A door opener for opening a door having an external surface comprises a screw mounted for rotary motion and a carriage mounted on the screw such that rotation of the screw causes motion of the carriage along the screw. A motor rotates the screw. An actuator arm has a first end and a second end, where the actuator arm is operatively connected to the carriage such that movement of the carriage causes the actuator arm to move between a retracted position where the door is closed and an extended position where the door is open. The first end of the actuator arm is in contact with but not connected to the external surface of the door such that the first end of the actuator arm rides over the external surface of the door.