Science corner

6th December 2002 at 00:00
Sophie Duncan explains how to launch a lesson about air cushion vehicles

The hovercraft or ACV (air cushioned vehicle) was invented by Christopher Cockerell in 1956. He worked on small boats and was looking for a way to make them more efficient by blowing air along the hull to reduce drag. His experiments were always very practical and included using a vacuum cleaner, some kitchen scales and a couple of old cans. Cockerell also came up with the name "hovercraft".

When you design and build a classroom hovercraft, the lift provided by a small cushion of air is fairly small, so it is important to keep the craft as light as possible and avoid unnecessary baggage. You also need to think about the source of the air.

Are you going to power the craft with your own breath or use a balloon? The craft can be made of thin plastic (try yoghurt cartons or margarine lids), CDs, thin cardboard, or polystyrene. The tube through which the air travels could be a cotton reel, a cardboard tube, or a film canister. A skirt could be made from plastic, foil or paper.

The device must direct the air to the bottom of the craft and you should check the design for leaks, and so on. One successful design uses a polystyrene tile cut into a circle and a cardboard tube (for example, from a kitchen roll). The tube is placed in the centre of the polystyrene circle and drawn around.

The small circle is cut from the centre of the tile and the cardboard tube is fixed into the centre with glue and tape, making sure that the join is airtight.

To launch the craft place it on a smooth surface and blow into the tube. The craft should hover above the table and can be moved with a gentle push.

Another great design makes use of a CD and a cotton reel. Attach the cotton reel to the CD. Blow up a balloon and twist the end. Feed this through the centre of the reel and then through the CD. Blow a little more air on to the balloon. Place the CD on a smooth surface and give it a push. It should move away over the desk.

Test your designs. Which travels the furthest? Which hovers for longest? Does using a skirt make a difference? Can you make it work on water?

Sophie Duncan is a physicist and programme manager with Planet Science (formerly Science Year) www.planet-science.com

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