The Power of the Wind

By Bill Kuhl

There are many similarities in the operation of windmills and airplanes. On modern wind turbines, wind blowing over the curved, airfoil surfaces produces lift to turn the blades. This is considerably more efficient for producing electricity than the many flat blades of a typical farm windmill, although the flat blades produce good torque for pumping water.   

Outdoor model airplane enthusiasts become very familiar with the wind and thermal air currents. For most types of model flying, the least amount of wind makes for the best flying conditions, RC slope soaring being the exception. Model flyers know that wind is usually light early morning and in the evening, thermal air currents are strongest in the middle of the day, and listen to weather forecasts for wind predictions.    

This small wind turbine supplies some of the power needed for one household. The vertical fin in the rear, guides the wind turbine into the wind.		Aermotor windmill has curved blades instead of the flat blades other farm windmills have. This makes it more efficient.

Video of Modern Wind Turbine -  1.7 mb Mpeg File    Video of Farm Windmill - 1.2 mb Mpeg File

People who fly model airplanes outdoors have learned much about nuances of the wind; how it normally blows at a higher speed the farther from the ground, how it does not blow steady, and how thermal air currents influence the wind.  Model radio sailplane pilots are particularly aware of the wind and thermal air currents.

Types of Radio Control Sailplane Flying

Slope Soaring Model of a Bald Eagle Eagle in Flight - 3.3 mb Birds such as eagles, hawks, and vultures use both slope and thermal lift to fly at times.	Hi-performance model sailplane in flight, thermal soaring. Notice the long-slender wings. This is known as "hi-aspect ratio" and makes for a more efficient glide ratio.

Basically two ways sailplanes are kept aloft; from thermal air currents - rising columns of air and slope lift - wind blowing against sloping surface that deflects upward. The avid sailplane pilot will know the sources for wind condition predictions and plan their flying sessions accordingly. Thermal flying is best in light wind on days when the temperature rises greatly from early morning to afternoon. Slope soaring is best in strong, steady winds that blow directly into the slopes that are available for flying.

Model Sailplanes Can Fly in High Winds - Video clip of  50+ mph wind in North Dakota -

Relating to Wind Turbines

The slope soaring pilot knows that objects such as trees and buildings block the wind as it flows up the slope, this is true of wind turbines as well. Placement of a wind turbine is critical in generating more electricity from the wind. The higher the better, with fewer objects blocking the flow of the wind.  Thermal pilots know that the wind will completely change directions for brief time from a thermal in the immediate area, or it can become completely still for a brief time.  This can help explain why a wind turbine can change direction so quickly or slow down completely at times.

Wind Power Experiments Web Link

Observation Activities

• Take notice when you are in areas where you can see more than one flag, do you notice that the flags might be blowing in different directions, or one flag is not blowing while another flag is almost straight out?
• Notice how the wind maybe stronger towards the top of a large hill than at the bottom of the hill on the same day.
• Make observations over several days, at different times during day and notice how hard the wind is blowing. 
• Observe birds using thermal or slope lift. Larger birds such as eagles, hawks, and vultures often used either type of lift for flight. 
• Listen and/or watch weather forecasts on radio or television that include wind predictions, how accurate do those predictions seem? 

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