How a
Balloon Flies.
A balloon
flies because the gas contained within the balloon weights less than
the surrounding air.
There are
two ways in which the gas within the balloon might be made lighter:
- by heating
it (a hot air balloon)
- by filling
the balloon with a lighter than air gas like hydrogen or helium (a
gas balloon)
Hot Air
Balloons
Hot air balloons
are filled with air which is heated to make it lighter than the air outside
the balloon. When the air inside the balloon is heated sufficiently the
weight of the air inside the balloon plus the weight of the balloon and
passengers will be less than corresponding volume of unheated air and
the balloon will float.
A heater/burner
unit, controlled by the pilot, is used to heat the air inside the balloon.
As the air inside the balloon is heated the air molecules spread out
forcing some of the air near the bottom of the balloon to be pushed
out. When enough air has been pushed out of the balloon it lifts off.
The burner
uses LP Gas just like a barbecue. Balloons are huge and contain a lot
of air - a 4 person balloon contains about as much air as 4 houses.
To be able to control the balloon in flight the pilot needs to be able
to heat the air inside the balloon quickly. To do this the burner needs
to burn a lot of gas quickly, the fast burning gas makes a lot of noise
hence the whooshing sound that is heard every time the burner is ignited.
In flight
the air contained inside a hot air balloon will typically be between
65oC and 120oC (150oF - 250oF).
Balloons are fitted with a gauge so that the pilot knows what the temperature
is in the top of the balloon.
During
flight, the pilot uses the burner to control the temperature of the
air inside the balloon. The air inside the balloon is constantly cooling
so the pilot needs to periodically add some heat to keep the balloon
flying. By adding a little extra heat the balloon will climb by adding
a little less the balloon will descend.
Gas Balloons
Gas balloons
fly because the gas contained within the balloon is lighter than air (even
at the same temperature). The most common gases used are hydrogen and
helium although a number of other gases such as ammonia, coal gas and
natural gas are used in some parts of the world.
To make
a gas balloon climb the pilot reduces the weight of the balloon by throwing
some ballast (water or fine sand) overboard. To descend a small amount
of gas is vented through a valve in the top of the balloon.
Gas ballooning
is almost completely silent!
Gas ballooning
is not as popular as hot air ballooning, in fact there aren't any gas
balloons in Australia. This is because in most parts of the world helium
is quite expensive and the other gases used for lift are either flammable,
explosive or noxious and require special handling as a result.
