Why do Rockets Have Fins?

Have you ever wondered why rockets, planes, arrows and other things that fly often have fins at the end? Here is a nice NASA activity to help you understand how fins help something fly. In this activity you make a small flying rocket out of paper. You then blow through a straw to make it fly. It is a great activity for experimenting with fins. Here is what you will need to make your small paper rocket:

* Typing or construction paper
* Cellophane or scotch tape
* Scissors
* Ruler
* A sharpened fat pencil
* A milkshake or soda straw

Once you have gathered your materials, you are ready to make your paper rocket. You will probably want to work at a table or some other flat surface. Here are the steps:

1. Cut a narrow rectangular strip of paper about 5 inches long and roll it tightly around the fat pencil. Tape the cylinder and remove it from the pencil.
2. Cut crown points or “slits” into one end of the cylinder and slip it back onto the pencil.
3. Slide the crown points to the pencil tip and squeeze the points together and tape them together to seal the end to form a nose cone (the pencil point provides support for taping). An alternative to the crown points is to just fold over one end of the tube and seal it with tape.
4. Remove the cylinder from the pencil and gently blow into the open end to check for leaks. If air easily escapes, use more tape to seal the leaks.
5. Cut out four fins using a triangle design. If you fold down one side of the triangle, you can use it to attach the fin to the straw. Tape the fins near the open end of the cylinder. However, you will also want to be able to remove the fins so that you can later try flying your rocket without fins.

Now you are ready to fly your paper rocket! Slip the straw into the rocket's opening. Point the rocket towards a safe direction and sharply blow through the straw. The rocket will shoot away. Be careful not to aim the rocket towards anyone because the rocket could poke an eye. How straight does the rocket fly? How far does the rocket fly? Your rocket probably flies fairly straight and can go a considerable distance…..maybe even across the room! Now try removing the fins and fly the rocket again. Now how straight and far does the rocket fly? This time your rocket probably didn’t fly nearly as straight or far as when it had fins. Why not?

As you can see from the flight path of your rocket, a set of fins often helps a flying object have more stability in flight, or in other words, helps the flying object “wobble” less and use more of its energy to fly in a straight path. In our rocket activity, if the rocket begins to turn, the fin that is into the turn experiences a type of “lift effect”, not unlike the lift effect experienced by an airplane wing. This means that the fin will attempt to move the rocket in the direction opposite to that of the turn and thus make the rocket go straighter. Pretty neat huh?

You can also try more experiments with your flying paper rocket, like adding wings to see if it will glide. For more fun lessons involving aeronautics, you can of course see the back of poster resources on the AIA website, or go directly to a NASA Teacher Resource site referencing this flying rocket lesson at: http://www.reachoutmichigan.org/funexperiments/agesubject/lessons/other/paper_rocket.html