A Vertical axis wind turbine
You can build your own wind turbine to generate electricty at home.
Issue No. 32 - March/April 1975
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From the alternative energy experimenter's point of view,
"free as the wind" is better poetry than economics. The
power of the world's moving air masses can be harnessed, of
course (and often is, with great success) but the machines
designed for the purpose are generally heavy, complex, and
expensive. This drawback limits the use of windplants both
in developed countries where they usually can't compete
with conventional sources of electricity-and poorer nations
(which lack the capital for the large initial investment).
Over four years ago, two Canadian scientists-Peter South
and Raj Rangi, both affiliated with the National Research
Council of Canada's National Aeronautical Laboratory-began
work on a simple, lightweight, inexpensive wind device that
could be used in developing countries for irrigation and
electric power supply. Their finished design seems to offer
most of the conventional windplant's advantages without its
more serious faults and has aroused a good deal of interest
from some unexpected quarters.
The Rangi-South wind turbine
consists of two or three blades-of uniform width and
symmetrical airfoil shape attached to a vertical shaft. The
tower is mounted on ball bearing hubs at both ends and
braced with guy wires strung from the top.
The machine has
been nicknamed "eggbeater" because of its distinctive
curved blades which bulge outward from the vertical axis
with no central support at all. This rather eerie-looking
feature is an essential part of the design. The Canadian
researchers first experimented with straight vanes mounted
parallel to the shaft, and found that these needed
extensive bracing to withstand the centrifugal forces at
high speeds of rotation. Their solution was to redesign the
blades as catenary curves the pattern formed by a flexible
cord hung between two points. As they hoped, the new shape
reduced bending stress to a minimum and eliminated the need
for bracing. (A later search revealed an expired patent for
the same idea, taken out in 1931 by a French inventor named
Darrieus.)
The result is an amazingly simple device, light
in weight (onesixth to one-tenth that of a conventional
windplant), and able to pick up a breeze from any direction
without complex controls to point it into the moving air
mass. The only additions required by the basic design are a
modest self starting mechanism and a set of aerodynamic
'spoilers to limit the speed of rotation.
