Whatever happened to the specialized jet engines with exterior fan blades

[bcullman]

A few years back I recall some company testing a new jet engine that had 2 prop-like external counter rotating rings that was supposed to be more fuel efficient. what happened?

[NBYodo]

@bcullman

A few years back I recall some company testing a new jet engine that had 2 prop-like external counter rotating rings that was supposed to be more fuel efficient. what happened?

You’re probably remembering the GE39. It’s a demonstrator from GE.

They ultimately ran into problems with certification. They were apparently going to have to certify it as per a turbofan engine, which must be able to pass the blade-off test (where a fan blade breaks off, but must still be contained within the engine). Obviously difficult without a nacelle around the blades to catch them…
A bit of info here (not an official cite though): http://www.forpilots.com/archive/rec.aviation.misc/7/msg8146.htm
Cheers,
NB

[LSLGuy]

There are renewed efforts to bring them back again. I treid to find a cite for you but could not. There have been several articles in the trade press in the last 6 months.

The recent interest is driven by the fact they offer a 5-10% increase in fuel efficiency, which is seen as a key prerequisite for the next generation of narrowbody airliners to replace the current 737 & A320 series.

Downsides are as noted above (BTW it was the GE36, not 39), plus increased vibration & exterior noise. There is also the perception problem; the public firmly believes “prop = slow & dangerous, jet = fast & safe.”

So the airlines are concerned that they might end up with a sales problem, which in turn maens the airplane manufactuers have a sales problem which means the engine manufactuers have a sales problem. Demonstrating the engineering challenge of doing business with fundamentally irrational customers, the passenger perception issue is widely regarded as the real deal-killer; everything else can be solved.

[Xema]

Here’s a photo.

[Rocketeer]

@LSLGuy

There are renewed efforts to bring them back again. I treid to find a cite for you but could not. There have been several articles in the trade press in the last 6 months.

The recent interest is driven by the fact they offer a 5-10% increase in fuel efficiency, which is seen as a key prerequisite for the next generation of narrowbody airliners to replace the current 737 & A320 series.

Downsides are as noted above (BTW it was the GE36, not 39), plus increased vibration & exterior noise. There is also the perception problem; the public firmly believes “prop = slow & dangerous, jet = fast & safe.”

So the airlines are concerned that they might end up with a sales problem, which in turn maens the airplane manufactuers have a sales problem which means the engine manufactuers have a sales problem. Demonstrating the engineering challenge of doing business with fundamentally irrational customers, the passenger perception issue is widely regarded as the real deal-killer; everything else can be solved.

I think they’re worried too much about passenger perception. All the recent history of the airlines suggests that they go for the cheapest fare, period. Safe, unsafe, Boeing, Airbus, new, old–all irrelevant.

[mks57]

@Rocketeer

I think they’re worried too much about passenger perception. All the recent history of the airlines suggests that they go for the cheapest fare, period. Safe, unsafe, Boeing, Airbus, new, old–all irrelevant.

I don’t know how widespread it was, but I used to avoid flying on DC-10s after they had a string of accidents due to design and maintenance deficiencies.

[robby]

I first read an article about propfans over twenty years ago. As I recall, one of the big isssues is with excessive noise.

Here is a larger photo of a Soviet Progress model.

[scr4]

How would this be different from a conventional turboprop?

[NBYodo]

@LSLGuy

There are renewed efforts to bring them back again. I treid to find a cite for you but could not. There have been several articles in the trade press in the last 6 months.

The recent interest is driven by the fact they offer a 5-10% increase in fuel efficiency, which is seen as a key prerequisite for the next generation of narrowbody airliners to replace the current 737 & A320 series.

Downsides are as noted above (BTW it was the GE36, not 39), plus increased vibration & exterior noise. There is also the perception problem; the public firmly believes “prop = slow & dangerous, jet = fast & safe.”

So the airlines are concerned that they might end up with a sales problem, which in turn maens the airplane manufactuers have a sales problem which means the engine manufactuers have a sales problem. Demonstrating the engineering challenge of doing business with fundamentally irrational customers, the passenger perception issue is widely regarded as the real deal-killer; everything else can be solved.

Well, no wonder I couldn’t find any cites when I was looking for the GE39!

a summary here: General Electric GE36 - Wikipedia
a thesis (!) here: News, Politics, Sports, Mail & Latest Headlines - AOL.com

NB