Jump to main content

Efficient Propeller Design

497 reviews


How does a helicopter generate enough lift to fly? How does a speedboat get moving fast enough to pull someone on water skis? Here's a project on designing propellers to do the job.


Areas of Science
Time Required
Average (6-10 days)
Previous experience with aerodynamic design (e.g., model airplanes, gliders) is suggested.
Material Availability
Specialty items
Low ($20 - $50)
No issues

Andrew Olson, Ph.D., Science Buddies


The goal of this project is to investigate how changes in chord length affect the efficiency of propellers.


A propeller, like an airplane wing, is an airfoil: a curved surface that can generate lift when air moves over it. When air moves over the surface of a moving propeller on an airplane, the air pressure in front of the propeller is reduced, and the air pressure behind the propeller is increased. The pressure imbalance tends to push the airplane forward. We say that the propeller is generating thrust.

The same principle applies to helicopter propellers, only now the propeller rotates around the vertical axis. The pressure on top of the propeller is reduced, and the pressure underneath is increased, generating lift.

The illustration (Figure 1) defines some terms that are used to describe the shape of a propeller. The radius (r) of the propeller is the distance from the center to the tip. The chord length (c) is the straight-line width of the propeller at a given distance along the radius. Depending on the design of the propeller, the chord length may be constant along the entire radius, or it may vary along the radius of the propeller. Another variable is the twist angle (β) of the propeller, which may also vary along the radius of the propeller.

Diagram of a propeller with the chord, twist and radius labeled
Figure 1. Illustration of terms used to describe propellers. The radius, r, of the propeller, is the distance from the center to the tip, along the center line. The chord length, c, is the straight-line width of the propeller at a given distance along the radius. The twist angle, β, is the local angle of the blade at a given distance along the radius (Hepperle, 2006).

In this project you will investigate how changing the chord length affects the efficiency of the propeller. You will keep the other design features (radius and twist angle) constant, changing only the chord length of the propeller. To measure the efficiency of the propeller, you'll connect the propeller to the shaft of a small DC motor. You will use the breeze from a household fan to make the propeller turn, which will cause the shaft of the motor to spin. In this configuration, the motor will act like a generator. You'll monitor the voltage produced by the motor to determine the efficiency of the propeller.

Terms and Concepts

To do this project, you should do research that enables you to understand the following terms and concepts:



  • Wikipedia is a good place to start for basic information on propellers:
    Wikipedia contributors, 2006. Propeller, Wikipedia, The Free Encyclopedia. Retrieved November 21, 2006.
  • You'll definitely want to check out the Propellers section (among others) of NASA's Beginner's Guide to Aeronautics. This site is packed with useful information on the science of flight:
    NASA, 2006. Beginner's Guide to Aeronautics, NASA Glenn Research Center. Retrieved November 22, 2006.
  • For more advanced students, these webpages on aerodynamics of model aircraft by Martin Hepperle will be useful. There is even a Java program that you can use to test your design ideas on the computer before building them:

Materials and Equipment

To do this experiment you will need the following materials and equipment:

Disclaimer: Science Buddies participates in affiliate programs with Home Science Tools, Amazon.com, Carolina Biological, and Jameco Electronics. Proceeds from the affiliate programs help support Science Buddies, a 501(c)(3) public charity, and keep our resources free for everyone. Our top priority is student learning. If you have any comments (positive or negative) related to purchases you've made for science projects from recommendations on our site, please let us know. Write to us at scibuddy@sciencebuddies.org.

Experimental Procedure

  1. Do your background research so that you are knowledgeable about the terms, concepts, and questions, above.
  2. First you will need to make four (or more) different propellers, keeping the propeller radius and twist angle (pitch) constant, while systematically varying the chord length.
  3. For testing, attach a propeller securely to the shaft of the DC motor. Depending on the materials used for the propeller, it could be taped on to the motor shaft, or drilled and press-fit.
  4. Using the alligator clips, connect the 4.7 kΩ resistor across the terminals of the motor, and also connect the terminals to the voltage inputs for the multimeter, as shown in Figure 2. If you need help using a multimeter, check out the Science Buddies reference How to Use a Multimeter.
How to Use a Multimeter
Alligator clips attach a motor to probes on a multimeter
Figure 2. This picture shows the electrical connections for this experiment (but not the rest of the materials like the propeller and the fan). The 4.7 kΩ resistor is connected across the motor terminals with the alligator clips. The other ends of the alligator clips are connected to the multimeter probes.
  1. Turn the multimeter to read DC volts, in the range for tens of millivolts.
  2. Starting with the fan on low speed, hold the propeller/motor assembly in front of the fan. You'll want to test in the exact same spot each time.
  3. The propeller may need a small push to start turning in order to overcome the internal friction of the motor. The moving air from the fan should keep the propeller turning after this. If not, turn the fan to the next speed and try again.
  4. Observe and record the reading from the multimeter in a data table in your lab notebook. The reading will fluctuate slightly. You can round the reading to the nearest millivolt. Note that the reading will be quite sensitive to distance from the fan. Make sure that all of your measurements are taken at the same distance from the fan.
  5. The mounting of the propeller to the motor may also affect the reading. If you are taping the propeller in place, you should repeat your measurements after removing and remounting the propeller to see how consistent your results are.
  6. Repeat the measurements for each propeller.
  7. Calculate the average voltage reading from the measurements for each propeller. More advanced students should also calculate the standard deviation.
  8. Make a graph of the voltage produced (y-axis) vs. chord length of the propeller (x-axis). Is there a systematic relationship between chord length and rotational speed of the propeller?
icon scientific method

Ask an Expert

Do you have specific questions about your science project? Our team of volunteer scientists can help. Our Experts won't do the work for you, but they will make suggestions, offer guidance, and help you troubleshoot.

Global Connections

The United Nations Sustainable Development Goals (UNSDGs) are a blueprint to achieve a better and more sustainable future for all.
This project explores topics key to Industry, Innovation and Infrastructure: Build resilient infrastructure, promote sustainable industrialization and foster innovation.


  • Test different propellers with different chord lengths while holding twist angle and mass of the propeller constant. To keep the mass constant, you will need to reduce the radius somewhat as the chord length increases. Do you find the same results as when the radius was held constant? Why or why not?
  • Test the propellers at different fan speeds and compare the results. Do the same relationships between the propellers hold at all fan speeds?
  • There are a number of possible variations on this project. Instead of examining the effect of the propeller's chord, you could investigate:
    • twist angle (pitch); Freedom Flight Models sells a handy jig for measuring the twist angle of a propeller (see Figure 3, below), or you could make one of your own.
      Protractor measures the pitch of a propeller blade
      Figure 3. Propeller pitch gauge from Freedom Flight Models.
    • airfoil shape (camber of the propeller)
    • blade shape
    • number of blades
    • sweep (like a swept wing)
  • This project uses an indirect method for measuring the propeller's rotational speed. Devise a way to measure the thrust produced by the propeller directly. For example, you could design a low friction mount for the motor that allows the motor to slide back and forth (along the propeller mount axis). Connect the motor to a gram spring scale to measure the force produced when the motor turns the propeller. How does thrust produced change with voltage applied to the motor? (Increasing voltage increases the rotational speed of the propeller.) How does the thrust measurement compare to the rotational speed measurement from this project?


If you like this project, you might enjoy exploring these related careers:

Career Profile
Humans have always longed to fly and to make other things fly, both through the air and into outer space—aerospace engineers are the people that make those dreams come true. They design, build, and test vehicles like airplanes, helicopters, balloons, rockets, missiles, satellites, and spacecraft. Read more
Career Profile
Just as a potter forms clay, or a steel worker molds molten steel, electrical and electronics engineers gather and shape electricity and use it to make products that transmit power or transmit information. Electrical and electronics engineers may specialize in one of the millions of products that make or use electricity, like cell phones, electric motors, microwaves, medical instruments, airline navigation system, or handheld games. Read more
Career Profile
Mechanical engineers are part of your everyday life, designing the spoon you used to eat your breakfast, your breakfast's packaging, the flip-top cap on your toothpaste tube, the zipper on your jacket, the car, bike, or bus you took to school, the chair you sat in, the door handle you grasped and the hinges it opened on, and the ballpoint pen you used to take your test. Virtually every object that you see around you has passed through the hands of a mechanical engineer. Consequently, their… Read more
Career Profile
Aerospace engineering and operations technicians are essential to the development of new aircraft and space vehicles. They build, test, and maintain parts for air and spacecraft, and assemble, test, and maintain the vehicles as well. They are key members of a flight readiness team, preparing space vehicles for launch in clean rooms, and on the launch pad. They also help troubleshoot launch or flight failures by testing suspect parts. Read more
Career Profile
Industrial engineering technicians and technologists work in a lot of different places. They work side by side with engineers to set up and fix processes and machines. Do you like to work with puzzles? If so, you could apply problem solving skills to helping companies improve the way they make products or serve customers. Whether you'd like to work in a factory, office, repair shop or healthcare organization, there is a place for you as an Industrial Engineering Technician or Technologist. Read more

News Feed on This Topic

, ,

Cite This Page

General citation information is provided here. Be sure to check the formatting, including capitalization, for the method you are using and update your citation, as needed.

MLA Style

Science Buddies Staff. "Efficient Propeller Design." Science Buddies, 26 Oct. 2023, https://www.sciencebuddies.org/science-fair-projects/project-ideas/Aero_p018/aerodynamics-hydrodynamics/efficient-propeller-design?from=Home. Accessed 9 Dec. 2023.

APA Style

Science Buddies Staff. (2023, October 26). Efficient Propeller Design. Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/Aero_p018/aerodynamics-hydrodynamics/efficient-propeller-design?from=Home

Last edit date: 2023-10-26
Free science fair projects.