Strip away the romance and a hot air balloon is three machines working together: an envelope that traps hot air, a burner that produces the heat, and a basket that carries fuel, pilot and passengers. Every other component on board, the valves, vents, tapes and tanks, exists to control one of those three. This page walks the whole aircraft from top to bottom, so that on launch morning you know exactly what you are looking at and why each piece is shaped the way it is.
The envelope, gore by gore
The huge fabric bag overhead is the envelope, sewn from 24 or more vertical panels called gores, each cut from coated ripstop nylon. The coating keeps hot air from seeping through the weave; the ripstop grid of reinforcing threads stops a small nick from running into a long tear.
The fabric, though, is not what holds you up. That job belongs to the load tapes, webbing straps sewn over the seams, which carry the weight of basket and passengers down from the crown like the cables of a suspension bridge. The lowest ring of material, nearest the flame, is a skirt of Nomex, the same fire-resistant fiber used in racing drivers' suits.
The crown: a parachute that never leaves
At the very top of the envelope sits a circular opening, sealed in flight by the parachute valve: a disc of fabric held in its seat by the pressure of the hot air beneath it. When the pilot pulls the vent line, the disc drops inward and spills hot air, and the balloon descends. Let go, and internal pressure pushes the parachute back into place on its own. After landing, the pilot holds it wide open so the envelope empties in a minute or two.
Many balloons also carry rotation vents on the sides. These let air escape at an angle, slowly spinning the whole aircraft, so the pilot can point the basket, and your camera, in any direction, and can line up the long side of the basket with the direction of travel before touchdown.
The burner: heat on demand
The burner is the engine of the aircraft. Liquid propane runs up from the tanks, vaporizes inside stainless steel coils, and burns in a flame several metres long. Most ride balloons mount a double burner: two independent units with separate fuel lines and pilot lights, so a problem with one still leaves a full working flame on the other.
Most burners also have a second, much quieter valve that feeds liquid propane straight to the flame. Pilots call it the whisper burner, and its main job is courtesy: crossing low over farmland, the pilot switches to whisper mode so the roar does not panic livestock below. The propane itself rides in upright tanks strapped into the corners of the basket.
The basket and its instruments
Everything hangs from the basket, still woven from willow and rattan over steel frame cables that run beneath the floor and up to the burner frame. The load path from envelope to floor is steel and webbing all the way; the wicker is there to absorb landings and carry people comfortably. There are solid engineering reasons the material has never been replaced, and they get a full page of their own: why the basket is still wicker.
The instrument panel is refreshingly small: an altimeter for height, a variometer that shows the rate of climb or descent, a thermometer that reports how hot the fabric near the crown is running, and an aviation radio for the chase crew and other aircraft. Many pilots add a GPS, and that is the entire cockpit.
How big is a balloon, really?
Balloon size is measured by envelope volume, and the range is wider than most people expect. A sport balloon built for a pilot and one or two friends holds roughly 2,200 to 3,000 cubic metres of air. For comparison, an Olympic swimming pool holds about 2,500 cubic metres of water, so even a small balloon swallows a pool's worth of air. The big ride balloons flying in Cappadocia or over East Africa start around 6,000 cubic metres and can carry 16 or more passengers in partitioned baskets.
More volume means more lift, in direct proportion. The arithmetic of how much weight a cubic metre of hot air can actually carry is on our page about why hot air lifts, and the temperature limits the fabric can survive are covered in the life of a balloon envelope.
See the whole machine up close
On flight morning you can watch the crew unroll the envelope, rig the burner and inflate the aircraft from a few steps away. Here is what that first morning looks like, start to finish.
Balloon anatomy FAQ
What is a hot air balloon envelope made of?
Almost always coated ripstop nylon, cut into vertical panels called gores and sewn together with webbing load tapes over the seams. Some manufacturers use polyester instead. The skirt nearest the burner flame is Nomex, a fire-resistant aramid fiber.
Why is there a hole in the top of a hot air balloon?
The opening at the crown is sealed by the parachute valve, a fabric disc held shut by the pressure of the hot air inside. The pilot pulls a line to open it briefly for descents, and holds it open after landing to deflate the envelope quickly.
Can the parachute valve open by accident?
No. Internal pressure constantly pushes the disc into its seat, so it stays closed unless the pilot actively pulls the vent line. As soon as the line is released, the valve reseats itself.
How much fuel does a hot air balloon carry?
Balloons burn propane, stored as a liquid in upright tanks strapped into the basket corners. A sport balloon typically flies with two or three tanks, large ride balloons with more, and pilots plan every flight to land with a comfortable reserve on board.