How do hot air balloons work?

Hot air ballooning represents the ingenious application of basic scientific principles, allowing giant balloons to fly into the air while still moving at will.

Famous for a long time, hot air balloons have always been considered a rather impractical means of transportation, because few people actually need to go somewhere by hot air balloon. Simply because the flight speed is very slow, and depends a lot on the wind direction of this type of vehicle.

But if you just want to enjoy the experience of floating in the air, then this is probably extremely interesting. Many tourists have described flying in a hot air balloon as one of the most exciting and peaceful activities they have ever experienced.

1. Operating principle of hot air balloon

Hot air balloons operate based on a very basic scientific principle: hot air flies higher than cold air.

The reason for this is because hot air has less mass per unit volume than cold air. Specifically, 1 cubic foot of air (equivalent to 0.028 cubic meters) weighs on average about 28 grams. However, when this air mass is heated to 37 degrees Celsius, it only weighs about 7g.

The balloon part of a hot air balloon is usually made of nylon fabric, reinforced with ready-made fabric. This is the perfect material for hot air balloons, because it is lightweight, strong, and it does not melt as easily as other materials when exposed to high temperatures.

A combustion platform is placed below the balloon, using propane gas as fuel, stored in compressed liquid form in cylinders placed in the balloon basket. When the pilot lights a fire, the fire heats the air inside the balloon. The balloon began to expand, pulling the basket and everyone inside into the air.

2. How do pilots control the balloon?

Flying a hot air balloon requires skill, but overall, it's quite simple.

To lift the balloon, the pilot turns a control knob to open a propane valve, causing the gas flow to increase, and the flame to grow larger. This operation is quite similar to when we control a gas stove.

Additionally, many hot air balloons have a control that opens a second propane valve. This valve channels the propane through a hose that passes over the heating coils, allowing the pilot to burn liquid propane, rather than gas, creating a weaker, but much quieter, flame than burning gas.

The hot air balloon also has a rope to open the parachute valve above the balloon. When the pilot pulls the string, hot air escapes from the cover, reducing the temperature of the hot air inside, helping the balloon to slow down. If they stay open too long, the balloon will lose altitude.

These are essentially the only controls on a hot air balloon. This raises an interesting question: If pilots can only move the balloon up and down, how do they get the balloon from one place to another?

In the air there are many mixed winds blowing in different directions, and at different heights. To move in a specific direction, the pilot adjusts the balloon up and down to the appropriate level, and chooses the direction of the wind to move forward.

Since wind speed typically increases as you get higher in the atmosphere, pilots can also control horizontal speed by changing altitude.

Of course, even the most experienced pilot cannot completely control the flight path of the balloon. Often, wind conditions give pilots very few options, and they cannot actually steer the balloon on a precise route.

In fact, it is very rare that you will be able to fly the balloon back to your starting point. Unlike flying a plane, flying a hot air balloon is largely improvisational, and depends a lot on weather conditions.

So for some hot air balloons in tourist areas, there are often ropes tied to the ground to prevent the balloon from flying too far from the area where they operate.

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