An S-duct (or serpentine inlet) is a 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, above or below the stabilizer, while the exhaust and engine is at the rear of the aircraft. The S-duct is located in the tail, or empennage, of the aircraft. The shape of the S-duct is distinctive and easily recognized, and was used in several aircraft, beginning in 1962 with the Hawker Siddeley Trident. The Dassault Falcon 8X and Dassault Falcon 900 business jets are the only aircraft in production that use the S-duct design.
The S-duct was invented as a solution for positioning the central engine on trijets. The S-duct is easier to service than alternative trijet designs. [1] Most trijet designs opted for the S-duct layout. Only the McDonnell Douglas DC-10 and MD-11 trijets' designers chose not to use the S-duct and go with a "straight-through" layout. The straight-through layout leaves the engine high above the ground, making access difficult. The straight-through layout also increases total aerodynamic drag by 2–4%. [1]
Compared to the straight-through design on the DC-10 and MD-11, the S-duct allows a shorter fin and a rudder closer to the longitudinal axis.
On the Lockheed L-1011 TriStar, engineers were able to maintain engine performance comparable with straight-through designs by limiting the curve of the S-duct to less than a quarter of the radius of the engine intake diameter.[ citation needed ] The S-duct design also reduced the total empty aircraft weight. The research undertaken during the design of the L-1011 indicated that losses of using an S-duct were more than compensated for by the savings. [2]
The S-shaped duct is a complicated and costly design.[ citation needed ] Since modern jet engines have more power and reliability than those of the 1970s and can safely power the aircraft with only two engines, the trijet design is no longer used for large commercial airliners but is used on the latest Dassault Falcon 7X and Falcon 8X business jets in order to provide more total thrust while enabling the continued use of smaller engines in the 15–30 kN (3,400–6,700 lbf) class with which Falcons have historically been designed. In international aviation regulations the triple engine layout is also considered inherently safer for the increased redundancy, which allows the use of certain airfields at high elevation only for aircraft with more than two engines.
The S-duct is also used on combat aircraft, where it has the advantage of blocking the front of the jet engine from radar. The spinning compressor blades would produce a strong radar return, compared to the smooth sides of the duct.
Aircraft built with S-ducts are the:
Aircraft previously built with S-ducts, but no longer in production, are the:
The Boeing 747-300 Trijet (not to be confused with the later 747-300) was designed with an S-duct layout, but never built.
A short take-off and vertical landing aircraft is a fixed-wing aircraft that is able to take off from a short runway and land vertically. The formal NATO definition is:
A Short Take-Off and Vertical Landing aircraft is a fixed-wing aircraft capable of clearing a 15 m obstacle within 450 m of commencing take-off run, and capable of landing vertically.
A vertical take-off and landing (VTOL) aircraft is one that can take off and land vertically without relying on a runway. This classification can include a variety of types of aircraft including helicopters as well as thrust-vectoring fixed-wing aircraft and other hybrid aircraft with powered rotors such as cyclogyros/cyclocopters and gyrodynes.
The Lockheed L-1011 TriStar is an American medium-to-long-range, wide-body trijet airliner built by the Lockheed Corporation. It was the third wide-body airliner to enter commercial operations, after the Boeing 747 and the McDonnell Douglas DC-10. The airliner has a seating capacity of up to 400 passengers and a range of over 4,000 nautical miles. Its trijet configuration has three Rolls-Royce RB211 engines with one engine under each wing, along with a third engine center-mounted with an S-duct air inlet embedded in the tail and the upper fuselage. The aircraft has an autoland capability, an automated descent control system, and available lower deck galley and lounge facilities.
The Yakovlev Yak-40 is a regional jet designed by Yakovlev. The trijet's maiden flight was in 1966, and it was in production from 1967 to 1981. It was introduced to service in 1968, with export models following in 1970.
A business jet, private jet, or bizjet is a jet aircraft designed for transporting small groups of people, typically business executives and high-ranking associates. Business jets are generally designed for faster air travel and more personal comfort than commercial aircraft, and may be adapted for other roles, such as casualty evacuation or express parcel deliveries, and some are used by public bodies, government officials, VIPs, or even the military.
A jet airliner or jetliner is an airliner powered by jet engines. Airliners usually have two or four jet engines; three-engined designs were popular in the 1970s but are less common today. Airliners are commonly classified as either the large wide-body aircraft, medium narrow-body aircraft and smaller regional jet.
A vertical and/or short take-off and landing (V/STOL) aircraft is an airplane able to take-off or land vertically or on short runways. Vertical takeoff and landing (VTOL) aircraft are a subset of V/STOL craft that do not require runways at all. Generally, a V/STOL aircraft needs to be able to hover. Helicopters are not considered under the V/STOL classification as the classification is only used for aeroplanes, aircraft that achieve lift (force) in forward flight by planing the air, thereby achieving speed and fuel efficiency that is typically greater than the capability of helicopters.
The Yakovlev Yak-42 is a 100/120-seat three-engined mid-range passenger jet developed in the mid 1970s to replace the technically obsolete Tupolev Tu-134. It was the first airliner produced in the Soviet Union to be powered by modern high-bypass turbofan engines.
A tail-sitter, or tailsitter, is a type of VTOL aircraft that takes off and lands on its tail, then tilts horizontally for forward flight.
The Yakovlev Yak-36, also known as Izdeliye V, is a Soviet technology demonstrator for a VTOL combat aircraft.
The Dassault Falcon 7X is a large-cabin, 5,950-nautical-mile [nmi] range business jet manufactured by Dassault Aviation, the second largest of its Dassault Falcon line. Unveiled at the 2001 Paris Air Show, its first flight took place on 5 May 2005 and it entered service on 15 June 2007. The Falcon 8X, first delivered on 5 October 2016, is derived from the 7X and has an extended range of 6,450 nmi made possible through engine optimization, aerodynamic refinements as well as an increase in fuel capacity. Featuring an S-duct central engine, the 7X, 8X and the Falcon 900 are the only trijets still in production, as of 2024.
A supersonic aircraft is an aircraft capable of supersonic flight, that is, flying faster than the speed of sound. Supersonic aircraft were developed in the second half of the twentieth century. Supersonic aircraft have been used for research and military purposes, but only two supersonic aircraft, the Tupolev Tu-144 and the Concorde, ever entered service for civil use as airliners. Fighter jets are the most common example of supersonic aircraft.
The Dassault Falcon 50 is a French super-midsize, long-range business jet, featuring a trijet layout with an S-duct air intake for the central engine. It has the same fuselage cross-section and similar capacity as the earlier twin-engined Falcon 20, but was a new design that is area ruled and includes a more advanced wing design.
A trijet is a jet aircraft powered by three jet engines. In general, passenger airline trijets are considered to be second-generation jet airliners, due to their innovative engine locations, in addition to the advancement of 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.
The Hawker Siddeley HS-121 Trident is a British airliner produced by Hawker Siddeley. In 1957, de Havilland proposed its DH.121 trijet design to a British European Airways (BEA) request. By 1960, de Havilland had been acquired by Hawker Siddeley. The Trident's maiden flight happened on 9 January 1962, and it was introduced on 1 April 1964, two months after its main competitor, the Boeing 727. By the end of the programme in 1978, 117 Tridents had been produced. The Trident was withdrawn from service in 1995.
The Yakovlev Yak-43 was a Soviet VTOL fighter designed as the ground-based version of the ill-fated Yakovlev Yak-141, which failed to reach production. Like the Yak-141, the Yak-43 did not reach production. The Yak-43 would have been the third-generation VTOL/STOL fighter, to follow and eventually replace the Yak-141.
The China Aviation Museum is an aviation museum located in Beijing, China. It is affiliated with the People's Liberation Army Air Force and co-sponsored by the Aviation Industry Corporation of China. The museum is a national first-class museum accredited by the National Cultural Heritage Administration.