TRIJET

A 'trijet' is an aircraft powered by three jet engines. An aircraft with three piston engines is a trimotor.
Some trijets include:

★ Boeing 727 (1963)

★ Dassault Aviation Falcon 50, Falcon 900

★ Hawker Siddeley Trident (1962)

★ Lockheed L-1011 ''Tristar'' (1970)

★ McDonnell Douglas DC-10 (1970), MD-11 (1990)

★ Tupolev Tu-154 (1968)

★ Yakovlev Yak-40 (1966)

★ Yakovlev Yak-42
A planned trijet version of the Boeing 747 was designated the 747-300, but never produced as the 747's double-decker hump would have interfered with airflow to the central engine.
Today, trijet production has all but ceased, being replaced by twinjets which are quieter and more efficient. It can be argued that, with modern engines having extremely low failure rates and increased power output, more than two engines are no longer necessary except for very large aircraft, such as the Airbus A380 or Boeing 747. That being said, the ETOPS certification of recent twinjets has required notably large engines so that the remaining engine can provide sufficient thrust to keep the plane in flight.
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. A "straight" layout such as the DC-10 and MD-11 leaves the engine high above the ground, making access difficult. Another option is an S-shaped duct like that found on the Boeing 727, Tupolev 154 and Lockheed Tristar, which is a complicated and costly design.
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 airplanes 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.^[1]

Contents

References

References

★ ''Modern Commercial Aircraft'' Willian Green, Gordon Swanborough and John Mowinski, 1987
1. Table 1-13: Active U.S. Air Carrier and General Aviation Fleet by Type of Aircraft Bureau of Transportation Statistics


★ ''Engine Placement'' Stanford University Aircraft Aerodynamics and Design Group.[1]Accessed 2007-03-13