The Khom Loi in this book is a cylindrical balloon about 53 inches (1.3 m) tall and about 25 inches (64 cm) in diameter. It is made from four panels of tissue paper glued together with a circular tissue paper top. The balloon has a circular ring glued into the opening at the bottom made from rattan cane or split bamboo.
The Khom Loi has a special burner made from string wound into a thick ring and soaked in wax. The burner is supported on thin wires stretched across the rattan ring at the bottom of the Khom Loi.
The envelope of the Khom Loi is easy to put together, but you will need to use a calculator to determine how big to make the circular tissue paper top. You will need to take care not to get wax on yourself when melting wax for the burner, especially when soaking the string burner itself in the hot wax. Heatproof gloves and safety glasses are essential
The large cylindrical shape means that the Khom Loi contains a lot of air, so it has a lot of lift. This means that the balloon can lift a heavier burner, giving a longer flight and a rapid climb. However, because the Khom Loi is not tapered and has a large opening in the bottom, it does need a heavier base ring than either the Kongming Lantern or the Montgolfiere designs.
Khom Loi (floating lantern) and Khom Fai (fire lantern) are general names given to any paper hot air balloon in Thailand. The Thai people use a number of different designs during their festivals, but the cylindrical design shown on the previous page is one of the most common. Another common design has four straight-sided panels formed with a pointed end so that the panels can be glued together in much the same way as the Kongming Lantern and the balloon needs no separate top.
Thai Khom Loi are often made from rice paper, sometimes oiled to make it more airtight. The rice paper used to make the balloons is not the edible rice paper made from rice flour and tapioca, but a thin and very strong paper made from the bark of the mulberry tree. It is called rice paper because the thicker grades are used to make the sacks for storing rice. Tissue paper is a good alternative if rice paper is unavailable, although it is not as strong.
Thai balloons use a lot of different burner designs. Some burners have fabric patches soaked in wax; some have bundles of fibers like the burner in this chapter. One common type of burner is made by soaking wax into a roll of toilet tissue and then cutting off 1-inch (25 mm) rings like slices of bread. You suspend one of the rings in the middle of the base ring using thin wires. Whatever wax burner is used, the secret to getting it to light is to have a thin piece of stuff sticking out to act as a wick or touch-paper. With the toilet roll burner you unpeel a bit of the first few sheets; with the string burner you have a few inches of string sticking out from the ring.
Because you know how a gas expands and shrinks with temperature, you can use the lift from a hot air balloon to make an estimate of air density. To make the calculation you need to know the volume of the balloon, the temperature inside the balloon, the room temperature, the weight of the balloon, and the strength of the lift. It is important that the temperature inside the balloon and the lift are calculated at the same time, as they can go up and down quite quickly.
Measuring the lift is actually very easy. The trick is to put a 100-gram weight onto a set of electronic weighing scales and attach the balloon to the weight using thin sewing thread. When the balloon is lifting upward, the weight displayed by the electronic scales will appear to go down. You calculate the lift by figuring out how much weight has been “lost.” It is even easier if you use the zeroing or “tare” function. After you have tied the thread to the 100-gram weight and put it on the scales, you press the “zero” button and the display then reads zero. Now when the balloon pulls upward, the scales will give a direct reading of the lift (with a minus sign in front of the number).
The Khom Loi from this chapter is an ideal choice to use in this experiment, as it has a simple cylindrical shape. You only need to measure the diameter and the height to be able to calculate the volume inside the balloon.
You should heat the air inside with an electric heater rather than a wax or kerosene burner. The burner gets lighter as the fuel is used, so you cannot calculate the overall lift.
To measure the temperature inside the balloon, you are going to need a thermometer with a higher range than a normal room thermometer; the temperature inside the balloon can reach as high as 150°C (300°F). You can use some cheap oven thermometers (though make sure the thermometer reads down to about 50°C, or 120°F), a sugar thermometer for making jam and jelly (this is ideal), or a soil thermometer.
But the main difficulty is reading the scale on your thermometer when it is in position—right up at the top of your balloon. The simplest way is to cut out a small rectangle of paper from the side of the balloon and tape a clear polyethylene window into place. You can then read the thermometer through the side of the balloon. If you can get hold of a thermocouple temperature probe, or an oven thermometer with a separate display, then you can hold the probe inside the balloon and run the wire down through the opening at the bottom of the envelope.
Whatever type of thermometer you use, you will need to mount it on a stick so you can hold it up at the top of the balloon for long enough to make an accurate measurement without blocking the hot air going into the bottom of the envelope.
Materials
Khom Loi envelope with base ring (but no burner fitted)
Clear plastic bag
Thin clear tape, lightweight masking tape, or similar
Oven thermometer or similar
Room thermometer
Length of dowel or other stick to hold oven thermometer
Sewing thread
100-gram weight
Tools
Scissors
Ruler
Electronic scales
Pen
Paper or notepad
Electric toaster or similar electric heater
Making the Measurements
How to calculate the Result
To calculate the density of air from the experimental measurements, you need to use a mathematical formula that describes how the air behaves when heated. The formula is called the Ideal Gas Law, and it is usually written as:
pV = NkT
Where p is the gas pressure, V is the volume, N is the number of gas molecules, k is a fixed number called the Boltzmann Constant, and T is the temperature in Kelvin. It is not very easy to use this formula to calculate air density from your experimental data, and you don’t need to worry about the pressure effects as all of the experiment is done at atmospheric pressure. The formula is a lot easier to use if you simplify and rearrange it:
Where:
It’s time to look at an example. Here are some of my measurements to show you how to use the formula:
Measurements
Room Temperature: 20°C
Balloon Temperature: 90°C
Khom Loi Size: Diameter, 0.611 m; Height, 1.28 m
Khom Loi Weight: 0.048 kg
Measured Lift: 0.040 kg
The Khom Loi volume can be calculated using the formula for the volume of a cylinder:
Volume = π r2 h = 3.14 × 0.30552 × 1.28 = 0.375 m3
Convert the room temperature to Kelvin by adding 273:
Troom = 20 + 273 = 293°K
Convert the balloon temperature to Kelvin by adding 273:
Tballoon = 90 + 273 = 363°K
The Gross Lift can be calculated by adding the envelope weight to the measured lift:
Gross Lift = 0.048 + 0.040 = 0.088 kg
The air density is then calculated:
Density = 1.2kg/m3
Adult supervision required
Materials
10 sheets of tissue paper, 20 inches by 26 inches (50 cm by 66 cm) or larger
1 cup (240 mL) diluted white craft glue (1 part PVA glue to 5 parts water)
5 feet (1.5 m) fresh rattan center cane or split bamboo, ¼ inch (6 mm) diameter
5 feet (1.5 m) thin soft iron wire
1/3 ounce (10 g) soft jute string or soft cotton string
2 ounces (60 g) paraffin wax or beeswax
Tools
Narrow sponge or brush to apply glue
Pen
Ruler
Heavy books or food cans to keep the tissue paper from moving
Scissors
Clean sponge and dry cloth
Calculator to determine radius
Strip of cardboard, 40 inches (102 cm) long (to make a radius measure)
8 small pieces of cardboard, 3/4 inches by 2 inches (2 cm by 5 cm), to hold ring in place
8 paper clips, to hold ring in place
Hobby knife
8 clothespins
Small jar, about 2½ inches (64 mm) in diameter, to wind string around for the burner
Large jar, about 4 inches (10 cm) in diameter, to melt wax
Heatproof gloves
Safety glasses
Pencil
Newspaper
Pliers (with wire cutters)
You will need a large, flat surface to build your balloon. You can use a table or the floor, but whatever you use 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 Khom Loi will still fly well. You can find repair instructions in chapter 11 (page 211).
In fact, check chapter 11 if you have 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 a Tissue Paper Cylinder
Put the envelope onto the table or floor with one of the gaps at the front. Make sure that the edge of the envelope is pulled well forward so that there are no folds of tissue paper trapped underneath.
You are going to glue half of the gaps just as you did when gluing the paper circle into the top of the envelope. Lay the balloon back down on the table or floor with the next gap toward you. Tear down a flap and glue it as before. Repeat these steps until you have glued half of the gaps. Put the balloon to one side and prop the base ring up until the glued flaps are dry. Once the flaps are all dry, remove all of the clothespins and cardboard.
How to Make a Waxed String Burner
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 that the hot air from the toaster does not melt the wax or it will drip off and may set the toaster on fire. 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 (page 33).
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.
The easiest way to make a larger Khom Loi is simply to glue three sheets together instead of two in steps 1 to 5. This gives a Khom Loi that is about 6 feet (1.83 m) tall. The rest of the balloon is made in the same way.
You can also increase the lift in the balloon by making the diameter of the balloon bigger. Instead of gluing four panels together to make a 24-inch (60 cm) diameter envelope, you can glue five or even six panels together to make a 29-inch or 35-inch (74 cm or 89 cm) envelope. Because the diameter is so much larger, you will need to make a much larger pasted-together sheet for the circular top. Glue four sheets of tissue paper together as shown.
If you want to make the balloon fly for longer, you can wrap strips of aluminum foil around the string burner in between the string ties. This works by limiting the area of the waxed string that is exposed to burn. The wax in the shielded areas will melt and be fed into the flame by capillary action through the string fibers. You will have to experiment to see how much of the burner you can cover up before the lift is reduced too much.
If you want to fit a wire-free burner to the Khom Loi, you can use the design from chapter 6 (page 109).
