Here’s a helicopter rotor I created with a variable pitch propeller.  
The trick to this is the 40 tooth gear… I drilled out the center of 
the gear so it can spin on an axle without the axle moving.  The 
axle it spins on is used to change the pitch of the rotor blades by 
raising and lowering.  Rotary input is put into the rotor by the 
small 8 tooth gear. The only issue with this setup nothing anchors 
the rotor head.  If it created enough lift it could potentially lift 
the rotor off the assembly.  

This was just a quick exercise to see if I could create a variable 
pitch propeller.