Helicopters are complicated machines, but pull-string toy helicopters are simple. These devices have a propeller on the top, but the base is a simple stick. When you pull the string on the stick or spin it by hand, you can launch it high into the air. It's possible to purchase one of these toys or you can make your own.
Measure and mark 2 inches from either end of your tongue depressor. Mark also the exact centre of the depressor. Flip over and repeat the markings on the other side.
Drill a hole into the exact centre of the depressor.
Print out the bending jig pattern (see the Resources section) and place it over the block of wood. Drive nails into the wood on the dots of the pattern, which is in two rows of three, lining up with each other.
Bend the nails with the wire to a 30-degree angle (or 60-degrees horizontal to the block). Bend the nails on the left toward you (forward), and bend the nails on the right away from you (back).
Boil some water and place your tongue depressor inside to soak. Make sure that you soak it for at least 15 minutes.
Place the tongue depressor in the bending jig, making sure that they curve smoothly. Leave the sticks to dry overnight, so that they'll retain this shape when they're dry.
Remove the dry tongue depressors from the jig.
Print out the airfoil pattern (see the Resources section). Cut out two pieces of cardboard or construction paper to the specifications of the airfoil. The strips should be about 3-inches square before being folded into shape.
Fold and tape the airfoil pieces so they are open at each short side.
Cover the ends of the tongue depressors in glue up to the marks that you made in Section 1, Step 1. Slide the airfoils onto the glue, so that the taped edges of the airfoils face down.
Put a wire paper clip through the hole in the propeller to test that it's balanced. If either end dips, it's not balanced. Place small balls of modelling clay at the tip, inside the airfoil, to balance the propeller. When you've achieved balance, tape over the open ends of the airfoil.
Glue the propeller to a 6-inch length of dowel. Press the piece down, so the glue pushes into the hole. Leave the glue to dry overnight.
Hold the shaft of the dowel steadily and mark a point about two inches from the bottom. Drill a small hole, about one-sixteenth-inch or less, through the shaft at this point so that you can insert the pull-string through it.
Drill a hole at least one-quarter-inch wider than the dowel straight down into another block of wood, which will be used as a launcher. Use the largest bit that you have to drill another hole through the wood, so it meets up with the first hole.
Insert the shaft of the helicopter through the hole of the launcher.
Stick a string through the shaft-hole and wind the string around the shaft. Wind the string around itself to hold it in place, but do not tie or glue it on.
Pull the string fast to launch the helicopter.