Montshire Minute: Hot Air Balloons

Originally aired during the week of July 17, 2000

Monday

The Wright Brothers may be the most famous siblings in the history of aviation. But two French brothers, Joseph Michel and Jaques-Etienne Montgolfier (Mon-GOLF-eyay), made aeronautical history more than a century earlier. The Montgolfiers had been busy inflating paper balloons with hot air produced by straw fires and watched them soar. Chickens, ducks, and sheep were the first passengers in these experiments. Then, on November 21, 1783, before a vast throng of Parisian onlookers (including the king and queen of France), two brave Frenchmen made the first manned flight in Montgolfier's balloon. Shortly thereafter, physicist J.A.C. Charles successfully flew a hydrogen-filled balloon. A ballooning craze of sorts caught on. Suspicious farmers, frightened by the giant gas bags descending from the sky, sometimes attacked the balloons with pitchforks. So balloonists began the practice of offering champagne to landlubbers.

Tuesday

Here's an experiment you can do at home that shows how hot air balloons rise. Fit a balloon over the mouth of a bottle and place the bottle upright in a container full of hot water. (You may have to hold the bottle in place with your hand.) What happens to the balloon? You might see it start filling with air! Now put the same bottle and balloon in ice water and I'll bet you'll see the balloon stays limp. What's happening? Warm air expands and thins as its molecules spread farther apart. When air inside the bottle was exposed to the warm water, it expanded into the balloon. Air contracts when it is cooled, so the balloon didn't fill with as much air when exposed to ice water. Big passenger balloons work on the same principle. When filled with enough hot air, the balloons eventually become lighter than the cooler air surrounding them and can lift off the ground. Then it's bon voyage!

Wednesday

You think I'm full of hot air? Well, hot air balloons are pumped full of thousands of cubic feet of hot air, which gives them their lift. You see, air expands when heated. When a balloon rises, it's because the air inside the bag is warmer and lighter than the air on the outside of the bag. In order to go anywhere, a balloonist needs a stable, safe heat source to keep pumping warm air into the bag. A propane burner, which causes that loud roar you hear when a balloon is overhead, does the trick nicely. Propane is a relatively safe gas that makes a flame that can reach up into the bag. Of course, the balloonist's travel route is pretty much dictated by wind direction. But with the burner, they can control altitude by how much hot air they pump into the bag. Balloons are also equipped with rip panels or parachute tops, which slowly empty the balloon of air when it's time to make a descent.

Thursday

In the early days of hot-air ballooning, the aeronaut had to fill the bag with hot air on the ground, or he needed to carry dangerous open fires aloft. As you might imagine, accidents were frequent. In 1819 Madame Blanchard, the first woman aeronaut, was killed while ascending during a firework display. With no safe or sustainable way of keeping the air warm, early balloons were destined to come right back down when the balloon bag cooled. Modern methods make it possible for balloonists to have safer and more satisfying flights. The pilot spreads the bag out on the ground so that the top lies downwind from the basket. He then attaches the basket and lays it down sideways. A large fan is used to blow air into the mouth of the bag. When it's about half inflated, the pilot fires up the propane burner - as the bag fills with hot air it gradually rises, pulling the basket upright.

Friday

Pioneer balloonists managed to find a way to break the bonds of gravity, at least for a little while. The drawbacks to flying a "free balloon," of course, is that pilots have little control over which direction they fly in. Adventuresome aeronauts in began trying to develop a lighter-than-air craft that could be fully controlled by the pilot. In 1851, Henri Giffard (Gif-ARD) fitted a large balloon with a propeller driven by a steam engine. This early dirigible flew about 1,500 meters high but moved only slightly faster than a walking pace. When lightweight gasoline engines were developed, successful dirigibles could finally be built. As airship technology developed, "Zeppelins," as these airships were known, became a popular means of transportation for the wealthy. The Graf Zeppelin, longer than two football fields, flew from 1928 to 1939, crossed the Atlantic more than 125 times, and carried 13,000 passengers.