Take a trip in a hot air ballon


How are hot air baloons made

A hot air balloon for manned flight uses a
single layered, fabric gas bag (liftingA range of envelope sizes is available. The
"envelope"), with an opening at the bottomsmallest, one-person, basket-less balloons
called the mouth. Attached to the envelope is(called "Hoppers" or "Cloudhoppers") have
a basket, or gondola, for carrying theless than 1,000 cubic meters (35,000 ft3) of
passengers. Mounted above the basket andenvelope volume. At the other end of the
centered in the mouth is the "burner" whichscale are the balloons used by large
injects a flame into the envelope, heatingcommercial sightseeing operations that carry
the air within. Raising the air temperaturewell over two dozen people and have envelope
inside the envelope makes it lighter than thevolumes of up to 15,000 cubic meters (600,000
surrounding (ambient) air. This causes theft3). However, most balloons are roughly
balloon  and  its  payload  to  rise.2,500 cubic meters (100,000 ft3) and carry 3
to  4  people.
Modern hot air balloons are usually made of
synthetic fabrics such as ripstop nylon, aThe Rozier type of hybrid balloon, called
light weight fabric of high strength. Duringafter its creator, Jean-Francois Pilatre de
the manufacturing process, the material isRozier, has separate cell for helium as well
cut into panels and sewn together, along withas a cone below for hot air (as is used in a
structural load tapes (webbing) that carryhot air balloon) to heat the helium at night.
the weight of the gondola or basket. The
heater or burner is fueled by propane, aThe direction of flight depends on the wind,
liquefied gas stored in pressure vessels,but the altitude of the balloon can be
similar  to high pressure forklift cylinders.controlled by changing the temperature of the
air  inside  the  envelope.
The amount of lift (or buoyancy) provided by
a hot air balloon depends primarily upon theThe top of the balloon usually has a vent of
difference between the temperature of the airsome sort. The most common type of vent is a
inside the envelope and the temperature ofdisk-shaped flap of fabric called a parachute
the air outside the envelope. For mostvent. The fabric is connected around its edge
envelopes made of nylon fabric, the maximumto a set of "vent lines" that converge in the
internal temperature is limited tocenter. (The arrangement of fabric and lines
approximately 120 °C (250 °F). Itlooks roughly like a parachute -- thus the
should be noted that the melting point ofname.) These "vent lines" are themselves
nylon is significantly higher than theseconnected to a control line that runs to the
maximum operating temperature -- about 230basket. A parachute vent is opened by pulling
°C (450 °F). However the loweron the control line. Once the control line is
temperatures are generally used because thereleased, the pressure of the remaining hot
higher the temperature, the more quickly theair pushes the vent fabric back into place. A
strength of the nylon fabric degrades overparachute vent can be opened briefly while in
time. With a maximum operating temperature offlight to initiate a rapid descent. (Slower
120 °C, balloon envelopes can generally bedescents are initiated by allowing the air in
flown for between 400 and 500 hours beforethe balloon to cool naturally.) The vent is
the fabric needs to be replaced. Many balloonpulled completely open to collapse the
pilots operate their envelopes atballoon  after  landing.
temperatures significantly below the maximum
in order to extend the longevity of theirAn older, and today less commonly used, style
envelope  fabric.of vent is called a "Velcro-style" vent. This
too is a disk of fabric at the top of the
For typical atmospheric conditions, a hot airballoon. However, rather than having a set of
balloon requires about 3 cubic meters of"vent lines" that can repeatedly open and
envelope volume in order to lift 1 kilogramclose the vent, the vent is secured by "hook
(50 ft3/lb). The precise amount of liftand loop" fasteners (such as Velcro) and is
provided depends not only upon the internalonly opened at the end of the flight.
temperature mentioned above, but the externalBalloons equipped with a "Velcro-style" vent
temperature, altitude above sea level, andtypically have a second "maneuvering vent"
humidity of the surrounding air. On a hotbuilt into the side (as opposed to the top)
day, the balloon cannot be loaded as much asof  the  balloon.
on a cool day, because the temperature
required for launch will exceed the maximumSome hot air balloons have turning vents
sustainable  for  nylon  envelope  fabric.which are side vents which, when opened,
cause the balloon to rotate. Such vents are
In the lower atmosphere, the lift provided byparticularly useful for balloons with
a hot air balloon decreases about 3% for eachrectangular baskets in order to align the
1,000 meters (1% per 1,000 ft) of altitudewider side of the basket for landing.
gained.



1 A B C D 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117