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When you come across the title "Is Airbus hiding an evolution?"

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When you come across the title "Is Airbus hiding an evolution?"

Old 28th Feb 2024, 14:46
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When you come across the title "Is Airbus hiding an evolution?"



"We are signing today with @CBeaune and @GuillaumeFaury the contract 2024-2027 for the aeronautical sector"
Roland Lescure, French Minister Delegate for Industry

His tweet contained one interesting picture, tweeted after a meeting with Airbus. The European Pilot and youtuber Mentour Now picked it up and speculatesin a recent video. My Thread Title is taken from that.






On that picture, an aircraft in A321 class with high aspect wings (Mentour speculates foldable for gust relief) and wing mounted open fan engines. Wing with odd shape to accommodate these engines. Lookup "mentour now" on youtube, his speculation just a few days old.

Will this be the next bold step for a new gen of aircraft?

Last edited by waito; 28th Feb 2024 at 22:35. Reason: title correction
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Old 28th Feb 2024, 15:19
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Originally Posted by waito

"We are signing today with @CBeaune and @GuillaumeFaury the contract 2024-2027 for the aeronautical sector"Roland Lescure, French Minister Delegate for Industry

His tweet contained one interesting picture, tweeted after a meeting with Airbus. The European Pilot and youtuber Mentour Now picked it up and speculates. Thread Title is taken from his post.


On that picture, an aircraft in A321 class with high aspect wings (Mentour speculates foldable for gust relief) and wing mounted open fan engines. Wing with odd shape to accommodate these engines. Lookup "mentour now" on youtube, his speculation just a few days old.

Will this be the next bold step for a new gen of aircraft?
If so, it's being introduced in a rather timid manner!
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Old 28th Feb 2024, 16:21
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Originally Posted by John Marsh
If so, it's being introduced in a rather timid manner!
Better deliver a final result than just premature hot air for investors and the public, right?

Thoughts on the concept? IIR(the video)C that one is aiming the mid 2030s. So they need to start "soon".
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Old 28th Feb 2024, 16:33
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What illiterate ****** wrote that !
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Old 28th Feb 2024, 18:43
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Yea, I saw that - basically the Boeing 7J7 proposal from 45 years ago (but with the engines moved from the tail to the wing so that the passengers can enjoy that ear splitting sound from the counter-rotating unducted fan).
I give it about the same probability of actually turning into reality as well (as in slim and none). Until someone - somehow - comes up with a solution to the noise generated by counter-rotating unducted fans, they are going to be a non-starter.
The noise generated by the trailing fan slicing through the vortices from the leading fan create a noise that would put an early pure-jet 707 to shame - and being unducted there is no way to attenuate that noise.
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Old 28th Feb 2024, 19:29
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We were usually told that open rotor engines required rear mounts ! We'll see about that.
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Old 28th Feb 2024, 20:01
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Originally Posted by tdracer
Yea, I saw that - basically the Boeing 7J7 proposal from 45 years ago (but with the engines moved from the tail to the wing so that the passengers can enjoy that ear splitting sound from the counter-rotating unducted fan).
I give it about the same probability of actually turning into reality as well (as in slim and none). Until someone - somehow - comes up with a solution to the noise generated by counter-rotating unducted fans, they are going to be a non-starter.
The noise generated by the trailing fan slicing through the vortices from the leading fan create a noise that would put an early pure-jet 707 to shame - and being unducted there is no way to attenuate that noise.
Time has passed.
1. Noise Level is expected on par with LEAP now
2. Only one rotating fan, the second is variable stator
3. the above enables a simpler and single gearbox, fan speed can be reduced and noise will meet near future limitations.
4. efficiency step up by 20% compared to best in class engines today for single aisle market

I personally see noise level in 3. still as a dead end if no more improvement can be made thereafter.


Last edited by waito; 29th Feb 2024 at 10:07. Reason: typos
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Old 28th Feb 2024, 20:23
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Originally Posted by waito
Time has passed.
1. Noise Level is expected on par with LEAP now
2. Only one rotating fan, the second is variable stator
3. the above enables a simpler and single gearbox, fan speed can be reduced and noise will meet near future limitations.
4. efficiency step up by 20% compared to best in class engines today for single aisle market

I personally see nose level in 3. still as a dead end if no more improvement can be made thereafter.
You still have the vortices from the fan hitting that stator (basically the same noise generation mechanism as a siren - and we all know how quiet those are ) with no way to attenuate the sound.
In short, I'll believe it when I hear it. Nobody thought the unducted fan on the 7J7 was going to be as nearly noisy as it was until they stuck one on aircraft and flew it around at a few hundred knots airspeed .
There is also the issue of losing a fan blade without a containment system.
BTW, the engine for the 7J7 didn't have a gearbox - the fans were driven by free turbines.
Everybody knows the efficiencies that you can get from going to what's effectively a higher bypass with an unducted fan (without having to carry all that weight and drag of the duct). The trick is making it efficient and quiet in the 0.7-0.8 Mach speed range.
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Old 28th Feb 2024, 21:06
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Originally Posted by tdracer
You still have the vortices from the fan hitting that stator (basically the same noise generation mechanism as a siren - and we all know how quiet those are ) with no way to attenuate the sound.
Don't always assume that everybody else is stupid. There are 1.000 engineers presently working on this engine. Do you really think that not one of them has thought about the siren effect? If you look at current illustrations of this engine you can see that the rotor has a lager diameter than the stator. Your vortices will bypass the stator on the outside. RPM is much lower than a conventional fan, so blade separation is certainly something to worry about, but not more than with turboprop aircraft. For a recent picture see here: https://aviationweek.com/shownews/du...view-milestone
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Old 28th Feb 2024, 21:32
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what next tdracer is just arguing, which is perfectly fine. No need to assume he's thinking CFM engineers are stupid.

​​​​​​The engine does make one difference compared to Boeings concept a/c x66(?). And it's a bet on future. If the engine fails to meet the requirements, Airbus busts.

Next is on the wings with in-flight flex by folding wingtips. avoids the truss braced wing otherwise needed on those high aspect ratio wings. Airbus had been working on shape-flexible wings, but came as far as trailing edge independent control of ailerons (or flaps, dont remember) for the A380.

Another risky innovation in terms of maturity.
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Old 28th Feb 2024, 21:49
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Originally Posted by waito
And it's a bet on future. If the engine fails to meet the requirements, Airbus busts.
Maybe. But you cannot always continue doing what you have done since 30 years. Otherwise aircraft would still look like the Wright Flyer. And regarding Airbus getting bust over this engine, they are presently at the absolute peak of their corporate history. Order an A320 now and you can expect delivery not before 2031. When, if not now, is the right time to invest in the future? 20% gain in engine efficiency is the second largest leap forward since the evolution from turbojet to turbofan. And I am sure that in those days there were plenty of naysayers claiming that turbofan engines were full of potential problems due to their increased compexity...
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Old 29th Feb 2024, 00:41
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Originally Posted by what next
Don't always assume that everybody else is stupid.
OK, have they flown one yet? Because I'm going to remain highly skeptical until they do.
I was around the engine side for 40 years, and I've heard many, many proposals from the engine companies that sounded wonderful on paper. The number than actually panned out in practice was small.
The 7J7 unducted fan worked fine on the bench. No so much when they stuck it on an aircraft and flew it.
BTW, it's not just the engine companies. Boeing and Airbus both routinely release pictures of some revolutionary new aircraft design (MacDac did the same before they bought Boeing). Yet somehow, commercial jet aircraft still look pretty much the same as a 707/DC-8...
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Old 29th Feb 2024, 04:23
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what next said:

RPM is much lower than a conventional fan, so blade separation is certainly something to worry about, but not more than with turboprop aircraft.
Perhaps the open fan technology will no longer be subject to the blade-off containment regulations for low stage compressor fan blade failure?

They may be going to argue that with the planned slower rotating and shorter (and tapering) blades of the open fan that the blade off event will be less likely and with less energy than a propeller blade off event.

And the C-130 Hercules engines are approaching an open fan type engine by their multiple (propeller or fan) blades.

And there has never been protection in the regulations for trying to contain a propeller blade once it fractures (as far as I am aware).

It is very interesting to see the open fan technology arise from the ashes.
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Old 29th Feb 2024, 04:54
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Just found this on Youtube...well worth the watch.
They claim the noise will meet all current and future regs.
And the big kicker is that they will achieve bypass ratios of 20:1 with the open fan vs current ducted-fans 12:1.
And they are planning to test the engine on an Airbus A-380!

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Old 29th Feb 2024, 05:52
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Using latest fluid simulation on Computers, they claim significant progress for that CFM open fan RISE model. I understand tdracer in being sceptical until proved in reality. I picked up that flight test is scheduled for 2026 on A380.

To my surprise, NASA Boeing X-66A will be using the same engine, according to a publication on Aero Time from June 23. Design draft pix showed conventional Turbofans, so I don't know what's going to happen there.

Last edited by waito; 29th Feb 2024 at 10:28.
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Old 29th Feb 2024, 06:47
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I am rather skeptical as well because the fan(s) can be tested separately with electric motors on a test stand with a suitable fairing mock-up to establish the noise output of the fan(s) alone. There is no need to go to the trouble of also building a rather expensive engine core for the purposes of evaluating the fan(s) in early stages of development and doing so would lend the ability to better characterize the fan(s) and either tweak the fan design to the expected engine core performance or tweak the engine core to match the fan demand.

A risk mitigation policy would be to do such a test early on to prove the previously demonstrated problems, particularly sound output, had effectively been dealt with.

I don't doubt they can build an engine with the fan(s) on it - I have doubts it is anywhere nearly as quiet as they claim. Saying it is quieter than low-bypass turbojets engines is avoiding what could be easily demonstrated.

My aerospace degree was not in propulsion - just typical aircraft aerodynamics - so I don't have an estimate for shock wave formation at the blade tips, but I recall this is the effect that limits the speed of conventional propellers and the efficient speed of the aircraft.
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Old 29th Feb 2024, 08:31
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Don't underestimate progress in computer simulation. While reality is dirty and still unpredictable as a whole, the limit of predictability and computability of many more parameters should give a more precise estimation of what's feasible.

I guess CFM and partners did that.

Compare to the supersonic pax aircraft research in USA lately. Unthinkable 20 years ago to hope for a solution for sonic boom. Creativity, Simulation and Analysis also helped over there.

You think sonic boom can be solved, but not the open fan noise issues?

Last edited by waito; 29th Feb 2024 at 10:05. Reason: typos
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Old 29th Feb 2024, 12:10
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Originally Posted by MechEngr
There is no need to go to the trouble of also building a rather expensive engine core for the purposes of evaluating the fan(s) in early stages of development...
They already started the test program using the engine core of a military GE F110 engine.

Originally Posted by MechEngr
My aerospace degree was not in propulsion - just typical aircraft aerodynamics - so I don't have an estimate for shock wave formation at the blade tips, but I recall this is the effect that limits the speed of conventional propellers and the efficient speed of the aircraft.
This is what I remember too (and my degree is not in aircraft propulsion either) but for comparison: The Airbus A400M military transport has a maximum Mach number of .72 using 8-blade turboprop engines. With this aircraft, noise and passenger comfort are no major issues, but it already comes close to the speed range of the RISE engine.
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Old 29th Feb 2024, 12:28
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It's almost as if someone typed in "new gen turbo prop Airbus" into an AI Bot. 😁
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Old 29th Feb 2024, 14:45
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Originally Posted by what next
The Airbus A400M military transport has a maximum Mach number of .72 using 8-blade turboprop engines. With this aircraft, noise and passenger comfort are no major issues, but it already comes close to the speed range of the RISE engine.
The A400M is already extremely noisy, anything more than that will start waking up the noise lobby around airports with its additional restrictions .
As to speed / cruising altitude, there are fortunately very few A400M cruising above 30.000ft , but those that fly are already creating us some capacity issues. , If this Hybrid /ac is planning to be cruising at the same altitudes as the current Jetliners, but at much lower speed, and come in big numbers to replace the A32+s , 737s and 220s, we're going to have a major capacity issue when they arrive as they will not mix well with the current fleets. Or they are going to be left below FL290 , which will probably no be that fuel effective anymore..

BTW we already had this discussion when Boeing presented its 7J7 to us.in Le Bourget decades ago..

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