|
Balloon Flying Menu > Introduction to Ballooning >
Physics
Essentially there are two kinds of balloons:
hot air balloons and gas balloons. There is also the smoke balloon,
which is a hot air balloon without an airborne heater, and the
solar balloon, but they are rare and almost nonexistent. This
handbook primarily covers hot air balloons.
Gas is defined as a substance possessing perfect
molecular mobility and the property of indefinite expansion,
as opposed to a solid or liquid.
The most popular gas used in ballooning is
hot air. As the air is heated, it expands making it less dense.Because
it has fewer molecules per given volume, it weighs less than
non-heated ambient air (air that surrounds an object) and is
lighter in weight.
As the air inside a balloon envelope is heated,
it becomes lighter than the outside air the envelope, causing
the balloon to rise. The greater the heat differential between
the air inside the envelope and the air outside, the faster
the balloon rises.
Hot air is constantly being lost from the top
of the envelope by leaking through the fabric, seams, and deflation
port. Heat is also being lost by radiation. Only the best and
newest fabrics are nearly airtight. Some fabrics become increasingly
porous with age and some colors radiate heat faster than others
do.Under certain conditions, some dark-colored envelopes may
gain heat from the sun. To compensate for heat loss, prolonged
flight is possible only if fuel is carried on board to make
heat.
To change altitude, the internal temperature
of the air in the envelope is raised to climb, or allowed to
cool to descend. Cooling of the envelope is also possible by
allowing hot air to escape through a vent. This temporary opening
closes and seals automatically when it is not in use.
| 
