The Propfan

I’d written this as a brief essay in the ARCFT-115 class and figured it may be of value to the world:

The Propfan
Turbojet-based Unducted Fan

Turbojet-based engines — which continuously compress ingested air, combust the compressed air combined with injected fuel, and leverage the exhaust gases to drive the compressor assembly — provide a considerably higher power to weight ratio than reciprocating engines.

Presently, amongst fixed-wing, commercial airlines worldwide, there are two primary types of turbo-compound turbojet engines in use: the turbofan and the turboprop.

Subsequent to the oil crisis of 1973, NASA-guided research sought greater fuel efficiency gains in propulsion technologies for commercial aerospace than the ubiquitous turbofan and turboprop engines.

One of the proposed and tested implementations was of the “propfan” model.

The propfan combined the well-understood technologies of both the turbofan and turboprop puller-type designs but included a second, coaxial fan counter-rotating to negate the thrust torque imparted by a single-fan/single-propeller engine in a pusher configuration.

NASA installed a test engine, constructed by General Electric as the GE36 propfan, onto a Boeing 727-100 airframe replacing one of the aircraft’s three engines. Research on this test model found that the tested propfan realized 35% greater fuel efficiency than its turbo-compound counterparts. Additional tests were performed on a McDonnell Douglas MD-80 finding similar results.

The onboard perceived noise — described as “buzzsaw-like” by witnesses at the time — would be minimized at cruise speeds by mounting the engines aft of the passengers and crew. By modern standards, this requirement will present significant design challenges to the existing wing-nacelle preference.

Testing in the mid-1980s revealed that the ground-level noise pressure of 70 dBA from 30,000 ft overhead flights — as loud as a typical household vacuum cleaner. Testing revealed that the noise signature could be lessened, but with a complete loss of all efficiency-gains realized with the propfan model.

Combined development efforts on the planned Boeing 7J7 and McDonnell Douglas MD-94X were halted. The carbon-composite technologies realized in the GE36 Propfan have been implemented in the current generations of the GE90 and GEnx installed in the Boeing 747, 777, and 787 Dreamliner aircraft.

It would be a worthwhile model to investigate, learn, and explore further leveraging the combination of the additional 35 years of engine efficiency technology, noise abatement, and higher cruise altitudes.

And now, the addendum:

Celera 500L. Yes, it’s a V-12 reciprocating engine. But, what if…

What if engineers were to develop a suitably-sized propfan for it, might it be viable?


In Other News…

No, I’m afraid I cannot justify US$550 for a set of headphones.

Do they sound amazing? I’m certain they do.

Do they integrate seamlessly with the Apple universe that I already have? Yep, no doubt.

But it’s still $550 for a set of headphones and that alone is reason enough for it to wait for a long while.

Though, I admit that I am curious about how effective its noise-cancelation is and how it compares with the AirPods Pro.

Apropos of, well, everything…

“The major problem—one of the major problems, for there are several—one of the many major problems with governing people is that of whom you get to do it; or rather of who manages to get people to let them do it to them.

To summarize: it is a well-known fact that those people who must want to rule people are, ipso facto, those least suited to do it.

To summarize the summary: anyone who is capable of getting themselves made President should on no account be allowed to do the job.

To summarize the summary of the summary: people are a problem.”

— Douglas Adams, The Restaurant at the End of the Universe


Had to abruptly leave class today just before lunch.

Not because I wanted the day off nor that I’m sick (I feel fine and I’ve loads of things I wish to do) but because Daisy received positive test results.

Not positive “good” but positive “bad”.

She has had a sore throat a few days and a cough that was medically more likely an infection, but Covid tests were requested. Test results came back positive a few days later.

Notified the instructor, filled out a form for State & CDC tracking, clocked-out, grabbed my tools and quietly left the building.

Sucks. But, do the best we can.