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

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.

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

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.

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?

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.

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

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]

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

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.

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....  

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

Rgds

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.

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.

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.

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]

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.

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.

   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.

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.

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.

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).



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.

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.

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.   

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.

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.

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.

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   

A350

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

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 than an older larger engine.

There is not a lot of difference in overall weight for a twin versus quad but, you're right, a tri would almost certainly weigh more.

One large engine suffers a lot less drag than 2 smaller engines with the same total thrust, for reasons that are analogous to the explanation I gave earlier in this thread about turbulence. In general, larger sizes have large aerodynamic advantages. This is the overwhelming reason why the WhaleJet is currently the CASM leader.

Airbus A370 would be an adequate name for this   

Quoting Rheinwaldner (Reply 16): 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.

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 A358? Because technically the A358 is much more overbuilt. Also, why do you keep insisting that the 787 'barrel' approach will be outdated in the not so distant future? That comes across as if you are telling me you know more about CFRP construction than Boeing's engineering team. I'm not trying to be condescending, but I don't know why you keep saying that the CFRP barrel is outdated.

Quoting Stitch (Reply 21): 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.

   The only reason the DC-10/MD-11/L-1011 and other trijets were built is because they didn't have engines that could produce sufficient thrust to be a twin for each aircraft. Increased reliability of engines and the advent of ETOPS, as well as maintenance being much harder for trijets because where the #2 engine is placed. This is why the airlines dumped their DC-10/MD-11s for the 777, and to a lesser extent the A340.

I see an A350-1100 stretch with possibly wing extensions, larger taller landing gear, and higher thrust engines being more probable than a new trijet.

Quoting AirbusA370 (Reply 26): Airbus A370 would be an adequate name for this

Or WhaleSharkJet            

A350

Edit: smiley reducion

[Edited 2009-06-12 08:48:36]

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 the initial climb the current engines have more than enough thrust.

Quoting Keesje (Reply 7): Well 95% of current VLA's is service falls inbetween the A350 and A380.

Quoting Keesje (Reply 19): 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.

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:

Quoting VirginFlyer (Reply 2): 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...)

As I said, I don't see any evidence of a market between the A350-1000/777-300ER and the A380-800 which would justify the creation of a somewhat unique type. Since the advent of the 777-300ER and the A380-800, Boeing has failed to gain much traction with the 747. Airbus didn't go for the A3XX-50. If there had have been sufficient demand for it, then surely they would have tapped it in order to spread out the risk of the A380 programme. The fact they didn't speaks volumes about what size they see the bulk of their predicted 1300 aircraft in the VLA category being.

If they do decide the market justifies a product in the 400-450 seat range, I think the engineering expertise would be better spent developing a second stretch of the A350-900, rather than what is effectively a new type with common elements from the A350.

Oh, and just quietly, I was thinking the other week about what I would like Boeing's Y3 to be - I was thinking more or less exactly what you had for the A350/A370, although larger in scale (twins in the ~350 and ~450 seat market, tri in the ~550 seat market). More or less discounted it for the reasons I've stated on this thread. Maybe you and I have some sort of psychic thing going on?

V/F

Quoting JayinKitsap (Reply 29): 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 the initial climb the current engines have more than enough thrust.

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 engine?

IIRC, GE claims that the GE90 is capable of being scaled upwards of 150K, and with incorporation of GEnx tech, this could provide suitable power probably all the way up to 900K MTOW for a twin, should Airbus or Boeing produce a twin that heavy.

Quoting EA772LR (Reply 27): The only reason the DC-10/MD-11/L-1011 and other trijets were built is because they didn't have engines that could produce sufficient thrust to be a twin for each aircraft.

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 MD did not have the money which is a totally different story.

I have heard this before but if that was the case MD had the opportunity to remove the tail fin engine and made a design a lot more efficient than the MD11. When they were looking to get the A330/A340 wings their idea was joining forces with Airbus using Airbus state of the art technology and electronics with a derivative fuselage from the MD11 with A330/A340 wings increasing the range of the dying MD11. At the end Airbus refused to do it.

Quoting Stitch (Reply 21): The 777-200LR can take it's full payload out to around 7600nm, and yet not many airlines are interested in such a plane.

Capasity wise it is in a different segment. 300 seats vs 425. Capasity matters, even dominates outside a.net.

Quoting Stitch (Reply 21): 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.

Capasity agian. VLA like 747 and A380 are almost exclusively used on >10-12 hrs flights to from Asia.

Quoting Zvezda (Reply 23): 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.

130 klbs would cater for an MTOW of about 750-800klbs, a little more then 777-300ER. I think big twin design is limited by available engines. Developping a new much larger engines creates ground clearance / wing issues, 425 people on a single engine above the north pole, even bigger logistic nightmares then GE90 when stranded far away and a breakeven after 25 yrs..

I have no indication of a kind of "natural" gab in capasity range market demand. Nor do I see 160 klbs engines entering service. Also I do not see Boeing give up their 30 year dominance in the VLA segment.

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?

Yeah, you can make tired partisan arguments that the 747 is "ancient technology" and "an impractical design", but if you don't look at it in a partisan manner, but instead approach it with an open mind, it's clear that the 747-8I addresses the need for a plane between 375 and 475 seats with economy, capacity, range and quietness - if said need existed, of course.

If capacity matters, why didn't Airbus start with a 74m length for the A350XWB, making the shrink 68m and the stretch 80m? Since it's an all new design, there was no engineering reason preventing Airbus developing the A350-800XWB at 315 seats, the A350-900XWB at 350 seats and the A350-1000XWB at 385 seats.

As for engines, the GE90-115B is already rated for almost 119,000 lbs of take-off thrust with the "thrust bump" option. Additional improvements should get that above 120,000 pounds. The GE90-11xB would already be directly applicable to the 68-80m A350XWB (and nothing stopped them from adding it) and Rolls could have dusted off the Trent 8104 / 8115 designs.

And having enjoyed three decades of "dominance" in the VLA market, they've made a very nice profit. Staying in the game appears to be a recipe for losing money, not making it, at the moment, so I'd argue they're better off getting out while they're ahead in the game.  

[Edited 2009-06-12 09:40:57]

Quoting Stitch (Reply 34): If capacity matters, why didn't Boeing sell any 747-400s once the 777-300ER and A380-800 became available for offer?

Because of their efficiency, or better because of their lack of it.

A350

Quoting A350 (Reply 35): Because of their efficiency, or better because of their lack of it.

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 aircraft that could generally match it on range.

I don't argue that there is no demand for an aircraft in that size range, however I do argue that the aircraft below it (777-300ER / A340-600 / A350-1000XWB) and above it (747-8I and A380-800) are sufficiently efficient enough that their lower or greater capacity is not enough impediment to not choosing them.

Quoting Carls (Reply 32): 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 MD did not have the money which is a totally different story.

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 partially true anyways. The MD-11 was designed and EIS long before there were 80lb+ thrust twin engine aircraft. So again, let me re-iterate my point-Tri-jets were offered because the engine technology to offer a large long range twin wasn't available. Long range twins are the future and are far more efficient than, particularly tri-jets, but orders show, also more than quads for anything but a VLA.

Quoting Stitch (Reply 34): 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?

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 400-500 seater demand because nobody buys the 747-8i is a questionable conclusion I think.

There is a lot of 40 yr old technology in the 747-8. Investing in it for the next 30 yrs is not something airlines do lightly. It needs extensive inspections and components changes, obsolence is a topic for the next 30 yrs. The noisy cabin is 9.5 abreast, has the impracticle upperdeck and A zone (as a passenger I love it).

The OEW is high, as are all systems and structure related to the 4 powerplants and flight controls. The 747 needs a lot of runway (high minimum speed) creating far more noise for the environment then e.g. a A380.



Furthermore the word "Risk" was written all over the 747-8i, it took a yr after launch before LH signed up. Scares away others. Looking good, being an icon doesn't help.

Quoting EA772LR (Reply 37): Long range twins are the future and are far more efficient than, particularly tri-jets, but orders show, also more than quads for anything but a VLA.

I think twins are efficient and unfeasible for a 900 klbs 747 replacement. Twins are an alternative if capasity & payload-range are less important. They are not less important.

IMO good 400-500 seat long haul aircraft were not sold during the last 10 yrs because they didn't exist. If they existed they would have been sold. It's not very complicated IMO.

Quoting Keesje (Reply 38): The reasons have been summed up everywhere, by me, by 747 operators like SQ and QF. Mostly they are not accepted / denied.

Because they are both tired and pedantic and those of us with critical thinking skills know it.

[Edited 2009-06-12 14:50:34]

Quoting Stitch (Reply 21): 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

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 class which, at least in my experience, seems very close to offering the same standards of space and comfort as a 10-abreast 747. The 777 cabin is 10 inches narrower than the 747.

Quoting Viscount724 (Reply 40): 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 class which, at least in my experience, seems very close to offering the same standards of space and comfort as a 10-abreast 747

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 24cm of extra width the 747-400 has. The remaining four centimeters is either taken up by offset from the wall or by slightly wider armrests.

Quoting DocLightning (Reply 42):

OMG that is ugly   

Quoting Stitch (Reply 41): Quoting Viscount724 (Reply 40): 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 class which, at least in my experience, seems very close to offering the same standards of space and comfort as a 10-abreast 747 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 24cm of extra width the 747-400 has. The remaining four centimeters is either taken up by offset from the wall or by slightly wider armrests.

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 obvious. If they are so comparable, why would many 747 operators have chosen 9-abreast for their 777s rather than 10-abreast? I think they considered that they weren't comparable in terms of consistent service standards and that's my experience.

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 densities and with that part of the plane bringing in all the money (at the time), they may have felt less-dense Economy seating was acceptable since it was not as important to having a flight break-even (in terms of revenue generated).

Or maybe the airlines just decided to take some pity on the passengers in back.

Quoting Keesje (Reply 11): I think a much ignored disadvantage of the 747-8i is that it is unpracticle in meeting current passenger cabin standards.

Since when do carriers care (much) about economy class seating standards?

Quoting Keesje (Reply 11): The uppperdeck is constrained to use efficiently for new and future First and Business class cabins

How so? BA's current Business product is pretty leading edge and fits on the top deck of their 744's quite nicely.

Quoting Keesje (Reply 11): Also it has sixties roots under its skin, making extensive inspections and frequent swaps at component level neccessary unlike newer generation aircraft.

Which components require "frequent swaps"? That's not even true of the 747-400.

Quoting Rheinwaldner (Reply 20): 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.

It also means the engine is working harder, hence has shorter life and higher maintenance cost. No free lunch.

Quoting JayinKitsap (Reply 29): 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.

Yes, and incredibly inefficient. There's no good way to bridge the fact that APU's make lousy jet engines, and jet engines make lousy APU's. The power range and operating regimes are too different.

Quoting Keesje (Reply 38): he 747 needs a lot of runway (high minimum speed) creating far more noise for the environment then e.g. a A380.

As far as I know, the 748 meets the same noise requirements as the A380. Takeoff noise is far more tied to aerodynamics and engines than it is to speed.

Tom.

Quoting Tdscanuck (Reply 46): Which components require "frequent swaps"? That's not even true of the 747-400.

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 777 and A330. Its the technology. 747s are the money makers in MRO.

Quoting Tdscanuck (Reply 46): As far as I know, the 748 meets the same noise requirements as the A380. Takeoff noise is far more tied to aerodynamics and engines than it is to speed.

The 747-8 has significantlty higher take and landing speeds. More speed creates noise. Its about half the noise footprint of a 747-400. But new aircraft like the A380 have about half the noise footprint of the 747-8i.

Quoting Tdscanuck (Reply 46): Quoting Rheinwaldner (Reply 20): 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. It also means the engine is working harder, hence has shorter life and higher maintenance cost. No free lunch.

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 on twins that allow take off with one engine out running at max thrust. This large wing then supports higher altitude flight which reduces engine thrust to the point where twins are running on or close to their optimum sfc. Twins wing is sized for optimal ML/D (mach number times Lift / Drag) at 39,000 ft

(at 39000 ft thrust and drag is only 68% of 31000 ft)

The twins on Reply 7 graph clearly show the twins have less thrust then a simple 1 engine out model would suggest

Cumpsty covers this topic very well in chapter 20 of Jet Propulsion
http://www.amazon.com/Jet-Propulsion...odynamic-Performance/dp/0521541441

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

The A3456 is dead, DEAD, D E A D. Goes without saying.

Quoting Zvezda (Reply 5): I think your Ecoliner concept would be much, much more attractive to the airlines.

More attractive to the eye, yes. But nowhere near viable for an airline, neither technically nor economically. It is general consensus that the A388 is close to being the smallest viable design with a full double deck. Going smaller is not attractive at all. Guess why customers want Airbus to do a A389.

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

Whatever that secret is, applying it to a twin design would yield a superior product (unless you are going borderline in what's feasible in terms of thrust with two engines)

Quoting United Airline (Reply 8): Boeing's proposed BWB as well as Y2 double decker are tri-jets

That's apples vs grapes, because the BWB is a configuration class of its own, where more engines would probably yield a benefit in structural/aero efficiency that more than compensates for the penalty in propulsive efficiency (see below)

Trijets are dead. You may have seen a few patents recently - whoever has done those, he must have had a certain number of patents as a personal KPI...

Quoting Rheinwaldner (Reply 16): 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!

Well, commercial airplane designers have a rule of thumb that says everything else being equal, a quad burns about 10-12% more fuel than a twin.

Quoting Tdscanuck (Reply 46): Quoting Keesje (Reply 11): The uppperdeck is constrained to use efficiently for new and future First and Business class cabins How so? BA's current Business product is pretty leading edge and fits on the top deck of their 744's quite nicely.

The 747's upper floor is structurally limited and cannot take heavy premium class seats. If you ask me, that's not so much of a penalty because heavy premium class seats should be banned anyway if the airline industry wants anyone to take their green initiatives as serious.

Quoting Tdscanuck (Reply 46): There's no good way to bridge the fact that APU's make lousy jet engines, and jet engines make lousy APU's.

   We need to give them another dead horse to beat, so that they can put this one to rest