HOT AIR BALLOON
Grades 11-12

This lesson provides the students with an understanding of how hot air balloons are designed, tested and what factors affect flight. Through a problem solving approach, students will gain an understanding of balloon construction, history and types of materials used. Hands on activities and video have been incorporated to extend and reinforce the concepts.

Chemedia Videodisk (Prentice Hall)

Students will be able to:

• list the various types of lighter-than-air craft and describe their limitations;
• describe the procedure for launching a hot air balloon;
• describe the difference between hot air balloons and gas balloons;
• describe how a balloon floats in the atmosphere;
• demonstrate the principle that makes a hot air balloon rise (that warm air expands when heated);
• demonstrate the force of buoyancy;
• describe the characteristics of lighter than air flight;
• describe some of the problems that would be faced by an aeronaut during a flight;

per group of three to four students:

• several rolls of cellophane
• several pair of sharp scissors
• a tacking iron or small travel iron
• two hair dryers
• extension cords
• alternate heat source (propane torch and striker or sterno stove with can of sterno)
• safety glasses
• for safety a fire extinguisher should be on hand
• hot plate or Bunsen burner
• tissue paper
• glue sticks
• string
• wire coat hanger
• tyvex

• aeronauts - A pilot of a lighter-than-air craft
• atmosphere - the gaseous mass surrounding the earth
• ambient temperature - temperature of the air surrounding a balloon
• ballast - heavy material added to the gondola of a balloon to increase stability
• barometric pressure - atmospheric measurement used in weather forecasting
• blimp - a lighter-than-air craft with control surfaces and motor power
• Btu's - British thermal unit, a measurement of energy
• buoyancy - the upward force that a fluid exerts on a object less dense than itself
• casks - wooden containers or barrels
• contract - to reduce in size
• cubic foot - a measurement of space one foot wide by one foot deep by one foot high
• density - the volume of a substance per unit of mass
• expand - to increase in volume or size
• fluid - a substance that has no definite shape and has a tendency to assume the shape of the container it is held in water and air
• free balloon - a balloon that has no control surfaces, hence can not be directed
• gores - the individual panels that make up the envelope of a balloon
• gondola - the basket that is used to hold passengers on a balloon
• gross weight - the total weight of a balloon, including passengers
• helium - a colorless, odorless inert gas used to provide lift for balloons
• humidity - moisture in the air
• hydrogen - a colorless, highly flammable gas formerly used in gas balloons
• hygrometer - an instrument used to measure the humidity in the atmosphere
• inflammable gas - gas that will not burn or ignite
• inert - a substance that does not show any chemical activity, will not combine with other substances
• inflating appendix - the nozzle or orifice used to inflate a gas balloon
• keel - a rigid fixture attached below a dirigible or as a structural member of a rigid dirigible running lengthwise to which the frames are attached
• latex - a rubber product used to coat envelope material in a balloon
• load tapes - the vertical tapes sewn into a balloon onto which the load of the gondola is attached
• meteorology - the study of weather
• nylon - a high-strength man made material used in the construction of balloon envelopes
• nonrigid - a LTA craft having no keel, but a soft envelope, similar to a balloon
• pressurized - a cabin or airframe that is built to maintain normal atmospheric pressure inside
• polyester - a synthetic resin used to waterproof cloth
• rip panel - a panel in the envelope of a balloon that can be opened rapidly to deflate the balloon upon landing
• rigid - a dirigible that has a soft envelope with a rigid keel attached below the mesosphere
• semirigid - a dirigible that has a soft envelope with a rigid keel attached below for structural strength
• stratosphere - a region of the atmosphere above the troposphere and below the mesosphere
• spherical - shaped like a globe, round three dimensional, like a ball
• specific gravity - the ratio of the mass of a solid or liquid to the mass of an equal volume of distilled water at 4 degrees C or of gas to an equal volume of air or hydrogen under prescribed temperature and pressure

Arrange the class into groups (two to three per group) and have them discuss and develop strategies for researching and answering the following questions:

What factors affect the mass that a hot air balloon can lift?
What are the parts of your balloon system and how will they be connected?
How will you heat the air in your balloon? What is the maximum safe temperature for the materials you will use in your balloon?
What material(s) should you use for the balloon envelope?
Does the shape of the balloon make a difference?

The focus for viewing is a specific responsibility or task(s) students are responsible for during or after watching the video to focus and engage students viewing attention. Say, "As you watch this video it will be your responsibility to answer the following: What is the effect of temperature and humidity on lift? In what kind of weather would you use the least amount of fuel?"

START laser disk at chapter 12 and let it run to the first pause. At this point have students think about why Goodyear chose He gas instead of H gas to fill its blimps? List the reasons on the board. Also have them discuss the problems of expansion in the blimp's envelope and how can they keep the gas He in? Have them discuss this in groups and then have them discuss their answers with the whole group. RESUME the disk and go to the next pause. During this section, have the students pay attention to the examples illustrated in the video. Have the students calculate how much the blimp's envelopes would expand if the temperature changed by 20 K. Have them discuss the landing procedures of blimps and how they might change or use the balloonist to raise the blimp's nose for landing. RESUME the disk and go to the end of this chapter. STOP and ask the students to discuss how blimps hold their shape and what factors affect the balloons shape.

START the laser disk at chapter 15 and stop at the end of this section. As the students are watching the demonstration have them think about how many moles of air are inside the balloon. How hot is the air inside the balloon after it has been heated with the hair dryer? How is a simple barometer constructed? What is it used for? They should be able to answer all the questions above. RETURN to the beginning of the section and when the section on inflating the balloon starts, frame each segment to illustrate what is happening.

START the disk at chapter 17 and STOP at the end of this section. The students will be watching the inflation of a hot air balloon. When the segment stops, they will be presented with some information about gases inside a balloon. With this information they will have to create a table (see sample) and organize the data that was presented.
As they organize this data, they will have to answer the following questions:
During cold inflation, what happens to the density of the gas?
Also during cold inflation, why is the volume increasing?
After the burner is ignited, why is the volume increasing?
What happens to the density of the gases in the balloon's envelope as the temperature increases?

START the disk at chapter 18 and stop at the end of this section. As they view this section they will be presented with three pairs of data. This time they will be analyzing the impact of temperature and relative humidity on a balloon lift. As they watch the segment they should think about the following :
What is the effect of temperature and humidity on lift?
In what kind of weather would you use the least amount of fuel?

START the disk at chapter 2. PAUSE at the statement "We have visual" and ask the students why it is easier for pilots to control the vertical direction of a balloon's flight than the horizontal direction? PLAY the disk forward to the statement "they don't cause us as much problems" and PAUSE. Ask the students, "Why did Julie say that thermals is not a good word for balloonists?" RESUME and go to the end of the section. STOP and ask the students, " Why is propane a good fuel to heat the air inside the balloon's envelope?"

Arrange the class into small cooperative groups. A good size is four, optimum is three. One member of the group should be assigned the role of foreman or leader and be responsible for coordinating the groups effort. Another member should be responsible for equipment. The third member is the recorder who will write, record and keep all written material organized. The fourth member is the reporter who is responsible for giving the oral reports, making presentations and for recording events through video or photographs.

Say, "Remember what you have just seen. It is your task to construct a hot air balloon using dry cleaning bags." Explain that the bag comes off a roll and it has perforations (holes) at the top that will have to be sealed. The procedure is to use a hot iron or a tacking iron to melt the plastic along the top.

Note to the teacher: Safety Note: Irons are HOT and must be handled carefully. Do NOT lay the iron down on any surface other than on the stand provided. NEVER touch the hot iron directly on the plastic material.
Cut the plastic bag using a pair of scissors so that the top of the bag has an arched top.
Fold the seam along the top over about 1" along the entire surface that has been cut.
Use a sheet of newspaper to cover the plastic material.
Use the hot tacking iron to heat the seam, melting the plastic together to seal the seam completely.
Place a strip of cellophane tape along the bottom edge of the bag (balloon envelope).
Attach four clips, spaced evenly along the bottom edge of the balloon.

Checking the balloon envelope:
Visually inspect the heat sealed seam.
Inflate the balloon with cold air from a hair dryer to make sure the seam along the top is completely sealed.
Drop the inflated balloon to determine the gravity gradient.
Hold the balloon at the top of the envelope and drop to the floor. The balloon should stay upright, having the heavier end with the tape and paper clips toward the bottom. The paper clips can be moved to balance the balloon if it seems to be heavier on one side.
Inflate the balloon with a hair dryer, using the highest temperature setting.

Procedure:
Two students should hold the balloon up by the top with one hand. With the other, hold the bottom edge out so that the air from the hair dryer can be forced up into the open envelope.
Determine if the balloon has gained buoyancy by letting go of the edge of the balloon and watch it rise.
If the balloon does not gain buoyancy the temperature inside the envelope is not warm enough. (Ambient temperature difference is not great enough).
When the bag begins to float, let it go. Watch the balloon as it rises. If the balloon tips over soon, it is not balanced. This can be eliminated by adjusting the position of the paper clips.
When cooled, the balloon will descend.
If there are any air currents in the location, the balloon will "travel" with the air currents.
Students should observe the flight characteristics of the balloon during its short flight.

Note to Teacher: An additional heat source may be needed. The following procedure should be accomplished by the Teacher only. Use an open flame from a propane torch or Bunsen burner to heat the air inside the envelope. EXTREME CAUTION must be taken to ensure that the plastic bag does not contact the open flame. Hold the flame under the bag , at least 12 inches below the edge of the envelope. Use an open flame from a camp stove or sterno stove as a heat source. Use caution. Place the stove on the floor and hold the bag over the rising heat. Do not lower the bag any lower than 12 inches above the open flame. Assign a "safety officer" to have a fire extinguisher at the ready during the experiment. Also, it is best to do this outside away from buildings.

Note: You may want to have a student videotape the flight of each balloon for study later or for presentation purposes.

Have an aeronaut come in to talk to the students about what is actually required to fly a balloon. They can also talk about preparations they have to go through and what factors affect flight.

Have an aeronaut inflate a balloon and give the students a ride.

Attend a balloon festival and have the students talk to various pilots about the craft and their experiences.

Math: Have students calculate net lift of their balloon and compare their findings.

Science: Have students research, design and build a gore panel hot air balloon.

Science and Math: Review the principles of density, buoyancy and expanding molecules and perform the following experiment:

Use one large, clear beaker and pour in water to approximately 1/3 the beaker depth. Add to the container three liquids of different density. Show students that the three fluids will not mix, even when stirred and that they will layer in the container according to density.

Density can be compared to weight. Notice that the less dense (lighter) liquid will float above the denser (heavier) liquid. To prove that the material will float according to density, weigh each bottle and note the weight of the same amount of liquid. Which is heavier?

When a fluid is heated, the molecules begin to travel at a faster rate, occupying more space, hence becoming less dense. You can prove that the molecules in a heated fluid travel faster by the following experiment:

Place cold water in a clear beaker. Drop several drops of food coloring into the container. Note how slow the color spreads in the cold water. With another beaker placed on a hot plate, heat clear water until it almost boils (if it boils let it cool enough so that it is not bubbling). Place food coloring into the heated water. Notice how fast the color spreads throughout the beaker! What caused the color to spread so rapidly?
Explain that air and water react in the same way when heated because they are both fluids. When air is heated the molecules travel around rapidly, causing fewer molecules to occupy the same space. If there are fewer molecules in the space, the density will be less and this is what causes a hot-air balloon to rise.

Social Studies: Have the students research various areas of the world that played an important role in the development of hot-air balloons.

Master Teacher: John Schott