Hot Air Balloon
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Hot air balloons are a leisure flying air vessel that uses warm air from burning propane, as energy. Hot air balloons have three main parts: an envelope or balloon, a basket, and burners. The envelope is a bag of strong nylon fabric with an opening at one end called a mouth. The basket is used to carry passengers and is attached to the envelope with very strong metal cables. These balloons can carry 2-24 people depending on their size. The burners of the balloon are the "engine". A simple scientific principle powers hot air balloons: warm air rises in cooler air. The mass per unit of volume of warm air is less than cold air.
To keep the balloon moving, there must be a way to keep reheating the air; this is where propane comes in. Under the envelope there are burners positioned with propane tanks connecting to them. The propane tanks mix with pressurized oxygen and ignite it. The pilot directs the flames into the mouth of the balloon to heat the air through a small valve. To make the balloon move downwards, the pilot opens the parachute valve. The parachute valve is a circle of fabric cut at the very top of the balloon, or envelop, controlled by a long cord. The cord runs down the envelop to the basket. To land, the pilot pulls the cord to let the hot air escape. The cool air lets it ascend. Since they are not like helicopters or planes they cannot land in pre-designated places, this is the reason air balloons are flown in the countryside or empty plots of land.