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Abstract Torque it Up! Multiple Rotors: A Novel Approach to Windmill Design The purpose of this project was to determine if multiple rotors would increase the torque of a horizontal axis windmill. Torque is the force created by a rotating shaft and is measured in Newton- Meters. Since mechanical power (watts) is the product of torque and rotational speed, revolutions per minute (RPM) were also measured. My hypothesis was that if a three-blade rotor on a horizontal axis windmill produced a given amount of torque and mechanical energy, then adding another three-blade rotor would increase the amount of torque and mechanical energy produced. I predicted that the size, distance apart and orientation (inline or offset) would affect the amount of torque and mechanical energy produced. The experiment was designed to measure the effect of the independent variables (rotor size and placement, fan speed) on the dependent variables (wind speed, torque and RPM). Weight in Newtons was measured using a spring scale that was connected perpendicular to the rotating axis with fishing line and the torque was calculated. Wind speed was measured with an anemometer and RPM with a digital tachometer. Each measurement was repeated ten times. In all, fourteen different rotor variables were tested at low, medium and high fan speeds. My hypothesis was correct. Every test using multiple rotors produced more torque than a single rotor. There were large differences in the amount of torque depending on blade size and orientation, and distance apart. The RPM and wind speed measurements were used to calculate tip speed and mechanical energy, in watts, was calculated for each rotor variable. Over all, two 28-centimeter (cm) rotors, placed 3.5 cm apart with the blades offset produced the most torque and mechanical energy. This rotor variation produced more than double the amount of torque and mechanical energy than a single 28 cm rotor. This research could impact on the construction of wind turbines. Increased torque may permit increased turbine size and produce more electricity than that of a single rotor wind turbine. The use of multiple rotors to increase torque could result in lower construction costs because rotor blades would be smaller, fewer support towers would be required and the overall efficiency of wind turbines would increase.
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