The Lockheed L-1011, the largest and only widebody aircraft to feature an S-duct

An S-duct is a unique type of jet engine intake duct, used only on trijet 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 1963 with the Boeing 727. Currently, the Dassault Falcon 7X and Dassault Falcon 900 business jets, and the Tupolev Tu-154M narrow-body airliner in limited production, are the only aircraft in production that use the S-duct design.

[edit] Benefits and drawbacks

The S-duct was invented as a solution for positioning the central engine on trijets. The S-duct was easier to service than alternative trijet designs.^[1] Most trijet designs opted for the S-duct layout.

In fact, only the DC-10 and MD-11 trijets 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 layout also increases total aircraft drag by 2-4%.^[1]

On the L-1011, engineers were able to maintain "straight-thru" engine performance by limiting the curve of the S-duct to less than 25% of the radius of the engine intake diameter.^{[citation needed]} The S-duct design also reduced the total empty aircraft weight.^[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 1970s, and can safely power the aircraft with only two engines, the trijet design is no longer used on large jet aircraft.

[edit] List of S-duct aircraft

Aircraft currently built with S-ducts are the:

• Dassault Falcon 7X
• Dassault Falcon 900
• Tupolev Tu-154M

Aircraft previously built with S-ducts, but no longer in production, are the:

• Boeing 727
• Dassault Falcon 50
• Hawker Siddeley Trident
• Lockheed L-1011
• Tupolev Tu-154
• Yakovlev Yak-40
• Yakovlev Yak-42

The Boeing 747-300 Trijet was designed with an S-duct layout, but never built.[1]

[edit] Gallery

The Dassault Falcon 7X, currently in production

Rear view of a Russian Tu-154 S-duct aircraft

[edit] See also

• Trijet
• Empennage
• ARA Computation Aerodynamics S-Duct animation
• "Giant Tri-Jets Are Coming", Ben Kocivar, Popular Science, December 1970, Vol. 197, No. 6, ISSN 0161-7370, pp. 50-52, 116

[edit] References

This aircraft-related article is a stub. You can help Wikipedia by expanding it. v • d • e