BALLAST - LIFT - DAY - NIGHT

the physics to fly for 100hours with "Zero CO2 Emission”

As the gasballoons continue their trek across Europe, flying the balloon will be a full-time job for pilots. The gas balloon they are flying is very different from the hot-air balloons that most people may be familiar with from events like the Albuquerque International Balloon Fiesta, the Saga International Balloon Fiesta, and the Lorraine Mondial Air Balloons event in France.

Gas balloons use a lighter than air gas such as helium or hydrogen to provide lift. These particular balloons were filled with hydrogen at the beginning of the flight, and the hydrogen has to last all the way until their landing. After all, there are no mid-air refueling stations!

The balloon loses gas in the course of the flight, because the balloon over-pressurizes and “burps” gas through an opening (appendix) at the bottom of the balloon as it heats during the day, and because the pilots release gas to maneuver. Therefore, in order for the balloon to maintain altitude, the pilots have to get rid of weight. For that purpose, the pilots carry expendable weight, called “ballast,” in the form of sand and water, carried in bags that hang outside the capsule. The Gordon Bennett-Balloons took off with almost half a ton of sand, contained in 40-pound bags.

You might think of the combination of gas and ballast as fuel. If the pilots want to go up, they get rid of ballast. To come down, they can open a valve at the top of the balloon to release gas. Because valving and ballasting are the equivalent of burning fuel, the pilots try to do as little of both as possible. Loss of gas and ballast equals loss of duration (potential time aloft) and, therefore, distance.

The balloon is also affected by solar heating. In the early morning as the sun comes up, it heats the gas inside the balloon, which causes it to expand and provides lift. The pilots in essence get a “free ride” to a higher altitude without having to expend ballast. As the sun goes down, the process reverses. The gas contracts, which causes the balloon to come down. In order to maintain altitude, the pilots have to ballast.

For the next several days pilots will use this combination of solar heating and cooling, ballasting, and valving gas to steer the balloon. Wind direction and speed varies with altitude, and so the pilots will ascend and descend to find winds that will take them where they want to go.

Gas Ballooning "FAQs”

What makes gas balloons fly?

Gas balloons ascend because the gas inside is less dense and lighter than the air on the outside of the balloon. Heating up regular air makes its molecules expand, becoming lighter than the surrounding atmosphere. That’s what causes hot-air balloons to lift off. Gas balloons used in races such as the Coupe Aéronautique Gordon Bennett use either helium or hydrogen, both lighter-than-air gases in their natural, unheated state. But any gas that is lighter than air, including ammonia, will give a balloon lift, meaning the ability to rise.

So how have pilots flown around the world on even longer flights?

Those flights are made in special, and rare, balloons called Rozier-type balloons, named for the Frenchman who invented them around 1783. They use double envelopes containing both hot air and gas, and they use a heater to gain more lift.

How are gas balloons different from hot-air balloons?

First, they are alike in some ways. The part of the balloon that holds the hot air or gas is called the envelope. The basket that carries the pilot and passengers is the gondola. With both types of lighter-than-air flight, pilots try to control their direction by taking advantage of different wind currents at different altitudes. Both kinds of balloons are classified as aircrafts by Civil Aviation Authorities, and pilots must get separate licenses to fly each type. Gas balloon pilots typically started out flying hot-air balloons, and then decided they wanted to be able to fly further, higher and longer. Because gas balloons cost more to fly, they usually aren’t flown as often. Their flights can last for days, unlike hot-air flights, which usually last about an hour. Gas balloon pilots may prepare for months before a competition, and when they’re racing, they sometimes fly into dangerous weather conditions or over open seas, where an emergency landing could be a disaster. They even have to be careful not to fly over certain countries, where political conditions could make them targets of hostile fire. Gas balloons usually need more people to help with their launch than hot-air balloons. For a competition, the pilots also use the services of meteorologists who understand their needs, and even personal air traffic controllers to assist in race strategies . The pilots’ strategies are largely based on weather conditions. The only way they can “steer” a balloon is to catch the best wind currents.

How are gas balloons launched and kept aloft?

The gas balloon is inflated through a tube, called an appendix, and it takes hours for the inflation to be completed. The appendix stays open during flight to let excess gas escape and keep the balloon from bursting. Pilots make gas balloons rise by dropping weights, called ballast, from the balloon. Ballast is usually sand. The balloonists descend by letting some of the gas out of the envelope through a valve at the top of the balloon in a procedure called valving. There’s usually a cycle to a gas balloon flight. As the sun heats the gas-filled envelope, the balloon gets even more lift and can rise higher, to several thousand feet. At night, the gas inside the balloon cools off, and pilots drop bags of sand to keep from hitting objects on the ground. Then as the sun rises and heats the envelope again, the balloon gains even more lift since its load is lighter. The process usually lasts up to three cycles in a competition. When all the ballast is gone, the pilots have to land.

How do gas balloon pilots decide which gas they will use?

They compare costs, availability, and safety. Helium is the most popular gas for competition in the United States because it isn’t flammable like hydrogen, and there is a good supply of it here. Balloons using helium don’t lose as much of their gas through diffusion. In Europe, most pilots use hydrogen because helium is much more expensive and difficult to get there. It costs roughly $3,500 to inflate a racing gas balloon with helium in the United States, and these balloons usually hold about 35,000 pounds of gas. The cost of using helium in Europe would be two or three times as high. It costs about $1,000 dollars to inflate a racing balloon with hydrogen in the United States, but some pilots see using hydrogen as taking on extra risk. Ammonia costs less, but it has only about half the lifting ability of helium or hydrogen, so it’s not popular for competition.

What do pilots carry with them?

They carry many things, but they try to keep them as light as possible, including themselves! (See equipment list for details.) Modern pilots can’t take off like the early aeronauts, who flew mainly on nerve. The basic instrument list now includes:

Altimeter – Measures altitudeVariometer – Displays the rate of climbTransponder – Used to let flight control centers monitoring airspace see the altitude and speed of the balloon. It also helps other aircraft see the balloon in clouds, darkness or near airports with an electronic signal.Barograph – Used to record the balloon’s flight length and altitude during competition. It documents the flight altitude during specific time intervals.GPS – Global positioning system. This instrument helps track the balloon and give the pilots detailed information about their location.Aircraft radio – Used to communicate with flight service and the chase crew.Satelite Telephones – Used to communicate over large areas of water.

Pilots usually carry survival gear, in case they have to make an emergency landing, but not parachutes. They also carry easy-to-eat food, warm clothes, maps, passports, and a Porta Potty-type bathroom device.