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How Does A Hot Air Balloon Work?

a close up of clouds in the sky

How Does A Hot Air Balloon Work?

Hot air balloons aren’t just a whimsical trope from fantasy movies. When most people find out that hot air balloons are available to the public for tours, one of the first questions they ask is this: how does a hot air balloon work? Let’s dive into some fundamental physics and mechanics to demystify how hot air balloons fly so high.

a group of colorful hot air balloon in the sky

How Do Hot Air Balloons Fly?

Hot air balloon flight is based on the principles of thermodynamics. On a molecular level, the more energy (heat) is imbued in particles, the faster they move. The faster the molecules move, the more space they take up. As the particles’ volume increases, their density decreases. Have you ever heard that hot air rises? This is because particles of differing densities will naturally separate, like oil and water. Simply stated, hot air is less dense than cold air and therefore floats upward.

So what does this scientific explanation look like in practice? A propane-fueled burner is used to shoot fire directly inside the balloon. The fire heats the air inside the balloon, while the air on the outside remains cool. As a result, the balloon eventually inflates and begins to rise, bringing along the basket dangling underneath it.

a close up of a fire

Hot Air Balloon Mechanics

Flying is not just a matter of applying the laws of physics, but it also requires understanding hot air balloon mechanics. Let’s look at a more detailed step-by-step process to setting up and inflating a hot air balloon.

  1. First, the basket is set up on its side in a flat, open area like a field or parking lot. One or more propane-fueled burners are connected with supports and suspension cables to hang above the basket. A safety check is conducted before moving to step two.
  2. The envelope, or the colorful fabric hot air balloons are known for, is unfolded across the lawn and attached to the basket with carabiners.
  3. The parachute and valve cord, which operate as an air vent and pulley system, are connected to the top of the balloon.
  4. Since the envelope is over 100 feet long, it would be challenging to keep it open wide enough to shoot flames inside without catching it on fire. Instead, the envelope opening is manually held open while several fans inflate it first with cold air.
  5. Finally, the burner is turned on. In bursts, vaporized propane is ignited and blasted into the opening of the envelope until it stands upright.

a close up of an umbrella

How Do You Steer A Hot Air Balloon?

Once the balloon is fully inflated and standing upright, and the safety checks are complete, you’re ready to fly! To rise into the air, the pilot simply turns on the burner to further heat the air inside the balloon. If you want to stay at a certain height for a while, the burner must be activated regularly to maintain the current temperature inside the envelope. Descending and landing require cooling the balloon. The pilot uses a pulley system to open the parachute at the top of the envelope, which releases a controlled amount of hot air.

Since hot air balloons rely on wind direction, steering a hot air balloon to go left or right can be tricky, even for the most skilled of pilots. A green cable and a black cable will turn the basket in the desired direction; however, the balloon can only move up or down. Thankfully, wind currents also flow in different directions at varying heights. The pilot can bring the balloon to higher or lower altitudes to find a wind blowing in the direction you want to go.

a person flying a kite on a cloudy day

How High Do Hot Air Balloons Fly?

Hot air balloons are capable of flying at least as high as 70,000 feet. Dr. Vijaypat Singhania of Mumbai, India, is known for the highest hot air balloon flight at 68,986 feet — almost twice as high as most commercial airplanes at around 35,000 feet. However, the legal maximum altitude for flying hot air balloons is 3,000 feet, and the legal minimum for populated areas is 1,000 feet.

Hot air balloons work thanks to a clever combination of thermodynamics, mechanics and skilled piloting. As a result, we can reach heights and enjoy open-air views that aren’t possible with more common forms of flight. On a ride with Asheville Hot Air Balloons, you’ll get to see up-close how to fly and steer a hot air balloon to reach stunning views of the Appalachian Mountains.

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