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. 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. 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] 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 (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. $_{Figure 11-10.}$  A gas balloon, shortly after the weigh off procedure,  ascends into the sky. 11-10 Solar Heating Inflight Procedures Launch