Propeller Blade Size and Thrust

Hard

Does a bigger propeller push harder? Propeller blades work by pushing air backward. The reaction force moves the vehicle forward. Larger blades move more air with each spin. You build three propellers from zinc sheet metal in different sizes. Each one mounts on a 12V DC motor attached to a shoe box on wheels. You time how long the box takes to travel two meters. The largest propeller (30mm x 50mm) moves the box in 17 seconds. The smallest (20mm x 30mm) takes 51 seconds. Bigger blades produce noticeably more thrust at the same motor speed.

Hypothesis

The hypothesis is that increasing the propeller size will produce a larger amount of thrust.

Science Concepts Learned

Thrust

Propeller blades work by pushing air backward — the reaction force moves the vehicle forward. To test how blade size affects that push, you build three zinc sheet metal propellers in different sizes, each mounted on a 12V DC motor attached to a shoe box on wheels. Then you time how long the box takes to travel two meters. The largest propeller (30mm x 50mm) crosses the distance in 17 seconds, while the smallest (20mm x 30mm) takes 51 seconds. Bigger blades move more air with each spin and produce noticeably more thrust at the same motor speed.

Newton's Third Law

Newton's Third Law explains why propeller blades generate thrust: the spinning blade pushes air backward, and the air pushes the vehicle forward with an equal and opposite force. Larger blades move more air per rotation, so the reaction force pushing forward is greater. The largest propeller moved the box in 17 seconds while the smallest took 51 seconds, showing that increasing the backward push on air directly increases the forward push on the vehicle.

Propeller

A propeller's spinning blades push air backward, and the reaction force drives a vehicle forward. Larger blades move more air per rotation, generating greater thrust. This experiment demonstrates that relationship directly: a 30mm x 50mm propeller moves a shoe box in 17 seconds, while a 20mm x 30mm propeller takes 51 seconds at the same motor speed.

Method & Materials

You will build a propeller using a 12V DC motor, a zinc sheet, a wooden block, and other materials. You will then measure the thrust it produces by recording how long it takes for a shoe box to travel 2 meters.

You will need a 12V dc motor, a piece of zinc sheet, a pair of scissors, 3 wooden blocks, an electric hand drill and drill bits, a protractor, a screw driver and some screws, a shoe box, 4 toy car tires with 2 metal rods for support, a DC12V battery, a stopwatch, a ruler, and black masking tape.

Eureka Crate — engineering & invention kits for ages 12+ — monthly projects that build real-world skills. (Affiliate link)

See what’s included

Results

The results show that increasing the size of the propeller will make the box move faster. The hypothesis that increasing the propeller size will make the box move faster is proven correct.

Why do this project?

This science project is interesting because it demonstrates how a simple device like a propeller can produce a powerful force. It also shows how the size of the propeller affects the amount of thrust it produces.

Also Consider

Consider mounting the blades at different angles or changing the rotational speed of the motor. Also consider if the thickness of the propeller blade or the rigidity of the material used to make the propeller make a difference.