To build a homemade helicopter, carve or file a strip of soft wood into propeller blades, shape the blades into airfoils, and glue a small dowel rod in a hole in the middle of the strip. To fly the helicopter, stick the dowel rod between your palms and rapidly move them in the opposite direction.
On a piece of pine about 8 inches long and 1/4 inch thick, use an electric drill to make a hole in the center to accommodate a dowel rod that is 1/4 inch thick and 7 1/2 inches long. Use a knife or wood rasp to carve the pine into a propeller, slanting the blades into airfoils that face the opposite direction. Use fine sandpaper to sand the blades smooth, and then glue the dowel rod into the hole.
When the glue dries, spin the stick between your palms, and let go to make it fly. If the stick strikes your hand, reverse the direction of the spin. If the helicopter flies poorly, reshape the blades, or shorten one of them until the flight is steady. To improve lift, try shortening the dowel rod.
On a proper flight, the air pressure below the blades lowers, lowering the air pressure above the blades even more. The two pressures combine to lift the helicopter straight up for a short flight, before eventually settling it gently, stick-end down, to the ground.