Has anyone ever heard of a geared turbofan in which the axis of rotation of the fan is offset from (i.e. not the same as) the axis of rotation of the turbine? In all the current geared turbofans I've encountered, the input shaft from the turbine to the gearbox is co-axial with the output shaft to the fan.

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    $\begingroup$ This seems like it would cause issues, because unlike a turboprop, the core of a turbofan is very dependent on the fan flow and compression. $\endgroup$ – fooot Oct 15 '15 at 19:45
  • $\begingroup$ The Wikipedia entry for Geared Turbofans lists just six examples, and non of those are offset. Unless there's something exceptionally new, or exceptionally weird out there, no, an off-centre geared turbofan doesn't exist. This shouldn't come as a surprise given the obvious problems with airflow through a kinked engine, but...Never say never! $\endgroup$ – user11516 Oct 16 '15 at 5:21
  • $\begingroup$ great, thanks for the help! $\endgroup$ – Mike Oct 16 '15 at 17:43

There are no off-centered turbofan engines in service today. However, United Technologies Corporation (UTC), has patented an engine with an angled core (Pratt & Whitney is a part of UTC).

Angled Engine

Image from US patent Gas turbine engine with separate core and propulsion unit US 8789354 B2

Air from the fan is ducted around the side and back of the core to enter from the opposite direction. The hot gas will be discharged forward through a power (low-pressure) turbine connected to the fan via a gear system. The turbine, gearbox and fan will be connected through a short shaft.

Angled engine

Source: aviationweek.com

The design is expected to have some advantages due the unconventional layout adopted, like:

  • As the core and fan are separate, core can be easily removed for maintenance.

  • As the compressors (in cores) are at an angle to each other, the possibility that uncontained failure in one engine will damage another engine is reduced (when the engines are installed in the double bubble D8 configuration)

  • $\begingroup$ great information, thanks! $\endgroup$ – Mike Oct 16 '15 at 17:44

In case you're interested, US Patent 7,752,834 has what I was looking for. US-7752834

  • $\begingroup$ Interesting. I guess one benefit is smaller fan diameter. $\endgroup$ – fooot Oct 16 '15 at 21:11
  • $\begingroup$ Did you have an application in mind / what sparked your interest? Just curious. $\endgroup$ – Hephaestus Aetnaean Oct 17 '15 at 2:07

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