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The bottom end of the cabling is gathered at a load ring which acts as the interface between the envelope and the gondola cables. The load ring also serves as the system’s strong point for attachment of inflation harnesses or trail ropes. Equipment
Equipment carried varies with the purpose of the flight. A minimum equipment list should include an altimeter/variometer, compass, global positioning system (GPS), aircraft position lights, several flashlights (for night flights), oxygen (for high altitude flights), aircraft radio, and aircraft sectional maps for navigation and communication. [Figure 11-6] Other items which may be included for safety and occupant comfort may include: a first aid kit, adequate food, water, warm clothing, and toilet facilities for both the planned flight and for the postflight period before the recovery crew arrives.
Theory of Gas Ballooning
Complete books have been written on the theory of gas ballooning and a full discussion of the topic is not possible here. At the very least, three topics must be understood by the competent gas pilot: physics, weather aspects, and the significance of different lifting gases. Physics of Gas Ballooning
Four main factors are instrumental in determining lift:
1. Type of lifting gas used (e.g., helium, hydrogen, or anhydrous ammonia)
2. Amount of lifting gas in the envelope (usually equal to the envelope’s total capacity)
3. Outside air temperature
4. Ambient barometric pressure (which is directly related to altitude and local weather conditions).Lift at Sea Level
The generation of buoyancy (commonly referred to as “lift”) in a gas balloon is somewhat different from that of a hot air balloon. The basic principle is the same, but for different reasons.
One cubic meter of air weighs 2.702 pounds at sea level under International Standard Atmosphere (ISA) conditions (29.92 inches of mercury ("Hg) and 59 degrees Fahrenheit (°F) at sea level). At the same time, and also under ISA conditions, a cubic meter of helium weighs 0.3729 pounds. The difference between these two numbers, 2.329 pounds, is the gross lift of a gas balloon with a volume of one cubic meter. To determine the gross lift under ISA conditions, it then becomes a simple multiplication of 2.329 pounds times the volume of the envelope. For the standard 1,000 cubic meter gas balloon, the gross lift is 2,329 pounds.
The above calculation is valid for helium. If, however, hydrogen is used as the lifting gas, the factor is 0.189 pounds per cubic meter; anhydrous ammonia’s weight is 1.583 pounds per cubic meter. As compared to helium, hydrogen has 8 percent more gross lift per cubic meter, while ammonia has approximately 50 percent less lift than helium under ISA conditions.Lift at Altitude
As a balloon ascends, it is generally true that temperature, atmospheric pressure, and gross lift all decrease. Gross lift decreases as pressure decreases, but increases as temperature decreases. Thus, as a gas balloon rises in the atmosphere, the decreasing pressure and temperature oppose each other. The decreasing temperature increases lift while the decreasing pressure decreases lift. Atmospheric pressure changes are more significant than temperature changes. Thus, net lift decreases as altitude increases in a standard atmosphere.
11-6
When calculating the effect of changing pressure and temperature, it is necessary to multiply the sea level lift by the ratio of pressures and temperatures. For a nonstandard ambient pressure, multiply the lift at the ISA level either by 29.92 "Hg or 1,013.25 millibars (mb).
Temperatures at altitude must also be calculated and compensated for. The factor for temperature is a ratio of absolute temperatures expressed in either degrees Kelvin or Rankine. To get temperature in degrees Rankine, simply add 459 to the normal Fahrenheit temperature. For a new temperature, multiply the lift calculated at the ISA by the factor: (59 °F+ 459)/(new temperature + 459). When using temperature in degrees Centigrade (°C), add 273 to convert to absolute temperature (i.e., Kelvin). This is: (15 °C + 273)/(new temperature + 273). Various lift factors at differing altitudes, comparing helium and hydrogen, are illustrated in Appendix F.Pressure Ceiling
The pressure ceiling is the altitude at which the lifting gas inside the envelope would expand to just completely fill the envelope, assuming the balloon rose to that altitude. Rising above the pressure ceiling causes lifting gas to be expelled from the appendix and establishes a new, higher pressure ceiling. Exceeding the current pressure ceiling causes loss of lifting gas, reduces gross lift, and typically causes the balloon to eventually begin to descend. Ballast must be expended to maintain the new higher altitude. However, maneuvers that result in altitude changes below the pressure ceiling, do not result in loss of lifting gas or gross lift. Very little ballast is required to ascend while below the pressure ceiling. For these reasons, the gas pilot should always be aware of what the approximate current pressure ceiling is and should consider the consequences of penetrating that ceiling.
　
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