Summary

This a flying helicopter toy which has adjustable pitch of the blades. It is rather heavy when printed and is difficult to get to fly by hand (can't get it to spin fast enough by hand). The best method to get it to fly is to wrap a string around the stem, place in a PVC pipe and pull the cord gently to get the needed rotational speed.

Instructions

For the best results, I used Cura as a slicer and printed the rotors with the teardrop shape on the bed. I used a bottom/top layer thickness of 6mm so that the tear drop and stem would be solid plastic. 20% infill is plenty to get lots of strength, I've bashed the toy into several things when its flying and it still survived. Everything else should be printed 100% infill, especially the stem, for the needed strength (and weight at the bottom for stability). I had to do some filing on the rotor shafts to get them to fit into the slot gears, but not very much.
Assembly is a bit tricky. One has to place the small gear in between the two slot gears with the key-ways at the bottom (key-ways of the slot gears) and then insert the entire assembly into the gearbox. Once in, the rotors can be slid into place (point part of the teardrop is pointing up). Once the rotors are in, they can be rotated and the cotter pins put into the slots. These cotter pins are important, they prevent the rotors from popping out and hitting you in the face!! (A feature I had to add after getting hit a few times). One also needs to glue the stem into the gearbox (I used Elmer's white glue so I could remove it with hot water if I needed to disassemble the toy).
I will be adding a launching tube soon (to hold the Twirlybird when using a ripcord) to the list of parts.

TwirlyBird - Adjustable blade pitch hand helicopter