
Propfan - starpilot
https://en.wikipedia.org/wiki/Propfan
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starpilot
So with renewed interest on aircraft emissions (due to Greta Thunberg et al.),
I thought of drawing attention to this promising concept from the 80s. It's
still being worked on by Safran: [https://www.avweb.com/recent-
updates/business-military/safra...](https://www.avweb.com/recent-
updates/business-military/safran-starts-open-rotor-ground-testing/) with
apparently the noise problems addressed. The basic idea is it generates
similar amounts of thrust as a turbofan while consuming 35% less fuel. It was
a great idea, but fuel prices were low and aeroacoustics wasn't at a state to
handle geometry this complex. I wouldn't be surprised to see us flying on
these in 50 years though.

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LargoLasskhyfv
Interesting! By from the 80ies you mean [1]
[https://en.wikipedia.org/wiki/Boeing_7J7](https://en.wikipedia.org/wiki/Boeing_7J7)
?

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JanSolo
Propfans are great in theory; extra efficiency! More power! Less weight!
However in practice, things are not so rosy. The biggest downsides to propfans
are Noise and Safety. Propfans are LOUD! Much louder than the current
generation of turbofans. The lack of a fan-case means the tips of the blades
are whirling right next to the passenger compartment. Which leads to safety;
there's no fan-case to protect the passengers if one of the blades were to
detach from the engine. Turbofans all have very stout fan-cases (they're the
single heaviest part of all turbofan engines) and the certification processes
include a blade-off test to make sure that the case can contain it. A blade
puncturing the fuselage would be a big problem.

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boarnoah
How does the blade detach scenarios differ from turboprops in this case?

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marcosdumay
Props are way slower moving and more resistant to breaking up than fans.

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aidenn0
They also have far fewer blades.

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bronco21016
All one has to do is look at the issues plaguing the current crop of geared
turbo-fans to see where this really struggles in the real world. Attaching an
ultra high RPM gas turbine to a relatively slow moving fan, whether a prop or
ducted fan, is not an easy engineering exercise. The amount of heat generated
in the gear box, the expensive materials that heat requires, and the
operational needs of many start/stop cycles are making these engine styles
difficult. That's not to say its not a worthy goal. It just seems that we're
just on the cusp of making these things a reality and I think the geared
turbofan will end up being the winner vs the propfan.

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cushychicken
Is the idea with this design that it would allow for planes as fast as jet
aircraft, but with turboprop efficiency? Is the implication that this might be
a way to preserve air travel with a lower carbon footprint?

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atomicbeanie
I am guessing the "Tic Tac" ufos are drones with prop fans.

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GhettoMaestro
No... these engines would still produce a very visible infrared signature from
the exhaust gases. The Tic Tac ufo from what we understand had essentially
zero IR signature.

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atomicbeanie
Super interesting. Thanks for the info!

