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.
American Sign Language University ™ ASL resources by Lifeprint.com © Dr. William Vicars