A twin tail is a type of vertical stabilizer arrangement found on the empennage of some aircraft. Two vertical stabilizers—often smaller on their own than a single conventional tail would be—are mounted at the outside of the aircraft's horizontal stabilizer. This arrangement is also known as an H-tail,Schiff, Barry: Flying, page 15. Golden Press, New York, 1971. Library of Congress 78-103424 as it resembles a capital "H" when viewed from the rear. The twin tail was used on a wide variety of World War II multi-engine designs that saw mass production, especially on the American B-24 Liberator and B-25 Mitchell bombers, the British Avro Lancaster and Handley Page Halifax heavy bombers, and the Soviet Union's Petlyakov Pe-2 attack bomber.
It can be easily confused for the similarly named twin-boom (or "double tail") arrangement, which has two separate tail-booms from the same fuselage rather than a single tail with twin stabilizers (a singular "twin tail" vs. two identical tails).
One variation on the twin tail is the triple tail, but the twin-boom arrangement can also be considered a variation of the twin tail .
Twin tails with canted fins lean outboard of the turbulence created by the that huge, wide fuselage, improving stability and control especially at high angles of attack.
Most often, the twin vertical surfaces are attached to the ends of the horizontal stabilizer, but a few aircraft, like the Armstrong Whitworth Whitley, Mitsubishi G3M and Dornier Do 19 bombers, had their twin vertical surfaces mounted to the upper surface of the fixed stabilizer instead, at some distance inwards from the horizontal stabilizer's tips.
A special case of twin tail is the twin-boom tail or double tail, where the aft airframe consists of two separate fuselages, "tail booms", which each have a rudder but are usually connected by a single horizontal stabilizer. Examples of this construction are the twin-engined Lockheed P-38 Lightning; Northrop P-61 Black Widow; Focke-Wulf Fw 189; the single jet-engined de Havilland Vampire; cargo-carrying Fairchild C-119 Flying Boxcar and the little known Transavia PL-12 Airtruk.
The V-22 Osprey uses a twin tail arrangement.
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