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.

Дата добавления: 2015-07-11