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Balloons and Airships
Published in James DeLaurier, Aircraft Design Concepts, 2022
The source of heat was damp burning straw in a brazier. This produced considerable smoke, which the Montgolfier brothers wrongly assumed caused the buoyancy. The envelope was made from paper, and floating embers from the fire burned holes. This was a very hazardous and lucky flight. Just a month later Jacques Charles and Nicolas-Louis Robert successfully flew in a hydrogen-filled free balloon of their own design, and free ballooning for nearly the next two centuries consisted solely of gas balloons. Hot-air balloons only became practical after the development of modern fabrics (usually rip-stop nylon) and propane burner units (which produce heat with no embers).
Air, Noise, and Radiation
Published in Gary S. Moore, Kathleen A. Bell, Living with the Earth, 2018
Gary S. Moore, Kathleen A. Bell
Gravity pulls the atmosphere to earth with the densest part of the atmosphere closest to the surface. About 99 percent of the atmospheric mass is below 30 kilometers, 90 percent is below 12 kilometers, and 75 percent of the atmosphere is below 10 kilometers (Figure 10.5). A column of air exerts a pressure on an object at sea level of 43 Kg.cm2. This pressure can be demonstrated by creating a vacuum in a plastic bottle. The external atmospheric pressure will cause the bottle to collapse. Pressure is defined as the force per unit area and is related to the density of the air such that there is both low pressure and low density at higher altitudes. This can be demonstrated by boiling water first at sea level and then at high altitude. The temperature remains steady at 100°C as gases are released from the boiling water. Boiling the water atop a high mountain peak will occur at a lower temperature of perhaps 90°C, since the pressure is lower and gaseous vapors can escape more readily under lower pressure (Figure 10.6). Atmospheric pressure is measured by a barometer and normally expressed in millimeters or inches of mercury. The pressure at sea level is equal to 760 millimeters mercury (Hg), 29.92 inches of mercury, or 1010 millibars. Pressure and atmospheric density in the troposphere is not constant and varies in response to changes in thermal radiation and air movement. Air that is warmed rises in contrast to the cooler air around it. A hot air balloon uses a propane burner to heat the air inside a fabric envelope causing the balloon and its passengers to rise. The energy driving air movement in the atmosphere is sunlight, which strikes the earth at varying angles, warming the air unevenly. Warmer air becomes less dense, expands, and rises, thereby creating a column of air that is lower in pressure. Cooler air is denser, settles, and is characterized by higher pressure. Differences in pressure cause air to move in both horizontal and vertical patterns. Air tends to move from regions of high pressure to low pressure. Therefore, as sun heats a body of air and it rises, a region of low pressure is created into which flows cooler air. The greater the temperature differences, the larger the pressure differences will be, and the more rapid or violent will be the flow of air. If the air flows horizontally, this is known as wind. The direction of the wind is influenced by the rotation of the earth (Coriolis force—Chapter 1), friction, and the differential warming provided by the sun. Such forces cause air to flow into regions of low pressure in a cyclonic motion and then to rise. This cyclonic motion is counterclockwise in the northern hemisphere and clockwise in the southern hemisphere (Figure 10.7). When cool air descends in the northern hemisphere it is radiated outward in a clockwise motion known as an anticyclone (Figure 10.7). The direction is reversed to a counterclockwise motion in the southern hemisphere. These represent very large-scale air movements and play important roles in the dispersion of air pollutants. Low-pressure migrating cyclones usually are associated with inclement weather including precipitation, clouds, and windy conditions. High-pressure systems normally signal cooler dry air with sunny conditions.
Tubular polythene film balloons for load lifting in the construction, mining and recreation industries
Published in Australian Journal of Multi-Disciplinary Engineering, 2022
In the recreational ballooning industry passenger flights, usually about an hour in duration, are made with spherical hot air balloons carrying up to 20 passengers. However, for long distance three day races such as the Gordon Bennett Cup, hydrogen gas filled balloons are used each carrying two passengers and ballasts bringing the total load to about 1 tonne (Figure 6). The cost of the spherical balloon envelopes used is about US$40,000 (Cameron Balloons 2021a).°