How to fly (and steer) a hot air balloon- a moment of science

The oldest form of flying takes advantage of the properties of hot air, or as balloon pilot Dwight Cramer says, “We put the hot air in, and it rises! But there is math to it, there’s math and science in everything.”

That’s my line- but he’s right!

Hot air balloons float by hot air alone, no hydrogen or helium here like other balloons that fly by gas. Hot air rises because it’s lighter, but just how much?

Room temperature air weighs about 28 grams per cubic foot, while warm air around 100 degrees weighs 7 grams less. That doesn’t seem much but it does add up! Especially with a balloon, known as an envelope, this large- nearly 7 stories tall. By capturing it, the balloon and its cargo will rise according to the laws of buoyancy as the air around the balloon is cooler and therefore heavier. As the air inside cools, the balloon will settle and sink. As long as the pilot keeps the hot air coming, the balloon will rise or keep gliding along until landing.

Setting Up for Flight

Dwight travels around the country- taking passengers on both tethered and untethered flights in his balloon- which takes awhile to set up safely.

“So what we’ll do once I do a burner test to make sure 1.) we have enough fuel and 2.) the burner is working correctly. We’ll lay the basket down and attach the envelope to these suspension ropes. So (once) we hook it up, stretch the envelope out, we’ll then start up our inflation fan. That’ll put out enough air to inflate the balloon with regular outdoor air.”
Dwight Cramer, Hot Air Balloon Pilot

Once inflated enough from this cold start, they’ll switch on the burner and fill the balloon with hot air to bring the basket and balloon upright.Then they’re off!

Steering Through Science

I seriously respect Dwight and other pilots as they know just as much about weather as a meteorologist as hot air balloons are at the mercy of the wind, but they can steer by understanding meteorology on a micro scale. He says,

“The reality is that we do have a lot of control. While we can’t fly upwind or crosswind- we can change altitudes. So as we climb we can catch a right turn or a left turn.”

As winds change at different levels through the atmosphere. Balloonists can also catch currents coming down from different terrain, “that cool air settles and so if we launch in and stay in a valley, we’re going to go…downhill just like water coming down from a river.”

As I finished my interview with Dwight, he added, “I say that hot air ballooning is an art, you’re really learning how the atmosphere works, you’re working with it, you’re not fighting with it, you’re going with it,”