| By :
Roger Brown
The design of wind turbine blades is a lot like the propeller of an airplane. Once you understand what moves a light plane forward, the science of wind turbine blades is a lot more clear. Occasionally, blades on residential wind turbine need to be replaced, so it\'s important to understand what separates the good ones from the not so good ones. The system is also subject to the same kind of problems, like stalls. Once the blades stall, it is difficult to get them turning again. It simply takes a lot more energy to get them moving. The key element of wind turbine blade design is "angle of attack". That is, the angle at which the blade encounters the relative direction of the wind. This is important. For the turbine to be the most effective and harvest the most wind energy, the system needs to be facing into the wind. The aerodynamic qualities of the blades need to be such that they maximize lift and minimize drag. The blades themselves produce drag. Actually, it is the drag on the materials that in-part creates the mechanical action needed to push the blades and turn the shaft of the turbine. But, there is a fine line between enough drag and too much drag. The blade curvature or camber actually creates the aerodynamics to drive the blade. Wind tunnel testing of various designs is done to understand the options available to the designer to produce the most rpm in the lowest wind conditions. The blades on most small wind turbines are bolted in place directly on to the turbine shaft. One in place, there is not enough stress present to damage or loosen them -except in cases of very high wind. Replacement blades are readily available and can be tailored to the wind speed in your particular area. There are blades and wind turbine systems that function quite well with winds lower than 5 mph. These are typically the smaller systems. The larger windmills or turbines require much more wind to turn the blades. Those are the type you see arranged in fields, taking advantage of large, consistent wind patterns. Be careful when considering replacement blades. You must make sure the blades you choose fit your system and are of a low enough inertia that they will continue to turn even in low wind situations. Stalling of blades is a significant factor in blade design. The lowest speed that the blades stall, or quit turning is very significant. You must make sure that the stall speed stated in replacement blades is consistent with the wind conditions where you are located. Even though it would seem this wind turbine blades area would be straight forward, there is still more art than science here.
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