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Airbus Inbetween A350 & A380, Market?  
User currently offlineKeesje From , joined Dec 1969, posts, RR:
Posted (5 years 5 months 3 weeks 7 hours ago) and read 32767 times:

Based on A350 XWB

- Beefed up where neccesary, new tail section
- 160 Klbs left after an engine failure
- 425 Seats, lots of cargo capasity
- ULH without ETOPS



(Based on drawing from Flightglobal.com)

Would there be a market for such a derivative?

http://www.google.com/patents?vid=USPAT7240877

72 replies: All unread, showing first 25:
 
User currently offlineNorCal From United States of America, joined Mar 2005, 2459 posts, RR: 5
Reply 1, posted (5 years 5 months 3 weeks 7 hours ago) and read 32767 times:



Quoting Keesje (Thread starter):
Would there be a market for such a derivative?

Nope because it is a tri-jet. As nice as they are to look at it is no longer a practical design. A larger (than A350) composite twin with engines that can produce 115-120 lbs of thrust each would be a better bet to fill that gap.


User currently offlineVirginFlyer From New Zealand, joined Sep 2000, 4575 posts, RR: 41
Reply 2, posted (5 years 5 months 3 weeks 4 hours ago) and read 32767 times:



Quoting Keesje (Thread starter):
ULH without ETOPS

ETOPS is slowly, but surely, going the way of the dodo. I am not certain about in other jurisdictions, but here in Australia it has already been replaced as a concept by EDTO (Extended Diversion Time Operations), which allows flights beyond 180 minutes from a suitable alternate, subject to certain conditions, and requires all aircraft, not just twins, to meet conditions for flights beyond 180 minutes from a suitable alternate. I summarised the relevant regulations in QF To Defer 787s (by NA Jun 9 2009 in Civil Aviation) and I'll do so again here:

Quote:
EDTO is detailed in CAO 82.0, which can be downloaded at http://www.casa.gov.au/wcmswr/_asset...in/download/orders/cao82/8200.pdf. Sections 3B, 3BA, 3BB, 3BC and 3BD, and appendices 3, 4, 5 and 6 are the relvant sections.

In summary: operations by a twin turbine-engined aeroplane up to 180 minutes from an EDTO (extended diversion time operation) alternate aerodrome at 1 engine inoperative cruise speed in ISA and still air conditions may be permitted if certain conditions are met.

For operations beyond 180 minutes from an EDTO alternate aerodrome at 1 engine inoperative cruise speed in ISA and still air conditions for any aeroplane, the operator must meet the conditions for issue of an EDTO approval, and the aircraft must have serviceable for dispatch:

• an FQIS (fuel quantity indicating system)
• if it is required for EDTO - the APU (including electrical and pneumatic supply to its designated capability)
• a communication system, in addition to any mentioned in the AIP [Aeronautical Information Publication], capable of providing direct communication of landline voice quality between the flight crew and air traffic services, and the flight crew and the operator.

Additionally, for twin turbine-engined aircraft, the specific airframe/engine combination must already be authorised for operations up to 180 minutes from an EDTO (extended diversion time operation) alternate aerodrome at 1 engine inoperative cruise speed in ISA and still air conditions, and the auto throttle system must be serviceable for dispatch.

For operations beyond 240 minutes from an EDTO alternate aerodrome at 1 engine inoperative cruise speed in ISA and still air conditions for twin turbine-engined aeroplanes, approval may only be granted if the specific airframe/engine combination has been operating for a minimum of 24 months under an EDTO approval.

I believe the FAA had a notice of proposed rulemaking along the similar lines, I think they may have termed in LROPS. Last I heard is that there were some disagreements, and it wasn't being implemented in its entirety, but that it was remaining on the agenda. Admittedly I haven't been following it too closely, so I'm not certain where the FAA or other NAAs are at with it as of today.

Personally, I believe the 747 and the A380 will be the last subsonic commercial jet airliners not to be twin-engined. As for what Airbus chose to place between the A350 and the A380? Well, I'm not convinced there is a strong need for such an aircraft. Anecdotally, the only aircraft occupying that size category, the 747, has not seen orders for its passenger version in substantial numbers for the last decade. I don't buy into the argument that it is not experiencing success because it is an old design. I think the more significant issues are that the two main selling points of the 747 - range and capacity - are now being occupied by the other aircraft. The 777/787/A350 are all offering range, and the A380 is offering capacity (and evidently range as well...) I think if Airbus thought this market between the big twins and the A3XX-100 was enough to justify an aircraft, they would have sized the A380 such that it could have been shrunk to the A3XX-50 that they had been studying. Instead, we saw them size the aircraft such that the A3XX-100, which we now know as the A380-800, was the minimum size variant.

V/F



"So powerful is the light of unity that it can illuminate the whole earth." - Bahá'u'lláh
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 3, posted (5 years 5 months 3 weeks 3 hours ago) and read 32767 times:



Quoting Keesje (Thread starter):
ULH without ETOPS

Not in the US. Just as VirginFlyer described above for Australia, FAA extended the ETOPS rules to all aircraft, not just twins.

Quoting Keesje (Thread starter):
425 Seats, lots of cargo capasity

Isn't that bumping pretty hard against the A340? Airbus hasn't said they're shutting that down yet.

Tom.


User currently offlineScouseflyer From United Kingdom, joined Apr 2006, 3398 posts, RR: 9
Reply 4, posted (5 years 5 months 2 weeks 6 days 23 hours ago) and read 32767 times:



Quoting Tdscanuck (Reply 3):
Isn't that bumping pretty hard against the A340? Airbus hasn't said they're shutting that down yet.

Aren't the customers doing that for them by not buying any A340s anymore?


User currently offlineZvezda From Lithuania, joined Aug 2004, 10511 posts, RR: 64
Reply 5, posted (5 years 5 months 2 weeks 6 days 22 hours ago) and read 32767 times:

I agree with the other posters that ETOPS will not be an issue after the time needed for development because tris and quads are being subjected to the same requirements as twins.

I also agree that the airlines are not interested in tris. The efficiency of a twin is too much better.

Your design would need a fifth pair of doors.

Although a third engine and all the structure needed to support it would be very heavy, I don't believe it would be heavy enough for to balance adding 12 frames forward of Door 2. Probably 2 or 3 of those frames would need to be aft of Door 3. That might require taller maingear to avoid tail-strikes. I expect the 6-wheel bogeys of the A350-1000's maingear would suffice after strengthening.

I think your Ecoliner concept would be much, much more attractive to the airlines.


User currently offlineGlobeEx From Germany, joined Aug 2007, 742 posts, RR: 5
Reply 6, posted (5 years 5 months 2 weeks 6 days 21 hours ago) and read 32767 times:

I will bring up another arguement against a tri-jet on the bases of an A350.
The A350 is already narrower than the 777. We all know that the lenght of the A340-600 already hurt the performance of latter, as due to lenght some extra weight was needed to get certain stability. Now imagine an A350, longer than the A350-1000. With the extra weight of a third engine in the back you would at least need as much strengthening as you did on the A340-600 making it most probably not (even) competitive to the B748, which isn't quite a hotseller right now.

GlobeEx



As you may presently yourself be fully made aware of, my grammar sucks.
User currently offlineKeesje From , joined Dec 1969, posts, RR:
Reply 7, posted (5 years 5 months 2 weeks 6 days 21 hours ago) and read 32767 times:

Quoting VirginFlyer (Reply 2):
Anecdotally, the only aircraft occupying that size category, the 747, has not seen orders for its passenger version in substantial numbers for the last decade.

Well 95% of current VLA's is service falls inbetween the A350 and A380.

The secret behind this trijet would be superior MTOW compared to any twin, around 900 klbs.



An OEW of about 420-430 klbs (50 klbs more then 777-300ER) leaves 450 lbs for fuel and payload. This making feasible city pairs twins cannot do in an efficient way.



More importantly it can do more Asia-Europe and Asia-US flights faster with lots of Cargo, superior to big twins like 777NG and A350XWB, with far less diversions.

A similar twin engined aircraft would require engines of at least 175.000 lbs each (asymetrical thrust compensation). That is 50% more then a GE90-115. I think thats a step to far for engine OEMS, ROI would never be achieved.

A trijet could use existing ~80 klbs RR, GE and EA engines variants. An additional center gear A340-600 style would probably be most suitable. http://widebodyaircraft.nl/a346virg.jpg. Systems, CRFP fuselage, cabins, cockpit would be A350XWB, CRFP wings would be strenghtened and probably require adjusted high lift devices.

A trijet would enter quad territory, not the segment where twins excel.

[Edited 2009-06-12 02:27:28]

User currently offlineUnited Airline From Hong Kong, joined Jan 2001, 9191 posts, RR: 15
Reply 8, posted (5 years 5 months 2 weeks 6 days 21 hours ago) and read 32767 times:

Boeing's proposed BWB as well as Y2 double decker are tri-jets

User currently offlineYULWinterSkies From United States of America, joined Jun 2005, 2184 posts, RR: 5
Reply 9, posted (5 years 5 months 2 weeks 6 days 20 hours ago) and read 32767 times:



Quoting VirginFlyer (Reply 2):
I don't buy into the argument that it is not experiencing success because it is an old design.

You're right i think. Boeing developed a 744ER and a 744ERF (both are modern derivatives of the 744) and these did not meet much success. And this is not including the 748, which has yet to be qualified as successful in my opinion.
Speaking of design, the 737 is much, much older and still very successful since it's been upgraded the right way. The 744 may have an old design, but i hardly qualify it as 'old' airplane, and it still is the backbone of the long-haul high-yield fleet of many carriers (QF, LH, BA, CX to name a few)

Quoting Tdscanuck (Reply 3):
Isn't that bumping pretty hard against the A340? Airbus hasn't said they're shutting that down yet.

For the -600, yes, it would be bumping hard. The A350-1000 already does that job though.

Quoting Scouseflyer (Reply 4):
Aren't the customers doing that for them by not buying any A340s anymore?

This is true for the A340-300, the -600 is somewhat different for now.



When I doubt... go running!
User currently offlineAstuteman From United Kingdom, joined Jan 2005, 10189 posts, RR: 97
Reply 10, posted (5 years 5 months 2 weeks 6 days 20 hours ago) and read 32767 times:
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Quoting Tdscanuck (Reply 3):
Isn't that bumping pretty hard against the A340? Airbus hasn't said they're shutting that down yet.

The A350-1000 is actually bigger than the A340-600 already - just....  Smile

So Airbus have actually already closed the gap below the A380 in their range (a tiny, tiny bit..  Wink )

Rgds


User currently offlineKeesje From , joined Dec 1969, posts, RR:
Reply 11, posted (5 years 5 months 2 weeks 6 days 20 hours ago) and read 32767 times:



Quoting YULWinterSkies (Reply 9):
Quoting VirginFlyer (Reply 2):
I don't buy into the argument that it is not experiencing success because it is an old design.

You're right i think. Boeing developed a 744ER and a 744ERF (both are modern derivatives of the 744) and these did not meet much success.

I think a much ignored disadvantage of the 747-8i is that it is unpracticle in meeting current passenger cabin standards. 10Aabreast seating gives seatwidth uncompetative with 777, A350 and A380, specially for long flights.

The uppperdeck is constrained to use efficiently for new and future First and Business class cabins and the Azone seating hard to make compatible with angular shaped cabins in the rest of the fleet.

Then there is a 6 or 7 abreast business class maindeck trade off. 777, a380, 787, A330/40 and A350 have pretty straight forward cabin flexibility meeting industry standards.

On maintenance : the 747-8i has some state of the art systems similar to 787. Also it has sixties roots under its skin, making extensive inspections and frequent swaps at component level neccessary unlike newer generation aircraft.


User currently offlineJerseyFlyer From United Kingdom, joined May 2007, 665 posts, RR: 0
Reply 12, posted (5 years 5 months 2 weeks 6 days 19 hours ago) and read 32767 times:

What would a "minimum cost" stretch of the A3510 deliver?

Say to the length of the A346 (for which the additional width of the A3510 over the A346 should require less strengthening and so not lose so much efficiency due to weight gain).

Plus 77W class engines but with Trent XWB or GenX technology.


User currently offlineZvezda From Lithuania, joined Aug 2004, 10511 posts, RR: 64
Reply 13, posted (5 years 5 months 2 weeks 6 days 19 hours ago) and read 32767 times:



Quoting Astuteman (Reply 10):
The A350-1000 is actually bigger than the A340-600 already - just.

That's right. The cabin floor area of the A350-1000 will be 4.4 square meters larger than that of the A340-600 which is about one row of Y seats.

I don't see much chance that the A350 will be stretched beyond the A350-1000, but it's possible. If there ever would be an A350-1100, I would expect it to be a twin and keep the A350's wings. It would need taller and stronger landing gear.


User currently offlineGlobeEx From Germany, joined Aug 2007, 742 posts, RR: 5
Reply 14, posted (5 years 5 months 2 weeks 6 days 19 hours ago) and read 32767 times:

Quoting JerseyFlyer (Reply 12):

The engines, if needed to be devoloped (with some current technology) could make an investment of around 1 billion alone(think, that's what was invested for the Trent 556 on the A340-500/600). That's why GE jumped of the A340-600 waggon even though they already signed, as they couldn't see how they could get a return on their estimated 1 billion investment.

So the whole project would cost around 3,5 billion bucks.

[Edited 2009-06-12 04:28:23]


As you may presently yourself be fully made aware of, my grammar sucks.
User currently offlineZvezda From Lithuania, joined Aug 2004, 10511 posts, RR: 64
Reply 15, posted (5 years 5 months 2 weeks 6 days 18 hours ago) and read 32767 times:



Quoting JerseyFlyer (Reply 12):
What would a "minimum cost" stretch of the A3510 deliver?

Say to the length of the A346 (for which the additional width of the A3510 over the A346 should require less strengthening and so not lose so much efficiency due to weight gain).

Plus 77W class engines but with Trent XWB or GenX technology.

A minimum cost stretch of the A350-1000 would use Trent XWB engines with the same fan diameter. I'm sure RR could find some additional thrust in the future. However, it would probably not be enough to raise MTOW to the extent needed to maintain the full passenger range of the A350-1000 -- even if fuel capacity were not an issue. To achieve the same field performance with the same wing, an increase in MTOW of X% requires an increase in thrust of X^1.5%. So, a minimum cost stretch of the A350-1000 would involve compromises of range, MTOW, and field performance.


User currently offlineRheinwaldner From Switzerland, joined Jan 2008, 2262 posts, RR: 5
Reply 16, posted (5 years 5 months 2 weeks 6 days 18 hours ago) and read 32767 times:



Quoting Zvezda (Reply 5):
The efficiency of a twin is too much better.

Why? Just because current market trends seem to suggest that there is no dogma that says that!

Quoting GlobeEx (Reply 6):
The A350 is already narrower than the 777. We all know that the lenght of the A340-600 already hurt the performance of latter, as due to lenght some extra weight was needed to get certain stability.

That is true. However I consider the A350 a far better platform to grow beyond A351/773ER size than the 787:
- It has a 9 abreast cross section vs. 8.5 for the 787
- It has built-in more MTOW/wing area reserves. The wing is huge.
- The 787 uses a production/outsourcing model which already now seems to be less than optimal.
- The 787 is somehow heavier than it should. I assume it is overbuilt. In ten years the technology that makes the 787 look old fashionned will probably be here.
- The engines for the current A350 models already cover a larger thrust range than those of the 787.

Quoting Keesje (Reply 7):
The secret behind this trijet would be superior MTOW compared to any twin, around 900 klbs.

 checkmark  This is very true and could indead be the reason for a big surprise to the twin fans in the future. There are some smart aspects of the quad-/trijet solution:
- All other things equal a quad only needs 66% of installed thrust (you know that already)
- In theory this allows to reduce the weight of the installed engines (not by 66% but with net gains). I see no reason why one day this theoretic advantage will not materialize.

Looking from the other side taking a twin and putting four engines on it would increase the available MTOW capability significantly (as smart Keesje said, I really mean it). In other words it may take a small effciency hit but any of the 787, 777, A330, A350 could offer a large MTOW boost just by mounting four engines on it. Ah, I forgot in case of the A330 it is exactly what happened and has been sold in the hundreds! By this simple measure (offering the 2- or 4-engine option) the A330/A340 became the aicraft family that covers by far the largest payload/range area.

Quoting Keesje (Reply 7):
A trijet could use existing ~80 klbs RR, GE and EA engines variants.

That is an important aspect that is ignored almost all the time. The engine industry does not support the whole thrust range with top-notch engines. There are engine classes. E.g. the A340NG uses an engine that is off the beaten track for engine classes. This simple fact damaged the A340NG's prospects probably quite a bit. In such cases there is no incentive to reach the highest heights by the egine OEM's. Often there isn't even a second offering that pushes the technology by competition. The 777 is a rare example where a single product defined an engine class and made it a success (but even here the fact that three vendors went after the cake should not be underestimated). But don't expect a larger twin that requires even more thrust than the 777 to repeat that success story on the engine side. That is not a given. Especially as a larger plane than the 777 would not generate the same market volume as the 777 did.

I can see even a pattern that the size of the most modern engine at a time (which usualy is accompanied by similar engines from other OEM's) dictates the size of the aircrafts on the market that use a different number of engines. E.g. the engine class used to power the 747 resulted in a plane with 3/4 of the 747-size when installed on the trijets. Later the same power class was used for twins with roughly half the size of the 747.

B.t.w. thinking in engine classes also reveals why this big gap between the A321 and the 783 exists. It exactly reflects the lack of modern engines in the required thrust range. There is simply not the incentive to cover the thrust range between the CFM and the GEnX engines with new top-notch engines by several engine OEM's. The A340NG is the last airframe which required a new engine class. The success is not so convincing.


User currently offlineGlobeEx From Germany, joined Aug 2007, 742 posts, RR: 5
Reply 17, posted (5 years 5 months 2 weeks 6 days 18 hours ago) and read 32767 times:



Quoting Rheinwaldner (Reply 16):
Quoting GlobeEx (Reply 6):
The A350 is already narrower than the 777. We all know that the lenght of the A340-600 already hurt the performance of latter, as due to lenght some extra weight was needed to get certain stability.

That is true. However I consider the A350 a far better platform to grow beyond A351/773ER size than the 787:

Of course it is! I only said that the A350 is smaller in diameter than the 77W. As the 787 is even smaller than the A350, it is obvious what I would think about such an idea concering the 787. The fact that Boeing doesn't even seem to bring out the 787-10 in the near future says enough I guess.



As you may presently yourself be fully made aware of, my grammar sucks.
User currently offlineZvezda From Lithuania, joined Aug 2004, 10511 posts, RR: 64
Reply 18, posted (5 years 5 months 2 weeks 6 days 17 hours ago) and read 32767 times:



Quoting Rheinwaldner (Reply 16):
Why? Just because current market trends seem to suggest that there is no dogma that says that!

You're right that the market trends don't explain why twins are more efficient, though they certainly provide evidence that's it's true. Every twin now in production sold well during the last sales boom (with the arguable exception of the 767). Every quad sold poorly. The reason for that has everything to do with efficiency.

I can give you two reasons why a smaller number of larger engines is more efficient than a larger number of smaller engines.
- Thrust is proportional to the square of the fan diameter. Fan tip clearance losses are proportional to the fan diameter.
- The turbulence created by pushing air through a turbofan is a type of inefficiency. The turbulence is proportional to the fan diameter, while the thrust is still proportional to the square of the fan diameter.
So, doubling the fan diameter yields about four times the thrust, while substantial components of inefficiency are only doubled.

Quoting Rheinwaldner (Reply 16):
I consider the A350 a far better platform to grow beyond A351/773ER size than the 787:
- It has a 9 abreast cross section vs. 8.5 for the 787
- It has built-in more MTOW/wing area reserves. The wing is huge.
- The 787 uses a production/outsourcing model which already now seems to be less than optimal.
- The 787 is somehow heavier than it should. I assume it is overbuilt. In ten years the technology that makes the 787 look old fashioned will probably be here.
- The engines for the current A350 models already cover a larger thrust range than those of the 787.

I agree completely that, for any given length longer than the mooted 787-10, the A350 is a better candidate for a stretch than the 787 and I agree with your first, second, and fifth reasons why. Regarding your third reason, I don't see any evidence that the 787's outsourcing/production model is suboptimal and I don't see how that could be relevant to suitability for a stretch. Regarding your fourth reason, being overbuilt makes an airliner more not less suitable to be stretched. We hear this ad nauseum as a justification for the proposed A380-900.


User currently offlineKeesje From , joined Dec 1969, posts, RR:
Reply 19, posted (5 years 5 months 2 weeks 6 days 16 hours ago) and read 32767 times:

For a 425 seat ULH aircraft of 900 klbs an a engines for a twin configuration does not exist. Nor are there any plans. Nor can I imagine a good business case for one either.



To conclude there can be no market in the 370-500 seat segment is risky / speculative. As said all VLAs' (except 20) currently in operation fall in the this segment. Many say the A380 is just to big for many airlines.

Twins are not everything for everybody. Above 5000nm you start off loading payload in most cases. Yes an A350XWB / B777-300ER can do 8000nm. Sea level, still air, straight line, zero cargo, limited reserves. At max payload the 777-300ER is limitted to 5500nm (sea level, still air, straight line, limited reserves).

http://www.airliners.net/uf/536877400/1178389999oRBNuS.jpg

This A370 would be a different segment. Payload range nearly a 1-1 Boeing 747-400 replacement. State of the art with bigger, less, more fuel efficient engines. For relative low development costs (compared to something entirely new) and commonality to the A350XWB family.


User currently offlineRheinwaldner From Switzerland, joined Jan 2008, 2262 posts, RR: 5
Reply 20, posted (5 years 5 months 2 weeks 6 days 16 hours ago) and read 32767 times:



Quoting Zvezda (Reply 18):
So, doubling the fan diameter yields about four times the thrust, while substantial components of inefficiency are only doubled.

I can follow your analysis and I agree except with this:

Quoting Zvezda (Reply 18):
The turbulence is proportional to the fan diameter

The turbulence is IMO proportional to the fan area which mean it is proportional with the square of the fan diameter too.

And - those effects are not significant. We speak of thermic machines not yielding ever more than about 30% efficiency. That means the big losses (~60..70%) are not affected by the fan diameter.

Plus the quad only needs 66% of the installed power. That means at cruise the engine operates closer to the max thrust point. In other words the thrust range to be covered is more narrow.

Quoting Zvezda (Reply 18):
Regarding your third reason, I don't see any evidence that the 787's outsourcing/production model is suboptimal and I don't see how that could be relevant to suitability for a stretch.



Quoting Zvezda (Reply 18):
Regarding your fourth reason, being overbuilt makes an airliner more not less suitable to be stretched.

Overbuilt in the sense of too rigid. On the save side regarding mechanical stability. Virtually unusable, subject to being stripped down over time. Concessions to CFRP uncertainties. There is not a 100% knowledge how much material is required to support force X. There are margins built in. The A388 has the physical configuration (wing form, area, high lift devices, real MTOW boost supporting structure) to grow. That is different.


User currently offlineStitch From United States of America, joined Jul 2005, 31262 posts, RR: 85
Reply 21, posted (5 years 5 months 2 weeks 6 days 16 hours ago) and read 32767 times:
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There already is a 1:1 747-400 replacement that is "state of the art" and more fuel efficient. It's called the 777-300ER and in under a decade it's wracked up over 400 sales.  sly 

The 777-200LR can take it's full payload out to around 7600nm, and yet not many airlines are interested in such a plane. The A350-500 can do it to around 7000nm, and even less airlines are interested in it.

So color me skeptical that a fat tri-jet is going to suddenly set the market on fire.

I mean McD already tried this with the MD-XX LR and MD-XX Stretch in 1996 and the market yawned.


User currently offlineZvezda From Lithuania, joined Aug 2004, 10511 posts, RR: 64
Reply 22, posted (5 years 5 months 2 weeks 6 days 16 hours ago) and read 32767 times:



Quoting Rheinwaldner (Reply 20):
The turbulence is IMO proportional to the fan area which mean it is proportional with the square of the fan diameter too.

The turbulence results from the sheer of a rough cylinder of air moving relative to the air around it. That boundary is the circumference of a circle, which is proportionate to the diameter, not the area.


User currently offlineZvezda From Lithuania, joined Aug 2004, 10511 posts, RR: 64
Reply 23, posted (5 years 5 months 2 weeks 6 days 15 hours ago) and read 32767 times:



Quoting Keesje (Reply 7):
A similar twin engined aircraft would require engines of at least 175.000 lbs each (asymetrical thrust compensation).

Not necessarily. This is a question of field performance, which depends as much if not more on the low-speed aerodynamic characteristics of the wing as on thrust. Put 80 meter wings with good low-speed lift devices onto a twin with 130K lbs thrust engines and you should be able to get the same single-engine thrust to MTOW ratio as the 787-9. Extrapolating from your very nice chart gives a MTOW of about 1,050,000 lbs with 130K lbs thrust engines. I have no doubt that GE and RR are capable of developing 130K lbs thrust engines. PW probably could too.


User currently offlineA350 From Germany, joined Nov 2004, 1101 posts, RR: 22
Reply 24, posted (5 years 5 months 2 weeks 6 days 15 hours ago) and read 32767 times:

I too think it's better to just go for a quad. The Breguet equation ignores the number of engines while some of it's parameters are very well influeneced by the number and choice of engines, mainly probably OEW, SFC and drag. Let's look at the single parameters. My educated guess here is the following:

  • - OEW: twin and quad are probably about equal here while tris have a significant disadvantage
  • - SFC: probably an advanantage for bigger engines, but there are other factors. E.g., the GeNX outperforms the GE-90-110s here
  • - probably a slight favor for twins

Following this considerations four GeNX should do very well. Please keep in mind that the A340 had significant trouble here sine it didn't find suited engines: the A343's hairdrayers are too small and suffer poor SFCs while the Trent 500s are enjoying great SFC but are just too heavy since they are too big.

Quoting Zvezda (Reply 18):
I can give you two reasons why a smaller number of larger engines is more efficient than a larger number of smaller engines.
- Thrust is proportional to the square of the fan diameter. Fan tip clearance losses are proportional to the fan diameter.
- The turbulence created by pushing air through a turbofan is a type of inefficiency. The turbulence is proportional to the fan diameter, while the thrust is still proportional to the square of the fan diameter.
So, doubling the fan diameter yields about four times the thrust, while substantial components of inefficiency are only doubled.

Thanks for that great overview! However, your points show advantages of more powerful engines, not direct advantages a twin (although that's correlated for obvious reasons). Since an aircraft of the size of the discussed one could have four GeNX I'm not sure weather the cons of small engines still apply. And keep in mind, your points are already included in the SFC. On a more theoretical basis, while fully agreeing with your points, I wonder if they:

  • - Run into saturation at very large engines.
  • - Get compensated by other issues, e.g. weight of the pylons, wing reinforcing etc.
  • - The advantages of sharing latest technology engines, including their regular upgrades, with other programs, economically just eclipse the theoretical .


P.S.: sorry that I forgot that: Keesje: Thanks a lot for another great airliner study  champagne 

A350

[Edited 2009-06-12 07:44:10]


Photography - the art of observing, not the art of arranging
25 Zvezda : For any given level of technology, a larger engine will have lower SFC than a smaller engine. Of course, a newer smaller engine can have lower SFC tha
26 AirbusA370 : Airbus A370 would be an adequate name for this
27 EA772LR : I'm not sure why you started comparing the A350 to the 787 Using your logic, can we assume that the 789 will be a more efficient aircraft than the A3
28 Post contains images A350 : Or WhaleSharkJet             A350Edit: smiley reducion[Edited 2009-06-12 08:48:36]
29 JayinKitsap : There have been discussions about the APU providing take off thrust. One that provided the thrust of a V2500 or CF-6 should be sufficient. Once out of
30 VirginFlyer : And yet the first tier operators of these VLAs seem to be consistantly replacing them with either A380s, 777-300ERs, or both. As I said: As I said, I
31 EA772LR : But if you're going to go through with the complexity of an APU that produces that much thrust, then why not follow through and just build in a 3rd e
32 Carls : Wrong, at the time the MD 11 was offered there was the A300, 767 out there and A330 was on its way. There were engines availables for such task but M
33 Post contains images Keesje : Capasity wise it is in a different segment. 300 seats vs 425. Capasity matters, even dominates outside a.net. Capasity agian. VLA like 747 and A380 a
34 Post contains images Stitch : If capacity matters, why didn't Boeing sell any 747-400s once the 777-300ER and A380-800 became available for offer? Why isn't the 747-8I selling? Yea
35 A350 : Because of their efficiency, or better because of their lack of it. A350
36 Stitch : It was still a very efficient plane for it's capacity. If it wasn't, Boeing would not have sold close to 500 of them over two decades against smaller
37 EA772LR : Uh, please don't quote part of my quote...in case you didn't notice Carls, I also listed the DC10/L1011 and other trijets. What you're saying is only
38 Post contains images Keesje : The reasons have been summed up everywhere, by me, by 747 operators like SQ and QF. Mostly they are not accepted / denied. Stating there exists no 40
39 Stitch : Because they are both tired and pedantic and those of us with critical thinking skills know it.[Edited 2009-06-12 14:50:34]
40 Viscount724 : That's only true with 10-abreast Y seating on the 77W which is not comparable to 10-abreast on the 747. Most 777 customers have chosen 9-abreast in Y
41 Stitch : At 10-abreast, seat width on a 777 and 747 is effectively identical at just under 44cm. The 747-400 has 10cm wider aisles which eats up 20 of the 24c
43 EA772LR : OMG that is ugly
44 Viscount724 : You seem to be jammed together much more noticeably on a 10-abreast 777 than on a 747. The armrest width is a factor and the narrower aisles are very
45 Stitch : The 77W might have low enough costs compared to the 744 that they can go with a less-dense seating arrangement. Or with similar premium cabin seating
46 Tdscanuck : Since when do carriers care (much) about economy class seating standards? How so? BA's current Business product is pretty leading edge and fits on th
47 Keesje : You obvious don't know, doesn't matter. But older generation aircraft like a300, 767 and 747's have much higher maintenance cost then newer ones like
48 Post contains links Jambrain : As I'm sure you both know both A&B have reduced the difference in installed power between quads and twins (per unit MTOW). They both use larger wings
49 Rheinbote : The A3456 is dead, DEAD, D E A D. Goes without saying. More attractive to the eye, yes. But nowhere near viable for an airline, neither technically n
50 Tdscanuck : I know information that conflicts with what you claimed, which is why I asked the question. The fact that you made a claim then don't want to reveal
51 Stitch : The A380 really is just that quiet, but the 747-8 is, I believe, expected to meet the same QC standards the A380-800 does at LHR and it's noise footpr
52 VirginFlyer : On the contrary, I think Boeing's experience with the 737 suggests that an aircraft designed in the 1960s can be successfully modernised and compete
53 Rheinbote : Can't quote a weight, but whatever Emirates wanted to put up there, it didn't work.
54 Rheinwaldner : I know it is a minor aspects regarding the topic of this thread. The notion was only to compare the prospects Boeing has to grow into the larger-than
55 Post contains links Carls : While I agree with you about the DC10 and L1011, I disagree about the MD11. When Airbus offered the A330-300 which was the first variant that went on
56 Burkhard : If there is a variation of the 350 that is above the -1000, and no suitable twin engine around, my bet would be on a quad and not on a tri jet. Don't
57 EA772LR : Hmmm...Interesting. I guess we shall see in the future if barrels are dropped Interesting history behind the MD-11, kind of sad too that MD missed th
58 Keesje : It's a VLA, significantly larger / heavier then a 777-300ER. No twin engine exists / is in sight.. The 777-300ER does 350 seats in a "typical" lay ou
59 Stitch : Range at MZFW is 5750nm - 500nm more than a 747-400. And twins pretty much have no restriction on where they can fly now. ETOPS now officially stands
60 Post contains links and images EA772LR : I thought the 77W was closer to 6,000nm with full payload now?? http://boeing.com/commercial/airports/plan_manuals.html
61 Post contains links VirginFlyer : I don't know if you read the recent Flight article on this, but the suggestion was made that such technology is still some way off from being ready f
62 Phollingsworth : The 77W can carry it's maximum payload ~5,700nm (Your payload range chart was replaced by Boeing in April), which is farther than the 744 can. It als
63 Astuteman : That's about the same as the 744 IMO In fact, it will carry the 744's max payload further than the 744 will Posting the right chart is usually a good
64 Post contains images EA772LR : Ahhh crap...I grabbed the wrong one thanks for the heads up Astuteman. Let's try again: Sorry guys, I posted the range/payload chart for the 777-200L
65 Astuteman : No worries And it does indeed show MSP range as 5 700Nm.. Pretty good show IMO.. Rgds
66 EA772LR : I wonder if Boeing can creep that range up past 6,000nm without increasing the MTOW...I guess we'll save this for the 'Re-Winged 777 thread'
67 Rheinwaldner : Good remark and article! The ACCA flew before the 787 so its useless for my "the 787 will be the last airliner using barrels..."-forecast!
68 Astuteman : Just cautionary note that there may other reasons why the 772ER outperforms the MD11 besides it being a twin (e.g. greater wingspan..) Rgds
69 Dennys : If Airbus wanted , they could make a new version of its A340-500/600 HGW provided with a new longer range and a new bigger cabin . dennys
70 EA772LR : But do you think, even with a greater wingspan, the MD-11 or any trijet would still be in production? I do think had MD hit their targets initially w
71 Stitch : They already have introduced an A340-500HGW and A340-600HGW, however only a handful have been sold. EK canceled their A346HGW order in favor of the 7
72 EA772LR : The 77W/L still has more range and and significantly less fuel burn. I believe the 77W at MTOW weighs over 27,000Kg less than the 346HGW, and still h
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