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After this, an equipment list can be developed and a system weight and ballast calculation should be performed. Permission to use the desired launch site must be confirmed and the availability of adequate gas supply and launch and chase crew must be assured. A concise schedule should be sent to all crew members, defining when decisions are made and how these decisions are communicated to the crew.
Finally, all inflation and flight equipment must be assembled and checked out for proper functioning. The chase vehicle selected should be able cover the expected distance and bring all participants back home.Layout and Inflation
When the day comes, all equipment is transported to the launch site. A site “walk-around” is performed to remove
11-10
Figure 11-10. A gas balloon, shortly after the weigh off procedure, ascends into the sky.Inflight Procedures
All other things being equal, a gas balloon’s natural tendency is to find its equilibrium altitude and to fly level at that altitude. By contrast, a hot air balloon’s natural tendency to descend must be counteracted with periodic infusions of heat. In a gas balloon, pilot action is only required to initiate or arrest an ascent or descent or to counter atmospheric or other disturbances. A gas balloon may fly for an hour or longer with no intervention by the pilot. Pilot initiated altitude changes with gas balloons tend to occur at a slower rate over a longer time period as compared to hot air ballooning.
Ascents are initiated by jettisoning ballast (usually sand or water) while descents result from releasing lifting gas from a valve at the top of the envelope.
Significant midflight altitude changes are often undertaken as part of a long-term strategic plan rather than for short term tactical reasons. The consequences of any maneuver should be considered carefully before being undertaken. It is often stated that ballast is the fuel of a gas balloon and well before all ballast has been expended, the aircraft must be safely back on the ground. Use of large amounts of ballast to execute a major ascent invariably shortens the potential duration of a flight.
For example, in a distance competition, an ascent from the surface to 12,000 feet MSL may be executed to enter more favorable winds. This may take 1 hour to accomplish but that altitude may then be maintained for the next 8 hours if weather conditions are stable.
Two additional concepts that must be understood to pilot gas balloons are solar heating and lifting gas purity.Solar Heating
Solar heating (also called super-heating) occurs when the heat of the sun is trapped inside the balloon’s envelope and causes the temperature of the lifting gas to exceed the outside air temperature. As the heated lifting gas expands, one of two things will happen. If the envelope is flaccid, the less dense gas occupies a larger fraction of the envelope’s volume and displaces more air and the system’s gross lift temporarily increases. This causes the balloon to rise towards its pressure ceiling and it also temporarily causes the pressure ceiling to drop. When the envelope becomes full (i.e., reaches its pressure ceiling), gas is expelled and a new ceiling is established.
A good rule of thumb is to take no more time than is necessary to complete the fill. This is especially true in windy conditions. Launch
With the use of a checklist, confirm that all required equipment items and pilots are on board. A launch master is usually assigned to direct removal of excess inflation ballast until the system is neutrally buoyant. Desired ascent rate determines how much additional ballast is removed to attain the proper amount of positive buoyancy. The launch master should be an experienced gas balloonist and direct crew to allow the balloon to rise several feet off the ground several times to test the buoyancy before instructing the crew to bring it back to the ground one last time before final release. If the ascent rate is too slow, additional ballast are removed until the proper rate is achieved. After a final check for airspace clearance above, the “Hands off!” command is given and the balloon is allowed to fly free. [Figure 11-10]
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If the flight is continued through sunset, loss of solar heating results in a cooling of the lifting gas and a resultant loss of gross lift. Ballast must then be used to maintain buoyancy.Purity of Lifting Gas
A final topic of interest is the effect of mixing air with the lifting gas. It may seem that since air is heavier than the lifting gas, the air would have a tendency to pool at the bottom of the envelope and be expelled through the appendix as the balloon rises into less dense air. However, this is not what happens. The forces of molecular attractions cause the air and lifting gas to become permanently mixed and a generally less pure mixture occurs. When this happens, some of the benefits of operating under the pressure ceiling are lost and every up/down maneuver causes the loss of lifting gas along with the expelled air.
　
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