© 2019 by Pernille Dahl & Cole Robbins. 

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Flying Fish

Parts needed:
  • 2 Models

  • 1 Motor

  • 2 AA battery

  • Connection wires 

  • Popsicle sticks

  • File folders or stiff paper

  • Aluminum foil

  • Paper clips

  • String

  • Push pins/nails

  • Ribbons

  • 2-liter bottles, marked for propellers

Extra Tools: 
  • Drill

  • Drill platform

  • Small nail bit

  • Hole punches

  • Long 5/16” dowels (for hanging the fish)

  • Black tape

  • Duct tape

Project Description:

Propellers and fans push air.  They go around in circles, but they push air perpendicular to the plane of rotation. Most of us are more familiar with fans than with airplane propellers, but they are essentially the same. Fan blades are at an angle such that each bit of air they encounter bounces off toward the front or back.  If something perfectly flat, like a Popsicle stick, goes in circles, it does not push much air, and thus would not make the fish move.

 

In this toy, the propeller can push air forward away from the fish or back across the fish depending on which way the motor is turning.  Newton said that for every action there is an equal and opposite reaction.  In this project the action is the propeller pushing the air back across the fish; the reaction is the fish being pushed forward through the air. 

 

Center of mass and gyroscopic effects also play in on this project. It gets a bit complicated, but for most fish we have made one direction of flight is much more stable than the other direction.  The body of the fish is not symmetric, that is, the batteries and motor put nearly all the weight on one side.  The orientation of the fish is diagonal as it traces out its circular flight path, and usually the fish is most stable if the battery side is down.  But the rotation of the motor-propeller system makes gyroscopic forces that also effect which direction is more stable.  This is an example of a complex combination of linear and rotational motion.

 

The battery gives the energy for this process.  The motor takes the energy from the battery and gives force to the propeller.  The propeller then gives force to the air (action), which then pushes back on the propeller (reaction) to make the fish move through the air.  Thus, the fish is pushed forward by the air coming off the propeller, just as a rocket is pushed forward by the air it is expelling backward through the rocket nozzle.

How we Built it:

Draw a fish or any other figure on the stiff paper. Cut it out.  

 

Draw lines on a two-liter bottle at a slight incline.  Cut out one for the propeller.  

  

Fold two pieces of aluminum foil and tape them tightly to the ends of the battery with black tape.  

 

Strip both wires at both ends and attach them to the motor.  Attach paperclips to the other ends of the wires. 

  

Hot glue the motor to the end of a Popsicle stick so that the shaft sticks off the end.  

 

Cut a ½”piece of hot glue stick. Drill a hole in the piece with the nail bit.  Press this on the shaft of the motor. 

  

Glue the propeller onto the bit of glue stick. Make sure it is exactly in the center, and don’t let it get deformed by the hot glue.  Sometimes you should wait a few seconds for the glue to cool down a bit before pressing the propeller on.  

 

Glue the battery onto the Popsicle stick then glue the Popsicle stick onto the fish.  

 

Punch a hole near the top of the fish so that the fish will hang level, that is, without pointing its head too far up or down. Tie a length of string to the fish.  

 

Decorate the fish.  You can tie a length of ribbon onto the tail.  Hang the fish from something, or the stick taped to a chair if there is nothing else, and try to get it to fly around.  Launch it straight down the circular path it will follow.

Concepts:

  1. Propellers throw air (or any fluid) backward or forward.  (Impellers, like in the Tornado project, throw fluid out.)

  2. To make something move forward from rest requires a force forward.  But a force forward always comes together with a force backward.  This is Newton’s third law: for every action there is an equal and opposite reaction. 

  3. The energy for making the fish fly comes from the battery.  The force comes from the motor and propeller.

 

Questions:

  1. What pushes or pulls the fish through the air?

  2. What happens if you change the direction of the motor? 

  3. Can you make the fish go in both directions?

  4. What would happen if you put another battery on the fish?