Introduction
This chapter presents an introduction to the history of flying balloons, the physics of balloon flight, balloon components,
balloon terminology, support equipment, and how to choose a balloon.
History
Hot air balloons are the oldest successful human flight technology. The first recorded manned balloon flight was made on
November 21, 1783, in a hot air balloon developed by the Montgolfier brothers of France. [ Figure 2-1] Flown by Pilatre
de Rozier and the Marquis d’Arlandes, the flight lasted 23 minutes and covered 5.5 miles. Although the Montgolfiers are
given credit for the first documented flight, there are some earlier claims. The Chinese are credited with using manned
kites, and perhaps hot air balloons, some 2,000 years ago, and the Nazcas of Peru may have used smoke-filled balloons.
Figure 2-1. Model of the Montgolfier brothers balloon.
Ten days after the successful flight of the Montgolfier balloon, a young physicist, Professor Jacques Charles flew the first gas
balloon made of a varnished silk envelope filled with hydrogen. His flight lasted two hours and covered 27 miles, reaching
an altitude of 9,000 feet. Begun as an attempt to duplicate and validate the achievements of the Montgolfier brothers,
Charles based his experiment on misinformation. He mistakenly believed the Montgolfier brothers used hydrogen to
inflate their balloon, so he used hydrogen. Thus, the two kinds of balloons flown today—hot air and gas—were developed
in the same year.
Gas ballooning became a sport for the affluent and flourished on a small scale in Europe and the United States. Since
ballooning drew crowds, one way to offset the cost of a flight was to charge admission. Ballooning was a perilous
Chapter 2: Hot Air Balloon Design,
Systems, & Theory
undertaking that drew male and female daredevils eager to court danger. The parachute, invented by balloonist Andre
Garnerin in 1797 as the means of performing a daring stunt, is probably ballooning’s most significant contribution to flight.
At the turn of the century, the smoke balloon (a canvas envelope heated by fire on the ground) was a common county fair
opening event. As the smoke balloon ascended, a man or woman rider balanced on a trapeze attached to the balloon.
After the initial climb (about 3,000 feet per minute (fpm)) the hot air cooled and the rider separated from the balloon,
deploying a parachute to return to earth.
Balloons also found a home with the military. Napoleon used anchored observation balloons in some of his battles and
considered using balloons to ferry troops in his proposed invasion of England. During the American Civil War, both the
North and South used tethered observation balloons. In Europe, balloons were used during the 1870 siege of Paris (Franco-
Prussian War) to carry messages and important people out of Paris. World War I saw balloons used by both sides for
artillery spotting. By World War II, airplanes had replaced balloons for observation and reconnaissance purposes although
barrage balloons (several large balloons tethered close together) were often used to discourage low level bombers or dive
bombers. The United States Navy contracted with the General Mills Company in the 1950s to develop a small hot air
balloon for military purposes. The Navy never used the balloon, but the project created the basis for the modern hot air
balloon. With the use of modern materials and technology, hot air ballooning has become an increasingly popular sport.
Physics
In concept, the balloon is the simplest of all flying machines. It consists of a fabric envelope filled with a gas that is lighter
than the surrounding atmosphere. Since air in the envelope is less dense than its surroundings, it rises, taking the basket
filled with passengers or payload with it. A balloon is distinct from other aircraft in that it travels by moving with the wind
and cannot be propelled through the air in a controlled manner.
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 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.
Figure 2-2. The air inside the balloon envelope is heated to create buoyancy.
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 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.
Deflation port
Envelope
Horizontal load tapes
Vertical load tapes
Basket
Crown line
Heating system
Mouth/Throat
Skirt or scoop
Figure 2-3. Basic balloon terms.
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.
The deflation port is located at the top of the envelope and allows for the controlled release of hot air. It is covered by the
deflation panel sometimes called a top cap, parachute top, or spring top. [ Figure 2-4] In a balloon with a parachute top,
partial opening of the parachute valve is the normal way to cool the balloon. Balloons with other types of deflation panels
may have a cooling vent in the side or the top. Many balloons are also equipped with turning vents, which allow for the
pilot to turn the balloon on its vertical axis while in flight. Turning vents help a pilot align the basket for landing, or in the
case of commercial balloons, align the balloon’s logo toward the crowd.
Overlap for air seal
Actuation line
(deflation/vent)
Figure 2-4. Deflation system.
Special Shape Balloons
Balloons that do not have a traditional “teardrop” shape are called special shape balloons. [ Figure 2-5] They may be
completely engineered systems which have been designed to resemble cans, sports balls, cartoon characters, cars, etc.
Figure 2-5. Special shape balloons
Some balloons have appendages added to the envelope. Appendages are pieces added to a balloon envelope in order
to create a particular shape or rendition, not necessarily keeping with a standard shape balloon. To be designated an
appendaged envelope, less than 10 percent of the total capacity of the balloon is contained within the appendage. While the
appendaged envelope has the same general flight characteristics as a standard balloon shape, there are some differences.
For example, the added weight of the appendage may cause the overall envelope to weigh significantly more than teardrop
balloons of equal size. Appendage balloons also have the tendency to rotate during aggressive climbs and descents.
A special shape envelope requires a substantial amount of engineering to ensure the envelope is properly stressed, and the
balloon has no undesirable flight characteristics due to the shape. Special shape balloons built in the United States or the
United Kingdom are normally issued Standard Airworthiness Certificates, but special shape balloons imported from other
manufacturers in other countries may be issued an Experimental Airworthiness Certificate. A balloon with an Experimental
Airworthiness Certificate usually may not be flown for compensation or hire, which negates the marketability of such a
balloon. Additionally, an experimental balloon may not be flown over congested areas, per Title 14 of the Code of Federal
Regulations (14 CFR) part 91, section 91.319. Experimental balloons also require specific documentation when flown
outside of an area of 50 miles from its home port. Pilots of special shape balloons with an Experimental Airworthiness
Certificate should coordinate their activities with their local Flight Service District Office to avoid problems
Thermal Airships
A thermal airship combines the characteristics of a hot air balloon, with respect to lifting force, and an airship, with respect
to its capacity of being steered while in flight. To develop proficiency in this aircraft, knowledge is required of not only
hot air balloon operations and physics, but also of airship operations. It is estimated that there are currently less than 10 of
these aircraft in the United States, and there is no specific pilot certificate for thermal airships. These aircraft are extremely
expensive to purchase, and have some significant operating limitations with reference to winds. Any further discussion is
outside the scope of this handbook.
Heater System
The heater system consists of propane burners (one or more), fuel tanks that store liquid propane, and fuel lines that carry
the propane from the tanks to the burners. The burners convert ambient air into hot air, which in turn provides the lift
required for flight. [Figure 2-6 and Figure 2-7]
VALVE BLOCK
ASSEMBLY
BURNER CAN
COIL ASSEMBLY 6
4 1
4 3
SINGLE BURNER CONFIGURATION
LIQUID FIRE JET
ASSEMBLY
IGNITOR ASSEMBLY
PILOT LIGHT ASSEMBLY
Figure 2-6. Typical single heater (burner)
BURNER CAN
COIL ASSEMBLY
LIQUID FIRE JET ASSEMBLY
IGNITOR ASSEMBLY
PILOT LIGHT ASSEMBLY
COIL POST
LIQUID FIRE VALVE ASSEMBLY
HANDLE TUBE
MAIN VALVE ASSEMBLY
SWIVEL ASSEMBLY
GIMBAL BLOCK CAP LOWER
GIMBAL BLOCK CAP UPPER
PRESSURE GAUGE ASSEMBLY
GIMBAL TENSION ADJUSTMENT SCREW
GIMBAL MOUNTING SCREW
8 9
DOUBLE BURNERS CONFIGURATION
Figure 2-7. Typical double heater (burner)
Propane fuel is used to heat the air which generates buoyancy for flight. The propane is stored in one or more fuel tanks
located in the basket. A withdrawal tube attached to the liquid tank valve permits liquid propane to be drawn from the
bottom of the fuel tanks. The liquid propane is supplied to the burner assembly through the fuel hoses that connect the fuel
tanks to the heater assembly (commonly referred to as the burner). The fuel system also provides propane to the pilot light.
There are two types of pilot light systems: liquid and vapor. In a liquid pilot light system, liquid propane is diverted from
the main supply line at the heater via a pilot shut-off valve. The fuel goes through a vapor converter and regulator, and is
distributed through a pilot head. A piezo-electric system ignites the vapor at inflation for most heaters, but many balloonists
choose to use a striker.
In a vapor pilot light, a second fuel hose is used to supply vapor to the heater assembly pilot light from the pilot light tank
valve located on top of the fuel tank. A regulator is used to decrease the pressure of the propane vapor for proper pilot
operation. A pilot light valve located on the heater controls the flow of propane vapor to the pilot light.
The main liquid tank valve controls the flow of liquid propane to the burner, while the blast valve controls fuel flow at the
heater. With the liquid tank valve open, opening the burner blast permits liquid propane to enter the heat exchange coil
where it is either completely or partially vaporized. After exiting the heat exchange coil through the orifices in the lower
portion of the coil, the propane is ignited by the pilot light. [Figure 2-8]