How Do Hot Air Balloons Really Work?

Have you ever wondered to yourself, “How do hot air balloons work”? I mean, sure, hot air rises, but is that it? How does it really work? How do they steer the balloon? How fast and how far do they go? Can they fly for hours, days…weeks?  What’s it made of? Well, while the experience of flying in a hot air balloon is certainly magical, hot air balloons operate on some pretty basic scientific principles.

So let’s start with the balloon itself.  For now we will just focus on three structural elements: the envelope, the basket, and the burner system. The fabric that we think of as the “balloon” part of the balloon, is called the envelope.  The envelope’s fabric needs to be both strong and lightweight and is often made of Dacron or ripstop nylon, which are both synthetic fabrics.  In the envelope we have a pyrometer which lets us monitor the heat so as not to damage our fabric’s integrity.  If balloonists treat their fabric well, the envelope can last 300-500 flights hours.

The basket is typically made out of rattan, and it hangs beneath the envelope supported by cables or Kevlar lines, and it carries the pilot and passengers (in our case, 6 passengers and a pilot).  Rattan makes an ideal material for a basket. Not only is it a handsome aesthetic choice, but it is also flexible, lightweight, and shock absorbent.

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The burners are hooked up to propane fuel tanks within the basket, and sit above the pilot on uprights. The burners heat the air inside the envelope, which give the balloon the lift it needs to fly.  How much heat do the burners put out? Try 30 MILLION British thermal units. That’s about 100,000 times more heat than a Bic lighter. So, pretty hot.  But we’re not quite ready for the burners yet.

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Before you fly, you must inflate the balloon. Each balloonist has a chase crew that helps with all aspects of the flight—to insure it goes quickly, safely, and smoothly from start to finish. They help stretch out envelope and attach it to the basket’s uprights. The envelope is then inflated with ambient air from a very large fan. While the envelope is being filled, a member from chase crew pulls a rope which is attached to the top of the balloon called a crown line.

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This helps create pressure and tension on the balloon which allows the envelope some stability. When it is nearly inflated, it’s time to start up the burners and fly….

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So how does it fly? Well, hot air is lighter and less dense than cool air. This is why hot air always rises. Just as air is lighter and less dense than water—you might imagine a bubble floating to the top of a glass of water. Our balloon works on this same principle of buoyancy.  If you think of the envelope as a bag, trapping that hot air—we are able to utilize that upward lift and catch a ride into the clouds, kind of like an air bubble shooting up through water. Several factors influence the amount of heat needed to lift off, such as differing weight in the basket or the temperature outside. On a cool day, it takes much less fuel to heat the air than on a very hot day. Once we have lift off, we must rely on the wind.

Wind is everything to a hot air balloon. We are not able to steer in the traditional sense, but we are able to use the wind to our advantage. Wind moves at different speeds and in different directions depending on the altitude you are at. You may feel very strong breezes on the ground, but notice the clouds are not moving very fast. We are able to use this phenomenon by adjusting our altitude and “hopping a ride” on the different ways of the wind. This gives us some control over where we are headed, but ultimately—we go with the wind.

While the balloon is in the air, members of the balloon chase crew follow along in a van keeping contact with the pilot through two-way radios. It is the chase crew’s job to help find potential landing sites and assist the pilot in the inflation, deflation, and packing up the balloon.

Because balloons move with the wind, you don’t feel much breeze. This is why balloon flights are so peaceful—you are literally one with the wind.  Pilots prefer to fly with winds less than 10 knots (11.5 MPH).  There have been long distance flights, but for commercial flights we have to consider weather conditions, time of day, fuel resources, and availability of landing sights. This means commercial flights tend to last about an hour and span the distance of around 5-12 miles.

When it’s time for landing, the pilot often chooses a field that is on public lands, or one the crew is able to obtain permission to use. This is when the pilot will balance both adding hot air with the burner or releasing hot air through a vent in the envelope to masterfully descend in such a way that sets the balloon down as gently possible.  When the basket touches the ground, the envelope peacefully collapses into the grass and the chase crew packs it up into a large bag.

Then it’s time for the traditional, post-flight champagne toast. The pilot, passengers, and crew then recount the evening’s many beautiful sights and experiences. By harnessing the very simple principle of hot air being lighter than cool air, hot air balloonists are able to soar over the world in fabulous flying machines. As it turns out, sometimes even science can be magical. 

Click on the video below for a sense of how a hot air balloon ride with AeroWorks balloons feels...