How Do Hot-Air Balloons Work and What Are They Made Of?
Hot-air balloons are a technology that go back to the Revolutionary War. But while they have improved in safety and in structure, they're basically still flying the same way people did in the 1700s.
Hot air rises
Barry DiLibero has been piloting hot-air balloons since 1991. He's a commercial pilot -- technically, any commercial pilot is also able to pilot hot-air balloons, and the licenses for both are the same.
"I was working part-time for a major Philadelphia radio station in 1990," said DiLibero. "I told them I thought a hot-air balloon would be great promotional device. They landed on my farm quite often, and I thought they were cool." Halfway through his first flight, he decided he had to have one for himself. Three weeks later, he did.
Hot-air balloons are very weather-sensitive, so they are typically only flown in the early morning hours. The main thing to remember is that mild wind speeds on the ground translate to much higher wind speeds further up. What's nice and breezy on the ground can get dangerous at higher altitudes. Winds are lowest in the mornings. Once the sun comes up and heats up the atmosphere, winds start stirring to life.
The basic mechanic of hot-air balloon flight is that hot air is sent up into the balloon. Hot air is lighter than cold air, so the hot air lifts the balloon up. Pilots take the day's temperature, add the passenger load and then calculate how warm the air needs to be inside the balloon -- or as pilots refer to them, envelopes.
We have a very scientific method to measure the wind speeds," he said. "We spit. We spit over the side and watch where it goes. Some competitive pilots will use shaving cream, an as it falls, they watch which direction it breaks.
"So, for a 70-degree day, you're going to need the insdie of the envelope to be around 100 to 125 extra degrees higher to get it to lift," said DiLibero. "And every time you hit blast valve for 5-6 seconds, you get a five-degree raise in temperature."
A five-degree raise in temperature can raise a balloon by 300 feet per minute (3-4 mph). But you can't just shoot straight up. DiLibero said the balloon needs to hit "an equilibrium." That allows the balloon to hover and coast.
"Plus, once you're up, you can burn a lot cooler than you can when you take off," he said. "Because you have less fuel. You're lighter than when you started."
How do you steer this thing?
The real skill to piloting a hot-air balloon is knowing how wind patterns work. A hot-air balloon has no steering wheel, nor does it have brakes. Once you're in the air, you need to know where the wind is going to take you.
"The cooler the air is, the denser it is, and it acts like pouring water," said DiLibero. "It always wants to go to the lowest point. The lowest point in El Paso is the Rio Grande. The cooler air flows there, so in the mornings, the air should pull you down toward the river."
But winds aren't always predictable. They blow in different directions at different altitudes. You might be flying northwest at one height, but if you go up a few hundred feet, the wind might be going northeast. The truck to piloting is to know where those different winds are.
"We have a very scientific method to measure the wind speeds," he said. "We spit. We spit over the side and watch where it goes. Some competitive pilots will use shaving cream, an as it falls, they watch which direction it breaks."
So you can't steer a balloon, but you can use your knowledge of the wind to give you some control over where the balloon goes. (Also some modern instruments help make the task easier.) Pilots also let hot air escape through the top of the balloon to cause it to sink -- or apply more fire to lift the balloon.
So where do you land? Well, wherever you can. Sometimes you aim for a field. Sometimes you aim for a parking lot. Sometimes you land in someone's backyard. It's all part of the adventure.
"Personally, I don’t care to land in fields," said DiLibero. "Usually there are crops or livestock, and I don’t want to buy crops or disturb livestock. I like to land in neighborhoods with cul-de-sacs. I find they have lots of kids in them who are excited to see us -- and then we sucker them into helping us pack up the balloon!"
What are they made of?
Construction of hot-air balloons hasn't changed very drastically over the years. The materials are stronger and more resilient, but the structure remains the same. The balloon -- or envelope -- is usually made of nylon or polyester. But that skin doesn't bear all the stress of the hot air. That's borne by the "load tapes."
"Load tapes are similar to the seat belts in your car," said DiLibero. "There's no pressure on the fabric -- it's all on the load tapes."
The number of load tapes determines how scalloped or "bumpy" the outside of the envelope looks. The fabric stretched in between the load tapes is called a "gore." The fewer gores, the "bumpier" a balloon looks. The more gores, the flatter it looks.
DiLibero said balloons can be constructed in special shapes -- much like the American flag shape or the Space Shuttle shape you may see at this year's Balloon Festival. Basically, an envelope is constructed with load tapes into a tube shape, and the "extra parts" of the shape are just filled with leftover air. Basically, you have a balloon within a balloon.
Beneath the envelope is a wicker gondola -- or basket. The wicker is there more for decoration and tradition. It's actually a steel or aluminum frame with a wooden bottom. Steel cables and carabiners keep the envelope attached to the gondola.
Then you add in the fuel -- specifically, propane. One to six tanks of it.
The modern home furnace rates at about 100 to 150 BTUs," said DiLibero. "These burners are rated at approximately 15 million BTUs."
The number of burners on the balloon tells you how many people the balloon can carry. One burner can support 1-4 people. Two burners can support around 12 people. After that, you need more burners.
How do you fill them up?
First, you unroll the envelope and stretch it all the way out. Next, you hook up a gas-powered fan and literally blow the balloon up. One person ties a rope to the very top of the envelope -- called a crown line -- and holds the it steady so it does roll around while it inflates.
It's a very social activity," he said. "That's what makes it so fun.
"The crown line holds the balloon steady as the heat makes it lighter and lighter," said DiLibero. "The crown line person's job is to make sure the envelope doesn't stand up before we're ready. Guys can get dragged across a field sometimes, especially if they trip.You have to be as surefooted as possible."
Next, you lay down the gondola on its side and start shooting flames into it. The hot air lifts the balloon, pulls the gondola up straight and allows you to get ready. The balloon remains tethered to the ground at this point until it's time to lift off.
You need about a half-dozen people to get a balloon operational, between holding the cables steady and getting everything set. DiLibero said it makes ballooning a community activity.
"It's a very social activity," he said. "That's what makes it so fun."
So how can I be a pilot?
Want to fly a hot-air balloon? It's going to take two things -- patience and money. DiLibero said it cost him around $10,000 for a used balloon in 1991. Then you'll need money for your license -- maybe another $5,000. But you are also at the mercy of the weather. Since you need good conditions to fly, you'll need to be in an area that allows you do fly often. Plus, you also need a good instructor. There are schools in New Mexico and California that can help you get certified in a week or so, but you'll need to be able to invest that time.