Choice of:

• Two Vouchers: Each Good for One 20-Pound Propane Tank Refill
• Three Vouchers: Each Good for One 20-Pound Propane Tank Refill

Hot-Air Balloons: How a Sheep Learned to Fly

Hot-air balloons are one of the oldest methods of human flight. Check out Groupon’s guide to discover the science—and surprising history—behind these early sky voyagers.

Before supersonic jets, helicopters, or single-engine Cessnas, mankind ruled the skies with an even greater technology: a basket, suspended under a sheet and lifted into the air by a burning pile of straw and manure. Since then, hot-air balloons have gotten more advanced, but the principle behind them remains largely the same. A flame heats the air inside a parachute, causing the air molecules to gain energy and expand as they push on the balloon’s walls. With equal air pressure inside and outside the balloon, the hotter air is less dense, and the balloon rises. Pilots control the elevation by increasing the flame from the burner—thus adding more hot air—or releasing air by opening a vent on the top of the balloon. To steer, they rely on wind currents, which vary by altitude. Changing direction can be as simple as ascending 100 feet, but the flight path is always at the mercy of the gods’ drafty air vents.

Whereas early hot-air balloons were made of paper-covered cloth, most modern versions consist of an airtight nylon-polyester parachute, with flame-resistant Nomex fiber on the bottom, near the torch. Propane gas serves as fuel, creating a powerful but easily regulated flame. Yet even with the advancement of metal alloys and plastics, the basket hasn’t gotten much of a facelift. It’s still usually woven of kooboo and palembang cane for their strength and ability to absorb some of the force of landing.

Just as NASA sent monkeys into space before humans, the inventors of the first hot-air balloon didn’t want to risk their own hides in an initial flight. So, in demonstrating their new contraption to King Louis XVI in 1783, the Montgolfier brothers chose a chicken, sheep, and duck as test pilots. The trio rose 1,500 feet before drifting safely back to earth, making it the world’s first successful air-passenger flight. Since then, the technology in balloons has evolved to include a second control valve on the burner, which enables pilots to use the quieter alternative of liquid propane—a technique often used to avoid startling the livestock when passing over farms, as if in respect for the animals’ intrepid forebears.