Wind-powered vehicle

Let's take a look!

What type of experiment is this?

Experimental procedure and explanation:

• Make a car that runs by rotating a propeller using rubber power.
• Fix the propeller shaft with a rubber attached to the car (the rubber power part uses the parts of a model airplane work kit). Allow the shaft of the tire to rotate freely.
• First, rotate the propeller in the reverse direction to twist the rubber.
• The propeller rotates when you release the hand holding the propeller, and then, the wind blows backward. At this time, the propeller pushes the air backward, and therefore, the rebound (reaction) causes the car to move forward.
• Let us take a closer look at this (enlarged view). The wind that hits the rotating propeller is turned by the propeller and bends backward. At this time, a force called “lift” acts on the propeller in the direction opposite to the force applied to the air to bend the flow. This force acts on all blades, and the resultant force becomes the force to move forward.
• This wind-powered car is similar to the previously released “Wind Car.” However, the working principle is exactly the opposite. Wind-powered vehicles use their own energy (the energy of rolled rubber) to blow the wind. The wind car absorbs the energy of the wind blowing around it, turns the propeller, and uses that energy to rotate the tires.

【発展】	Let us look at the wings of an electric fan in the house from the side. Both the blades of a wind-powered vehicle and the blades of the electric fan are curved rather than flat (called a “sled”). You will notice that it is bent in the opposite direction from the figure of the propeller of the wind-powered vehicle. The difference is that “the propeller of the wind-powered vehicle (convex to the front) allows air to flow backward,” and “the propeller of the electric fan (convex to the rear) allows air to flow forward.” The direction of rotation is also reversed. Thus, the direction of the lift acting on the propeller is reversed, which leads to the difference in letting the air backward or forward.
[Keywords]	Rotary wing, Momentum theory
[Related items]	Jet Propulsion, Wind Car 1, Wind Car 2
[Reference]	“The Wonders of Flow”, Japan Society of Mechanical Engineering, Kodansha Blue Backs, P114-117 and P192-197. “Illustrated Fluid Dynamics Trivia,” by Ryozo Ishiwata, Natsume Publishing, P222-223.

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