The empennage ( or ), also known as the tail or tail assembly, is a structure at the rear of an aircraft that provides stability during flight, in a way similar to the feathers on an arrow. The term derives from the French language verb empenner which means "to feather an arrow". Most aircraft feature an empennage incorporating vertical and horizontal stabilising surfaces which stabilise the flight dynamics of yaw and pitch, as well as housing control surfaces. In spite of effective control surfaces, many early aircraft that lacked a stabilising empennage were virtually unflyable. Even so-called "tailless aircraft" usually have a tail fin (usually a vertical stabiliser). Heavier-than-air aircraft without any kind of empennage (such as the Northrop B-2) are rare, and generally use specially shaped airfoils whose trailing edge provide pitch stability, and rearwards swept wings, often with dihedral to provide the necessary yaw stability. In some aircraft with swept wings, the airfoil section or angle of incidence may change radically towards the tip. Structure Structurally, the empennage consists of the entire tail assembly, including the tailfin, the tailplane and the part of the fuselage to which these are attached. On an airliner this would be all the flying and control surfaces behind the rear pressure bulkhead. The front (usually fixed) section of the tailplane is called the horizontal stabiliser and is used to provide pitch stability. The rear section of the tailplane is called the elevator, and is a movable aerofoil that controls changes in pitch, the up-and-down motion of the aircraft's nose. In some aircraft the horizontal stabilizer and elevator are one unit, and to control pitch the entire unit moves as one. This is known as a stabilator or full-flying stabiliser. The vertical tail structure has a fixed front section called the vertical stabiliser, used to control yaw, which is movement of the fuselage right to left motion of the nose of the aircraft. The rear section of the vertical fin is the rudder, a movable aerofoil that is used to turn the aircraft's nose right or left. When used in combination with the ailerons, the result is a banking turn, a coordinated turn, the essential feature of aircraft movement. Some aircraft are fitted with a tail assembly that is hinged to pivot in two axes forward of the fin and stabiliser, in an arrangement referred to as a movable tail. The entire empennage is