Together, they test an experimental balloon that makes flying even more spontaneous. If you live in the Tri-State, chances are you've seen the bright blue, green and red airship at some time or another. The balloon is so compact that Bond says he managed to check it as luggage during his trans-Atlantic flight and easily pack it into a subcompact rental car in Portugal. Unlike standard-size balloons, which hold about 77,000 cubic feet of hot air, the experimental balloon holds about 44,000 cubic feet. Despite the difference, the smaller balloon flies by the same basic principles.
Hot air rises because it is only about half as dense as cold air.
Consequently, a balloon rises because the hot air inside the envelope is much lighter than the air around it. Hot-air balloons typically are powered by propane burners. Aside from using the burners, a pilot controls flight by opening a vent at the top of the balloon. He or she does this with a cord than dangles into the basket. Balloon pilots can control only a balloon's altitude.