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

[waito]

https://cimg5.ibsrv.net/gimg/pprune.org-vbulletin/275x353/airbus01_9e39a97d50afeab6539e1b29ee462334f6b9c936.png

"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.


https://cimg7.ibsrv.net/gimg/pprune.org-vbulletin/322x175/airbus02_93e5b1800115f51451f886968822112e4a2bcb71.png


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?

[John Marsh]

"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!:)

[waito]

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".

[Mad Monk]

What illiterate ****** wrote that !

[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.

[CVividasku]

We were usually told that open rotor engines required rear mounts ! We'll see about that.

[waito]

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.

[tdracer]

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 :uhoh:) 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 :eek:.
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.

[what next]

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 :uhoh:) 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/dubai-airshow/cfm-rise-open-fan-passes-conceptual-review-milestone

[waito]

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.

[what next]

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...

[tdracer]

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...

[FlexibleResponse]

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.

[FlexibleResponse]

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!

https://youtu.be/DIm_vBAArrI

[waito]

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.

[MechEngr]

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.

[waito]

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?

[what next]

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.

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.

[TURIN]

It's almost as if someone typed in "new gen turbo prop Airbus" into an AI Bot. 😁

[ATC Watcher]

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..

[Dave]

https://www.youtube.com/watch?v=1BMNaXc1rL8

36 years ago..... at Farnborough airshow.

MD-80 with un-ducted fan.

Good luck to the engineers and designers involved :)

[BFSGrad]

36 years ago..... at Farnborough airshow. MD-80 with un-ducted fan.Got a bit of that P180 vibe.

[DaveReidUK]

Got a bit of that P180 vibe.

I recall it doing a good impression of a flying buzz-saw.

[tdracer]

And they are planning to test the engine on an Airbus A-380!


Makes a lot of sense if you think about it. Four engine aircraft, so lots of redundancy is something goes seriously wrong and does secondary damage (GE already has a 747-400 based Flying Test Bed - which replaced their 747-100 FTB). Boeing very nearly lost its 'prototype' 767 (VA-001) doing flight testing of the PW4000/94" when it went into non-recoverable surges at 50 ft. during takeoff (and the left seat pilot responded by pulling back both thrust levers :eek: - fortunately the guy in the right seat quickly responded by firewalling both throttles - the PW4000 responded by continuing to surge but the JT9D kept them flying).
Boeing long used the prototype 747 (RA-001) as a test bed for new engines (it's part of the Seattle Museum of Flight now). I suspect if Airbus is putting a lot of money and emphasis on the project they wouldn't want to see it flying on a 747 :O.
Plus, early build A380's are readily available cheap...

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
This was an issue for the 737-3/4/500 series - it cruised significantly slower than other jetliners (although quite a bit faster than 0.72 Mach) - as a result it tended to get less than optimum routing to keep it out of the way of the faster traffic. It was one of the big drivers for the 737 NG program - to modify the wing so it could cruise faster.

[what next]

... as a result it tended to get less than optimum routing to keep it out of the way of the faster traffic.

This is mainly history now. Air traffic, at least in my part of the world, does not fly along airways - which were mandated by ground based navigation aids - any more. There is a growing number of countries that have abolished airways altogether. Aircraft now fly direct routes between convenitntly located waypoints. Therefore it does not matter what speed you fly at, because no other aircraft is flying the exact same route as you. There are exceptions like north Atlantic tracks, but I am certain that a solution to that problem will be found as well.

[Less Hair]

It is optimised to need less fuel. Batteries won't work for big passenger aircraft, so something like the CFM RISE is the next best thing. At least 15 percent less fuel. Plus a new "gull" wing with provisions for even larger diameter engines and possibly moving outer wings, lightweight CFRP-fuselage with wide diameter in the back. Sounds reasonable. I wonder how many seats they install in the cockpit? The funny windows might intend to give some clue?
Anyway, so much better than hydrogen fantasies.

[fleigle]

The Piaggio certainly has that extra “vibe”, due to the closeness of the the prop blades to the trailing edge of the wing?.

[Herod]

Some 45 years ago, I was regularly flying a very high bypass unducted fan. Built by Rolls Royce. It was called the Dart :ok: Nothing much new under the sun.

[20driver]

Yet somehow, commercial jet aircraft still look pretty much the same as a 707/DC-8...
I started thinking about learning to fly in the early 90's and started hanging around the local FBO's etc. There was no end of publications full of all the amazing new concepts that were going to revolutionize flying. Well as td says nothing in the basic shape has changed.
At the same time the industry has done an amazing job of incrementally squeezing a bit more juice out of the lemon every year. I have seen the figure 1.4% annual improvement in fuel efficiency often quoted.
The same people who were promoting the "revolution "were also saying this improvement in fuel efficiency would stop.
Still it makes some sense for Airbus to take a flutter on the UDF - They have the money and you never know what you will learn along the way.
As they say never let perfection get in the way of good.

[Joe_K]

Funny that this is being bandied about as "news", Airbus and CFM launched an open fan flight test demonstrator programme back in July 2022, with press release and everything...

https://www.airbus.com/en/newsroom/press-releases/2022-07-airbus-and-cfm-international-launch-a-flight-test-demonstrator-for

[waito]

Funny that this is being bandied about as "news"

So you have seen this plane rendering with its cues before?

BTW, mentour pilot speculates about option for hydrogen tanks in the aft. Giving another purpose for the mid cabin doors.