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Saturday, May 19, 2018

Making A Flying Polystyrene Helicopter Science Toy

This educational polystyrene toy can be made easily at home. Polystyrene is also called as styro foam. The polystyrene is a used rectangular dish-shaped food container. As below photo, the polystyrene is used as apples container.

There is a container with corrugated surface, choose a container with flat and smooth surface. The container is cut into a propeller shape, then sanded so that the top becomes convex to form an airfoil. If the propeller is rotated, it will produce lift force that makes it glide in the air. It is like a real helicopter.

The following video shows the procedure for making this simple helicopter.

The propeller is flown by turning the handle with fingers. The handle is made of 12 mm diameter drinking straw, also called bubble straw.

Because of propeller blade sides are designed symmetry of the left and right, the rotation of the blades can be counter clockwise and can also be clockwise. And the propeller can still glide well in the air.

The following video shows the propeller rotated by fingers then floating and then landing gently. The propeller still spin a few moments after landing on the floor, like a real helicopter.

Video 240 fps (frame per second) shows details of the rotation of the blades when flying. But this type of helicopter is slightly different. Because it has additional red cardboard at the tip of propeller to make it look clear.

The first step to make this helicopter propeller is to cut the polystyrene container to get its base. The thickness of this container is about 3-4 mm.

Then depicted the shape of square rectangle measuring 80 x 80 mm, as the photo below.

Then draw diagonal lines on all corners of the rectangle, in order to make it easier to draw symmetrical blades. As the picture above, blade width is about 14 to 16 mm.

Cut the blade carefully, do not to cut the center part, as the photo below.

The top side of the blade is then sanded with fine sandpaper to form the airfoil.

Preferably the propeller and sandpaper are wetted with water so that the dust does not fly.

Once sanded the propeller will be shaped an airfoil with the upper cross section convex and the bottom straight, as the photo below.

The shape of the left and right side of blade are symmetrical. Unlike most helicopter blades, these blades do not have angle of attack. Because of this design, the propellers can be rotated left or right to produce lift.

Prepare drinking straws 12 mm in diameter, cut a 25 mm length.

Cut one end about 5 mm length to form 4 pieces of tongue.

The four tongues are expanded as below photo.

Use paper insulation tape to attach straw to the bottom side of propeller. Make sure its position in the center. If using glue then it should be a special glue for polystyrene.

Note that the convex part of the airfoil must face upwards.

The helicopter is ready to fly by rotating it with fingers. If the propeller is positioned with slightly tilt angle as the photo above, it will fly in the direction of the lowest blade position. In the case of the photo above, it will fly to the right of the photo. The same principle is applied to the actual helicopter blade to move forward, sideways, and even backward.

This propeller produce lift because of differences in airflow velocity at the top and at the bottom.

In the above figure, due to the convex shape at top of the wing and straight at the bottom, the airflow from the left that goes to the top of the wing (point A) must pass a distance further than the airflow passing under the wing.

The two streams will be reunited in the right-hand side of the image. Due to distance A is further from distance B, then the flow velocity of A will be faster than flow B.

Because the speed of A is higher, then the pressure of A is lower than B. The air pressure at B will press the wing upward resulting in lift. 

Symmetrical blade allows this propeller to be rotated clockwise and counterclockwise to produce lift.

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