Tail unit

Empennage (pronounced /ˌɑːmpɨˈnɑːʒ/ or /ˈɛmpɨnɪdʒ/) is an aviation term used to describe the tail section of an aircraft. The empennage is also known as the tail or tail assembly; all three terms may be used interchangeably. The empennage gives stability to the aircraft and controls the flight dynamics of pitch and yaw.

Structurally, the empennage consists of the entire tail assembly, including the fin, 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 stabilizer and is used to balance and share lifting loads of the mainplane dependent on centre of gravity considerations by limiting oscillations in pitch. The rear section is called the elevator and is usually hinged to the horizontal stabilizer. The elevator is a movable airfoil that controls changes in pitch, the up-and-down motion of the aircraft's nose. Some aircraft employ an all-moving stabilizer and elevators in one unit, known as a stabilator.

The vertical tail structure (or fin) has a fixed front section called the vertical stabilizer, used to restrict side-to-side motion of the aircraft (yawing). The rear section of the vertical fin is the rudder, a movable airfoil that is used to turn the aircraft in combination with the ailerons.

Some aircraft are fitted with a tail assembly that is hinged to pivot in two axes forward of the fin and stabilizer, in an arrangement referred to as a movable tail. The entire empennage is rotated vertically to actuate the horizontal stabiliser, and sideways to actuate the fin.^[3]

The aircraft's cockpit voice recorder and flight data recorder are often located in the empennage, because the aft of the aircraft provides better protection for these in most aircraft crashes.

In some aircraft trim devices are provided to eliminate the need for the pilot to maintain constant pressure on the elevator or rudder controls. The trim device may be:

• a trim tab on the rear of the elevators or rudder which act to change the aerodynamic load on the surface. Usually controlled by a cockpit wheel or crank.

• an adjustable stabilizer into which the stabilizer may be hinged at its spar and adjustably jacked a few degrees in incidence either up or down. Usually controlled by a cockpit crank.

• a bungee trim system which uses a spring to provide an adjustable preload in the controls. Usually controlled by a cockpit lever.

• an anti-servo tab used to trim some elevators and stabilators as well as increased control force feel. Usually controlled by a cockpit wheel or crank.

• a servo tab used to move the main control surface, as well as act as a trim tab. Usually controlled by a cockpit wheel or crank.^[

Multi-engined aircraft often have trim tabs on the rudder to reduce the pilot effort required to keep the aircraft straight in situations of asymmetrical thrust, such as single engine operations.

Tail assembly parts (normal configuration).

The horizontal tail, similar to the vertical tail, is composed of the horizontal stabilizer and the elevator. The horizontal stabilizer is fixed rigidly to the fuselage and provides stability about a horizontal axis directed along the wing and through the center of gravity, and known as the pitch axis. The elevator is hinged to the rear of the horizontal stabilizer and rotates up and down as the pilot moves the control column fore and aft. The elevator also contributes to stability about the pitch axis, but its main purpose is to provide a pitching moment about the pitch axis, which causes the airplane to nose up or down.

Airplanes that operate at supersonic speeds usually have the horizontal tail swept back and in one piece that is movable and is controlled by the motion of the pilot's control stick. Such a surface is frequently called a stabilator. Many airplanes employ empennages that depart from the normal configuration.

The rear portion, or complete tail unit, of an airplane. The empennage stabilizes the airplane in flight and causes it to rotate aboutіts vertical and lateral axes.

The hinged rear portion of an airplane's vertical tail. The vertical tail is composed of the vertical stabilizer and the rudder. The vertical stabilizer is mounted to thefuselage and is fixed relative to it. The rudder is hinged to the rear of the vertical stabilizer (see illustration) and moves to the left or right in response to control inputs from the rudder pedals or from an automatic stability and control system.

The empennage consists of a) vertical tail; b) horizontal tail; c) dorsal fin; d) elevators; e) rudder; f) vertical stabilizer; g) horizontal stabilizer; h) side engine nacelle; i) tail cone; j) ventral fin; k) APU air intake; l) bullet (stabilizer fairing)

The rudder provides an aerodynamic moment about the aircraft's center of gravity for the purpose of yaw control. When the rudder turns clockwise, for example, as viewed from above, its trailing edge moves to the left, effectively adding camber to the vertical tail. The result is that an aerodynamic side force is produced on the vertical tail to the right. This force, in turn, produces a counterclockwise yawing moment about the airplane's center of gravity, resulting in a turn to the left.

An additional, small,movable surface, known as a trim tab, may be hinged to the rudder. When deflected to a fixed position, the tab causes the rudder to deflect to, and hold, a desired angle.

The hinged rear portion of the longitudinal stabilizing surface or tail plane of an aircraft used to obtain longitudinal- or pitch-control moments. The angular setting of the elevator is controlled by the human or automatic pilot through the flight-control system. A typical elevator control surface is shown in the illustration.

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Elevator control surface (left-hand side).

The elevator is used to perform pitching maneuvers, or maneuvers in which the aircraft's plane of symmetry is not disturbed. These maneuvers include airspeed adjustments and acceleration normal to the flight path (pull-ups or push-downs). The elevator also serves to adjust the aircraft's attitude with respect to the ground for takeoff and landing.

In aviation, the stabilizer (empennage or tail) provides stability when the aircraft is flying straight, and the airfoil of the horizontal stabilizer balances the forces acting on the aircraft.

While the vertical stabilizer and rudder are always placed on the rear of the aircraft (either on the aft fuselage, or at the ends of aft-swept wings), the horizontal surfaces can be placed on the front or the rear. When placed at the rear, the horizontal stabilizer is called a tailplane. When placed at the front, it is called a canard. horizontal stabilizer is used in the V-tail configuration.

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