I just opened up the .pdf, looks good and strong. If someone put some wire inside those rotors, you could almost make it kid proof. What child wouldn't want this to play with!
Could I recommend the Sikorsky X-2 next?
or it's propgenitor the Sikorsky ABC:
or even, the rarely spoken of Sikorsky X-Wing, where the rotor actually did stop rotating!:
This last picture is the X-Wing mounted on the Sikorsky" RSRA" (RotorSystemsResearchAircraft), which has never been modeled. I did a lot of work on these. Very Hush hush at the time. It was designed so that it could blow off the rotor system if there was a problem and the craft could fl back down safely.
There there is the Sikorsky Black Hawk, (not the Blackhawk). You don't hear of this one much: