonius design's greatest assets, in fact, is that it can take a wind from any direction at any time.
That same characteristic also gives the S-rotor a great advantage in durability. In a steady, low-speed wind the swinging of the Stuart mill is mechanically acceptable, but at higher speeds it's another story. The spinning propeller is just one big gyroscope, and its constant adjustment to the direction of the moving air exerts tremendous forces. The resulting "gyroscopic vibration" has sent many a propeller, generator and tower crashing to earth. The non-tracking Savonius unit experiences no such problems.
Even if the S-rotor did break loose, though, it wouldn't have far to fall. Unlike the conventional wind plant-which rotates horizontally and is mounted, along with its generator, on top of a tower-the Savonius device spins about a vertical shaft. This means that its alternator can be mounted on or near the ground. It also means no tower just a pole-with some guy wires. Think about that: easy access to the alternator, easy lowering of the unit and easy relocation, all minus the expense of an elaborate supporting structure!
If you watch the two units in action side by side, you'll note another major difference: The S-rotor appears to turn very slowly, with only one revolution for up to eight of the Stuart mill's. If you think that speed is necessary to a wind charger's function, however, think again. True, the conventional wind plant must attain a high rpm to operate but the S-rotor-which presents 10 to 20 times-as much surface area to the moving air mass-develops the same power at low rotational speeds.
Also, due to the Savonius plant's relatively slow rotational speed, its power output must be stepped up through some rather high gear ratios to drive an alternator fast enough to produce a meaningful amount of electricity. But so what? Such ratios create no re-starting problems for the S-rotor (as they do for a propeller driven unit) and are entirely practical for the Savonius machine.
The S-rotor has yet another advantage over the Stuart mill. The faster-turning blades of the second design must be well designed and balanced to operate at such speeds. Since few folks have the tools or know-how to do this, the airfoils (or the whole propeller) mutt often be purchased at high cost. By contrast, the slower moving S-rotor needs minimal or no balancing and its "wings" can be constructed quite simply and easily:
