Trijet
The most common configuration is having the central engine located in the rear fuselage and supplied with air by an S-shaped duct; this is used on the Hawker Siddeley Trident, Boeing 727, Tupolev Tu-154, Lockheed L-1011 TriStar, and, more recently, the Dassault Falcon 7X.
Because takeoff performance for aircraft is usually calculated to include an extra margin to account for a possible engine failure, trijets are better able to take off from hot and high airports or those where terrain clearance near the runway is an issue.
)[2] This is advantageous if the aircraft is not near one of the operator's maintenance bases, as the pilots may then continue the flight and land at an airport where it is more suitable to perform repairs.
The rear-mounted engine and wings shift the aircraft's center of gravity rearwards, improving fuel efficiency, although this will also make the plane slightly less stable and more complex to handle during takeoff and landing.
(The McDonnell Douglas DC-9 twinjet and its derivatives, whose engines are mounted on pylons near the rear empennage, have similar advantages/disadvantages of the trijet design, such as the wings located further aft and a more rearward center of gravity.
[4] Early American twinjet designs were limited by the FAA's 60-minute rule, whereby the flight path of twin-engine jetliners was restricted to within 60 minutes' flying time from a suitable airport, in case of engine failure.
For second-generation jet airliners, with the innovations of the high-bypass turbofan for greater efficiency and reduced noise, and the wide-body (twin-aisle) for greater passenger/cargo capacity, the trijet design was seen as the optimal configuration for the medium wide-body jet airliner, sitting in terms of size, range, and cost between quadjets (four-engine aircraft) and twinjets, and this led to a flurry of trijet designs.
The four-engine Boeing 747 was popular for transoceanic flights due to its long-range and large size, but it was expensive and not all routes were able to fill its seating capacity, while the original models of the Airbus A300 twinjet were limited to short- to medium-range distances.
Thus trijet designs such as the DC-10 and L-1011 TriStar represented the best compromise with medium- to long-range and medium size that US airlines sought for their domestic and transatlantic routes.
Further advancements in high-bypass turbofan technology and subsequent relaxation in airline safety rules made the trijet and even the quadjet nearly obsolete for passenger services, as their range and payload could be covered more efficiently with large twinjets powered with purpose-designed engines such as the 777's General Electric GE90.
During the 1980s, McDonnell Douglas was the only Western manufacturer to continue development of the trijet design with an update to the DC-10, the MD-11, which initially held a range and payload advantage over its closest medium wide-body competitors which were twinjets, the in-production Boeing 767 and upcoming Airbus A330.
The MD-XX Long Range aircraft would have been capable of traveling distances up to 8,320 nautical miles (15,410 km) and had a wingspan of 65 metres (213 ft).
A study to remove the MD-11's tail-mounted engine (which would have made it a twinjet) never came to fruition as it would have been very expensive, and the MD-11 had very little in common in terms of design or type rating with other Boeing airliners.
The only other notable trijet development during the 1980s was in the Soviet Union, where the Tupolev Tu-154 was re-engined with the Soloviev D-30 engine as well as a new wing design and entered serial production from 1984 as the Tu-154M.
Airbus filed a patent in 2008 for a new, twin-tail trijet design, whose tail engine appears to use a "straight" layout similar to the MD-11, but it is unknown if and when this will be developed or produced.
Since the aircraft's serial number (36011) begins with '36,' following the People's Liberation Army Air Force convention, this model was presumably designated as J-36, but further information is limited.
