HOVERCRAFT

You Will Need:

• A Small Funnel (the top of the funnel must be flat, not angled)

• A Balloon (large round ones work the best)

• Medium grit sandpaper

• A Smooth Table

• Some Large Books

TO MAKE YOUR HOVERCRAFT

Place a sheet of medium grit (aprox 150 grit) sandpaper on the table, rough side up.  Place the funnel on the sandpaper, top (large opening) side down.  Rub the funnel over the sandpaper until the edges are flat and smooth.

Inflate the balloon as full as it will go.  Twist the nozzle to keep the air from escaping, but don't tie it.  While holding the mouth of the balloon shut, stretch it over the bottom (small) end of the funnel.

Turn over the funnel and balloon, place the top opening of the funnel on the table.

EXPERIMENTING WITH THE HOVERCRAFT

1 - Let go of the balloon, allowing the air to go into the funnel.  Try pushing the funnel around the table.  Compare how easy it is for the funnel to be moved while the air is flowing to how easy it is for the funnel to be moved when the balloon runs out of air.

2 - Using some large books, raise the legs at one end of the table slightly (about 3 inches).  Place your hovercraft, with the balloon full of air, on the uphill end of the table.  Let go of the balloon, allowing the air to go into the funnel.  See how far the hovercraft can go before it runs out of air.

EXPLAINING HOW IT WORKS

A hovercraft works by forcing a cushion of air between the vehicle and the ground, or water that the vehicle is traveling over.  Since the friction of the air against the ground is less than the friction of the object against the ground, it allows the hovercraft to move forward with much less force than would otherwise be required.

On your hovercraft, the air pressure in the balloon was much greater than the air pressure around the balloon.  So, when you let go of the balloon, that air tried to escape.  The only way out of the balloon was through the funnel.  However, once the air was in the funnel, it was still trapped.

To escape from the funnel, the air had to push its way through the space between the funnel and the table.  This in turn lifted the hovercraft slightly off of the table.  As I stated earlier, the lower friction between the air and the surface allowed your hovercraft to move easily.

In a real hovercraft, the "air cushion" between the vehicle is produced by large fans pointing downward.  That way, it has a continuous supply of air holding  it up.  The hovercraft will also have a thick curtain around the edges, to help keep the air from escaping.  This increases the efficiency of the fans creating the air cushion.  Additional fans, that look like aircraft propellers are pointed backwards, to push the hovercraft forward.  Steering is provided by an aircraft type tail and rudder.

Since a vehicle of this type can't be stopped quickly, or make sharp turns, they are usually not used over land.  You wouldn't want one following you down the street.  If you stopped, it might not be able to.

Today, we find hovercrafts being used instead of boats for car ferries across the English Channel, and other bodies of water.  Since there is little friction, they can travel much faster than normal boat type ferries. When the hovercraft reaches land, it has no problem going right up the beach to where it will unload.

The military has also found uses for hovercrafts.  In World War 2, the Allied forces arrived in England in landing craft. These were boxy boats, able to carry about a company of infantry, or a couple of tanks.  The problem with these landing craft were that they had to stop before they ran aground on the beach.  The soldiers then had to wade to the beach, while being fired upon.  Today, this same task can be done much quicker and more efficiently with hovercraft.  Not only can the hovercraft move faster, but they don't have to stop at the beach. Instead they can drop the soldiers off well up on land.