Engineering design challenge: Build a hovercraft

Courtesy of: Engineers and Geoscientists British Columbia – Vancouver Branch 

Hovercrafts are used today for many reasons. The Coast Guard uses them to perform rescues; the military uses them for transporting equipment over challenging terrain; environmental companies use them to access sensitive ecosystems without causing a disturbance; they can also be used as transportation or for recreational purposes. Did you know there is even one at Vancouver International Airport? They can travel over grass, swamps, ice and snow, bodies of water, sand, and mud. 

Goal 

Build and test a hovercraft. 

Materials 

  • Straw 
  • Ping pong balls 
  • Hot glue gun 
  • Old CD or disc 
  • Balloon 
  • Pop-up top from a water bottle 
  • Penny 

Instructions 

  1. Explain how hovercrafts work:  
    Hovercrafts work by creating a thin cushion of air under the large, flat bottom of the vehicle. Think of an air hockey table, except instead of the air coming up from the table, it comes down from the hovercraft. The air cushion reduces friction between the bottom of the hovercraft and the surface underneath. Think about rubbing your hands together (or try it!) and then think about how they are more slippery if you rub them together with soap. The soap reduces friction between your hands.  
     
  2. Demonstrate an air cushion and get participants to give it a try:  
    1. Place the straw upright and hold or balance the ping pong ball on top. 
    2. Tilt your head up and start blowing through the straw. 
    3. Keep blowing until it lifts off the straw. The space between is an air cushion!

      Side Note: For older participants, you can talk about forces and how the force from the air cushion pushing up is what counters the gravitational force of the hovercraft pushing down. When they are equal, the hovercraft hovers. When the force from the air cushion is greater, the hovercraft will rise until they are equal. When the gravitational force is greater, the hovercraft will descend until they are equal. The same goes for the ping pong ball.
       
  3. Build a hovercraft: 
    1. Divide participants into groups of two to three and each group will receive the supplies to make one hovercraft together. 
    2. Securely hot glue (recommended) and/or tape the pop-up top over the hole in the disc. There should be no gaps for the air to leak out between where the pop-up top and the disc meet. 
    3. Inflate the balloon and pinch the base about an inch above the tip. Stretch it over the bottle cap (and make sure the bottle cap is open).  
    4. Continue to pinch or twist the neck of the balloon to keep the air in while placing the hovercraft flat on the ground. 
       
  4. Test the hovercraft: 
    Set up a start and finish line on a smooth flat surface. Wood, tile, laminate, etc. flooring or a large table are good options. Carpet will not work well. Line up all of the hovercrafts with balloons filled and pinched shut. Start the race with “Ready, Set, Go” and have the participants let go of the pinched balloons and push the hovercrafts forward. The first one to the finish line wins. If none of the hovercrafts make it to the finish line, the one that went the farthest wins.  
     
  5. Try the alternative options below to experiment with the hovercrafts: 
    1. Size of balloon: Inflate the balloon different amounts (small, medium and large) and see what happens to the hovercraft. 
    2. Amount of force: Inflate the balloon and push the hovercraft with different amounts of force (a little, moderately and a lot). 
    3. Payload: Add a penny to the edge of the hovercraft and see if it will still hover. What happens if you add more than one? 
    4. Multiple: Find another group to partner with and tape your hovercrafts together. Fill up both balloons and let them go at the same time. 
       
  6. Come back together into a circle and talk about what the participants learned. Refer to the questions from the introduction, as well as the additional questions below. 
    1. Did your hovercraft work? Why or why not? 
    2. Do you think problems are always solved with the first solution you try? 
    3. Can you think of anything else you want to investigate about this problem? 
    4. What would you do differently if you tried this again (different curtain material, fins, different shape of balloon, etc.)? 
    5. What would you do the same?