HOT- AIR BALLOONS!

SCIENTIFIC COMPANION EVERY YEAR, more than 550 balloons fly in the Albuquerque International Balloon Fiesta, the largest balloon festival in the world. The nine-day celebration attracts nearly 1 million spectators. And it involves a lot of very cool scien

HOW TO FILL A HOT-AIR BALLOON

First, you have to fill the deflated balloon with air, says Sam Parks, a 30-year veteran hot-air-balloon pilot. After unfolding the balloon so it lies flat on its side, pilots use a huge fan to partially inflate it with cool morning air. Next, they turn on propane burners, which put out 15 to 20 million Btu of heat, to heat the air. Like any gas, air expands when heated, becoming less dense – and rising above denser elements. When the air inside the balloon gets to around 40°C above the temperature outside the balloon, the balloon lifts into the air. Once full, the typical modern-day hot-air balloon carries about 2 250 m3 of air. (That’s about the equivalent of 80 000 basketballs!)

HOW TO CHANGE ALTITUDE

To increase the balloon’s altitude, the pilot fires one of the balloon’s two propane burners to heat the air inside the balloon and raise its pressure. To bring down the hot-air balloon, the pilot can either wait for the balloon to cool off by itself, or open a vent called the parachute valve and release some air to lower the temperature instantly.

HOW TO CHANGE DIRECTION

The balloon itself has no steering mechanism. Instead, pilots use air currents, which typically travel in different directions based on altitude. So if you increase or decrease altitude, you change the direction the balloon is blown in. It’s not an exact science, which means balloons usually can’t land in the same spot they took off from. Unless…

WHY ALBUQUERQUE?

The festival’s spectacular flights rely on a weather phenomenon called the Albuquerque Box. At higher altitudes, the winds blow consistently to the north. At lower altitudes, they blow consistently to the south. That balance gives balloon pilots better control, and often they can land in nearly the same spot from which they took off.

COLLISIONS

To keep hot-air balloons from bumping into each other – called ‘kissing’ – 90 launch directors, dressed like NFL referees, patrol the field. They use whistles and hand signals to coordinate, and send radio updates to the chief director, who oversees the whole field.