The Effect of Blade Separation and Windspeed on a Savonius Rotor Windmill

Researched by Hank H.



The purpose of this experiment was to determine the diameter and height of a Savonius Rotor Windmill so that it will produce the most power. 

I became interested in this idea because I have always been fascinated by the air that can lift a plane and blow down trees even though you can’t see it. I wanted to know the best way to use catch it and make things spin, in this case, a Savonius Rotor Windmill.

The information gained from this experiment will help power companies or people with wells (Savonius Rotor Windmills are more often used with pumps that power generators) to build the most efficient windmill.


My first hypothesis was that the largest separation would produce the most power.

My second hypothesis was that the highest wind speed would produce the most power with either height of blades.

Experiment Design

The constants in this experiment were Blade diameter and wind speed of fan.

The manipulated variables were Height, blade separation and distance of fan from rotor.

The responding variable was the power output of a motor connected to the windmill. 

To measure the responding variable I connected a voltmeter to the generator.

Quantity  Item Description
1 Reasonably Sized Baseboard
2 12'' by 4'' halves of a pipe
2 18'' by 4'' halves of a pipe
2  2'' by 4'' boards at least 24'' long
1 2'' by 4'' board at least 17'' long
2 1' by 1’ pieces of sand paper
2 1' by 1’ pieces of sand paper
1 1' diameter plastic plates
1 generator (coils of wire and magnets)
1 voltmeter that can measure millivolts
1 3' steel pole with bolt threads


To build the Savonius Rotor Windmill
1.Cut in half 12’’ by 4’’ and an 18’’ by 4’’ pipes. 
2.Construct a frame at least 20’’ wide and 25’’ tall, drill a hole through the middle of the top board.
3.Saw a space so a 1 cm. wide steel pole may enter, then drill a hole half way through the base board and place a bearing so the pole may freely turn.
4.Cut and glue the sandpaper to the plastic plates.
5.Drill a hole in the middle of the plates, the place the steel pole through them.
6.Place either 12’’ or 18’’ blades between the plates.
7. Use nuts and washers to keep them in place.
8. Connect a rubber band to steel rod and an electric motor.
9. Connect a milivolt meter to the electric motor.
10.Place a fan in front of windmill and make sure milivolt meter is receiving electricity. 

Testing the Savonius Rotor
1.Loosen sandpaper and adjust 12 in. blades so they are 0 in. apart.
2.Place fan directly in front of the windmill.
3.Wait approximately 1 minute for windmill to be at full speed. Record output.
4.Repeat steps 1-3 with blades separated 1,2,3, and 4 in. apart. Record output
5.Repeat steps 1-4 with 18 in. blades. Record output.


The original purpose of this experiment was to find out the best separation of blades and wind speed of a Savonius Rotor Windmill so that it will produce the most power.

The results of the experiment indicate that the largest blade separation and highest wind speed produce the most power.

See my table and graphs


My first hypothesis was that the most blade separation would produce the most power.

My second hypothesis was that the highest wind speed would produce the most power with either of the blade heights.

The results indicate that my first and second hypothesis will be kept.

Because of the results of this experiment, I wonder if I put a different diameter blade that windmill would put out more or less power. 

If I were to conduct this project again I would add different heights and diameters of blades with higher wind speeds to test. 

Savonius Windmill

 The word "windmill" comes from the words wind and mill. Mill means machine that grinds grain, so natually windmill would mean a wind powered machine that grinds grain. Another word for windmill is turbine, which means transforming the kinetic energy of the fluid(the wind) into mechanical energy which can be used or transformed into electricity.
 There are many types of windmills, for example, a Savonius, Darius or a Aeration windmill. Every windmill is either a verticle-axis or a horizontal-axis windmill. Savonius and Darrieus windmills are both verticle-axis windmills, whereas Aeration windmills are horizontal-axis windmills.
 Verticle-axis windmills were first invented in 1500 bc to grind grain, the meaning of the word windmill. They are also much easier to use because you can use the spinning rotor at ground level, instead at the top of your windmill in horizontal-axis windmills.
  I chose to study Savonius Windmills because of their simple design. They only have one rotating axis and have multiple purposes. They can create power just as well as a normal windmill but also have potential for pumping water. Savonius Windmills can be created with easily attainable parts, such as buckets and pipes. This allows one to be created without much difficulty in construction or use.
 The savonius is a simple design that includes two blades, usually half-circles opposite of each other. There are other designs as well, but not as common or easily constructed. 
 The topic I studied was which wind speed and blade separation was most efficient. I found that blades slightly overlapping each other with the highest wind speed produced the most power. For my project, I used the most easily constructed design, not, however the most efficient. I simply used half circles by cutting pipes in half, the most efficient is a blade with a curved section on the outer part of the windmill, and a straight section in.
 In 1922, Anton Flettner, a German engineer and the University of Gottingen, invented a boat that had Savonius windmills  instead of sails. He found that a Savonius windmill propelling the boat instead of a sail puts our 15 times as much momentum. The reason it is not use today is the vibration of the rotor which led to mechanical problems. 
 In 1985, Jacques Cousteau made a similar Savonius rotor boar called the Alcyone. The rotors were not used as a main source for propulsion but reduced the fuel usage by more than 30%.
 The Savonius Rotor is not only used for boats, but it can do anything any other windmill can do but much more simply.



Plotkin, Allen "Wind Tunnel" Worldbook Encyclopedia, 1999, volume 21, Pg. 333
Banks, Howard "Gliders"  Worldbook Encyclopedia, 1994, Volume 8, Pg. 228
McCormick, Barnes "Helicopters"  Worldbook Encyclopedia,, 2001
Weather Fundamentals, Wind, Schlessinger, 1998
Savonius Rotor, <>
Wind Power and Windmills, <>



First of all, I thank my dad, for helping me conduct my experiment and helping me do everything.
I will also thank Mrs.Helms, for always being their when you ask for her, always knowing what to do next.
Mr.Newkirk helped with every big thing that needed changing, guiding me along the way.
The other people I'd like to thank are my fellow students for answering my questions when I asked and telling me the answers to the questions they asked.

Top of page

Menu of 2002-2003 Science Projects

Back to the Selah Homepage