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A study of propeller designs for wind generators

A study of propeller designs for wind generators

Introduction: (Initial Observation)

Wind power generators use the wind power to run an electric generator in order to produce electricity. In a wind power generator, propellers must be able to get the highest amount of wind kinetic energy and transmit it to the electric generator. The design of propellers, determines the rate of such energy conversion.

In this project you study some of the fundamentals of interaction between air current and solid objects (propeller in this case). Similar techniques are being used to design cars, airplanes, buildings and bridges.

The only difference is that in such applications the purpose is minimizing the forces caused by air current, but in propeller design we intend to maximize such forces.

You research on the propeller design factors that affect the energy production of wind generators.You will make models and calculate the amount of energy in Jules while changing one variable at a time. Each design factor is one variable for your research. You may focus on one design variable or expand your research to multiple variables or factors. Some of the factors that you may study are: Size, Diameter, Pitch, blade area, blade angle, weight, ..


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Find out about what you want to investigate. Read books, magazines or ask professionals who might know in order to learn about the effect or area of study. Keep track of where you got your information from.

If you like to collect information from the Internet, you may start from www.WindPower.org for some general information. You can even use some parts of the same website for more details.

Also see some cool pictures of windmills?

Introduction to wind energy

We have been harnessing the wind’s energy for hundreds of years. From old Holland to farms in the United States, windmills have been used for pumping water or grinding grain. Today, the windmill’s modern equivalent – a wind turbine – can use the wind’s energy to generate electricity.

Wind turbines, like windmills, are mounted on a tower to capture the most energy. At 100 feet (30 meters) or more aboveground, they can take advantage of the faster and less turbulent wind. Turbines catch the wind’s energy with their propeller-like blades. Usually, two or three blades are mounted on a shaft to form a rotor.

A blade acts much like an airplane wing. When the wind blows, a pocket of low-pressure air forms on the downwind side of the blade. The low-pressure air pocket then pulls the blade toward it, causing the rotor to turn. This is called lift. The force of the lift is actually much stronger than the wind’s force against the front side of the blade, which is called drag. The combination of lift and drag causes the rotor to spin like a propeller, and the turning shaft spins a generator to make electricity.

Wind turbines can be used as stand-alone applications, or they can be connected to a utility power grid or even combined with a photovoltaic (solar cell) system. Stand-alone wind turbines are typically used for water pumping or communications. However, homeowners or farmers in windy areas can also use wind turbines as a way to cut their electric bills. For utility-scale sources of wind energy, a large number of wind turbines are usually built close together to form a wind plant. Several electricity providers today use wind plants to supply power to their customers.

To see a detailed diagram of a real windmill, you can visit the website of some windmill manufacturers.

The workings of a windmill:

Look at the diagram and fill in the blanks.

(a) A system of cogs change the turning movement from horizontal to ___________.

(b) The small wheel at the back acts as a sail and pushes the top of the windmill around so that it _________ into the wind.

(c) The __________ makes the sails turn in a big circle.

(d) The top of the windmill is separate from the rest of the mill and can move around on _________.

(e) The ____________ central column makes the grindstone turn.

(f) Grains of wheat, oats, barley or other cereals are __________ into the mill.

(g) _________ is produced when the grains are ground.

Modern Windmills:

1. Modern blades are specially designed to capture more energy from the wind. They are made from light (yet strong) composite materials to enable them to survive gusty winds, and they use aerodynamic controls or “brakes” to control speeds.

2. The latest rotor hub designs are flexible, allowing increased rotor efficiency, while minimizing damaging drive train and structural loads.

3. Innovative direct-drive low-speed generator and power train designs allow a wind turbine to produce power at variable rotor speeds. This allows designers to make machines more efficient and easier to control, while eliminating or reducing the size of expensive gearboxes.

4. Special tower designs and construction materials allow designers to use taller towers to place the turbine higher, where the wind is stronger and more energy is available.

5. Advanced power control systems improve the control of the wind turbine in constantly varying wind conditions, continually optimizing the power produced while minimizing fatigue damage.

More advanced and older students may make wind powered electric generators that really works. Making a working generator requires some craft and mechanical skills. Following link is a good sample and help for such project. http://www.otherpower.com/woodmill.html.


Wind Power, Components:

Propeller (Blades)
The blades of a propeller catch the wind. When the wind blows against them, they change the horizontal movement of the wind into a rotational force turning the shaft. The generator then turns this movement into electricity. Blades come in many sizes; the longest blades in use today are over 50 meters long.

The generator converts the mechanical energy of the rotating shaft into electrical energy. This electricity is then sent to homes and businesses where machines change the electricity into forms that consumers can use such as heat and light.

The tower lifts the wind turbine up high so that it can take advantage of the stronger, more consistent winds which blow above the ground. The world’s tallest towers are more than ten stories high.


Batteries are an important part of remote wind systems because they serve to stabilize the power fluctuations from the wind turbine and store the excess energy production. This stored energy is then available to supply the loads during low wind periods.

Wind Power Site

Finding the best site for a wind turbine is essential. The wind itself is rarely a steady, consistent flow, and obstructions such as nearby buildings or hills can reduce the performance of the turbine. Furthermore, wind speed varies naturally with the time of day, the season, and the height of the turbine above the ground.

Samples of propellers

Many windmills such as those in the right picture directly use the wind energy to do a work like grinding grain into flour.

Windmill using coat hangers

We received this creative design from Mr. Philippe Paul.

He has used coat hangers and a bicycle rim to make a windmill propeller. This is how he describes his design.

Using a coat hanger, I traced the inner enclosed area on a piece of ceiling Styrofoam. I then cut nine pieces with a razor blade to fill in the nine coat hangers that make up the windmill (27 spokes or 3 times 9 repeat patterns).
I used Styrofoam on the model that is shown in the picture, but later (shrink wrapped) covered the coat hangers with plastic. I used a sealer and a heat gun to make the plastic tight.
The other “ingredient” was scotch tape. I wrapped some tape around the corner of the hanger to hold the Styrofoam pieces in place. So far I taped the hanger corners that are near the rim and will not try to put any tape near the axle until a strong wind proves to me that it is needed.

I gently jammed the corner of a plastic coat hanger in a triangular opening created by two spokes connecting to the axle. The tip of the corner of the coat hanger itself could be touching the chrome shinny part of the axle. The next step is to wrap the hook of the coat hanger around a spoke that is connecting to the outer rim. After these two steps, the coat hanger will swing loosely but is already attached to the wheel. The next step is to gently push the other corner of the coat hanger (with the palm of your hand) as close to the rim as possible. This is when you decide what the angle of inclination of the blades will be relative to the plane of rotation of the wheel itself.

At the chosen angle, the coat hanger will make contact with the adjacent spokes at two locations. This is when I started to get the feeling that the thing was building itself. While holding the coat hanger at the proper angle, wrap five turns or more of shinny scotch tape around the two contact points where the coat hanger touches the adjacent spokes. Once you install the first coat hanger, count 1,2,3 and install another one. The shinny scotch tape can be as strong as you need it to be by adding more turns. However some kind of metal clip with chew the plastic in the long run. I prefer the tape.

Question/ Purpose:

What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.

The purpose of this project is to study experiment different propeller designs to find out which propeller design can get the highest wind energy.

Identify Variables:

When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.

Design factors or independent variables that we study are:

  • Number of blades
  • Length of blades
  • Position of blades in relation to the axel or shaft
  • Angel of blades
  • Width of the blades at different distances from the center of propeller
  • Cone in the center of propeller

Dependent variables are speed and power of propeller at a certain wind speed.


Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.

Experiment Design:

Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”

There are two different ways that you can test your propeller.

In the First method you use the wind power to lift a weight. You will then calculate the amount of work (in Joules) by multiplying the weight (in kilograms) by the distance (in meters) that it is lifted. You may then divide the work by the number of seconds that it took to move. That gives you the power in watts. Again you modify the design and repeat your tests to find which design produces the highest power.

In the Second method, you connect your propeller to a generator such as a bicycle dynamo and you will measure the voltage. Higher voltage often means a higher power and a better propeller design. So you start to modify the design and repeat your test to see which design produces a higher voltage. If you want to calculate the power in watts, connect a light bulb to the circuit and measure the current as well as voltage, then multiply the current by the voltage. Watts = Volts x Ampers

Experiment 1:

In this experiment you will make a model of a wooden windmill. This windmill can be used to lift a weight and for some additional experiments such as measuring the power of windmill.

The way that this experiment is being proposed here requires adults help and supervision. If you don’t have an expert adult and proper tools, simply eliminate all cuttings and drillings and try to assemble all pieces just by glue. Even instead of a piece of wood, you can glue a few pieces of cardboard in a multi layer form to build a similar piece. You will have to wait a longer time for glue to dry, but being safe is better than being sorry.

Procedure: (Change the design based on material and tools that you have access to)

Use about 3 feet long piece of 1 x 2 wood. (It is known as one by two, but it’s real size is 0.75″ x 1.5″).

Start by cutting a square piece of wood to be the center of the blades. Sample in the picture is 1.5″ x 1.5″ x 0.75″, but what you make can be larger or smaller.

Sand it so it will have smooth surface and edges.

This is going to be the center of the propeller.

Locate the center of the square and make a hole on that. This is the axis hole. I used a 1/8 inch drill bit, because the nail that I used as axis is slightly ticker than 1/8 inch. (10d 3 inch nail).

Secure the square wood by an adjustable clamp and use a saw to cut diagonal 0.25″ groves on all rectangular sides.

Sand one side of each Popsicle stick so it will fit the grove. Then apply some wood glue and insert the Popsicle sticks. Allow about 8 hours for the glue to dry.

How? Place the sand paper on a table and push one end of the Popsicle stick in a 30 degree angle on the paper and move it to left and right.

Insert the nail in the center hole, so it goes trough and comes out of the other side. It should take some force and may cause your wood to break if it is not strong enough.

Make another hole using a larger drill bit (slightly larger than the thickness of the nail that you are using.) on the long piece of wood, about 1 inch from one end.

Inset the nail that is now the axis of your blades into this hole. It should spin freely. You may use a spacer between the blades and the long wood that is now your windmill tower. A few small metal washers can be used as spacers. Spacers will make sure that the body of the blades will not touch the tower and cause friction.

Now hold the windmill in a windy area and blades should start to spin.

You can make a wooden base for your windmill or insert it in an empty plastic or metal container and fill around that with sand. We temporarily used a clamp to hold it for taking a picture.

You can use your newly built windmill to do some tests and some more experiments.

For example you may want to use the windmill to do some work such as lifting a weight. We want to see what is the heaviest weight that the windmill can lift.

Tightly attach a string to the nail. You can use any glue or adhesive tape to attach the string to the rod. Now, attach the weight to the bottom of the string letting it hang from the string.

Next, expose the windmill to wind and see whether or not the weight gets coiled up. If there is no wind, you can use an electric fan or blower to test your windmill. Do several tests with different weighted objects to see how much weight the windmills can lift.

You may alter the design of propeller and repeat the test.

For each design that you make, see if that is good for low speed or high speed winds.

Experiment 2:

In this experiment, you connect your propeller to a generator such as a bicycle dynamo and you will measure the voltage. Higher voltage often means a higher power and a better propeller design. So you start to modify the design and repeat your test to see which design produces a higher voltage. If you want to calculate the power in watts, connect a light bulb to the circuit and measure the current as well as voltage, then multiply the current by the voltage. Watts = Volts x Ampers

Note: Electric generators are hard to spin. You need a higher force than your previous experiment. Make a larger propeller for this experiment and test it under a stronger wind.


Make a propeller with a center hole of 3/4″ and mount it directly on a 12-volt bicycle generator. Now you have a wind generator. Place your wind generator in a wind channel and record the produced voltage. You may use an electric fan or blower to make your own wind channel.

Propeller for this experiment can be made similar to the one in previous example. When you need to change the with of blades at some points, you can cut pieces of card board or balsa wood and glue it on your existing propeller.

Your wind generator that now consists of a propeller and a bicycle generator can be hold in a wind current and tested by turning on a light bulb.

It can also be mounted on the top of a wooden tower that you may make.

Please note that bicycle generators are designed to be used in high number of cycles per minute. When you connect a propeller directly to a generator, it usually does not spin very fast, so the produced voltage is much less than the maximum ability of the generator. For example when you use a 12 volts generator, you will probably get about 2 volts power unless you have access to a very high speed wind. If you want to connect your generator to a light bulb, select a low voltage light bulb for your initial tests so you will get some light.

If you want to install your generator on a tower, you may secure it using a screw or additional pieces of wood.

After completing all your tests, you may also do some decorative work to cover the generator and give a good shape to your wind mill.

Materials and Equipment:

Make a list of material that you use for this part of your report.

Results of Experiment (Observation):

Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.

When you change a variable and repeat the experiment, you will know the effect of that variable on the results. Record the results of all your experiments related to one variable in a table. For example when you are testing the number of blades, Start from 2 blades and go up and record the voltage that you get for different number of blades. Following is a sample:

Number of blades on propeller Wind source Maximum Voltage
2 Electric Fan 1.2 Volts


Make a similar table for every variable that you test.


No calculations are required, however if you do any calculations during your design, write your calculations in your report.

Summary of Results:

Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.

It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.


Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.

Related Questions & Answers:

What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.

Possible Errors:

If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.

If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.