The Montgolfiere balloon has a classic modern hot air balloon shape—an upside-down teardrop. It is about 48 inches (120 cm) tall by 32 inches (80 cm) across and made from six flat panels of tissue paper cut so that when they are glued together, the balloon has an elegant curved shape.
The balloon has a wooden frame glued into the opening at the bottom and a burner made from aluminum foil and a cotton ball. No wire is used in this balloon, so it is a good balloon to make if you live in an area with a lot of livestock that could injure themselves by eating the wire in a crashed balloon.
Any thin wood can be used to make the wooden frame: 3/16-inch (5 mm) square balsa makes a very light but fragile frame; a ¼-inch (6 mm) hardwood dowel makes a heavier and much stronger frame. Both fly well.
Because the balloon is made with six panels rather than four, the envelope has a bigger diameter than the other tissue paper balloons in this book and holds a lot of air. This gives the balloon a lot of lift, even though it is not very tall.
The shape of the balloon is based on the designs of the French Montgolfier brothers, who flew the first manned hot air balloon in 1783, and on the designs of the American Ed Yost, who developed the first modern hot air balloon in 1955.
The balloon in this chapter is called the Montgolfiere because of its teardrop shape, but in the world of balloons the term Montgolfiere has nothing to do with a balloon’s shape. A Montgolfiere is a balloon that uses only hot air to keep it flying, so technically all of the balloons in this book are Montgolfieres. Most full-size hot air balloons are Montgolfieres, because it is the cheapest and safest form of balloon. Some long-distance balloons, called Roziers, have special chambers built into the envelope to hold helium gas as well as the hot air, but these are much more expensive to build and more difficult to fly.
From Jacques Charles’s balloon in 1783 until Ed Yost’s modern hot air balloon in 1955, almost all free-flying balloons were made with spherical envelopes filled with hydrogen. A sphere uses the smallest amount of fabric for a given volume, so the envelope will be lighter and the lift will be greater. The only thing you need to do with a gas balloon is let out a little bit of gas so the balloon doesn’t fly too high and burst, and let out a bit more when you want the balloon to come down. But to keep a hot air balloon flying, you must keep feeding hot air into the envelope to replace the air inside as it cools—there needs to be a hole in the bottom of the envelope for the hot air to enter. Because of this, the most efficient shape for a hot air balloon is an upside-down teardrop, and almost all full-size hot air balloons have been made this way.
Hot air balloons can be made in a lot of different shapes, and if you go to a hot air balloon festival you will see balloons shaped like cartoon characters, beer bottles, and animals. But these special balloons are more difficult to fly and use a lot more fuel to keep them flying. The best shape is the simple upside-down teardrop.
Because of its tapered shape, the Montgolfiere is also a very stable balloon and will right itself quickly if a gust of wind tips it up. But why does the shape make a difference?
Along with having plenty of lift and a good, airtight, lightweight envelope, one of the most important things about a model balloon is how it behaves in windy weather. Often a gust of wind will catch a balloon just after it has launched and tilt it on its side. If the balloon tilts too easily, it will lose hot air, and if it takes too long to right itself, then the burner flame could set the envelope on fire.
So what makes a balloon sit back upright after it gets pushed sideways? A scientist would call a balloon that quickly rights itself a stable balloon, but how do you make something stable? It has to do with where the weight is in the balloon.
Cut two 4-inch (10 cm) squares of thin cardboard (from a cereal box) and draw diagonal lines from each corner to find the center of each square. Push a thumbtack through the center of one square and put the other square over the top so the head of the thumbtack is sandwiched in the middle. Join the two squares together with tape along the edges. Carefully push the thumbtack into a cork message board so that the cards are held in place, yet free to spin around.
If you managed to get the pin exactly in the center, the spinning cards can come to rest with any side pointing up. And because the cards are balanced, they can spin for a long time and you can’t tell where they will stop.
Now use a bit of poster putty or modeling clay to attach a penny to the center of the cards. The cards should still spin around easily and if the penny is exactly in the middle, the cards will still come to rest in any position.
Move the penny so that its edge lies at the center of the cards. When you spin the card this time, it won’t spin for nearly as long and will always come to rest with the penny underneath the pin. If you flick the card it will swing back so the penny is at the bottom again, maybe swinging back and forth a couple of times.
Next, move the penny so that it is right down in the corner of the cards. Now when you try and spin the card, it will probably only go around once and then quickly settle. So, the farther away the penny is from the pin, the quicker the card settles, and a heavier weight would also make the card settle more quickly.
A balloon doesn’t have a pin through the middle, but it does swing around a fixed point: the middle of the volume of hot air. Imagine a gas balloon in the shape of a perfect sphere. It can revolve around so that it is any way up because no part of the skin is heavier than any other. But if you tape a penny to the balloon, the skin will roll around until the penny hangs down underneath.
So, the spherical balloon revolves about the middle of the gas volume. A cylinder-shaped hot air balloon like the Khom Loi also revolves around the middle of the hot air volume, but, like all hot air balloons, the envelope is open at the bottom. This means that the envelope is not balanced: there is a circle of paper missing from the bottom of the envelope. This makes the envelope heavier at the top than at the bottom, so that if you fill the paper envelope of a Khom Loi with hot air, it tries to turn upside down.
All of the hot air balloons in this book suffer from this problem. The shape of the envelope puts a little bit more weight at the top of the balloon than at the bottom, so all these designs are unstable when filled with hot air. They need an extra weight at the bottom to make sure that the balloon stays upright. You add the weight by fixing a wire ring around the opening at the bottom of the balloon—the farthest point away from the center of the hot air—so that the weight can be as small as possible while still keeping the balloon upright.
Some balloons are more nearly balanced than others. The long, tapered shape of the Kongming Lantern envelope puts more hot air toward the top of the envelope so it is very nearly balanced; it needs only a thin wire ring to keep it upright.
Adult supervision required
Materials
Newspaper or wallpaper to make a template
Thin clear tape, lightweight masking tape, or similar
12 sheets of tissue paper, 20 inches (50 cm) by 26 inches (66 cm) or larger
1 cup (240 mL) diluted white craft glue (1 part PVA glue to 5 parts water)
Undiluted white craft glue (PVA glue)
¼-inch (6 mm) hardwood dowel, 5 feet (1.5 m) long
Empty cereal boxes (or other source of thin cardboard)
Cotton ball (or balls), large enough to make a wad 3 inches (75 mm) long by 1½ inches (38 mm) wide
Aluminum foil
1 fluid ounce (30 mL) kerosene
Tools
Ruler
Pen
Scissors
Narrow sponge or brush (to apply glue)
8 or 10 straight (dressmaker’s) pins
Heavy books or food cans to hold down the tissue paper
Hobby knife
8 clothespins
Before You Start
You will need a large, flat surface to build your balloon. You can use a table or the floor, but whatever you use you is going to get glue on it, so make sure the glue won’t damage it. You can help to protect the table or floor by cutting trash bags into large plastic sheets to cover the work area.
If you do cover your table with plastic sheets, you can leave the balloon on the table to dry, as white craft glue will not stick to the plastic used to make trash bags. The balloon will dry more slowly if you leave it on the table rather than hang it up, but it is a lot easier.
As with any tissue paper balloon, it is a good idea to have the bottom 12 inches (30 cm) of the balloon coated with a fire retardant. You need to coat the tissue paper before you create the balloon—see chapter 11 (page 221) for instructions.
When you make a tissue paper balloon, most of your time is spent waiting for the glue to dry. If you have a blow-dryer, you can make a balloon much more quickly by using the blow-dryer to blow warm air at the glued seams. Don’t use a fan heater or other room heater as they can set the tissue paper on fire.
What to Do If Things Go Wrong
Holes in the tissue paper are easy to fix, and the Montgolfiere will still fly well. You can find repair instructions in chapter 11 (page 211).
In fact, check chapter 11 if you have accidentally glued parts of the panels that shouldn’t be glued together, if you need a recipe for a different glue, if you cannot find the right materials, or if you have any other problems.
How to Make the Envelope
Template Measurements
| Point | Distance Along Fold | Distance Across from Fold |
| 1 | 0 | 3/4 inches (19 mm) |
| 2 | 4 1/8 inches (105 mm) | 2 7/8 inches (73 mm) |
| 3 | 8¼ inches (210 mm) | 4 7/8 inches (124 mm) |
| 4 | 12 3/8 inches (314 mm) | 6 5/8 inches (168 mm) |
| 5 | 16½ inches (419 mm) | 7 7/8 inches (200 mm) |
| 6 | 20 5/8 inches (524 mm) | 8 3/4 inches (222 mm) |
| 7 | 24 3/4 inches (629 mm) | 9 inches (229 mm) |
| 8 | 29 inches (737 mm) | 8 3/4 inches (222 mm) |
| 9 | 49¼ inches (1,251 mm) | 5 7/8 inches (149 mm) |
Repeat steps 4 and 5 for each of the rows in the table, measuring along the fold by the distance in the middle column and then across the sheet by the distance in the right-hand column.
How to Make the Wire-Free Burner
What to Do Next
Check the envelope for any leaks by inflating it over an electric toaster or blow-dryer. Look for gaps in the seams or holes in the tissue paper and repair them (see instructions in chapter 11, page 211). Take care not to scorch the cotton ball in the burner or the exposed wood in the base frame. Once you have fixed any leaks, the balloon is complete and ready to fly. See chapter 2 for instructions on flying a balloon with a burner.
Applying a fire retardant to the tissue paper will almost completely eliminate burn-ups on launching. If the wind catches the burner flame and pushes it onto the side of the envelope, all that will happen is the flame will scorch a hole through the tissue paper.
Because the Montgolfiere envelope has a lot of lift, you can use any of the burners in this book. To use a burner supported by a wire you will need to fit a rattan base ring (chapter 7, page 138) or a thick wire base ring (chapter 8, page 164) instead of the wooden frame.
If you want to make a larger and more elegantly shaped Montgolfiere envelope, start by taping together a strip of newspaper large enough to make a 75-inch-by-20-inch (190 cm by 50 cm) template. Use the following table to make the template:
| Point | Distance Along Fold | Distance Across from Fold |
| 1 | 0 | 3/4 inches (19 mm) |
| 2 | 4 1/8 inches (105 mm) | 2 7/8 inches (73 mm) |
| 3 | 8¼ inches (210 mm) | 4 7/8 inches (124 mm) |
| 4 | 12 3/8 inches (314 mm) | 6 5/8 inches (168 mm) |
| 5 | 16½ inches (419 mm) | 7 7/8 inches (200 mm) |
| 6 | 20 5/8 inches (524 mm) | 8 3/4 inches (222 mm) |
| 7 | 24 3/4 inches (629 mm) | 9 inches (229 mm) |
| 8 | 29 inches (737 mm) | 8 7/8 inches (225 mm) |
| 9 | 49¼ inches (1,251 mm) | 5 7/8 inches (149 mm) |
You then need to join together three sheets of tissue paper by gluing them together along their narrow edges, like this:
Repeat this until you have six long sheets of tissue paper and then follow the instructions in this chapter starting with step 14.
