This is how I build my helicopter rotary system:

INSTRUCTIONS:
1) Put 1 Spinning Block on where you want to put the helicopter rotor.
2) Put Steering Blocks on all sides except on top (Not Steering Hinges).
3) Change the controls of the Steering Blocks, LEFT = Any DESCEND button you desire, RIGHT = Any ASCEND button you desire.
4) Put a pole or a two block high wood block on top of the Spinning Block.
5) Put 2 Spinning Blocks on top of the pole or 2 block high wood block and flip them.
6) Put Steering Blocks on all sides of the top most Spinning Block except on top of it.
7) Change the controls of the top Steering Blocks, LEFT = ASCEND, RIGHT = DESCEND (Opposite controls of #3).
8) Put Wing Panels on the Steering Blocks.
9) Fly.

It might not be as clear as it sounds but I have an example available for download.
Just put the files inside the ZIP file in your SavedMachines Folder inside your Besiege Data Directory.

A PICTURE:


DOWNLOADABLE FILE CONTROLS:
ASCEND - 8
DESCEND - 5
FORWARD - UP
BACKWARD - DOWN
LEFT - LEFT
RIGHT - RIGHT
(Note: Forward and Backward Keys don't always work. The Heli might tilt and go backwards or forwards (Vice Versa).