A good general way to show "helicopter" is to flutter a "5 hand" on top of an index finger:
Here is a variation that uses a "classifier three handshape." (CL:3)
Stick the palm of your right "five hand" on top of the tip of
the thumb of your left CL:3 hand.
Flutter the right hand from the wrist, (the fingers do not individually move
up and down but rather the whole hand flutters) representing the whirling
blades of the helicopter.
HELICOPTER: