viewtopic.php?f=3&t=1374685&hilit=boeing+officially+forms&start=1100#p20181211

Stein further says wing configurations will have to be modified for the very-high-bypass architectures under development for the UltraFan. A gear-driven fan sized to produce about 70,000-75,000 lb. of thrust, for example, will likely have a diameter of 140 in., compared to the 112-in.-dia. fan of the similarly rated Trent 1000 of today. “One option [the airframe-makers] could consider is to go for gullwing configurations and short nacelles mounted close to the wing,” he adds.

Ultrafan type engines would lift the 777x and A350 to ranges it wouldn't need to go only increasing weight for no practical benefit. Apart from that, such bypass ratios would lead to ~160'' fans on a 777x (currently 134'') and over ~150” for the A350 as well (118'' now). Modifications to these airframes would be extremely costly or perhaps impossible in economic sense. Improving chances (CAPEX and SFC wise) for airframes (new and old) that can more easily integrated such fan diameters. For the A350 it would perhaps mean an explosively successful, yet shortcut production run.

Both RR and GE recognise that long term gearing will be the way to go,particularly where there is a long cruise element to the flight.
To this end RR is working with a German company (subsidiary?) and GE has bought the Itslian company that provides the gearboxes for P&W.
Since no one is ever going to trust P&W to build a new Engine again and they are not on any widebodied aircraft these days there is simply no rush from the 'big 2'.Both have/are investing in 2 state of the art engines for their wide bodied customers and will be in no rush at all to replace these.They will need a decade or so to earn a good profit on them.
After that? Who knows -but yes probably.
The present flurry of activity has only been because there might be a pitch for a new 50klbs engine.
But as of the moment this looks like it will be a GE scale up of their direct drive leap engine.After all the 797 (if built) is not designed to be a long distance aircraft.No doubt the aircraft (if built) will be designed to take ultra high bypass engines to future proof it.

It depends on how easily the OEMs can take structure out of the airframe for lower MTOW, without significantly affecting payload-range, as any re-engine of the A350 or 777X will likely have to make do with less engine thrust than the originals, due to ground clearance issues, reducing max MTOW (i.e fuel volume). If sufficient weight can be taken out due to less fuel volume carried, the Re-engine may not have a range penalty due to the SFC advantage of the new turbofans.

This paradigm will relatively favor the 787, which has lower thrust requirements (i.e less fan diameter increase) , and has variants that can significantly benefit from the range increase due to SFC improvements. I wouldn't be surprised if a "787neo" comes with a further stretch, going further into 777 territory and leaving the 779 as the only "VLA" offering from B.

I doubt that a GTF by itself will give that much of a SFC gain on a 3-spool engine where the LPC is already running at a more optimal speed.
While GTF might become a standard technology on turbofans, it also may not. In particular, at PW we see that some of the issues may be indirectly GTF related.

I think that the turbofan engine will see a step-up improvement in the next decade after being redefined.

I also think that the current patent system is an impediment to significant advances in technologies in aerospace, because by the time an invention is designed, tested, certified and starts being delivered, the patent protection doesn't hold for much longer and offers little to no exclusvity advantage. To invest in major research, at least 30 years of patent protection needs to be guaranteed, as at least 10 years of that is lost to make it to market.

parapente wrote:

Since no one is ever going to trust P&W to build a new Engine again

Would you mind expanding on that point for me?

JustSomeDood wrote:

It depends on how easily the OEMs can take structure out of the airframe for lower MTOW, without significantly affecting payload-range, as any re-engine of the A350 or 777X will likely have to make do with less engine thrust than the originals, due to ground clearance issues, reducing max MTOW (i.e fuel volume). If sufficient weight can be taken out due to less fuel volume carried, the Re-engine may not have a range penalty due to the SFC advantage of the new turbofans.

This paradigm will relatively favor the 787, which has lower thrust requirements (i.e less fan diameter increase) , and has variants that can significantly benefit from the range increase due to SFC improvements. I wouldn't be surprised if a "787neo" comes with a further stretch, going further into 777 territory and leaving the 779 as the only "VLA" offering from B.

Your first paragraph confuses me. Yes, the propulsive efficiency is better with a larger and slower rotating fan with the same core. Separately the hotter the core, the more energy it can extract from the fuel. These are both desirable objectives, but have to be considered along with other issues including installation in the aeroplane, and its design objectives. From there on I am baffled.

The UltraFan concept will have a new set of gears to enable the larger slower fan, whilst allowing the core to rotate faster and thus be shorter, smaller and lighter. The RR Advance core probably will have some 'hotter' benefit, but maybe not as much as the GE 'much hotter' tech; but it will have lots of other new core tech in a two shaft design. We don't know if either the production UltraFan or the production Advance will have the benefit of a much hotter core, GE style. The P&W GTF has the benefit of gears and propulsive efficiency, but appears to lag both GE and to a lesser extent RR in the 'hotter' race.

If you presume that the UltraFan has been created to be ultimately fitted to a design which is already in production, then I suspect it may be an incorrect assumption. We have all seen the gull wing of the A380, long legged landing gears which will accommodate a large fan or propeller, and the rear mounted huge noisy fast rotating propellers of open rotor concepts.

There seems to me to be the possibility that the optimum propulsive efficiency of a super large slow rotating enclosed fan to avoid un-contained failures might be an avenue to consider for the distant future. Along with the appropriate amount of 'hotter'. Yes, it may need a new design of aeroplane. So?

Meanwhile, the current choices for a MoM are all less than the optimum in terms of engines, and therefore its design may be only a stepping stone.

Tail mounted trijets, above/behind a lifting body (Aurora D8 style) are probably inevitable at some point as jacking up the frames via landing gear or oddball wing arrangements aren't particularly appealing for safety (think gear up) or weight reasons alike.

I do wonder if at some point two fans driven by three high pressure units, or two HP and one electrical, could help 'hybridize' and avoid the single engine out limitations/penalties of twin engine pax designs.

Airbus has a patent for a trijet design to counter the issue of engines getting too large and heavy....

What about the good old 4-engines aircraft design?

tomcat wrote:

What about the good old 4-engines aircraft design?

Taxi645 wrote:

Improving chances (CAPEX and SFC wise) for airframes (new and old) that can more easily integrated such fan diameters.

I know of one that is still in production and that is said to receive a "massive update" around the time the ultrafans arrive.....

Waterbomber wrote:

I doubt that a GTF by itself will give that much of a SFC gain on a 3-spool engine where the LPC is already running at a more optimal speed.

Isn't it ironic then that the manufacturer that actually has the 3-spool architecture (RR) is the one with defined programs working towards GTF capability, while the one with 2-spool (GE) shows no signs of such?

2175301 wrote:

ap305 wrote:

Airbus has a patent for a trijet design to counter the issue of engines getting too large and heavy....

Never heard of a tri jet before.... except of course the half dozen or more that were in service for decades... (and I believe some are still flying - mainly as P2F's at this point).

I don't think an Airbus patent for a tri jet would prevent anyone from building one. There is a reason the industry went away from tri-jets. Those reasons have not vanished and will not just because engines get bigger and heavier.

I think we would see a new multi-engine on wings (4, 6, etc) before we would see the classic tri-jet design again.

Have a great day,

I am well aware of that.I should have been clearer.... the patent is for a new design which lowers the noise and maintanence costs associated with a trijet.

ap305 wrote:

Airbus has a patent for a trijet design to counter the issue of engines getting too large and heavy....

Never heard of a tri jet before.... except of course the half dozen or more that were in service for decades... (and I believe some are still flying - mainly as P2F's at this point).

I don't think an Airbus patent for a tri jet would prevent anyone from building one. There is a reason the industry went away from tri-jets. Those reasons have not vanished and will not just because engines get bigger and heavier.

I think we would see a new multi-engine on wings (4, 6, etc) before we would see the classic tri-jet design again.

Have a great day,

globetrotter94 wrote:

Waterbomber wrote:

I doubt that a GTF by itself will give that much of a SFC gain on a 3-spool engine where the LPC is already running at a more optimal speed.

Isn't it ironic then that the manufacturer that actually has the 3-spool architecture (RR) is the one with defined programs working towards GTF capability, while the one with 2-spool (GE) shows no signs of such?

RR is walking the limits with its 3-spool design.
They probably want to compete in the next narrow body era. This is probably why they are trying to define something that works at all scales, unlike the 3-shaft design which is difficult to apply to a narrow body engine.

Their ultrafan is aiming at that, but I'm pretty sure that this is not the end of the line for improvements on the turbo fan architecture

I think that by 2050, aircraft should be able to fly with half the fuel burn of today's newest aircraft.

JustSomeDood wrote:

It depends on how easily the OEMs can take structure out of the airframe for lower MTOW, without significantly affecting payload-range, as any re-engine of the A350 or 777X will likely have to make do with less engine thrust than the originals, due to ground clearance issues, reducing max MTOW (i.e fuel volume). If sufficient weight can be taken out due to less fuel volume carried, the Re-engine may not have a range penalty due to the SFC advantage of the new turbofans.

This paradigm will relatively favor the 787, which has lower thrust requirements (i.e less fan diameter increase) , and has variants that can significantly benefit from the range increase due to SFC improvements. I wouldn't be surprised if a "787neo" comes with a further stretch, going further into 777 territory and leaving the 779 as the only "VLA" offering from B.

This is why I'm thinking a lightweight 787 will be the new NMA. It will use 50,000lb thrust current tech engines but keep the ground clearance of the current 787-10 76,000lb engines. In 20 years time it will evolve and be the only design that can accept 15:1 bypass ratio engines and the range will increase. So a 180T 787 in 20 years time might be flying the same payload the same distance as a current 220T 787.

The A350-1000 for instance would be worse off in terms of ground clearance.

Super27 wrote:

parapente wrote:

Since no one is ever going to trust P&W to build a new Engine again

Would you mind expanding on that point for me?

I would very much like to know this as well..

GatorClark wrote:

Super27 wrote:

parapente wrote:

Since no one is ever going to trust P&W to build a new Engine again

Would you mind expanding on that point for me?

I would very much like to know this as well..

Aircraft waiting for engines at unprecedented levels.
Engine shutdown/failures in flight at unprecedented levels.
Aircraft grounded at unprecedented levels.
Fixes introduced that then also failed.
Reverting back to the original design.

Pratt puts out press releases saying everything is now fine and then there's another massive problem. To put out such press releases they are either:
1) Flat out lieing.
2) Totally incompetent and they believe they have fixed it.
3) Extremely optimistic that it will get fixed so press release comes out too early.

This would be acceptable in 1960 not 2018.

Pratt could never be the single engine provider to a new design for at least a decade.

Egerton wrote:

JustSomeDood wrote:

It depends on how easily the OEMs can take structure out of the airframe for lower MTOW, without significantly affecting payload-range, as any re-engine of the A350 or 777X will likely have to make do with less engine thrust than the originals, due to ground clearance issues, reducing max MTOW (i.e fuel volume). If sufficient weight can be taken out due to less fuel volume carried, the Re-engine may not have a range penalty due to the SFC advantage of the new turbofans.

This paradigm will relatively favor the 787, which has lower thrust requirements (i.e less fan diameter increase) , and has variants that can significantly benefit from the range increase due to SFC improvements. I wouldn't be surprised if a "787neo" comes with a further stretch, going further into 777 territory and leaving the 779 as the only "VLA" offering from B.

Your first paragraph confuses me. Yes, the propulsive efficiency is better with a larger and slower rotating fan with the same core. Separately the hotter the core, the more energy it can extract from the fuel. These are both desirable objectives, but have to be considered along with other issues including installation in the aeroplane, and its design objectives. From there on I am baffled.

The UltraFan concept will have a new set of gears to enable the larger slower fan, whilst allowing the core to rotate faster and thus be shorter, smaller and lighter. The RR Advance core probably will have some 'hotter' benefit, but maybe not as much as the GE 'much hotter' tech; but it will have lots of other new core tech in a two shaft design. We don't know if either the production UltraFan or the production Advance will have the benefit of a much hotter core, GE style. The P&W GTF has the benefit of gears and propulsive efficiency, but appears to lag both GE and to a lesser extent RR in the 'hotter' race.

If you presume that the UltraFan has been created to be ultimately fitted to a design which is already in production, then I suspect it may be an incorrect assumption. We have all seen the gull wing of the A380, long legged landing gears which will accommodate a large fan or propeller, and the rear mounted huge noisy fast rotating propellers of open rotor concepts.

There seems to me to be the possibility that the optimum propulsive efficiency of a super large slow rotating enclosed fan to avoid un-contained failures might be an avenue to consider for the distant future. Along with the appropriate amount of 'hotter'. Yes, it may need a new design of aeroplane. So?

Meanwhile, the current choices for a MoM are all less than the optimum in terms of engines, and therefore its design may be only a stepping stone.

Let me break this down for you:
-OEMs want better ROI for their clean-sheet designs(A350/777X-ish) -> Re-engine as way to reduce costs vs another clean-sheet design.
-GTF/ultrafan style turbofans require significantly larger fan diameter for a given amount of thrust
-Therefore, hanging ultrafans of the same thrust class to the A350/777X may cause ground clearance issues. (A 97k ultrafan would likely drag the ground on an A35k).
-To accept a re-engine, the OEMs must then accept turbofans with less thrust than the originals (A 777X neo is likely going to be restricted to turbofans <100k lbf)
-Less thrust = less MTOW for a given airframe, which can only come out of 3 things, fuel volume (range), payload, and airframe weight.
-OEMs would loathe to have to market an aircraft re-engine with less capability than its original, so the other option must be to reduce airframe weight, such that the inevitable fuel volume reduction can be balanced out by the SFC improvements of the new engine.

GatorClark wrote:

Super27 wrote:

parapente wrote:

Since no one is ever going to trust P&W to build a new Engine again

Would you mind expanding on that point for me?

I would very much like to know this as well..

Pretty straightforward really...

Pratt's had a rather unbroken streak of abject f#ckups on widebody engines (PW4092, PW4098, PW4173, etc), which is why they haven't been chosen by Boeing nor Airbus to power a new widebody on their own for the last 19yrs.

Considering how terrible Pratt's rollouts of recent narrowbody applicants have been, it isn't all that inconceivable that the OEMs might not seriously consider them for upcoming new narrobodies either. Sad, but certainly plausible.

I know I raised the OP's point in the A380-900NEO thread, but I'm not sure I was totally right.
The OEM's (engine and frame) are working on new slim-line nacelles that could dramatically shrink ratio of nacelle/fan diameters.
Check out page 12 of this RR pdf: https://www.aerosociety.com/Assets/Docs ... 4_RR_1.pdf

Eyeball estimate is that nacelle diameter is only ~5% more than fan diameter. So a 75k engine's nacelle diameter would be ~147in.
A350's nacelle diameter is 155in, so 75k fan should be fine. 97k as for A35K? Maybe not, unless RR supercharges an ~85k engine, which would impact SFC and mx.

If the OEM's succeed in shrinking nacelle size, this will probably come at some Cdp penalty. But that's worth it for the SFC gain.

What are the downsides​ of putting the engines above the wing like the Honda bizjet?

Just as additional info: the diameters for the A350 and 777x I estimated in the opening post already incorporate a ~9% thrust reduction.

spudh wrote:

What are the downsides​ of putting the engines above the wing like the Honda bizjet?

There's a different magnitude of support structures needed to support a turbofan that a strong guy at the gym could deadlift above the wing vs doing the same with something like a Trent XWB....

Boeing and Airbus will definitely avoid any P+W offering for their widebodies.

P+W has failed to deliver on the GTF and has caused Airbus serious harm. This will not be lost on Boeing as it works towards choosing an engine for 797.

Buyers remorse...ask Akbar alBakkar...

To this end RR is working with a German company (subsidiary?)

For clarification:
On the one hand, RR has its very own site in Berlin-Dahlewitz, which does design & assembly of small engines. It is there that the UltraFan is being tested. The site comes from their former JV with BMW to produce the BR700 engine.
On the other hand, RR has estalished a JV with Liebherr in Friedrichshafen, for the manufacturing of gearboxes for the UltraFan.

JustSomeDood wrote:

Egerton wrote:

JustSomeDood wrote:

It depends on how easily the OEMs can take structure out of the airframe for lower MTOW, without significantly affecting payload-range, as any re-engine of the A350 or 777X will likely have to make do with less engine thrust than the originals, due to ground clearance issues, reducing max MTOW (i.e fuel volume). If sufficient weight can be taken out due to less fuel volume carried, the Re-engine may not have a range penalty due to the SFC advantage of the new turbofans.

This paradigm will relatively favor the 787, which has lower thrust requirements (i.e less fan diameter increase) , and has variants that can significantly benefit from the range increase due to SFC improvements. I wouldn't be surprised if a "787neo" comes with a further stretch, going further into 777 territory and leaving the 779 as the only "VLA" offering from B.

Your first paragraph confuses me. Yes, the propulsive efficiency is better with a larger and slower rotating fan with the same core. Separately the hotter the core, the more energy it can extract from the fuel. These are both desirable objectives, but have to be considered along with other issues including installation in the aeroplane, and its design objectives. From there on I am baffled.

The UltraFan concept will have a new set of gears to enable the larger slower fan, whilst allowing the core to rotate faster and thus be shorter, smaller and lighter. The RR Advance core probably will have some 'hotter' benefit, but maybe not as much as the GE 'much hotter' tech; but it will have lots of other new core tech in a two shaft design. We don't know if either the production UltraFan or the production Advance will have the benefit of a much hotter core, GE style. The P&W GTF has the benefit of gears and propulsive efficiency, but appears to lag both GE and to a lesser extent RR in the 'hotter' race.

If you presume that the UltraFan has been created to be ultimately fitted to a design which is already in production, then I suspect it may be an incorrect assumption. We have all seen the gull wing of the A380, long legged landing gears which will accommodate a large fan or propeller, and the rear mounted huge noisy fast rotating propellers of open rotor concepts.

There seems to me to be the possibility that the optimum propulsive efficiency of a super large slow rotating enclosed fan to avoid un-contained failures might be an avenue to consider for the distant future. Along with the appropriate amount of 'hotter'. Yes, it may need a new design of aeroplane. So?

Meanwhile, the current choices for a MoM are all less than the optimum in terms of engines, and therefore its design may be only a stepping stone.

Let me break this down for you:
-OEMs want better ROI for their clean-sheet designs(A350/777X-ish) -> Re-engine as way to reduce costs vs another clean-sheet design.
-GTF/ultrafan style turbofans require significantly larger fan diameter for a given amount of thrust
-Therefore, hanging ultrafans of the same thrust class to the A350/777X may cause ground clearance issues. (A 97k ultrafan would likely drag the ground on an A35k).
-To accept a re-engine, the OEMs must then accept turbofans with less thrust than the originals (A 777X neo is likely going to be restricted to turbofans <100k lbf)
-Less thrust = less MTOW for a given airframe, which can only come out of 3 things, fuel volume (range), payload, and airframe weight.
-OEMs would loathe to have to market an aircraft re-engine with less capability than its original, so the other option must be to reduce airframe weight, such that the inevitable fuel volume reduction can be balanced out by the SFC improvements of the new engine.

Thanks. The target of a new engine design is to reduce the weight of fuel being used, because of its effect on the fuel costs and the scale of aeroplane required to lug the dead weight of said fuel from A to B. Two ways to reduce fuel weight are better propulsive efficiency and a hotter core.

Whether this new engine design is used on an existing aeroplane or a new design of aeroplane is a matter for the joint efforts of the engine and aeroplane OEMs. There are trade-offs, the details of which are above my pay scale. But:

1. Airline customers decide which trade-off suites them best. They are a driving force, and they themselves are driven by their customers.
2. After a time, there is a cross-over between the cost/benefit of the existing aeroplane design and its manufacturing infrastructure, and a new design.
3. If the benefits of a step change in fuel weight are large enough, new aeroplane designs will be offered to accommodate the better engines.
4. Aero engine design is generally the critical path towards better aeroplanes.
5. The current optimum trade-off suggests 2 large engines under the wings.
6. Future trade-offs may include 3, 4 or 6 lower thrust but more efficient engines.
7. This may result in lighter smaller aeroplanes being much more efficient than today's best to deliver the same payload the same distance.

I hope this helps?

DoesGTF gear box scale well with power?

LDRA wrote:

DoesGTF gear box scale well with power?

To some large extent I an guessing, but I guess that there may be 3 basic gearboxes, aligned to small, medium and large engines. Within that, the large seems to me to be the most difficult, it is transmitting enormous amount of power, and in doing so it is generating a lot of heat. Mechanical efficiency (ME) is the key here. If RR achieve say 1% ME on a 100,000 horse power gearbox, that produces 1,000 hp's worth of heat, which has to be dissipated. With a small gearbox this is much more manageable. I stand ready to be corrected.

spudh wrote:

What are the downsides​ of putting the engines above the wing like the Honda bizjet?

Aerodynamically, I believe a smooth and uninterrupted airflow on the upper surface is more important to wing performance than that on the lower surface.

SomebodyInTLS wrote:

spudh wrote:

What are the downsides​ of putting the engines above the wing like the Honda bizjet?

Aerodynamically, I believe a smooth and uninterrupted airflow on the upper surface is more important to wing performance than that on the lower surface.

I think that is correct. The lower pressure on that side of the wing means the airflow is more vulnerable to becoming detached prematurely decreasing lift.

It's the same reason why you see swannecks to mount the rearwings on the high pressure side on a racing car.

parapente wrote:

Since no one is ever going to trust P&W to build a new Engine again and they are not on any widebodied aircraft these days there is simply no rush from the 'big 2'.Both have/are investing in 2 state of the art engines for their wide bodied customers and will be in no rush at all to replace these.They will need a decade or so to earn a good profit on them.
After that? Who knows -but yes probably.

Agreed. However I do expect ultrafan bypass class engines to arrive on a few other platforms first. If the economic pressure from those models, even if their capacity or range doesn't completely overlap, becomes too great their hand might be forced sooner or later.