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.