The Science of Hot Air Ballooning

Curious about how hot air balloons work?
We love telling people about all things ballooning!

Science Drawing - Chicago Hot Air Balloon

What is a Hot Air Balloon?

A hot air balloon is a unique flying craft, which works because hot air rises. There are two main types of hot air balloon. Both were developed in the late 18th century Europe and are still used today.  Recent evidence suggests that indigenous S. Americans and the Chinese may have attempted similar styles of flight! Hot air balloons are the oldest form of manned flight.

How Do Hot Air Balloons Work?

The modern hot air balloon uses fire to heat the air inside the balloon to gain lift. Another kind is a pure gas balloon, which doesn’t use hot air, and dropping ballast or venting the gas can only control the altitude. We do not use those balloons for passenger transport because they can cost $11,000 – $18,000 to fill each flight and can last up to a week in flight weather permitting!

Hybrid and gas balloons have been used for many long-distance ballooning records, as they require less fuel to stay airborne for extended periods of time. Pilots from all over the world compete in gas balloons for the famous International Gordon Bennett Cup.

All of our balloons are the hot air type, so that’s what we will describe below.

What are the parts of a hot air balloon?

A modern hot air balloon is made up of the following things:

Balloons or Envelopes

The balloon or ‘envelope’ is a fabric bag made of strong, light nylon with an opening at one end called the mouth.

The envelope is laid out on the ground before a flight and partially inflated with cold air from high-powered fans before the air is heated with the burners to create lift required.  Do not expect the balloon to be inflated or visible before you show up at the balloon port.

Passenger-carrying balloons range in size from those holding 77,000 cubic feet of air (called a ‘77’) to 600,000 cubic ft (a ‘600’). Our biggest passenger balloon is 210,000 cubic ft. Considering a basket ball is about a cubic foot, Our largest balloon can hold up to 210,000 basket balls in its envelope when inflated!

Envelopes are traditionally a familiar ‘inverted tear drop’ shape like ours, but some famous brands have ‘special shape’ hot air balloons for advertising purposes. Most balloons have a vent at the top and at the sides, so the pilot can let out air or rotate the balloon by pulling certain ropes as required.

Hot Air Balloon Baskets

The balloon basket, which carries passengers, is attached to the bottom of the envelope by extremely strong metal cables. Baskets have reinforced steel frames and are clad in woven wicker, which is traditional, but also sufficiently light, strong and durable.

Balloon baskets vary in size from holding two people up to 24 people. Our hot air balloons carry between 2 and 12 passengers and are approximately the size of large board room table. Balloons have set minimum and maximum loading capacities.

Surfaces are covered in smooth leather and there are foot holes in the side of the basket so passengers can climb in and out..

Hot Air Balloon Burners

The burner is essentially the ‘engine’ of the balloon. It is fixed to a metal frame attached above the basket under the mouth of the envelope. The burner mixes liquid propane from pressurized gas tanks with oxygen and ignites it. The pilot pulls a small valve, which fires the burner and aims the flame into the mouth of the balloon to heat the air inside.

Our balloons have two burners including one, which lets propane out more slowly making it quieter. This is called the ‘whisper burner’ and it is used when flying over residential areas or livestock.

Some of our balloons also have specially-fitted heat shields below the burners which stop it getting too toasty for you (but we still recommend a hat).

How do Hot Air Balloons Work?

Hot air balloons work because hot air rises. By heating the air inside the balloon with the burner, it becomes lighter than the cooler air on the outside. This causes the balloon to float upwards, as if it were in water. Obviously, if the air is allowed to cool, the balloon begins to slowly come down. Pilots have a great deal of control over the altitude of the balloon, which they monitor with various instruments. They develop incredible anticipation skills over time and can often control a balloon’s decent within centimeters.

Steering a Hot Air Balloon

Balloons cannot be steered in the normal sense of the word so they travel in the direction of the wind, which varies at different altitudes. Pilots skillfully use this as a way of changing direction by burning to go up, or allowing the air to cool to go down, and catch different airstreams at different heights.

Pilots can use turning vents in the side of the balloon to rotate it 360 degrees so you have a full panoramic view and to make the broad side of the basket lead for landing.

Landing in a Hot Air Balloon

Hot air balloons don’t land in pre-decided locations like planes or helicopters do. They can’t be steered in the same way (that’s why it’s always an adventure!). Pilots bring the balloon into land, usually after around an hour in the air on a passenger flight, when they see a safe open space often out in the countryside.

The pilot asks all passengers to crouch down in the seated landing position (knees bent, back facing in the direction of travel and holding ropes provided). As the balloon approaches the ground, the pilot releases the vent at the top of the balloon letting the hot air escape.

When the basket touches down, often there is a bump, a skid and the basket can occasionally tip over slightly. This is quite safe and normal. Balloons have been landing like this for over two hundred years and modern balloon baskets are designed for this. After a serene hour or so in the clouds, most people thoroughly enjoy the excitement.

Of course, the best way to learn about hot air balloons is to experience ballooning for yourself.