rotated vertically to actuate the horizontal stabiliser, and sideways to actuate the fin. The aircraft's cockpit voice recorder, flight data recorder and emergency locator transmitter (ELT) are often located in the empennage, because the aft of the aircraft provides better protection for these in most aircraft crashes. Trim 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 stabiliser into which the stabiliser 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 configurations Aircraft empennage designs may be classified broadly according to the fin and tailplane configurations. The overall shapes of individual tail surfaces (tailplane planforms, fin profiles) are similar to wing planforms. Tailplanes The tailplane comprises the tail-mounted fixed horizontal stabiliser and movable elevator. Besides its planform, it is characterised by: Number of tailplanes - from none (tailless or canard) to three (Lockheed Constellation) Location of tailplane - mounted high, mid or low on the fuselage, fin or tail booms. Fixed stabiliser and movable elevator surfaces, or a single combined stabilator or "[all]-flying tail". (General Dynamics F-111 Aardvark) Some locations have been given special names: Cruciform tail - The horizontal stabilisers are placed midway up the vertical stabiliser, giving the appearance of a cross when viewed from the front. Cruciform tails are often used to keep the horizontal stabilisers out of the engine wake, while avoiding many of the disadvantages of a T-tail. Examples include the Hawker Sea Hawk and