Toy helicopter launcher

See it in action here: 

Built with OnShape here.

In addition to the printed parts, you'll need a strong string and a rubber band.

The rubber band connects the “Rotor” and “Bottom” passing through the central hole in the “Shaft”.

The hooks in “Rotor” and “Bottom” have integral supports, you will have to cut them by hand after printing. See the attached pictures for details.

About the string you will need about half a meter of it. Do a knot on one end, and pass the string through the “Toggle” hole, then through the “Nut” hole and then wrap it around the center hole in the “Rotor”.

Screw the “Nut" into the top of the “Shaft”, taking care of not entangling the string. Do not over-tigthen the “Nut” or the “Rotor” may get stuck.

Finally you have to rotate a few dozen times the base counter-clockwise, until the string rewinds all by itself.

If the “Rotor” does not rewind by itself, try helping it a little by hand. If that doesn't work, a bit of lubricant may be welcome on the bottom and the sides of the “Rotor”. 

I've included a 3MF file will all the pieces with the suggested settings for printing: there is some support required for the blades and the rotor. And the blades are best printed hollow at the center but solid at the tips, to maximize angular momentum.

Have fun!