Three-engine aircraft

Boeing 727 - passenger aircraft of Iberia with three engines

In three-engine aircraft ( English trijet ) two of the jet engines are typically attached to the side of the rear fuselage or under the wings, the middle engine is attached to almost all models below the rudder. In 2010 around 3200 trijets were in use worldwide in the civil and around 60 in the military sector, including the narrow-body aircraft Boeing 727 , Jakowlew Jak-40 and Jak-42 as well as Tupolev Tu-154 , the wide-body aircraft DC-10 and MD-11 as well as business aircraft the Dassault-Falcon family.

historical development

HS Trident 3B - a three-engine British short and medium-haul aircraft of the 1960s and 1970s

This type was common in medium- haul aircraft and long-haul aircraft during the 1970s and 1980s. In the early 1960s, the three-engine design was initially used for larger short and medium-haul aircraft ( Boeing 727 , Hawker Siddeley Trident , later also Tupolew Tu-154 ). With the advent of the wide-bodied aircraft (the Boeing 747 entered service in 1970), larger models were also equipped with three engines. Between the beginning of the 1970s ( DC-10 ) and the beginning of the 1980s, the large three-jet models DC-10 and Lockheed TriStar were indispensable for low-volume long-haul routes and, at the same time, served short and medium-haul routes, especially in the USA. At that time, twin-jet models were not permitted for crossing oceans (see ETOPS ) . Three instead of four engines were expected to be more economical. While the three-jet designs initially closed the gap between the smaller, older four-jet engines (mainly DC-8 and Boeing 707 ) and the significantly larger Boeing 747 , they formed the "substructure" of the medium and long-haul fleets when the smaller four-jet engines were taken out of service. In the mid-1980s, however, twin-engine aircraft such as the Boeing 767 had proven so reliable that they were also approved for transoceanic missions. This was the reason for the airlines to replace their aging three-engine wide-body aircraft with more modern machines (initially Boeing 767, later also Airbus A330 and A340 and Boeing 777), which were almost entirely two-engine, and more rarely four-engine. The MD-11 , introduced in the early 1990s as a revision of the DC-10, could not establish itself on the market in the long term. During the 1980s, the Boeing 727 also slowly disappeared from short and medium-haul routes.

McDonnell Douglas DC-10 - cargo aircraft from FedEx with three engines

Three-beam today

In the western industrialized countries in particular, only a few three-engine aircraft can be found in passenger service today. The most common pattern is currently the MD-11 . The older DC-10 and Boeing 727s, on the other hand, have almost completely disappeared from European airports and the passenger versions are now almost only used in the third world. They have been replaced by twin jets .

In the air freight sector, on the other hand, there are still many three-jet engines in use, as many DC-10s and especially MD-11s have been converted into cargo planes after they were retired from passenger service. As a very modern, economical aircraft, the MD-11 is of particular importance in this regard. The largest operator of three-engine aircraft today is the US cargo airline Federal Express , which has the largest fleet of the Boeing 727, DC-10 and MD-11 models worldwide. In the military sector (freight, troop transport, air refueling), three-jet models can still be found (e.g. KC-10 ). However, there is no longer a three-engine passenger aircraft in production today. New models are only being built in the business jet segment ( Dassault Falcon 7X and Dassault Falcon 900 ).

Special design features

Rear of a Lockheed TriStar from Thai Sky Airlines with an S-shaped air inlet ( S-duct ) that leads from the tail unit into the rear

Tail unit with integrated engine on a Tu-154

Three-engine aircraft generally require the installation of an engine on the longitudinal axis of the aircraft. This poses greater structural problems with jet engines than with fan guns, where, as in the famous Junkers Ju-52, the middle engine was integrated directly into the nose of the fuselage. The positioning of the third engine is generally considered to be technically difficult. In the construction of three-engine passenger aircraft, two basic concepts for the assembly of the middle engine have prevailed:

1. An engine is mounted in the rear of the aircraft and the air inlet is at the lower end of the fin.
2. The engine sits under the fin in a continuous tube (stern nacelle) that begins in front of it and ends behind it.

The S-shaped air inlet

In the case of the design (referred to as S-duct ), only the air inlet is located on the front edge of the fin and leads in an approximately S-shaped curve into the aircraft tail, where the actual engine is mounted. The outlet of the turbine then usually forms the tip of the stern. The engine is integrated into the rear end of the fuselage. This design has become particularly widespread and is used in these passenger aircraft:

• Boeing 727
• Dassault Falcon 50
• Dassault Falcon 900
• Dassault Falcon 7X
• Hawker Siddeley Trident
• Lockheed L-1011 TriStar (largest aircraft ever built with an S-shaped inlet)
• Tupolev Tu-154
• Yakovlev Yak-40
• Yakovlev Yak-42

With the exception of the Lockheed TriStar, the S-shaped inlet is always combined with the other two engines on the rear of the fuselage. Only Lockheed decided to mount the two remaining engines under the wings. Boeing planned an engine arrangement comparable to the TriStar in the 1970s for a shortened three-engine variant of the Boeing 747 , but this was not implemented.

The stern gondola

Engine above the rear of the fuselage on a KLM MD-11

The stern nacelle is an engine suspension in which the fin is completely placed on the engine. The middle engine is mounted on the rear of the fuselage and the vertical stabilizer is located above the nacelle. This design was mainly used for the DC-10 and MD-11 wide-body aircraft from the American company McDonnell Douglas.

Other constructions

In some experimental types (e.g. Sud-Ouest SO9000 / 9050 ) the third engine was installed directly in the fuselage.

Future developments

Future production of trijets in the narrow-body and wide-body aircraft sector is unlikely. Airbus SAS had a trijet design with the third engine in a nacelle above the fuselage and a double vertical stabilizer patented in 2008, but whether this type will ever be produced is very uncertain.

The business jet Falcon 900 and Falcon 7X from Dassault Aviation are expected to continue to be manufactured with three jet engines. New developments from other manufacturers are currently not announced.

By merging with McDonnell Douglas in 1997, Boeing took over designs for a new Trijet family called the MD-XX . However, this project of a larger and modernized DC-10 with a longer range was ended in 1996.

Since 2004, Boeing and NASA have been experimenting with the Boeing X-48 , a 6.4 m long unmanned three-engine experimental aircraft , in order to test the properties of a Blended Wing Body (BWB), a special form of flying wing .

The future of the Russian Tupolev Tu-155/156 , powered not by kerosene but by hydrogen or natural gas, is unclear.

Classification of three-engine aircraft according to use, dimensions and production

Note on the table: For a quick overview, the aircraft types used in 2012 are highlighted in light blue. The columns can be sorted by clicking the small arrows in the heading bar.

Aircraft type	image	Production (period)	Piece production (2012)	Piece ready for use (2012)	country	Length (from – to) in m	Span (from – to) in m	Range in km	Starting weight in t	comment
Boeing 727		1963-1984	1,832	169	United States	40-46 m	32 m	4,020 km	95 t	Narrow-body aircraft
Boeing C-22		1963-1984	5	-	United States	40 m	33 m	3,220 km	77 t	military variant of the Boeing 727-100 / 200
Boeing X-48		2004-	2 (?)	1	United States	7 m (?)	6 m (?)			unmanned experimental aircraft of a blended wing body (BWB)
Dassault Falcon 50		1976-2008	352	342+	France	18 m	18 m	6,480 km	18 t	Business airplane
Dassault Falcon 900		1984–	500+	500	France	20 m	19 m	8,300 km	21 t	Business airplane
Dassault Falcon 7X		2001–	200+	200+	France	23 m	25 m	11,000 km	31 t	Long-haul business travel aircraft , series production from 2005
Hawker Siddeley Trident		1950s – 1971 (approx.)	117	-	United Kingdom	35-40 m	27-29 m	4,600 km	68 t	originally from de Havilland , narrow-body aircraft
Yakovlev Yak-40		1967-1981	1.011	104	Russia (former Soviet Union )	20 m	25 m	1,450 km	16 t	Short-haul airliner
Yakovlev Yak-42 Clobber		1979-2002	184	57	Russia (former Soviet Union )	36 m	34 m	4,100 km	57 t	Narrow-body aircraft
Jakowlew Jak-141 Freestyle (= Yak-141, Yak-41M)		1987-1991	1	-	Russia (former Soviet Union )	19 m	10 m	2,100 km	19 t	Supersonic VTOL fighter, prototype; 1 turbofan (thrust), 2 turbo jets (hub)
Lockheed L-1011 TriStar		1970-1984	250	11	United States	50-54 m	47-50 m	9,900 km	231 t	Wide-body aircraft , used as a transporter and tanker
Martin XB-51		1949	2	-	United States	26 m	16 m	1,730 km	28 t	Bombers , prototypes destroyed by accidents in 1952 and 1956
McDonnell Douglas DC-10		1968-1988	386	79	United States	55 m	47-50 m	7,400 km	251 t	Wide-body aircraft
McDonnell Douglas KC-10 Extender		1979-1990	60	59	United States	55 m	50 m	7,080 km	267 t	military wide-body tanker and transport aircraft, variant of the DC-10
McDonnell Douglas MD-11		1988-2000	200	173	United States	61 m	51 m	13,000 km	285 t	Greater - Passenger and cargo aircraft
Sud Ouest SO.9000 / 9050 Trident I / II		1953-1958	2	-	France	13 m	7 m		5 t	military experimental type with two jet engines and one rocket engine
Tupolev Tu-154 Careless		1968-2006	915	83	Russia (former Soviet Union )	48 m	37 m	4,000 km	100 t	Narrow-body aircraft
Tupolev Tu-155/156		1988-1989, 2008	1	-	Russia (former Soviet Union )	48 m	38 m	4,800 km	100 t	Variants of the Tu-154 with hydrogen and natural gas propulsion, test flights of the Tu-155 in 1989, Tu-156 not realized, narrow-body aircraft

See also

• Single-engine aircraft
• Twin-engine aircraft
• Four-engine aircraft
• Six-engine aircraft
• Eight-engine aircraft

Remarks

1. ↑ The respective model is classified under the name under which it became known or, in the case of current models, under which it is currently offered or listed by the manufacturers. Possibly. Several names are listed, for models from the former Soviet Union, Russia, China, etc. also the NATO names.
2. ↑ ^{a b} The numbers are taken from (a) surveys in Flight International ( Flight Global. Archived from the original ; accessed on 23 March 2020 .  (PDF; English): World Airliner Census (for civil aircraft stand each mid-year), Directory World Air Forces for military aircraft (as of each year-end). the overviews are all in use to respective closing date for airplanes and temporarily abandoned ( "parked") copies together except operated by leasing Company aircraft. (b) production data from Airbus at airbus.com ( constantly updated) under Aircraft families and Boeing at boeing.com . (c) Production figures for business jets, as well as the number of airworthy aircraft, are sometimes only published very sparsely by the manufacturers. Only reliable information is included in the table Numbers of items are partially not published and are different as far as possible Sources, e.g. B. the English language Wikipedia or other statistics from Flight International and Aviation Week . The overviews are at Flightglobal. Archived from the original ; accessed on March 23, 2020 .  available as PDF (English). Figures for China are generally not certain. a. sinodefence.com .
3. ↑ Country or countries with the seat of the manufacturer company or companies. In cooperation, e.g. B. EADS / Airbus all countries directly involved are listed. In the case of the countries of the former Eastern Bloc , the former USSR may also be listed for production before 1990.
4. ↑ ^{a b} The length and span dimensions are rounded to the nearest meter in order to keep the table clear. Different sizes for variants of a model: from – to  m, for swing-wing aircraft : maximum / minimum size.
5. ↑ The maximum range specified by the manufacturer as normal in kilometers with normal payload, the most powerful model of the type without taking additional tanks into account, except where applicable for specially listed ER models ( extended range ) in kilometers, rounded if necessary
6. ↑ Gross weight, in metric tons according to the manufacturer, most powerful model of the type, rounded if necessary, military models including weapon load.
7. ↑ including 54 aircraft in civil, 29 in military use

literature

• Rainer W. During: Tri-Jets competition. In: FliegerRevue , No. 9/2020, pp. 44–47

Web links

Commons : three-engine aircraft  - collection of images

• Overview of civil aircraft used worldwide in 2008 at Flightglobal (English)
• more overviews at Flightglobal (English)
• Photo collection at Planespotters
• Photo collection at Airliners-Net
• Flightglobal trade journal (English)
• Aviation Week trade journal
• Flugrevue trade journal

Individual evidence

1. ↑ World Airliners: Good times - Bad times, Oct. 2008 . Flightglobal; Overview
2. ↑ ^{a b} Berger (Ed.): 1000 aircraft . Cologne, undated, ISBN 978-3-625-10373-8 , p. 327
3. ↑ Information and sketch in Airbus files patent for new trijet design at Flightglobal (English)
4. ↑ MDC postpones MD-XX launch and MDC board dates MD-XX at Flightglobal (English)
5. ↑ Information based on the press release at dassaultfalcon.com (English), accessed on January 28, 2013
6. ↑ Information based on the press release at dassaultfalcon.com (English), accessed on January 28, 2013
7. ↑ Tu-155 in the English language Wikipedia and airwar.ru (English) with more information