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The Eternal Wing

Taking to the Air

Cockpit Confusion

Bird Man


Viewer Challenge
in the classroom


Motorized balloons, gas-powered model helicopters, tail sitters and other unusual designs were among the contenders in the Fifth Annual International Aerial Robotics Competition. The challenge? Have the robot locate and pick up a metal puck and drop it off at a designated point. Student teams tried their best to achieve success this year (in previous years, robots flew but could not pick up the pucks). As you see on FRONTIERS, the U.S. Department of Defense Global Positioning Satellite provides a strategic edge.

Curriculum Links
An Introduction: On Course, Of Course
Activity 1: Build and Race a Lighter-Than-Air Vehicle
Activity 2: The Ultimate Lighter-Than-Air Vehicle Challenge
For Further Thought



computer-assisted design
three-dimensional imaging

scientific method



projectile motion

flying machines


In 2000 BC, the Greek mathematician Archimedes established the principle that governs lighter-than-air flight. He stated that in order for an object to float or "hover," it must displace a weight of fluid exactly equal to its own weight.

For a balloon to hover, it must be large enough to displace a weight of air equal to the weight of its skin, structure and the gas inside it. To accommodate the other materials supported by the balloon, the gas must be extremely light. Because it is lighter than air, helium is ideal for this purpose.

The two activities for "RoboFlyers" challenge you to design, build and fly a rubber-band-powered, helium-filled lighter-than-air vehicle (LTAV) on a predetermined course. Activity 1 is suggested for elementary and middle schools. Activity 2 could be done in high school technology education, science or math classes. The objectives are to demonstrate the principles of flight with LTAVs and practice creative problem solving and teamwork.


AV Parts Your LTAV device must be powered only by a combination of a rubber band and propeller. Use a three-cubic-foot kitchen trash bag for the LTAV envelope. The envelope must have a filler valve to inflate with air from a hair dryer (use a funnel) during practices and helium for the actual competition. (You can't use the air from your lungs to inflate the envelope because of the moisture.)

The vehicle must have an adjustable rudder, and must fly freely and unassisted. You may adapt the course to any facility.


  • plastic straw
  • tape
  • scissors
  • string
  • funnel
  • hair dryer
  • large rubber band
  • .5mm plastic kitchen trash bag (3 cu. ft.)
  • rubber-band-powered balsa wood airplane kit ("Guillow's Jet Stream," found at hobby stores, is a good one)
  • index card (for the rudder)
  • helium tank (party balloon filler)


  1. To make the envelope, seal the open end of the trash bag with tape, leaving room to insert the straw for a filler valve.

  2. Use a funnel and hair dryer on the cool setting to inflate the envelope. Figure out a way to close the filler valve (straw) so it can be reopened (you can simply fold it over). Check for air leaks.

  3. Attach the propeller and rubber band to the fuselage of the balsa wood airplane. Attach the rudder.

  4. Suspend the fuselage with strings and fasten to the envelope with tape.

  5. For the competition, replace the air in the envelope with helium.

  6. Before the actual race, make a test run of the LTAV to determine the course. The LTAV may simply fly in a straight line for six feet and return.

  7. Conduct three trials; record the trial with the course closest to the predetermined path. You may adjust the rudder and fuselage between trials.

  8. Wind the rubber band and release the LTAV. Observe the course it takes. Experiment with the adjustable rudder to obtain the desired course, then race your LTAVs. Have fun!


The LTAV envelope must be no larger than three cubic feet in volume. The envelope may be constructed in any shape from any material. The device must be powered only with a combination of rubber bands and propeller(s).

Rubber bands may be any size. The envelope must have a filler valve to inflate with air from a funnel and hair dryer during practices and helium for the actual competition. The vehicle must have an adjustable rudder that will determine the course during testing and competition.

During the competition, the best of three trials in the predetermined course wins. The vehicle must fly freely and unassisted. You may adapt the course to different facilities. In a classroom, the LTAV may travel straight for 15 feet and then around a pylon or obstacle and return to the starting line.

LTAV Materials:

  • clothes iron
  • fishing line
  • newspapers
  • foam core
  • string
  • plastic straw
  • paper clips
  • scissors
  • propeller
  • hair dryer
  • funnel
  • large rubber bands
  • glue/hot glue gun
  • helium tank (party balloon filler)
  • tape (electrical, cellophane, masking)
  • .5mm plastic drop cloths or plastic dry cleaner bags or trash bags
  • construction paper
  • timing device
  • snap-blade knife


  1. Design and draw the pattern for the three-cubic-foot envelope on construction paper, using mathematical equations to determine the volume.

  2. Cut material for the envelope into desired shape.

  3. Seal material by experimenting with different sealing methods (iron, tape, etc.).
  4. Insert filler valve (straw) to inflate the envelope.

  5. Inflate envelope, close filler valve with tape and check for air leaks.

  6. Experiment with rubber bands, propeller and different materials to obtain the best superstructure for a propulsion system to power the LTAV.

  7. Suspend the superstructure from the envelope with various fastening devices.

  8. Design and construct a programmed navigational system; devise a timing device on the rudder to determine the course of the LTAV.

  9. Inflate the envelope with helium, establish neutral buoyancy, wind the propulsion system and set the navigation system.

  10. Observe vehicle results and use time/speed ratio to determine the outcome.

TE Notes:

This activity can be completed in three to four class periods, less if you have block time. Students should work in teams of three to four students each; encourage group problem solving. Brainstorm ideas for a timing device. Have a variety of materials available in advance for experimentation. Discuss the connections between technology, science and math concepts as they relate to volume, density, mass, weight, buoyancy, gas properties and measurement. You may need to provide equations to obtain volume. Use proper caution and supervision when working with potentially hazardous materials.


  1. Why does an LTAV hover?

  2. How can you make your LTAV more controllable?

  3. What do you know about flight and buoyancy as related to LTAVs?


  • Investigate the different shapes of envelopes (in hot-air balloons, blimps and other airships). How are shapes in nature aerodynamically designed (porpoises, whales, birds, etc.)?

  • Explore alternatives of propulsion and other methods of controlling the direction of the LTAV.

  • Investigate the properties of gases used for lift and how these have affected the history of LTAVs.


Scientific American Frontiers
Fall 1990 to Spring 2000
Sponsored by GTE Corporation,
now a part of Verizon Communications Inc.