Aircraft With Tail-mounted Engines - This article is about jet aircraft. For an aircraft with three propellers (powered by piston or turboprop engines), see Trimotor.
A trijet is a jet aircraft powered by three jet engines. The airline's trijets are generally considered second-generation jets, due to their innovative engine placements, as well as advances in turbofan technology. Trijets are more efficient than quadjets, but not as efficient as twinjets, which replaced trijets as larger and more reliable turbofan engines became available.
Aircraft With Tail-mounted Engines
Dassault Falcon 900EX. The 900 and its derivatives, the Falcon 7x and 8x are the only trijets in the world currently in production.
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One consideration with trijets is the location of the central engine. This is usually achieved by placing the motor along the cter line, but it still presents difficulties. The most common configuration is to have the central engine located in the rear fuselage and supplied with air through an S-shaped duct; this is used on the Hawker Siddeley Tridt, Boeing 727, Tupolev Tu-154, Lockheed L-1011 TriStar and, more precisely, the Dassault Falcon 7X. The S channel has low resistance, and since the third engine is mounted closer to the cter line, the aircraft will normally be easy to handle in the event of an engine failure. However, S-channel designs are more complex and more expensive, especially for an aircraft. In addition, the central engine compartment will require structural changes in the event of a major rebuild (engine rebuild). For example, the central bay of the 727 was only wide enough to fit a low bypass turbofan and not the newer high bypass turbofans, which were quieter and more powerful. Boeing decided that a redesign was too costly and ended production rather than continue development. The rear section of the Lockheed Tristar was too short to fit an existing twin engine, as it was only designed to accommodate the new Rolls-Royce RB211 tricycle, and delays in the development of the RB211, in turn, pushed back the TriStar test. service that affected sales.
The McDonnell Douglas DC-10 and related MD-11 use an alternative "direct" central engine arrangement, which allows for easier installation, modification and access. It also has the added benefit of being much easier to redesign. However, this sacrifices aerodynamics compared to the S-channel. Also, since the engine sits much higher than wing-mounted engines, engine failure will result in a higher pitching torque, making it harder to control
The location of the remaining two genes varies. Most smaller aircraft, such as the Hawker Siddeley Tridt and Boeing 727, as well as the medium-sized Tupolev Tu-154, have two side-mounted engine pylons in a T-tail configuration. Lockheed TriStar and Larger wide-body DC-10/MD-11s mount one engine under each wing. Preliminary studies were done on the TriStar to reuse the fuselage and wing for a twin-engine design, although these were never realized due to Lockheed's lack of funds. In the late 1990s, Boeing, which had taken over McDonnell Douglas, considered removing the MD-11's tail engine to convert it to a twin jet, but instead canceled production of the MD-11.
One of the main advantages of the trijet design is that the wings can be placed further back in the fuselage, compared to twin and four engine aircraft with all engines mounted on the wings, allowing the main cabin to exit and test the doors. is more localized for faster boarding and disembarking. ensure a shorter response time. The rear-mounted engine and wings move the aircraft's gravitational character backwards, improving fuel efficiency, although this will also make the aircraft 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 tailplane, have similar advantages/disadvantages to the trijet design, such as trailing wings and a gravity further aft.)
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Trijets are more efficient and cheaper than quad jets, as the engines are the most expensive part of the aircraft and having more engines uses more fuel, especially if the quadjets and trijets share engines of similar power, making the trijet configuration more suitable for a fly. medium sized aircraft compared to the larger quad jets. However, the higher purchase prices, mainly due to the difficulty and complexity of mounting the third engine through the tail, would negate this advantage somewhat.
Because of their added thrust, threets will have somewhat improved takeoff performance compared to twinjets if an engine fails. Because the aircraft's takeoff performance is usually calculated to include extra margin to account for possible engine failure, trijets are better able to take off from high, hot airports or those where ground clearance near the runway is an issue.
Unlike twinjets, trijets are not required to land immediately at the nearest suitable airport if an engine fails (this benefit is also shared with quadjets).
This is advantageous if the aircraft is not located near one of the operator's maintenance bases, as the pilots can continue the flight and land at an airport where it is more suitable to carry out repairs. In addition, for trijets on the ground with one engine out of service, approval may be granted to conduct twin-engine ferry flights. Before the introduction of ETOPS, only trijets and quadjets could operate long international flights over areas without diversion airports. However, this advantage has largely disappeared in straight years, as ETOPS-certified twin aircraft can also do this.
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The biggest obstacle facing threes today is running costs, primarily fuel efficiency, as a three-engine design will almost certainly
This also greatly increases the difficulty of marketing a new trijet aircraft today, especially for passenger service. However, this was worth the trade-off between the 1970s and 1990s, when trijets and bijets shared engines of similar production, such as the DC-10, MD-11, Boeing's 767 and A300. Airbus A310 and A330. Geral Electric CF6, and the additional power of the third engine gave the DC-10/MD-11 longer range and/or heavier payload advantages over the twin-jet A300/A330. Since the 1990s, with further advances in high-bypass turbofan technology, large twinjets have been fitted with purpose-built engines such as the Boeing 777's General Electric GE90, which allow twinjets to perform the same tasks as most trijets and many quadjets, but more efficiently.
The first commercial trijets were the Hawker Siddeley Tridt (1962) and the Boeing 727 (1963). Both were compromises to meet airline requirements; in the case of the Tridt, it had to meet the changing needs of BEA, while the 727 had to be acceptable to three different airlines. Although cooperation between the producers was considered, it did not happen.
Early American twin-engine aircraft designs were limited by the FAA's 60-minute rule, where the flight path of twin-engine aircraft was limited to a flight time of 60 minutes from a suitable airport, in the event of engine failure. In 1964, this rule was lifted for trijet designs, as they had a greater margin of safety.
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For the second-generation jet, with the innovations of the high-bypass turbofan for increased efficiency and reduced noise, and the wide body (twice) for increased passenger/cargo capacity, the design of the trijet was considered the optimal configuration for the medium wide-body jet, considering in size, range and cost between quad-jets (four-engined aircraft) and twin-jets, and this led to a large number of tri-jet designs. The four-engine Boeing 747 was popular for transoceanic flights due to its long range and size, but it was expensive and not all routes could fill capacity, while the original Airbus A300 twinjet models were limited to shorts. - Average distances. During this period, various jet aircraft shared engines of similar output, for example when the McDonnell Douglas DC-10, Airbus A300 and Boeing 767 were powered by the General Electric CF6, the additional power of the third engine gave advantages to the DC-10. with longer range and/or heavier payloads over the A300 and 767 aircraft. Thus, trijet designs such as the DC-10 and L-1011 TriStar represented the best compromise between medium-long-haul and medium-haul aircraft American airlines were looking for for their domestic carriers and transatlantic routes. As a result of these widebody trijets, as well as the popularity of the Boeing 727, in its heyday in the 1980s, trijets made up the majority of all jets in the United States.
Between 1985 and 2003, the number of such aircraft in operation had fallen from 1,488 to 602. The number of twin aircraft, on the other hand, more than quadrupled in the same period.
Both Lockheed and McDonnell Douglas were financially weakened and competing in the wide-body market resulted in Lockheed producing the L-1011 in 1984 after producing only half the units needed to break the EV, while a number of lethal DC-10- accidents also slowed its production. sale
In 1984, Boeing stopped production of the 727, as the central engine compartment would require an extremely extensive redesign to accommodate quieter high bypass turbofans, and it was soon replaced by Airbus with the A320 and Boeing with the 737 and 757. Further advances in high -Turbofan bypass- technology and the subsequent relaxation of airline safety regulations made the trijet and possibly the quadjet almost obsolete for passenger services, as the range and payload could be covered more efficiently by large twinjets powered by a special design.
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