Ever since TC15, and @Lipko who (I think) came up with and @Rudivdk who used a great little variable pitch propellor system using the three-pin technic hub, I knew I had to use it for a little helicopter. I used it in a failed design, and a little executive helicopter that was not great. I wanted to try it again.
After playing with some panels, I decided to try my hand at one of my favorite little sets, 8640 from 1986. It is mostly the same size, but seats two technic figs and their skis and poles.
Both main and tail rotors spin, and the collective for the main rotor is controlled by the pilot.
Ski and pole storage
I hope you enjoy. I'll take it apart soon, and I'll make some photo instructions then.