Table of Contents


Literature Review

Experimental Design


Test Station Construction





Statistical Analysis

Sources of Error


Glossary of Terms




The purpose of this project is to determine if multiple rotors will increase the electrical energy output of a horizontal axis windmill. Torque, the force created by the rotating horizontal axis, will be used to turn the axle of various sized DC motors and generate electricity. A digital multimeter will be used to measure mAmps and mVolts and electrical energy output in mWatts calculated. Revolutions per minute (RPM) and wind speed measurements will be used to calculate tip speed ratio. Various sized motors were used to assess the ability of the rotor variation to start and continuously turn larger motors.

Opposition to the production of electricity from fossil fuels is rising and the earth's non-renewable resources are being depleted. Twenty percent of all greenhouse gases released in Ontario in 2001, were produced by five coal fired power plants. Wind power offers a pollution free, electricity generating alternative, using a renewable energy source. The cost of wind generated electricity is declining, in comparison with other energy sources. Wind power is currently one of the fastest growing sources of electricity generation in the world, growing an average of 25% per year.

Most wind turbines are the single rotor, classic Danish three-blade design. Although there has been a large amount of research on windmill design, there appeared to be none published on the use of multiple rotors.

Results from Phase 1 of this project (Torque it Up!), indicated that multiple rotors did increase the torque of a horizontal axis windmill and could potentially produce more electrical energy. Subsequent to my initial research, I did find that researchers in California have been testing a multiple rotor windmill.

This research could impact on the construction of wind turbines. Multiple small rotors weigh less, are easier to produce and transport and are less subject to fatigue. Multiple rotors turn at lower wind speeds and produce more torque. Increased torque may permit increased turbine size and produce more electricity than that of a single rotor wind turbine.

The use of multiple rotors 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.

Engineering Objectives

My engineering objectives were to design and build a multiple rotor, horizontal axis, laboratory scale windmill that could be coupled to the axle of various sizes of DC motors. The scale model was used to determine the effect of different rotor attributes (number, size, distance apart and orientation of the rotors) and size of DC motor on the resulting mAmps and mVolts generated. The rotor arrangement and motor that produced the most electrical energy output was identified.


If a three-blade rotor on a horizontal axis windmill generates a given amount of electrical energy, then adding additional three-blade rotors will increase the amount of electrical energy output.

I predict that the distance between the rotors will affect the amount of electrical energy produced and that there is an optimal distance.

I predict that the orientation of the rotors (i.e. blades off set or in line) will affect the amount of electrical energy produced.

I predict that the size of the rotors will affect the amount of electrical energy produced.

I predict that single rotors will be able to start and continuously turn smaller DC motors but will be unable to start turning larger DC motors.

Literature Review