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AT-tail is anempennageconfiguration in which thetailplane of anaircraft is mounted to the top of thefin. The arrangement looks like the capital letter T, hence the name. The T-tail differs from the standard configuration in which the tailplane is mounted to thefuselage at the base of the fin.
T-tails were common in early jet aircraft. Designers were worried that an engine failure would otherwise damage the horizontal tail.
The T-tail is very common on aircraft with engines mounted innacelles on ahigh-winged aircraft or on aircraft with the engines mounted on the rear of the fuselage, as it keeps the tail clear of the jet exhaust.[citation needed] Rear-mounting the engines keeps the wings clean and improves short-field performance. This was necessary in early jet aircraft with less powerful engines.[1]
T-tail aircraft can have better short-field performance,[1] such as on theAvro RJ-85. The disturbed airflow over a lower stabilizer can make control more difficult at lower speeds.[citation needed]
During normal flying conditions, the tailplane of a T-tail is out of the disturbed airflow behind thewing and fuselage,[1] which provides for more consistent elevator response.[citation needed]
The design and structure of a T-tail can be simpler.[1]
For atranssonic aircraft a T-tail configuration may improve pitch control effectiveness, because the elevator is not in disturbed air behind the fuselage, particularly at moderate angles of attack.[citation needed]
Depending on wing location, the elevator may remain in undisturbed airflow during astall. (However, T-tail aircraft may be vulnerable todeep stall, seeDisadvantages below.)
An aircraft with a T-tail may be easier to recover from aspin, as the elevator is not in a position to block airflow over the rudder, which would make it ineffective, as can happen if the horizontal tail is directly below the fin and rudder.[2]
The T-tail increases the effectiveness of the vertical tail because of "end plate" effect. The horizontal stabilizer acts like a winglet, reducinginduced drag of the rudder.[3][1] Smaller and lighter T-tails are often used on modern gliders.
When the vertical tail is swept, the horizontal tail can be made smaller because it is further rearwards and therefore has a greater lever arm. Tail sweep may be necessary at high Mach numbers.
A T-tail may have less interference drag, such as on theTupolev Tu-154.
T-tails may be used to increase clearance at the rear of a cargo aircraft such as theBoeing C-17 Globemaster, to provide extra clearance when loading the aircraft.[citation needed]
The aircraft may be prone todeep stall (or super stall) at highangles of attack, when airflow over the tailplane and elevators is blanked by the wings.[4][1] The AmericanMcDonnell F-101 Voodoo jet fighter suffered from this problem,[citation needed] as did the BritishGloster Javelin,Hawker Siddeley Trident andBAC One-Eleven. A stick-pusher can be fitted to deal with this problem.[1][5]
For propeller aircraft, a T-tail configuration may reduce pitch control effectiveness if the elevators are outside the propeller slipstream.[citation needed]
The vertical stabilizer must be made stronger (and therefore heavier) to support the weight of the tailplane.[citation needed] (However other factors may make the T-tail smaller and lighter, seeAdvantages above.)
A T-tail produces a strong nose-down pitching moment in sideslip.
T-tails can causeaeroelastic flutter, as seen on theLockheed C-141 Starlifter. The fuselage must be made stiffer to counteract this.
Many large aircraft can have the fin and rudder fold to reduce height in hangars, however this generally isn't feasible or useful if there is a T-tail.[citation needed]
The T-tail configuration can also cause maintenance problems. The control runs to the elevators are more complex,[citation needed] and the surfaces are more difficult to inspect from the ground. The loss ofAlaska Airlines Flight 261 was attributed to improper maintenance of the T-tail.[citation needed] T-tails can be harder to inspect or maintain, due to their height.[citation needed]
The T-tail can often be found on military transport aircraft, such as theAirbus A400M, theBoeing C-17 Globemaster III and theEmbraer C-390 Millenium. It was used in the 1950s by combat aircraft such as theGloster Javelin,McDonnell F-101 Voodoo, andLockheed F-104 Starfighterinterceptors, and on theBlackburn Buccaneerattack aircraft.
T-tails are often used on regional airliners and business aircraft, especially when rear-fuselage-mounted turbofan engines are used.
In the 1960s, T-tails were used on theBAC One-Eleven,Vickers VC10,McDonnell Douglas DC-9,Boeing 727,Fokker F28 Fellowship,Ilyushin Il-62 andTupolev Tu-154. It has been used by theGulfstream family since theGrumman Gulfstream II. It has been used by theLearjet family since their first aircraft, theLearjet 23. It has also been used by the Embraer'sPhenom 100,Phenom 300 andLegacy/Praetor business jet families.
In the 1970s it was used on theMcDonnell Douglas MD-80 andIlyushin Il-76, as well as the twin turbopropBeechcraft Super King Air. In the 1980s it was used on theFokker 100 and theBritish Aerospace 146.
In the 1990s it was used on theBoeing 717,Bombardier CRJ-Series,Embraer ERJ family,Fokker 70 andMcDonnell Douglas MD-90, as well as the single turbopropPilatus PC-12.
T-tail is especially popular on moderngliders because of the high performance, the safety it provides from accidental spins, and the safety it provides the stabilizer and elevator from foreign object damage on take-off and landing.