Summary

A whirly-bird like thing with a pull string that sends the rotor flying into the air.

Also includes a handled version.

Instructions

Print the build plate (with tear-away support) and any additional rotors you want. (2 shells w/ 10% infill works OK, not perfectly)
Clean out any strings inside the hand block... this is the winding area for the string and should be reasonably clear.
Thread a 1 ft. long piece of (strong) string or twine through the "bolt" thingy, tie a large, strong knot at one end... then, thread both ends through the hole and then the rectangular opening of the hand block. (see image whirly_one_string.jpg) The point of this step is to avoid the need to pull a large knot through the sliver of an opening between the "bolt" and hand block.
Tug both ends to force the "bolt" into the block.
Place a rotor on the bolt (by the square peg) and wind counter clockwise 4 or 5 turns. Avoid over winding the string since it will bind up the "bolt" (you'll notice it rise out of the handblock) and prevent a clean spin when you're ready to pull.
After winding counter clockwise, hold the block firmly and give a strong, fast pull on the cord. Viola, it soars into your ceiling (and sometimes scoots around up there)

N.B. the peg is somewhat fragile (using the slicing params cited above) and if you wind clockwise and launch over a hard floor the rotor will very effectively smash itself into the floor and crack the peg off. doh.

Notes for the OpenSCAD model: The rotor wing pitch is parametric and the default is 30deg... 45deg works, but poorly, and I'll bet an aerospace engineer or hobbist can instruct as to the optimal angle.

The outer rotor ring is also optional with a flag "outer_ring = 1;"

There's also support for a "handle" which will work without the hand block.

The hand block is only slightly parametric, with way too many constants, and other ad hoc stuff... but it's in there. It might be an interesting example to you if you've ever wondered about the minkowski and hull operators!

Whirly One (OpenSCAD)