Trijet
Encyclopedia
A Trijet is an aircraft
powered by three jet engine
s. Early twin-jet designs were limited by the FAA
's "60-minute rule
", whereby the flight path of twin-engined jetliners was restricted to within 60 minutes' flying time from a suitable airport, in case of engine failure. In 1964 this rule was lifted for trijet designs, as they had a greater safety margin. This led to a flurry of trijet designs, which by 1980 had become the most popular airliner configuration.
Generally, passenger airline
trijets are considered to be second generation Jet airliner
s, due to their innovative engine locations, in addition to the advancement of turbofan technology.
Other variations of three-engined designs are trimotor
s, which are aircraft with three piston engines.
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During the late 1970s and early 1980s, three was the most common number of engines on US jet airlines, making up a majority of all such aeroplanes in 1980. From 1985 to 2003 the number of such planes in service has sunk from 1488 to 602. The number of twin-jets has more than quadrupled in the same period.
A real disadvantage with trijets is positioning the central engine. On most trijets they are placed at the tail along the middle, producing some technical difficulties. The central engine is most commonly supplied with air by an S-shaped duct
– this is used on the Boeing 727, Tupolev 154 and Lockheed Tristar, and is a complicated and costly design. The DC-10
and MD-11 use an alternative "straight" layout which is more efficient, but leaves the engine high above the ground, making access difficult. One major advantage of the trijet design is that the wings can be located further aft on the fuselage, allowing main cabin exit and entry doors to be more centrally located for quicker embarkation and disembarkation, ensuring faster turnaround times.
With ETOPS restrictions eased, twinjets became more suitable for long-haul overwater operation. With modern engines having extremely low failure rates and increased power output, more than two engines are no longer necessary except for large aircraft such as the An 225, Airbus A340-600, Airbus A380
or Boeing 747
.
McDonnell Douglas
had planned a new series of DC-10
family trijets called the MD-XX, which were lengthened versions of the MD-11
. The MD-XX Long Range would have been capable of travelling distances up to 8,320 nautical mile
s and a wing span of 213 feet. The project was cancelled in 1996, one year before McDonnell Douglas was taken over by Boeing.
and wide-body trijet production has ceased for almost all commercial aircraft, being replaced by twinjet
s. The trijet design is currently only built on a very limited production run of Tupolev Tu-154M narrowbody airliners, and the Dassault Falcon 7X
and Dassault Falcon 900 business jets, all three of which feature S-duct
s.
also said that they would make a Boeing 747 trijet. But again it is unknown if this will ever be developed or produced
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
powered by three jet engine
Jet engine
A jet engine is a reaction engine that discharges a fast moving jet to generate thrust by jet propulsion and in accordance with Newton's laws of motion. This broad definition of jet engines includes turbojets, turbofans, rockets, ramjets, pulse jets...
s. Early twin-jet designs were limited by the FAA
Federal Aviation Administration
The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...
's "60-minute rule
ETOPS/LROPS
ETOPS is an acronym for extended operations as re-defined by the US Federal Aviation Administration in 2007 . This rule allows twin-engined airliners to fly long-distance routes that were previously off-limits to twin-engined aircraft...
", whereby the flight path of twin-engined jetliners was restricted to within 60 minutes' flying time from a suitable airport, in case of engine failure. In 1964 this rule was lifted for trijet designs, as they had a greater safety margin. This led to a flurry of trijet designs, which by 1980 had become the most popular airliner configuration.
Generally, passenger airline
Passenger airline
A passenger airline is an airline dedicated to the transport of passengers. Cf. cargo airline. Passenger airlines usually operate a fleet of passenger aircraft which, rather than being owned outright, are usually leased from commercial aircraft sales and leasing companies such as GECAS and...
trijets are considered to be second generation Jet airliner
Jet airliner
A jet airliner is an airliner that is powered by jet engines. This term is sometimes contracted to jetliner or jet.In contrast to today's relatively fuel-efficient, turbofan-powered air travel, first generation jet airliner travel was noisy and fuel inefficient...
s, due to their innovative engine locations, in addition to the advancement of turbofan technology.
Other variations of three-engined designs are trimotor
Trimotor
A trimotor is an aircraft powered by three piston engines.Trimotor designs were relatively common in the early days of aviation, as engines were less powerful and less reliable.-Notable types:* Armstrong Whitworth Argosy...
s, which are aircraft with three piston engines.
History
A real disadvantage with trijets is positioning the central engine. On most trijets they are placed at the tail along the middle, producing some technical difficulties. The central engine is most commonly supplied with air by an S-shaped duct
S-duct
An S-duct is a unique type of jet engine intake duct, used in several types of trijet aircraft. In this configuration, the intake is in the upper rear center of the aircraft, just below the stabilizer, while the exhaust is at the rear of the aircraft. The S-duct is located in the tail, or...
– this is used on the Boeing 727, Tupolev 154 and Lockheed Tristar, and is a complicated and costly design. The DC-10
McDonnell Douglas DC-10
The McDonnell Douglas DC-10 is a three-engine widebody jet airliner manufactured by McDonnell Douglas. The DC-10 has range for medium- to long-haul flights, capable of carrying a maximum 380 passengers. Its most distinguishing feature is the two turbofan engines mounted on underwing pylons and a...
and MD-11 use an alternative "straight" layout which is more efficient, but leaves the engine high above the ground, making access difficult. One major advantage of the trijet design is that the wings can be located further aft on the fuselage, allowing main cabin exit and entry doors to be more centrally located for quicker embarkation and disembarkation, ensuring faster turnaround times.
With ETOPS restrictions eased, twinjets became more suitable for long-haul overwater operation. With modern engines having extremely low failure rates and increased power output, more than two engines are no longer necessary except for large aircraft such as the An 225, Airbus A340-600, Airbus A380
Airbus A380
The Airbus A380 is a double-deck, wide-body, four-engine jet airliner manufactured by the European corporation Airbus, a subsidiary of EADS. It is the largest passenger airliner in the world. Due to its size, many airports had to modify and improve facilities to accommodate it...
or Boeing 747
Boeing 747
The Boeing 747 is a wide-body commercial airliner and cargo transport, often referred to by its original nickname, Jumbo Jet, or Queen of the Skies. It is among the world's most recognizable aircraft, and was the first wide-body ever produced...
.
McDonnell Douglas
McDonnell Douglas
McDonnell Douglas was a major American aerospace manufacturer and defense contractor, producing a number of famous commercial and military aircraft. It formed from a merger of McDonnell Aircraft and Douglas Aircraft in 1967. McDonnell Douglas was based at Lambert-St. Louis International Airport...
had planned a new series of DC-10
McDonnell Douglas DC-10
The McDonnell Douglas DC-10 is a three-engine widebody jet airliner manufactured by McDonnell Douglas. The DC-10 has range for medium- to long-haul flights, capable of carrying a maximum 380 passengers. Its most distinguishing feature is the two turbofan engines mounted on underwing pylons and a...
family trijets called the MD-XX, which were lengthened versions of the MD-11
McDonnell Douglas MD-11
The McDonnell Douglas MD-11 is a three-engine medium- to long-range widebody jet airliner, manufactured by McDonnell Douglas and, later, by Boeing Commercial Airplanes. Based on the DC-10, it features a stretched fuselage, increased wingspan with winglets, refined airfoils on the wing and smaller...
. The MD-XX Long Range would have been capable of travelling distances up to 8,320 nautical mile
Nautical mile
The nautical mile is a unit of length that is about one minute of arc of latitude along any meridian, but is approximately one minute of arc of longitude only at the equator...
s and a wing span of 213 feet. The project was cancelled in 1996, one year before McDonnell Douglas was taken over by Boeing.
Current status
Today, both narrow-bodyNarrow-body aircraft
A narrow-body aircraft is an airliner with a fuselage aircraft cabin width typically of 3 to 4 metres , and airline seat arranged 2 to 6 abreast along a single aisle...
and wide-body trijet production has ceased for almost all commercial aircraft, being replaced by twinjet
Twinjet
A twinjet or twin jet is a jet aircraft powered by two engines. Such configuration of an aircraft is the most popular today for commercial airliners, for fighters, and many other kinds, because while offering safety from a single engine failure, it is also acceptably fuel-efficient.-Aircraft...
s. The trijet design is currently only built on a very limited production run of Tupolev Tu-154M narrowbody airliners, and the Dassault Falcon 7X
Dassault Falcon 7X
|-See also:-External links:****...
and Dassault Falcon 900 business jets, all three of which feature S-duct
S-duct
An S-duct is a unique type of jet engine intake duct, used in several types of trijet aircraft. In this configuration, the intake is in the upper rear center of the aircraft, just below the stabilizer, while the exhaust is at the rear of the aircraft. The S-duct is located in the tail, or...
s.
Future of trijets
Airbus filed a patent in 2009 for a new, twin-tail trijet design, but it is unknown if this will ever be developed or produced. BoeingBoeing
The Boeing Company is an American multinational aerospace and defense corporation, founded in 1916 by William E. Boeing in Seattle, Washington. Boeing has expanded over the years, merging with McDonnell Douglas in 1997. Boeing Corporate headquarters has been in Chicago, Illinois since 2001...
also said that they would make a Boeing 747 trijet. But again it is unknown if this will ever be developed or produced
Notable examples
- Boeing 727Boeing 727The Boeing 727 is a mid-size, narrow-body, three-engine, T-tailed commercial jet airliner, manufactured by Boeing. The Boeing 727 first flew in 1963, and for over a decade more were built per year than any other jet airliner. When production ended in 1984 a total of 1,832 aircraft had been produced...
- Dassault Falcon 50Dassault Falcon 50|-See also:-References:* Taylor, John W R. . Jane's All The World's Aircraft 1988-89. Coulsdon, Surrey, UK:Jane's Information Group. ISBN 0-7106-0867-5.-External links:* *...
- Dassault Falcon 900
- Dassault Falcon 7X
- Hawker Siddeley TridentHawker Siddeley TridentThe Hawker Siddeley HS 121 Trident was a British short/medium-range three-engined jet airliner designed by de Havilland and built by Hawker Siddeley in the 1960s and 1970s...
- Lockheed L-1011 TristarLockheed L-1011The Lockheed L-1011 TriStar, commonly referred to as the L-1011 or TriStar, is a medium-to-long range, widebody passenger trijet airliner. It was the third widebody airliner to enter commercial operations, following the Boeing 747 and the McDonnell Douglas DC-10. Between 1968 and 1984, Lockheed...
- McDonnell Douglas DC-10McDonnell Douglas DC-10The McDonnell Douglas DC-10 is a three-engine widebody jet airliner manufactured by McDonnell Douglas. The DC-10 has range for medium- to long-haul flights, capable of carrying a maximum 380 passengers. Its most distinguishing feature is the two turbofan engines mounted on underwing pylons and a...
- McDonnell Douglas MD-11McDonnell Douglas MD-11The McDonnell Douglas MD-11 is a three-engine medium- to long-range widebody jet airliner, manufactured by McDonnell Douglas and, later, by Boeing Commercial Airplanes. Based on the DC-10, it features a stretched fuselage, increased wingspan with winglets, refined airfoils on the wing and smaller...
- Tupolev Tu-154Tupolev Tu-154The Tupolev Tu-154 is a three-engine medium-range narrow-body airliner designed in the mid 1960s and manufactured by Tupolev. As the mainstay 'workhorse' of Soviet and Russian airlines for several decades, it serviced over a sixth of the world's landmass and carried half of all passengers flown...
- Yakovlev Yak-40Yakovlev Yak-40The Yakovlev Yak-40 is a small, three-engined airliner that is often called the first regional jet transport aircraft...
- Yakovlev Yak-42Yakovlev Yak-42The Yakovlev Yak-42 is a 100/120-seat three-engined mid-range passenger jet. It was designed as a replacement for several obsolete Aeroflot jets as a mid-range passenger jet...
Proposed or suspended trijet developments
- Boeing 747-300 Trijet: never produced.
- Blended Wing Body Trijet
- McDonnell Douglas MD-XX: never produced.
- Airbus twin-tail trijet, status unknown.
- Dassault Supersonic Business Jet (suspended)