Can an S-duct fit a turbofan exhaust instead of the intake? Can an S-duct fit a turbofan exhaust instead of the intake? The idea here is to merge 2 exhausts into one at the exact center of the tail. This would be for twin-engine aircraft that have both engines at the tail, like the Boeing 717.

There are of course S-ducts for intakes, like on the Tu-154. I have never seen them for exhausts, however, probably because it's much harder due to the heat.

I know it is engineeringly possible somehow, because I've seen vectored thrust devices with variable geometry, like the iris types and swivel types. For a large commercial jet, it would be easier because the geometry would be static--no moving parts.

But I want to know if it is economically feasible. To take the heat, I think it just needs some super-pure graphite, which does not sound so expensive to me. But I am not an expert.
Yes they can, and it has been done in the Garrett AiResearch ATF3. Although the engine was not hugely successful, it is still being used in aircraft today.



From this answer:


  The hot exhaust stream is deflected back into the fan bypass, which cools it down and results in a low IR signature. This engine is used in the Dassault Falcon.


You can see several S-ducts leading the hot exhaust gases internally into the little staircase-like contraptions behind the fan.