Abstract: A thruster for a helicopter is mounted in a rear portion of a tail boom. Two sets of vanes deflect an airflow stream flowing along the tail boom respectively to opposed sides of the tail boom. Two shutters are pivotally arranged partly around the sets of vanes to leave two openings in respective sides of the tailboom. The shutters are pivoted in sympathy toward each other or away from each other to open/close the respective openings symmetrically and simultaneously such that a geometrical center line of each opening remains static irrespective of the status of the opening.