Aero-Terms!

Aero-Terms are designed to be a daily reminder of the terms, names, acronyms and explanations of the unique language that populates the aviation world. Aerospace, sport aviation, fixed wing, helo, you name it... it's all fair game.

Aero-Terms should serve as a quick but intriguing reminder of the terms you may use every day, or an introduction to an aspects of the Aero-World you may not yet be familiar with. ANN also encourages readers to go beyond the FMI link, and further research any intriguing terms.

Suggestions for future Aero-Terms are ALWAYS welcome, as are additions or discussion of the explanations given for each Aero-Term.

S-Duct

An S-duct is a unique type of jet engine intake duct, used only on trijets. The S-duct is located in the tail, or empennage, of the aircraft. As well, the shape of the S-duct is distinctive and easily recognized.  The S-duct was invented as a solution for positioning the central engine on trijets. The S-duct was easier to service that 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%. 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. The S-duct design also reduced the total empty aircraft weight.

FMI: www.ara.co.uk/content/2/160/s-duct.html