Empennage

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Empennage [ émpənij ] is an aviation term used to describe the tail portion of an aircraft. ("Empennage", "tail", and "tail assembly" may be interchangeably used.) The empennage gives stability to the aircraft and controls the flight dynamics: pitch and yaw. In simple terms the empennage may be compared to the feathers of an arrow, colloquially; "Tail Feathers"

Structurally, the empennage consists of the entire tail assembly, including the fin, tailplane and the part of the fuselage to which these are attached. On an airliner this would be everything 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.

On some aircraft, the horizontal stabilizer and elevator are combined into one movable unit called the stabilator or sometimes "flying tail" (see Anderson, John D., Introduction to Flight, 5th ed, p 517). In all cases some arrangement is made for the provision of trim to allow minor adjustment of airflow over the control surface and to unload the pilot from the need to maintain constant pressure on the elevator control. The trim may take the form of trim tabs on the rear of the elevators which act to force the elevator in the desired direction, or the stabilizer may be hinged at its trailing edge, forward of the elevator and adjustably jacked a few degrees in incidence either up or down. Early aircraft had a spring in the control circuit which provided an adjustable preload in the desired direction.

The vertical tail structure, or fin, also 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.

Occasionally the horizontal stabilizer may carry more than one fin and rudder (Avro Lancaster, Lockheed Constellation) or the stabilizer and fin may be combined into a "V" shaped structure (Ruddervators) with each of the angled airfoils performing both functions (Beechcraft Bonanza 35, Fouga Magister). Frequently the horizontal stabilizer is mounted atop the fin (Boeing 727, Piper Tomahawk) Additional fin area may be added to aircraft fitted with floats (seaplanes) usually beneath the horizontal stabilizer (ventral fin) and sometimes at the stabilizer extremities.

Multi-engined aircraft and some light aircraft also include trim tabs on the rudder when asymmetric forces would impose unusual loads on the pilot's rudder controls.

[edit] See also

• Fuselage
• Trijet