01 November 2009

## cardhelicopter.jpg

### Ingredients

 Some stiff card from a cereal box or something similar 3 pencils: 2 short and 1 long some tape scissors

### Instructions

Tape the three pencils together:

 Tape the two short pencils either side of the longer one. (The launcher) Cut a piece of card about 2cm by 10cm, and then mark two holes either side of the centre. Then punch two holes at these points ,using another pen or pencil.

It is a good idea to put something soft under the card when you are doing the punching  - otherwise you will probably either make a hole in your table, or your hand.

Make sure the holes are quite loose on the launcher, so that the card can lift off easily.

 make two diagonal flaps on opposite corners of the piece of card, both pointing down. Put the piece of card on the launcher and spin!

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### Result

With any  luck, and a bit of practise, you should be able to get the helicopter to take off and fly for 3-4 seconds.

### Explanation

When you spin the piece of card, it moves through the air like a wing. As the air hits the flaps, it is forced downwards. Isaac Newton worked out that if you push something one way, it will push you back; so the card pushing the air downwards means that the air pushes the card upwards.

Essentially you have built a rotating wing. The wing is moving through the air even if the card stays over the same place, therefore it can hover.

This is exactly the same principle as a helicopter, but a helicopter has added problems. Because its engine is always pushing the rotor blade around, the equal and opposite force should cause the helicopter to spin in the opposite direction. This is why helicopters have to have a tail rotor to provide a balancing force.

 The helicopter is twisting the blade in one direction (red) however the equal and opposite force twists the helicopter in the opposite direction (blue) The torque is canceled out by the tail rotor