| A hot air balloon for manned flight uses
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| | about 3% for each 1,000 meters (1% per
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| a single layered, fabric gas bag (lifting
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| | 1,000 ft) of altitude gained.
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| "envelope"), with an opening at the
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| | A range of envelope sizes is available.
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| bottom called the mouth. Attached to the
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| | The smallest, one-person, basket-less
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| envelope is a basket, or gondola, for
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| | balloons (called "Hoppers" or
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| carrying the passengers. Mounted above
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| | "Cloudhoppers") have less than 1,000
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| the basket and centered in the mouth is
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| | cubic meters (35,000 ft3) of envelope
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| the "burner" which injects a flame into
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| | volume. At the other end of the scale are
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| the envelope, heating the air within.
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| | the balloons used by large commercial
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| Raising the air temperature inside the
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| | sightseeing operations that carry well
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| envelope makes it lighter than the
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| | over two dozen people and have envelope
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| surrounding (ambient) air. This causes
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| | volumes of up to 15,000 cubic meters
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| the balloon and its payload to rise.
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| | (600,000 ft3). However, most balloons are
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| Modern hot air balloons are usually made
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| | roughly 2,500 cubic meters (100,000 ft3)
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| of synthetic fabrics such as ripstop
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| | and carry 3 to 4 people.
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| nylon, a light weight fabric of high
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| | The Rozier type of hybrid balloon, called
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| strength. During the manufacturing
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| | after its creator, Jean-Francois Pilatre
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| process, the material is cut into panels
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| | de Rozier, has separate cell for helium
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| and sewn together, along with structural
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| | as well as a cone below for hot air (as
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| load tapes (webbing) that carry the
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| | is used in a hot air balloon) to heat the
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| weight of the gondola or basket. The
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| | helium at night.
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| heater or burner is fueled by propane, a
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| | The direction of flight depends on the
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| liquefied gas stored in pressure vessels,
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| | wind, but the altitude of the balloon can
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| similar to high pressure forklift
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| | be controlled by changing the temperature
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| cylinders.
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| | of the air inside the envelope.
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| The amount of lift (or buoyancy) provided
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| | The top of the balloon usually has a vent
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| by a hot air balloon depends primarily
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| | of some sort. The most common type of
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| upon the difference between the
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| | vent is a disk-shaped flap of fabric
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| temperature of the air inside the
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| | called a parachute vent. The fabric is
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| envelope and the temperature of the air
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| | connected around its edge to a set of
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| outside the envelope. For most envelopes
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| | "vent lines" that converge in the center.
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| made of nylon fabric, the maximum
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| | (The arrangement of fabric and lines
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| internal temperature is limited to
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| | looks roughly like a parachute -- thus
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| approximately 120 °C (250 °F). It
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| | the name.) These "vent lines" are
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| should be noted that the melting point of
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| | themselves connected to a control line
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| nylon is significantly higher than these
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| | that runs to the basket. A parachute vent
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| maximum operating temperature -- about
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| | is opened by pulling on the control line.
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| 230 °C (450 °F). However the lower
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| | Once the control line is released, the
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| temperatures are generally used because
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| | pressure of the remaining hot air pushes
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| the higher the temperature, the more
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| | the vent fabric back into place. A
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| quickly the strength of the nylon fabric
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| | parachute vent can be opened briefly
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| degrades over time. With a maximum
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| | while in flight to initiate a rapid
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| operating temperature of 120 °C, balloon
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| | descent. (Slower descents are initiated
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| envelopes can generally be flown for
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| | by allowing the air in the balloon to
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| between 400 and 500 hours before the
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| | cool naturally.) The vent is pulled
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| fabric needs to be replaced. Many balloon
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| | completely open to collapse the balloon
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| pilots operate their envelopes at
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| | after landing.
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| temperatures significantly below the
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| | An older, and today less commonly used,
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| maximum in order to extend the longevity
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| | style of vent is called a "Velcro-style"
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| of their envelope fabric.
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| | vent. This too is a disk of fabric at the
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| For typical atmospheric conditions, a hot
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| | top of the balloon. However, rather than
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| air balloon requires about 3 cubic meters
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| | having a set of "vent lines" that can
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| of envelope volume in order to lift 1
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| | repeatedly open and close the vent, the
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| kilogram (50 ft3/lb). The precise amount
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| | vent is secured by "hook and loop"
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| of lift provided depends not only upon
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| | fasteners (such as Velcro) and is only
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| the internal temperature mentioned above,
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| | opened at the end of the flight. Balloons
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| but the external temperature, altitude
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| | equipped with a "Velcro-style" vent
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| above sea level, and humidity of the
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| | typically have a second "maneuvering
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| surrounding air. On a hot day, the
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| | vent" built into the side (as opposed to
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| balloon cannot be loaded as much as on a
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| | the top) of the balloon.
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| cool day, because the temperature
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| | Some hot air balloons have turning vents
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| required for launch will exceed the
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| | which are side vents which, when opened,
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| maximum sustainable for nylon envelope
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| | cause the balloon to rotate. Such vents
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| fabric.
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| | are particularly useful for balloons with
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| In the lower atmosphere, the lift
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| | rectangular baskets in order to align the
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| provided by a hot air balloon decreases
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| | wider side of the basket for landing.
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