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There are two main types of balloons, hot air and gas, but other specialty type balloons are also flown. The Rozier balloon is an example of a less common balloon. A hybrid balloon that utilizes both heated and unheated lifting gases for long distance record flights, a Rozier was flown by Steve Fossett in his record-setting first solo circumnavigation in 2002. A recent addition to the hot air balloon field is the solar balloon, which uses heat radiation from the sun to provide lift. This handbook primarily covers hot air balloons.
Why Do Balloons Fly?
The physics of balloon flight is based on the principles of fluid dynamics and associated theorems. Therefore, it is helpful to think of the air, the medium of balloon flight, as a fluid when discussing the concept of “buoyancy” as applied to balloon flight. In physics, buoyancy is the upward force of an object produced by the surrounding fluid (i.e., liquid or gas) in which it is fully or partially immersed, due to the pressure difference of the fluid between the top and bottom
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F
igure 2-1. Basic balloon terms.Deflation portEnvelopeHorizontal load tapesVertical load tapesBasketCrown lineHeating systemMouth/ThroatSkirt or scoop
Figure 2-3. Basic balloon terms.
Figure 2-2. The air inside the balloon envelope is heated to create buoyancy.
of the object. The net upward buoyancy force is equal to the magnitude of the weight of fluid displaced by the object. This force enables the object to float or at least to appear lighter. An object must make room for its own volume by pushing aside, or displacing, an equal volume of liquid. For example, an aircraft carrier exerts downward force on the water and the water exerts upward force on the aircraft carrier. A solid object floats when it has displaced just enough water, or air in the case of a balloon, to equal its own original weight.
To create the necessary buoyancy for flight, the air inside the balloon envelope is heated which causes the air to expand, making it less dense. [Figure 2-2] Once the interior air weighs less than the non-heated ambient air (air that surrounds an object), the balloon becomes lighter in weight and rises in an effort to find a level where the interior air density matches that of the exterior air density. The envelope is carried along “for the ride,” as it does little more than contain the heated air mass. The balloon rises to a point where the lift created by the action of heating the air is equal or greater than that of the balloon itself. The balloon rises because it has reached a state of “positive buoyancy” and the amount of lift is greater than the weight of the balloon.
The greater the heat differential between the air inside the envelope and the ambient air, 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 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.
The internal temperature of the air in the envelope is raised or lowered to change altitude. To climb, the temperature in the envelope is raised by heating the air which creates more lift. To descend, the air in the envelope is allowed to cool. Cooling of the envelope is also possible by allowing hot air to escape through a vent. This temporary opening closes and seals automatically, due to the upward pressure, when it is not in use.
A balloon’s weight when in flight is not only the figure as stated in the flight manual, but also includes the weight of the air within the inflated envelope, the balloon components and equipment, as well as the pilot and passengers. The average 77,000 cubic foot hot air balloon contains an air mass that weighs over 3,000 pounds. By adding all these factors together, it is easy to understand how weight influences the balloon’s response to pilot actions during flight maneuvers. The weight and sheer momentum of a balloon in flight make it difficult for a pilot to effect rapid changes. Balloon Components
A hot air balloon consists of three main components: envelope, heater system, and basket. In addition, flight instruments, fuel tanks, and other support equipment are needed for a safe balloon flight. [Figure 2-3] The most common ballooning terms are used in the following text, in
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Figure 2-5. Special shape balloons.
F
igure 2-2. Parachute value.Overlap for air sealActuation line (deflation/vent)
Figure 2-4. Deflation system.
the generic illustrations, and are also listed in the glossary which contains balloon and aeronautical terminology. Some terms and names used by manufacturers are also included. Envelope
The envelope is usually made of light-weight and strong synthetic fabrics such as ripstop nylon or Dacron®. The material is cut into panels which are sewn together in vertical rows that are called gores due to their triangular shape. The traditional envelope shape is a teardrop. The gores are reinforced with sewn-in webbing called horizontal and vertical structural load tapes which are continuous to the top center of the balloon where they are sewn into a load ring. Galvanized, stainless steel, or Kevlar® cables transfer basket loads to load tapes which in turn support the load. The nylon “skirt” at the base of the envelope is coated with special fire resistant material to keep the flame from igniting the balloon.
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Balloon Flying Handbook(21)
