1. Look at the provided pictures to familiarize yourself with the helicopter. It was designed to fly best with the tapered side of the blades down and also the tapered portion of the spool centers the propeller when launching in this orientation.
2. Print all parts and the propeller with the number of desired blades (at this time I have only tried the 5 blade). I printed in ABS using 3 perimeters, 0.2 mm layer height, 25% fill and a 1 cm brim to help hold the tall parts on the print bed. The narrow part of the spool was printed solid. No support was needed if printed in the given orientation. You know your setup best so adjust accordingly.
3. Cut 3.5 ft of string and tie a 2 in loop on each end. A thin strong material is ideal, I used 150 lb test spectra fishing line.
4. Find a rubber band in the 3 in x 0.25 in range, loop it through the bottom of the spool, back through the rubber band and pull snug.
5. Slide the rubber band and spool into the handle and attach one end of the string to the hole in the center of the spool using the same looping procedure. Attach the other end of the string to the pull.
6. Slide the propeller onto the spool, tapered side toward the spool, and wind the string onto the spool. Pull the rubber band through the end of the handle and loop it around the center of the plate. Twist the plate and rubber band a few times so the string retracts and then slide the plate into the handle. At this point the rubber band should not pull too heavily on the spool.
7. Oil the spool so it spins easily in the handle. If not oiled the plastic can friction weld together.
8. Give the helicopter a pull and try not to break too many things.