Introduction
This chapter discusses topics relating specifically to manned gas ballooning. The understanding and flying of gas balloons is
very similar to hot air ballooning, but there are also significant differences. This chapter generally discusses the differences
and assumes that the reader is familiar with the topics in the other chapters of this handbook. Frequent comparisons to hot
air ballooning are used to place discussions in a more familiar context for the hot air balloon pilot.
Much of this chapter relates to gas balloons with an envelope volume of 1,000 cubic meters (35,315 cubic feet). This is
by far the most common size and is the maximum volume allowed for the major competitions. Several types of lifting gas
are discussed, but the main emphasis is on helium and hydrogen. All discussions assume that the envelope is the “zero
pressure” type. Zero pressure envelopes have an open appendix, or tube, at the bottom that maintains a zero pressure
difference between the gas inside the envelope and the atmospheric air outside. Neither super-pressure balloons nor Rozière
(a type of gas-hot air hybrid construction) balloons are discussed
Gas ballooning was once the most common form of aviation in the United States. Today, due to the costs involved,
gas flights are most frequently undertaken for training, competition, or record breaking purposes. Short, recreational gas
flights, while not unheard of, are much less common than hot air.
The History of Gas Ballooning
The first gas balloon flight occurred just a few weeks after the first manned balloon flight of Jean-François Pilâtre de
Rozier and the Marquis d’Arlandes. While the Montgolfiers were experimenting with hot air balloons, the Robert brothers
and Jacques Charles were also experimenting with gas balloons.
The first gas balloon was small (13 feet in diameter) and was filled with what was called “inflammable air.” [Figure 11-1]
It generated 35 pounds of net lift and, when set free, remained aloft for 45 minutes and traveled 15 miles. Its final, sudden
descent was attributed to a rupture in the balloon.
Chapter 11: The Gas Balloon
Valve
Ripping panel
Valve line
Open neck
Hoop or load ring
Ballast
Basket
Neck line
Ripping line
Figure 11-1. Early style of gas balloon. Many of these terms still apply today.
With the success of the demonstration flight, Charles next made a 25.5-foot diameter globe of rubberized silk. A net was
fitted over the upper half of the balloon and tied to a loop around the middle of the bag. From this loop, a sort of car or boat
was suspended. The bag was tied at the bottom to contain the gas. Dropping ballast caused the balloon to rise, and releasing
gas through a valve at the top made it fall. On December 1, 1783, Professor Charles and Nicholas Robert made the first
manned gas balloon flight. The first flight lasted for 1 hour and 45 minutes, rose to 1,800 feet, and covered more than 27
miles. On landing, Robert got out of the boat and Charles, now flying solo, ascended to almost 9,000 feet. The balloon had
been flaccid on first landing, but filled out as it rose and gas was released to prevent it from bursting. Benjamin Franklin
was present for this lift off and recognized the potential for balloons in military operations.
Other ascensions followed, mostly to gather scientific data. It was through these early experiments that the design/shape of
gas balloons, lifting capacity, and weight of air were determined. One notable early flight was the crossing of the English
Channel from Britain to France by Jean-Pierre Blanchard and Dr. John Jeffries on January 7, 1785. Their balloon was
scarcely sufficient to carry them and they threw out their ballast, anchors, food, and clothing to complete the crossing.
In 1906, James Gordon Bennett needed news for his newspaper and having been successful in starting car and boat races,
decided to initiate a gas balloon race. The first race was organized for Paris, France. Each country could send contestants
to the race. This race, the Coupe Aéronautique de Gordon Bennett, is still held annually although there were years when
no race occurred due to wars. Today, the race is the most prestigious gas balloon race in the world. It is sanctioned by the
Fédération Aéronautique Internationale (FAI). The country of the previous year’s winner is entitled to host the race. In
2006, the 50th race was held flying out of Belgium.
The Albuquerque International Balloon Fiesta (AIBF) started the America’s Challenge Gas Balloon Race in 1995. It has
been conducted yearly, with the exception of 1999 when AIBF instead hosted the Gordon Bennett Race. This has become
a very prestigious and international race that offers pilots the opportunity for extremely long flights
Balloon Systems
Gas balloons designs are generally classified as netted or quick fill.
Netted Balloon Systems
The netted design [Figure 11-2] dates from the 18th century. A spherical balloon envelope is encased in a diamond mesh
net of light weight cord that runs around the balloon from the apex valve at the top of the envelope down to support points
on the gondola.
Figure 11-2. “Spirit of Springfield,” a netted gas ballon.
Inflation is accomplished by first bringing the inflation hose to the center of a ground tarp. The envelope is next laid over
the hose with the hose inserted into the appendix and with the apex of the balloon on top and centered. The net is deployed
over and attached to the envelope and as the lifting gas is flowed, sandbags are hung on the diamonds of the net at ground
level. As the balloon fills and forms a rising hemisphere, the crew moves the sandbags down the net to keep them at ground
level. Enough bags are added to keep the balloon anchored to the ground.
After the envelope is completely filled, it is raised and the basket is brought underneath and attached to the net. The
hemispherical shape is very stable in moderate to high ground winds as the flow is over the top of the shape. One drawback
of netted balloons is that more crew is required to manage the sandbags during inflation.
Quick Fill Balloon Systems
The quick fill design dates from the mid 20th century. A natural shape envelope is surrounded by vertical support tapes
that run from the apex of the balloon down to the gondola. [Figure 11-3] Several horizontal tapes extend circumferentially
around and are attached to the vertical tapes to stabilize the structure.
Figure 11-3. Quick fill design gas balloon.
Inflation is accomplished by laying out the envelope on the ground along its full length with the apex at one end and the
appendix (base) at the other. The gondola is attached to the load lines and is bagged down. As the lifting gas is flowed
in through the appendix, several crew members hold the apex of the balloon down. When enough gas has entered the
envelope to generate approximately 100 to 150 pounds of net lift, the apex is released, the envelope rises, and the inflation
is completed.
Lifting Gases
Modern gas balloons normally use helium or hydrogen as the lifting gas. Anhydrous ammonia and methane are two other
less common options. Helium is a monotomic, inert gas and must be refined to reach a purity of greater than 99 percent
from raw well gas at a purity of a few percent. Hydrogen typically exists in the molecular form H 2. It is flammable when
combined in a mixture of 25 percent H2 to 75 percent air. This means that this mixture supports an existing flame.
Helium is expensive but is more commonly used in the United States while hydrogen is more common in Europe. Helium
provides slightly less lift than hydrogen but is the more stable gas. (See subsection titled “Flying in Inversions” in this
chapter for a discussion of stability.) Balloon systems must not be prone to generating static electricity if they are to be
used with hydrogen.
There are at least six factors to consider when choosing a lifting gas. These are:
1. Compatibility with the balloon system being used.
2. Cost.
3. Lifting capacity.
4. Availability.
5. Locale of flight.
6. Inherent gas stability.
Normally, the gas selection process starts with the type of balloon. Hydrogen can be used if the balloon system is hydrogen
compatible, hydrogen is available, and local ordinances allow its use. If one of these conditions is not satisfied, as is often
the case in the United States, then helium is the likely choice. If a very short training or pleasure flight of several hours is
planned, the more economical alternative of ammonia or methane (natural gas) may be considered.
When inflating or landing with hydrogen or methane, care must be taken to ensure that no flame or material with the
potential to generate sparks is present in the launch locale. Lighted cigarettes, cigars, nylon clothing, cell phones, and other
electronic devices are examples of forbidden items. Only essential personnel should be allowed in the launch and landing
areas. For long, competitive flights, the increased stability of helium is a factor in its favor.
Components of the Gas Balloon
Gas balloon systems can be broken into four parts:
1. Envelope to contain the lifting gas.
2. Gondola for carrying pilots and equipment.
3. Support system to connect the envelope to the gondola.
4. Other equipment.
Envelope
The maneuvering valve [Figure 11-4] is at the apex of the envelope. It allows for the controlled release of a small amount
of gas to initiate a descent. It is usually spring actuated and controlled via a line that runs from the valve down through the
envelope into the gondola. On some balloons, a gas tight parachute top may be used instead of a valve. The envelope is also
equipped with either a rip panel or deflation port for rapid, total deflation during high wind landings. More information on
proper use of the valve and deflation ports is provided in the section titled “The Practice of Gas Ballooning” in this chapter.
Figure 11-4. Maneuvering valve on quick fill gas balloon.
Gondola
The gas balloon’s gondola [ Figure 11-5] is typically somewhat larger than ones used for sport hot air ballooning, with
four by five feet being a typical size. A foldable cot or sleeping pad normally runs along the long side of the gondola and a
“kick-out” panel in the side wall at one end of the cot may be used to provide additional legroom for sleeping.
Figure 11-5. Typical gondola layout.
A trail rope is slung on the outside gondola along with much of the remaining support equipment. The trail rope is typically
about 150 feet of natural fiber rope, one inch in diameter and weighs about 40 pounds. Its use is described in the landing
paragraph.
Support Cabling
The connection between envelope and gondola may be made of rope, flat tape, or steel cable. The total strength of the
cabling should have a breaking strength of at least five times the maximum gross load that is suspended on the cables.
This must include sand ballast, as well as the weight of the gondola, the occupants, and all supplies and equipment. For
hydrogen systems, the cabling must be electrically conductive. For ammonia systems, the cables should be long enough to
separate the occupants of the gondola from gas fumes coming out of the appendix.
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.
Figure 11-6. Instruments and radios are sometimes carried in a pod such as this.
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.