Windmills have been used for many generations for the purpose of pumping water from the ground and for generating electricity. The basic advantage of the windmill is that it uses the power of the wind to rotate a wheel having radially extending blades that are driven by the wind. This rotary movement is converted into various useful purposes. For example, wind turbines in the form of propellers mounted on towers have been placed in areas where steady winds are prevalent and the wind turbines are used to generate electricity.
The blades of the conventional wind turbines are very large and made of expensive rigid material and are constructed to have the blades extend radially from a central hub, with no extra support at the outer tips of the blades. The conventional wind turbine blades rotate at a high rate of revolutions and must withstand both the centrifugal forces generated by the fast revolution of the blades and the cantilever bending forces applied to the blades by the wind. Since the outer portions of the blades move at a very high velocity and are engaged by strong winds, the larger the blades the stronger they must be and the more expensive they become. Thus, there is a practical limit as to the length and width of the blades because of the expense of stronger materials for larger blades.
Another type of wind turbine is one that has sail wings constructed of cloth that are a substitute for the rigid blades of the conventional wind turbines described above. For example U.S. Pat. Nos. 4,330,714, 4,350,895, and 4,729,716 disclose wind turbines that do not use rigid propeller blades but use sails that catch the wind. The sails are mounted on radiating spars of the turbine. These particular wind turbines include circular inner and outer rims with the sails of the turbine supported by both the inner and outer rims. The outer rim supports the outer portions of the sails so that the force of the wind applied to the sails may be absorbed to a major extent by the outer rim so there is little if any cantilever force applied to the sails. This allows the blades of the wind turbine to be formed of lighter weight material, material that is not required to bear as much stress in comparison to the typical free bladed turbine. However, the relative speed of the wind on a turbine wheel is greater near the outer portions of the blades of the turbine wheel in comparison with the inner portions of the blades, and the above noted patents do not teach adjustments for changing the pitch or twist of the cloth blades in a turbine wheel for compensating for different wind loads on different parts of the blades.
A feature in some of the prior art wind turbines is the means by which the speed of the turbine may be adjusted when the wind velocity changes. For example, some of the wind turbines may be turned away from facing directly into the wind during high speed winds. Others may increase the load applied by the electrical generator that is driven by the wind turbine. However, it is desirable that the load of the generator be maintained at a desired level, and it is desirable to avoid frequent changes in the direction in which the wind turbine faces.
Thus, it would be desirable to produce and use a wind turbine that includes an outer support rim for supporting light weight sailwings that may assume the approximate shape of an airfoil with shape control means for adjusting the shape of the airfoil and to form a preferred shape for wind conditions.