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Effect of propeller size on thrust producedFeatured science projectScience project video

Abstract

This science fair project was done to determine how the size of a propeller will affect the amount of forward thrust produced by it. The experiment was done using 4 different propeller sizes.

Hypothesis

Increasing the propeller size will produce a larger amount of thrust.

Scientific Terms

Propellers, propulsion, thrust, Bernoulli’s Principle, Newton’s 3rd Law of Motion

Background

Propeller and thrust

Propellers are devices with blades that spin around like a fan.  They are used to produce propulsion on boats and planes. The force produced by propellers can be explained by Bernoulli’s Principle and Newton’s 3rd Law of Motion. The rotational movement of the blades causes a displacement of air molecules that produces a forward motion called thrust.

A propeller is built with 2 or more blades that are attached to a central hub. The blades and the hub are connected to a shaft that extend from the engines. When an engine is started, the shaft turns, causing the blades and the hub to rotate. Blades have an aerofoil shape and when they turn, a difference in air or water pressure is created between the area in front and at the rear of the blades. This causes air or water to rush forward and thrust is produced.

A propeller’s forward thrust and speed can be improved by increasing the size of the blades, the rotational speed or blade angles. Increasing blade size and rotational speeds may not be possible due to mechanical constraints (eg. the blades hitting the hull or the onset of mechanical fatigue). The angle of the blade is normally varied along the blade’s length because each part of the blade travels at different speeds.
 

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Complexity level:
7
Project cost ($):
60
Time required:
1 day to prepare, 1 day for experiment
Material availability:
Easily found
Safety concerns:

Ensure the blades are properly fixed to the wooden block so that they do not come loose when they rotate.