Build a Mini Hovercraft
The idea of a vehicle riding on a cushion of air dates back to the 1700s. Efforts to design such a way to travel faster and more efficiently continued throughout the centuries until English engineer Sir Christopher Cockerell (1910–1999) designed and built the first successful hovercraft, which crossed the English Channel on July 25, 1959. To understand the basic concepts of how a vessel is able to “ride on air,” make your own working model of a hovercraft!
- Air pressure
- Newton’s Third Law of Motion
Advantages to using hovercraft include their ability to travel on land or water and their ease of use in difficult terrain, including muddy and swampy areas, thin ice, rocks, rapids and sandbanks. Today hovercraft are used all over the world for commercial transportation, recreational sport, as rescue vehicles and by the military for ship-to-shore transport.
A simple hovercraft consists of three parts—platform, fan and curtain. The platform is the main structure of the hovercraft. One or more motorized fans are used to create lift and thrust. A curtain is used to trap the air between the platform and the ground or water, creating a plenum chamber. The plenum chamber is an area of positive pressure—the air pressure in the chamber is greater than its surroundings.
Lift occurs when the combined upward and downward pressure on an object results in a net upward force on the object. The fan moves enough air to change the air pressure under the platform, lifting it above the surface so the craft rides on a cushion of air. The effect may also be described in terms of Newton’s third law of motion—for every action force there is an equal and opposite reaction force. The hovercraft platform pushes the air downward and the air pushes upward on the underside of the hovercraft. When the upward force on the platform is equal to the weight of the hovercraft, combined with the thrust created by the spinning propeller blades pushing air out the back, horizontal motion above the ground may occur.
The purpose of the activity is to construct a miniature hovercraft. Once the hovercraft has been assembled and its motion observed, further experiments may be conducted to investigate the effect of different design modifications on the performance of the hovercraft.
Battery clip with wire leads
Cup, polystyrene, 16-oz.
Housing template, 2 sheets
Large open area with smooth surface (tile floor or smooth carpet)
Paper clip, large
Tray, polystyrene, 8
Wire, PVC-coated, 22 gauge, 6 ft
- A motorized fan creates thrust, which accelerates the hovercraft forward. Describe how thrust is created in terms of Newton’s third law of motion.
- Read through the Procedure. Why is it important to cover the 9-V battery terminals with tape until ready to test the direction of the air flow created by the spinning propeller?
- What safety precautions must be taken during the construction and operation of the mini hovercraft?
Although 9-V batteries do not have enough electrical current to be harmful, please exercise caution. Do not handle any electrical components with wet hands. Keep hands and other objects away from rotating propeller. Wear safety glasses during all parts of this activity. Wear long pants when operating the hovercraft and when any other hovercraft are in operation in the area. Please follow all laboratory safety guidelines.
Part I. Hovercraft Housing Assembly
- Using scissors, cut out the housing template by cutting along the solid lines only.
- Fold each dotted line toward the marked side of the template.
- Align the dotted edge of one triangular tab with the short edge of the trapezoidal side piece.
- Tape the tab to the side piece (see Figure 1).
- Repeat steps 3 and 4 with the other triangular tab.
- Carefully break a craft stick in half. Choose one piece that is no more than 6 cm in length.
- Trim any thin jagged pieces from the broken edge with scissors.
- Tape the craft stick half to the underside of the top of the housing, at the front edge (see Figure 2).
Part II. Hovercraft Assembly
- Place the assembled housing in the center of the polystyrene tray and mark each of the four corners on the tray with a pencil. Note: The top of the housing is the 2.5 cm x 6 cm rectangle and the back of the housing is the sloped side.
- Remove the housing from the tray and draw a 6 cm × 6 cm square on the tray, connecting the corner dots (see Figure 3).
- Carefully cut a hole in the tray that is the same size or slightly smaller than the outline of the housing.
- Place the tray upside-down on the work surface.
- Tape the housing over the opening in the tray. Be sure to cover any gaps between the three sides of the housing and the tray with tape (see Figure 4).
- Place the switch behind the housing and slightly to one side (see Figure 5).
- Carefully push the two metal terminals through the tray so the switch lays flat.
- Trace around the base of the switch with a pencil. Note: This does not include the tabs with the holes.
- Remove the switch and cut out the rectangle within the traced lines.
- Insert the switch in the rectangular hole so the tabs lay flat on the surface. If the hole is slightly larger than the switch and the switch is not secure in the hole, the switch may be taped down to cover any gaps after Part IV is complete.
- Unbend one end of a large paper clip and insert it through each hole in the metal tabs of the switch and through the tray.
- Rotate the paper clip in the hole to make the hole large enough in the tray to fit an insulated wire through.
- Attach the propeller securely to the motor shaft. Push on the center of the propeller, not the blades.
- Place the motor centered on top of the housing with the propeller toward the opening in the housing. Position the motor as far back on the housing as possible with the propeller able to rotate freely without hitting the housing or the tray.
- Securely tape the motor to the housing.
- Rotate the propeller by hand to make sure it does not touch the housing or the tray. Adjust the motor if necessary.
- Tape a 9-V battery to the tray directly behind the housing with the battery terminals on the same side as the switch.
- Loosely cover the battery terminals with a piece of masking tape. Note: This is a safety precaution to prevent completing the circuit until ready to test the motor.
Part III. Make the Blade Guard
- Place a 16-oz polystyrene cup upside-down on the work surface.
- Measure 9 cm from the open end of the cup and make several marks all the way around the cup.
- Cut off the bottom of the cup at the 9-cm marks. Discard the bottom.
- Cut the top 9-cm portion of the cup apart vertically—from top to bottom (see Figure 6).
- Reserve the blade guard for steps 36–38 of Part IV.
Part IV. Wiring the Hovercraft
- Obtain the 20-cm piece of insulated wire. If needed, carefully strip 1 to 2 cm of the insulation off each end of the wire.
- Attach one end of the insulated wire to one terminal of the motor by pushing the bare end of the wire through the hole in the terminal and wrapping the end around the terminal. Twist the end to secure.
- Insert the other bare end of the wire through one hole of the switch and through the tray.
- Lift the hovercraft up and turn over. Note: Do not set the hovercraft on the work surface upside-down!
- With a partner holding the hovercraft upside-down, attach the end of the wire to one of the switch terminals as in step 33. Make sure no part of the bare wire touches the second terminal or any other metal part of the switch.
- Align the battery clip with the correct terminals on the battery, but do not fasten down securely yet. Note: The battery terminals should still be covered with a piece of tape.
- Attach the black wire of the battery clip to the second terminal of the motor as in step 33. If needed, strip more of the insulation off the end of the wire before attaching.
- Obtain the blade guard from Part III.
- Spread the cup apart and place it over the housing so the larger opening in the blade guard is over the propeller (see Figure 7). Note: The back of the blade guard should not cover the battery. Adjust if necessary.
- Tape the blade guard to the platform of the hovercraft.
- Caution: At this next step, the motor may start unexpectedly if the tape over the battery terminals is not in place. The pro-peller blade will spin very fast.
- Push the red wire of the battery clip through the hole in the second tab of the switch, but do not let it touch either terminal underneath yet! Caution: If all the wires connect, the motor may run since you do not know if the switch is in the on or off position.
- Holding the hovercraft securely, remove the piece of tape from the battery terminal and fasten the battery clip to the battery terminals.
- Touch the bare end of the loose red wire under the hovercraft to the second terminal of the switch.
- If the motor does not run, remove the wire from the terminal and slide the switch to the opposite end.
- Repeat step 45. If the motor still does not run, check all connections and try again.
- Once the motor runs, slide the switch to the off position.
- Secure the red wire to the second terminal of the switch as in step 33.
- With all connections secure, one partner should hold the hovercraft, and slide the switch to the on position.
- Another partner should place one hand in front of, but not touching, the blade guard and the other hand behind the blade guard to determine the direction of the air flow.
- If the air is blowing out the back (toward the battery), slide the switch to the off position and proceed with step 55. If air is blowing out the front of the blade guard, turn the motor off and proceed to the next step.
- Remove the wires from the motor terminals and secure each to the opposite terminal.
- Repeat steps 50 and 51 to ensure the air is now flowing out the back of the blade guard.
- Tape any excess wire under the hovercraft to the bottom so it will not interfere with the motion of the hovercraft.
Part V. Testing the Hovercraft
- Do a final check of all electrical connections, making sure the bare ends of the wires are not touching any metal part of the motor or switch other than the terminal to which it is secured.
- Make sure all parts of the hovercraft are secure (the propeller is secure on the motor shaft, the motor is securely taped to the top of the housing, the battery and blade guard are securely taped to the hovercraft platform. If needed, tape the switch to cover any gaps between the switch and the platform.
- Test the hovercraft in an area designated by the instructor. The surface should be smooth and flat.
- Wear safety glasses at all times.
- Place the hovercraft on the floor, making sure plenty of open space is around the craft. Caution: Alert any others in the vicinity that testing is about to begin.
- Holding on to the platform, slide the switch to the on position.
- With the propeller turning, let go of the hovercraft.
- Following the hovercraft as it moves, make observations about the motion of the craft. What main direction does it travel? Does it move fairly straight? What happens if it hits an obstacle?
- After 30–60 seconds of observing the hovercraft, stop the craft and turn it off to conserve the battery.
- Repeat steps 60–64 if time allows.