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Will There Ever Be A Twin Larger Than A 777?

Wed Feb 18, 2009 4:12 am

Seeing the success that large twin jets has had over the decade, I wonder will we ever see a twin jet that is larger than a T-7? Is it likely, that down the line, when it time to start replacing A388, we will see an ultra wide twin jet with jet engines that has 160-200 inch wide fans? So could we see a bigger twin jet in the future, or is the T-7 likely to be the largest twin jet ever built?
 
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Starlionblue
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RE: Will There Ever Be A Twin Larger Than A 777?

Wed Feb 18, 2009 7:32 am

Maybe.  Wink

The economic equation is not that complex. "Needs to be cheaper (including purchasing cost and operating cost) than a quad of equivalent size given projected market demand."


The big cost item is engines. The GE90-115B is pretty much the current state of the art. Engines in this class are extremely expensive to design and build. The bigger the more expensive. From the other end, the bigger the aircraft (requiring ever bigger engines), the smaller the demand for said aircraft. That's why 320s/737s sell more than 747s/380s.

So you reach an economic "coffin corner" if you will.
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JoeCanuck
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RE: Will There Ever Be A Twin Larger Than A 777?

Wed Feb 18, 2009 7:58 am

I would think the cost of developing an engine that large for such a limited market would be prohibitive. Much larger than a 777 and, in my opinion, you'd be looking for at least a 3 holer.
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rheinwaldner
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RE: Will There Ever Be A Twin Larger Than A 777?

Wed Feb 18, 2009 10:03 am

Ever? Sure! There is no natural engine size limit.
 
Pagophilus
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RE: Will There Ever Be A Twin Larger Than A 777?

Wed Feb 18, 2009 10:38 am

Could you imagine how long it would take for those engines to spool up?
 
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Starlionblue
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RE: Will There Ever Be A Twin Larger Than A 777?

Wed Feb 18, 2009 11:52 am



Quoting JoeCanuck (Reply 2):
Much larger than a 777 and, in my opinion, you'd be looking for at least a 3 holer.

Nope. If you make it a three holer you can have engines that are about half as powerful. There are many more factors involved but in the roughest terms for a twin you would have, say, 2x 150k engines. For a triplet of the same weight you would have 3x 75k engines. Thrust with an engine out is 150k either way.

In any case three holers are dead for widebody tubes with wings. Makes much more sense to make a quad.
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WildcatYXU
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RE: Will There Ever Be A Twin Larger Than A 777?

Fri Feb 20, 2009 12:43 am

Considering the current A 388 and B748 sales, the question rather should be: Will we ever see a new jet larger than the 77W?
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RE: Will There Ever Be A Twin Larger Than A 777?

Fri Feb 20, 2009 12:50 am



Quoting Pagophilus (Reply 4):
Could you imagine how long it would take for those engines to spool up?

Well, I'd be more worried about the noise... But engine size and spool time aren't directly related. I'd be willing to bet the GE90 spools up faster than a CFM56...
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RE: Will There Ever Be A Twin Larger Than A 777?

Fri Feb 20, 2009 1:40 am

Quoting JoeCanuck (Reply 2):
Much larger than a 777 and, in my opinion, you'd be looking for at least a 3 holer.

A quad... imagine trying to mount an engine bigger than a GE90-115B in a vertical stabilizer    ... not going to happen.

I think the really big planes (A380 and anything Boeing may develop to compete with it) will continue to be quads.

First, there won't be enough demand to justify the enormous expense of developing an engine significantly bigger than a GE90.

Second, to make the quad decision even easier, the proper engines to power a quad VLA are the same size as those on midsize widebody twins. We've already seen the GEnx get reused on the 748, and the smart money is on the Trent XWB finding its way onto the A380.

[Edited 2009-02-19 17:41:22]
 
tdscanuck
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RE: Will There Ever Be A Twin Larger Than A 777?

Fri Feb 20, 2009 3:57 am



Quoting Metroliner (Reply 7):
Well, I'd be more worried about the noise...

Noise from turbomachinery scales with RPM to the 3rd (I think...might be 4th) power...bigger engines have to spin more slowly to keep the tips sonic, so they should get correspondingly quieter as they get bigger.

Quoting Metroliner (Reply 7):
I'd be willing to bet the GE90 spools up faster than a CFM56...

I'm not sure about that...rotating inertia scales with the radius squared and directly with the mass...a GE 90 has twice the diameter and certainly more than twice the rotating mass, so it's got at least 8 times the rotating inertia of a CFM56-7, but only 4 times as much power.

Tom.
 
XT6Wagon
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RE: Will There Ever Be A Twin Larger Than A 777?

Fri Feb 20, 2009 7:20 am

Yes we will, not soon though.

Mind, you can use a GE115 sized engine to power a plane LARGER than a 773. Use a higher lift profile and you can have a higher MTOW with the same engine. Course it will burn more fuel in cruise then.
 
nomadd22
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RE: Will There Ever Be A Twin Larger Than A 777?

Fri Feb 20, 2009 1:20 pm

The 90-115 can already be certified for something like 123,000lb thrust bumps. Maybe it wouldn't be that much to rate it for full time 125,000lb. That and a bunch of weight savings from composite and a new wing might let you add a few inches to the tube.
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ba97
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RE: Will There Ever Be A Twin Larger Than A 777?

Sat Feb 21, 2009 3:02 am

Never say never. I would suspect Mr Wittle never thought a GE90 was possible. Compare a DC7 to a A380. Is it possible in the next 5 or 10? I could not see the interest and market. 15-20 years.... 15 years after the 707 was the 747.
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MarkC
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RE: Will There Ever Be A Twin Larger Than A 777?

Sat Feb 21, 2009 3:31 am

I don't think the engines will be any problem at all. More it will be the size of the plane (length and wingspan), along with the height of the landing gear needed to clear bigger fans. But landing gear height is going to have to increase anyway knowing the way engine fans are going.
 
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RE: Will There Ever Be A Twin Larger Than A 777?

Sat Feb 21, 2009 9:45 am

I also think one of the factors might be the infrastructure at the airports - taxiways, gateways. There was already need for englargments for the B747, then now for the A380.

If anything bigger comes around in, say, 10-15 years, airports will need to adjust again and that's very costly.
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RE: Will There Ever Be A Twin Larger Than A 777?

Mon Feb 23, 2009 1:36 am

The engine manufacturers could make a 150k engine today. There have been quite a few advancements since the GE-90-115.

#1: Contra rotation.
#2: Higher mach number compressors
#3: IBR compressors (more efficient)

Note to mention the trend towards greater chord lengths (compare the GEnx low pressure compressor for the 748 vs. the 788. The technology is *that* new.) All allow for greater efficiency than the GE-90. Imagine if the GE-90 had been designed with the latest generation fans. It would improve performance with the bypass ratio.  spin 

Quoting SeaBosDca (Reply 8):
I think the really big planes (A380 and anything Boeing may develop to compete with it) will continue to be quads.

There is a huge integration advantage having the engines out on the wings. Because the weight of the engines pulls down against the lift of the wings, there is less stress on the wings (lighter). Not to mention weight outside of the landing gear reduces the stress at the wing root upon landing or striking a pot hole.

Having to convey the thrust of the tail engine to the wing (primary source of drag) is going to preclude 3-holers from the long haul market from now on. The only 3 engine plane we might ever see would be a BWB.

What should be also noted is the advantage of weight savings. The A350XWB will compete with the 77W with far less thrust. The same would be true of a 450 passenger twin (the largest I current conceive). Its possible to make a 400 seat replacement for the 77W that requires less thrust than the 77W with 8,000nm range!  wideeyed 

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JoeCanuck
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RE: Will There Ever Be A Twin Larger Than A 777?

Mon Feb 23, 2009 5:17 am

I will remain skeptical about the weight of the 350 until they are closer to being completed. So far, CFRP hasn't proven to have much in the way of weight savings, though it does have other advantages.

The 787 isn't significantly lighter than the 330. I really don't understand how the 350 will be so significantly lighter than the 777. The -1000 is supposed to be almost the same size as the -300er and yet it is supposed to be a lot lighter. Maybe Airbus has some magical form of composites that Boeing hasn't thought of but I doubt it.

I'm certainly not going to predict that the 350 will be much heavier than advertised but going by the latest 2 composite aircraft, (787 and A400), I won't be very surprised if it is.
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rwessel
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RE: Will There Ever Be A Twin Larger Than A 777?

Tue Feb 24, 2009 7:42 am



Quoting Lightsaber (Reply 15):
Having to convey the thrust of the tail engine to the wing (primary source of drag) is going to preclude 3-holers from the long haul market from now on. The only 3 engine plane we might ever see would be a BWB.

At cruise, parasitic drag is significantly larger than induced drag, and the fuselage is a major contributor to that. Purely from a drag perspective, some thrust on the fuselage will reduce the amount of structure needed because all that fuselage drag is now not being pulled by the wings. Optimally, if one-third of the total drag comes from the fuselage, then a tail mounted engine (plus two on the wing) will essentially zero the fore/aft stress at the wingbox.

The major structural advantage from wing mounted engines comes from reduced bending moment because the fuselage's mass is decreased (by not including heavy engines).

There are some lesser factors as well.

To some extent a completely drag producing tail (including everything behind the wing) can be simpler (and presumably lighter) structurally because all of it's fore-aft load is tensile, which is often easier to deal with than compressive loads, especially in long thin structures. That's complemented by avoiding the added structural requirements for the front end of a three-engine aircraft, because the fore section is becomes longer, and has to carry larger compressive loads.

Another factor is that with a tail mounted engine, the front section of the aircraft will require a stronger structure simply because it'll be longer.

IMO, most of the arguments against tri-jets are unsatisfying, and reflect current fashion and practical reality more than technical issues. It certainly makes sense to build a twin if you reasonably can. But the extreme cost of engine development means that there's an upper limit imposed by the limited market for very large aircraft - you simply don't get enough units to amortize your engine development expenses. But for an aircraft 30-50% larger than a 777, a tri-jet makes sense - except that there's already an aircraft in that niche (747). Even a A388 sized aircraft could be reasonably accommodated with a minor growth version of a GE-90, although anything much larger (A389) starts requiring a rather more substantial growth, and Airbus has availability issues for the big GE-90s anyway.

The "it's too big to fit on the tail" argument is a bit silly too - we're not talking about fitting such a thing on a DC-10, but on a rather larger aircraft. Compare the CF6-80C2 on an MD-11 with 61.5klbs of thrust - it has a fan diameter of 93 inches (overall 106 inches) and weighs about 9800lbs. A GE-90-115, produces 86% more thrust (115klbs), weighs 86% more (18260lbs), and has a fan diameter 38% bigger (128 inches) which works out to a frontal area about 89% larger than the CF6), and a overall diameter increase of 27% (135 inches), for a overall frontal area increase of 62%. IOW, if you scaled up a DC-11 86% (by mass) to GE-90 size, the proportions of the engines to the rest of the plane wouldn't change all that much.

Admittedly newer engines, like the GEnx do increase the fan-diameter to thrust ratio a bit. although not nearly so dramatically as often claimed. The GEnx-2B67 (intended for the 748), with 66.5klbs thrust will have a 105 inch fan, which if we scale it down to match the 61.5klbs of the CF6-80C2, is approximately 101 inches, which is only 8 inches (9%) bigger than the CF6 (18% increase in frontal area).

The difficulty of maintenance of the center engine argument is a bit specious too. First, engines are getting more reliable, which reduces the problem. And then a tri-jet is held up as a reasonable configuration for a BWB, where *all three* engines are difficult to access, not just one of them. Y'all can't have it both ways.

Unless the market changes to drastically increase the likely number of aircraft that can be sold into the segment, someone wanting to build a new aircraft covering the bigger-than-777-to-A380 size range will be significantly tempted by a three engine design.
 
rheinwaldner
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RE: Will There Ever Be A Twin Larger Than A 777?

Tue Feb 24, 2009 9:30 am



Quoting Rwessel (Reply 17):
But the extreme cost of engine development means that there's an upper limit imposed by the limited market for very large aircraft - you simply don't get enough units to amortize your engine development expenses.

I agree with that. I think it was more than good luck that the thrust requirement of new aircraft designs often was set as 2..3..4 times the thrust of existing engines. The 767 having two 747 engines would be an example.
 
slz396
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RE: Will There Ever Be A Twin Larger Than A 777?

Tue Feb 24, 2009 9:33 am

Well, isn't the A350-1000 going to be lager than the 77W???
 
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Starlionblue
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RE: Will There Ever Be A Twin Larger Than A 777?

Tue Feb 24, 2009 9:44 am



Quoting Rwessel (Reply 17):
The "it's too big to fit on the tail" argument is a bit silly too - we're not talking about fitting such a thing on a DC-10, but on a rather larger aircraft.

I think the lesson learned was that it was too big to fit on the DC-10 as well.  Wink McD had all sorts of issues with the tail engine on larger versions (including the MD-11). The banjo fitting was a tremendous piece of engineering, but it was also tremendously expensive to design.

As I understand it, part of the reason the DC-10 and Tristar became triplets was that the initial version developed for some quite stringent requirements, including transcon from LGA. The gate space requirement made a quad unpractical, while the total thrust and engine out requirements made a twin impossible.

Not saying that the DC-10 and the Tristar weren't great aircraft. They were.
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Max777geek
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RE: Will There Ever Be A Twin Larger Than A 777?

Tue Feb 24, 2009 10:00 am



Quoting Starlionblue (Reply 1):
From the other end, the bigger the aircraft (requiring ever bigger engines), the smaller the demand for said aircraft. That's why 320s/737s sell more than 747s/380s.

I would be wondering how, in your equation of "costs/dimensions vs paxcapacity" the fuelburn factor includes. Proportionally a bigger model fuel consumption pro passenger is less than a smaller model with less pax capacity (but with less fuelburning engines, less weight to carry etc) can anyone tell how the fuel consumption is comparable among those 2 classes of airliners ?
 
rwessel
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RE: Will There Ever Be A Twin Larger Than A 777?

Tue Feb 24, 2009 10:31 pm



Quoting Slz396 (Reply 19):
Well, isn't the A350-1000 going to be lager than the 77W???

A 77W (777-300ER) maxes out at 775,000lbs (351t), while the last number I saw for the A350-1000 was 657,000lbs (298t). The current plan seems to give the A350-1000 a few more inches length and wingspan.

The 50t less weight shows up in the planned use of 92klbs thrust engines vs. the 115klbs for the 77W.
 
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Starlionblue
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RE: Will There Ever Be A Twin Larger Than A 777?

Tue Feb 24, 2009 11:38 pm



Quoting Max777geek (Reply 21):
I would be wondering how, in your equation of "costs/dimensions vs paxcapacity" the fuelburn factor includes. Proportionally a bigger model fuel consumption pro passenger is less than a smaller model with less pax capacity (but with less fuelburning engines, less weight to carry etc) can anyone tell how the fuel consumption is comparable among those 2 classes of airliners ?

Well sure. The cost per pax on a widebody is typically lower than on a narrowbody.

My point was that there are more routes requiring narrows, so they sell more.
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PITingres
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RE: Will There Ever Be A Twin Larger Than A 777?

Wed Feb 25, 2009 12:48 am



Quoting Starlionblue (Reply 23):
The cost per pax on a widebody is typically lower than on a narrowbody.

To be nit-picky, I'm pretty sure you meant cost per seat. It only becomes cost per pax when there's a butt warming each seat. Which leads directly to your second, entirely inarguable point.
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tdscanuck
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RE: Will There Ever Be A Twin Larger Than A 777?

Wed Feb 25, 2009 6:29 am



Quoting Rwessel (Reply 17):
At cruise, parasitic drag is significantly larger than induced drag, and the fuselage is a major contributor to that. Purely from a drag perspective, some thrust on the fuselage will reduce the amount of structure needed because all that fuselage drag is now not being pulled by the wings.

I'm not sure how much benenfit you can get from that, given that the fore/aft load on the wing in cruise is about 5% of the vertical load. The wing is going to be overwhelmingly designed by vertical bending and torsion, not by fore/aft drag loading.

Quoting Rwessel (Reply 17):
The difficulty of maintenance of the center engine argument is a bit specious too. First, engines are getting more reliable, which reduces the problem. And then a tri-jet is held up as a reasonable configuration for a BWB, where *all three* engines are difficult to access, not just one of them. Y'all can't have it both ways.

It's not that the BWB is a good situation for engine maintenance, it's just that the third engine doesn't suffer any penalty because the other engines are already up there. If you've got two engines up high, having a third one up high is a very small incremental problem. If you've got two engines down low, putting one up high is a huge incremental problem.

Tom.
 
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RE: Will There Ever Be A Twin Larger Than A 777?

Wed Feb 25, 2009 7:03 am



Quoting Tdscanuck (Reply 25):
It's not that the BWB is a good situation for engine maintenance, it's just that the third engine doesn't suffer any penalty because the other engines are already up there. If you've got two engines up high, having a third one up high is a very small incremental problem. If you've got two engines down low, putting one up high is a huge incremental problem.

they are also in the open and easy to access with no structural elements runnign around them like a normal tail mounted engine for a 3 engine plane.
 
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Starlionblue
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RE: Will There Ever Be A Twin Larger Than A 777?

Wed Feb 25, 2009 8:15 am



Quoting PITIngres (Reply 24):
Quoting Starlionblue (Reply 23):
The cost per pax on a widebody is typically lower than on a narrowbody.

To be nit-picky, I'm pretty sure you meant cost per seat. It only becomes cost per pax when there's a butt warming each seat.

Oops.  Wink Yes quite right.
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rwessel
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RE: Will There Ever Be A Twin Larger Than A 777?

Wed Feb 25, 2009 8:49 am



Quoting Tdscanuck (Reply 25):
I'm not sure how much benenfit you can get from that, given that the fore/aft load on the wing in cruise is about 5% of the vertical load. The wing is going to be overwhelmingly designed by vertical bending and torsion, not by fore/aft drag loading.

I don't disagree. I was replying to the assertion that a major defect of an aft mounted engine is the extra fore-aft load it creates because it now has to push the wing.

Quoting Tdscanuck (Reply 25):
It's not that the BWB is a good situation for engine maintenance, it's just that the third engine doesn't suffer any penalty because the other engines are already up there. If you've got two engines up high, having a third one up high is a very small incremental problem. If you've got two engines down low, putting one up high is a huge incremental problem.

It's not the increment, rather the total bill that's of interest. I'm assuming that two low and one high engine makes for less maintenance cost than three up high. Some costs are fixed if you have any high engines - if you have any high engines you'll need extra scaffolding, cranes, etc. OTOH, other costs are per engine - the two low engines continue to be serviceable for most of the day-to-day stuff with a stepladder, and an engine change of the low engines continue to be possible with a quite small lift. Everything on the high engine(s) will take longer and be more complicated to do.
 
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RE: Will There Ever Be A Twin Larger Than A 777?

Wed Feb 25, 2009 7:55 pm



Quoting SeaBosDca (Reply 8):

A quad... imagine trying to mount an engine bigger than a GE90-115B in a vertical stabilizer ... not going to happen.

It needn't be that big, though. Remember, the problem with a twin is that if you have an engine out after v1, the remaining engine needs to provide 100% of the thrust to get you off the ground. In a trijet, the remaining engines only need to be able to provide about 50% of that thrust.

So suppose a 77W has a MTOW of 775,000 lb and 115 kN is enough to get that off the ground. If you now want to build a plane with 150% of the MTOW of a 77W (and this is a bit of a stretch; but it proves my argument), you have a MTOW of 1,162,500 lb. So to make that a twin you now need a 175kN engine. But to make it a tri, you only need 87.5kN engines.

Now, a plane with that kind of ridonkulous MTOW is going to have a HUGE tail and it can probably fit an 87.5kN engine up there. You could even use twin tails (a la AN-225) and mount the #2 engine between them.
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TrijetsRMissed
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RE: Will There Ever Be A Twin Larger Than A 777?

Thu Feb 26, 2009 2:31 am



Quoting Starlionblue (Reply 20):
McD had all sorts of issues with the tail engine on larger versions (including the MD-11).

All sorts of issues? The MD-11 may have had it's shortcomings, but the No. 2 engine was not the cause. Rather, an overweight fuselage that was more drag prone than conceived, and GE and PW not deliveries engines initially as efficient as advertised, were the problems.

Quoting Rwessel (Reply 17):
The difficulty of maintenance of the center engine argument is a bit specious too.

It's a bit humorous when you think about it. This was not a problem in the 70's, yet now with far more reliable engines, it's the worst thing known to man. At least with the MD-11/DC-10 design, the tailcone folded down, allowing for easier access than most seem to realize.
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Starlionblue
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RE: Will There Ever Be A Twin Larger Than A 777?

Thu Feb 26, 2009 4:38 am



Quoting Trijetsrmissed (Reply 30):

Quoting Starlionblue (Reply 20):
McD had all sorts of issues with the tail engine on larger versions (including the MD-11).

All sorts of issues? The MD-11 may have had it's shortcomings, but the No. 2 engine was not the cause.

Sorry I was unclear. The issues were not in service. They had issues with the cost and complexity of the design. Some argue that the projected cost of designing yet another new banjo fitting for the proposed MD-XX/MD-12 (trijet variant) was what doomed the company.

http://www.rosboch.net/aviationmedia/Proposed_MD-XX_MD-12_trijet.jpg

Quoting Trijetsrmissed (Reply 30):
It's a bit humorous when you think about it. This was not a problem in the 70's, yet now with far more reliable engines, it's the worst thing known to man.

Of course it was a problem in the 70s. Just because the aircraft was purchased and used didn't mean it didn't have all those extra associated costs. If a new trijet is to viable, the extra cost of maintenance for the middle engine position will need to be considered, just as it was in the 70s.
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astuteman
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RE: Will There Ever Be A Twin Larger Than A 777?

Fri Feb 27, 2009 7:09 am



Quoting Lightsaber (Reply 15):
What should be also noted is the advantage of weight savings. The A350XWB will compete with the 77W with far less thrust. The same would be true of a 450 passenger twin (the largest I current conceive). Its possible to make a 400 seat replacement for the 77W that requires less thrust than the 77W with 8,000nm range!

Reckon you've hit it right on there, L.

Quoting JoeCanuck (Reply 16):
The 787 isn't significantly lighter than the 330

Couple of things.....

Firstly the smart money is on later versions being lighter than earlier ones.
Secondly, it IS a bit lighter, and (as far as I can remember, will be 227t MTOW, compared to 233t (going to 238t) for the A330)
Thirdly, despite being that little bit lighter, because of the better engine SFC, a 227 tonne 787-8 should still outrange a 233t A330 by about 10%
Fourthly (relevant to the topic) it is also just that little bit wider, allowing an extra seat across in reasonable comfort.

So, as Lightsaber says, a fuselage a smidge bigger (6"-8"?) than the 773ER's, with genuine 10-across, and seating around the 400 mark, should be doable on an airframe about the same weight as a 773ER (possibly a tad heavier if the wingspan goes up by any great amount - which it might..  Smile )
But SFC improvements would allow it to burn less fuel to reach the same range, so the MTOW might well end up either the same or even lower.

Just my  twocents 

Rgds
 
joperrin89
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RE: Will There Ever Be A Twin Larger Than A 777?

Sat Feb 28, 2009 4:27 am



Quoting WildcatYXU (Reply 6):
Considering the current A 388 and B748 sales, the question rather should be: Will we ever see a new jet larger than the 77W?

I honestly think we will. Its just going to be a few years. This economic downturn is not going to last forever. I would be willing to bet the farm that that is one of, if not the biggest reason why the A380 and 748i are not selling well. Why buy a bigger plane when most people are cutting back and flying less. I think in 5 years things are going to look alot different. Just speculation but, I would expect that Y3 will be at least as big if not bigger than a 777-300ER.
 
TrijetsRMissed
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RE: Will There Ever Be A Twin Larger Than A 777?

Sun Mar 01, 2009 6:33 am



Quoting Starlionblue (Reply 31):
Some argue that the projected cost of designing yet another new banjo fitting for the proposed MD-XX/MD-12 (trijet variant) was what doomed the company.

I seriously doubt this. There was interest in this aircraft from several airlines but the engineers were not given the R&D needed to get the program going. Mismanagment, complacency, and the over reliance of needing the MD-90 to sell like hotcakes, just as the MD-80 had 5-10 years earlier, is what did them in. But that's an arguement for another thread.

Quoting Starlionblue (Reply 31):
Of course it was a problem in the 70s. Just because the aircraft was purchased and used didn't mean it didn't have all those extra associated costs. If a new trijet is to viable, the extra cost of maintenance for the middle engine position will need to be considered, just as it was in the 70s.

No, it wasn't. It was an inconvenience, there's a difference. I have family friends that worked for AA in the 70s and 80s in maintenance and management. They have gone on record to say that the dispatch reliability to the DC-10 was just as good as the newly delivered 762s. Believe it or not. Extra costs? Sure with fuel consumption (which was marginal in the 80s), but nothing that broke the bank on the maintenance side, until the aircraft became dinosours. And as Rwessell eluded to earlier, with such reliable engines of today, this is basically moot.

With the dominance of the 777, any justification for a trijet would be to take the place of a quad. And with McDonnell Douglas out of the picture, I think we all can agree that's not going to happen.
There's nothing quite like a trijet.
 
Tristarsteve
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RE: Will There Ever Be A Twin Larger Than A 777?

Sun Mar 01, 2009 8:06 am

Well Finnair has produced a brochure on flight in 2093
Check out their 7 engined airliner

http://www.departure2093.com/en/main_page/?id=2

Steve
 
Rheinbote
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RE: Will There Ever Be A Twin Larger Than A 777?

Sun Mar 01, 2009 8:45 am



Quoting Astuteman (Reply 32):
Thirdly, despite being that little bit lighter, because of the better engine SFC, a 227 tonne 787-8 should still outrange a 233t A330 by about 10%

 checkmark  The 788 still burns more than 10% less fuel per seatmile than the A330 - even in the current state of being overweight and with engines that are over book sfc.
 
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RE: Will There Ever Be A Twin Larger Than A 777?

Sun Mar 01, 2009 1:10 pm



Quoting TrijetsRMissed (Reply 34):
No, it wasn't. It was an inconvenience, there's a difference. I have family friends that worked for AA in the 70s and 80s in maintenance and management. They have gone on record to say that the dispatch reliability to the DC-10 was just as good as the newly delivered 762s. Believe it or not. Extra costs? Sure with fuel consumption (which was marginal in the 80s), but nothing that broke the bank on the maintenance side, until the aircraft became dinosours. And as Rwessell eluded to earlier, with such reliable engines of today, this is basically moot.

A rose by any other name... Extra cost is extra cost whatever you call it. Apparently today airframers and customers have decided that a quad is cheaper in these respects than a trijet.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
Alessandro
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RE: Will There Ever Be A Twin Larger Than A 777?

Sun Mar 01, 2009 9:17 pm

I doubt it, but I see further stretch of the B777 possible. Not a new airframe though.
From New Yorqatar to Califarbia...
 
rwessel
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RE: Will There Ever Be A Twin Larger Than A 777?

Mon Mar 02, 2009 11:07 pm



Quoting TristarSteve (Reply 35):
Well Finnair has produced a brochure on flight in 2093
Check out their 7 engined airliner

http://www.departure2093.com/en/main...?id=2

While I count seven horizontally mounted engines, I think there are also a dozen lift engines on there... I’m sure Boeing is hard at work on this one…  Wink
 
Max777geek
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RE: Will There Ever Be A Twin Larger Than A 777?

Sat Mar 21, 2009 9:13 am



Quoting TristarSteve (Reply 35):
Well Finnair has produced a brochure on flight in 2093
Check out their 7 engined airliner

http://www.departure2093.com/en/main...?id=2

Nice, but they reminds me more of sci-fi oriented kids draws fantasies than affordable projects, as now. Some of them don't look they can fly, the supersonic would be enormous.
 
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lightsaber
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RE: Will There Ever Be A Twin Larger Than A 777?

Sat Mar 21, 2009 7:27 pm



Quoting Rwessel (Reply 17):
At cruise, parasitic drag is significantly larger than induced drag, and the fuselage is a major contributor to that.

Technically correct. But when you break down the drag, greater than 50% is at the wing/wingroot.  spin  Whenever I've participated in a trade study with tail mounted engines, personally I cringe at the weight penalties of putting engines at the tail. It can be one or all of the engines.

www.onera.fr/daap/reduction-trainee-...vil-transport-aircraft-reneaux.pdf

Now take the engine out scenarios. Since the engine out in the tail is an easy case, its pretty much ignored. When a wing engine is out and you have the other wing engine and the tail engine running at MTOW... Not to mention the engine is mounted on a large moment arm and when all the considerations are put into effect, it adds thousands of pounds to an aircraft plus a loss of passenger volume having the engine in the tail. Now the loss of volume should be a non-event in a CFRP DC-10 like airframe... but its still a weight penalty.

Quoting Starlionblue (Reply 37):
Extra cost is extra cost whatever you call it. Apparently today airframers and customers have decided that a quad is cheaper in these respects than a trijet.

 checkmark  A big part of the penalty of body/tail mounted engines is the 'pothole' scenario. When the main gear hits a pothole, the wing mounted engines counterbalance the forces. Since those big tires end up being stored in the body, there must be more structure to handle the 'bounce.' We're talking widebodies here by the way, there will never be another mass produced narrowbody. Daussalt business jets being the exception.



Quoting Tdscanuck (Reply 25):
If you've got two engines down low, putting one up high is a huge incremental problem.

I used to think that until Honda designed standing platforms onto the Hondajet wings. So there are new solutions to old problems.  spin 

Quoting TrijetsRMissed (Reply 34):

With the dominance of the 777, any justification for a trijet would be to take the place of a quad. And with McDonnell Douglas out of the picture, I think we all can agree that's not going to happen.

That is an excellent point. The only reason to consider a tri-jet is in the quad marketspace. Just as a tri might be taking advantage of an existing design, so could a quad. e.g., We've had discussions on A.net about the A389 taking advantage of the Trent XWB.

Quoting Rwessel (Reply 39):

While I count seven horizontally mounted engines, I think there are also a dozen lift engines on there... I’m sure Boeing is hard at work on this one…

 rotfl  Integrating that many engines would be a nightmare. It would only be practical on a 'pure electric' airframe (no hydraulic takeoffs, pure electric start). But even then... that is a costly design to service. There is a reason BWB designs stop at 3 engines... it saves money.

Lightsaber
"They did not know it was impossible, so they did it!" - Mark Twain
 
jox
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RE: Will There Ever Be A Twin Larger Than A 777?

Tue Mar 24, 2009 6:36 pm

Now; Here is a, most likely, stupid thought.

Does all engines have to be of equal size? Would it make sense to combine two large wing-mounted engines with two mid-sized ones, mounted on the rear fuselage - MD-80 style ? That would ease service on the rear engines, as I understand the #2 in a tri-engine solution makes servicing much harder. Stupid idea? Probably...
 
tdscanuck
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RE: Will There Ever Be A Twin Larger Than A 777?

Tue Mar 24, 2009 11:25 pm



Quoting Jox (Reply 42):
Does all engines have to be of equal size?

Technically, no. Economically, yes.

Having two types of engines instantly doubles your spares inventory. It also doubles your certification and integration work, although that may be surmountable.

Tom.
 
nomadd22
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RE: Will There Ever Be A Twin Larger Than A 777?

Wed Mar 25, 2009 12:10 am

Quoting Jox (Reply 42):
Does all engines have to be of equal size? Would it make sense to combine two large wing-mounted engines with two mid-sized ones, mounted on the rear fuselage - MD-80 style ? That would ease service on the rear engines, as I understand the #2 in a tri-engine solution makes servicing much harder. Stupid idea? Probably...

If you make that two large wing engines and one small tail engine you're talking about the thrusting APU that's been bantered about in a few threads. The small one would be mainly used for backup on takeoffs so you could use smaller main engines and still have enough power in case one of the mains gave out.
It's not a dumb idea. Just not too practical when you add all the details up.

[Edited 2009-03-24 17:12:00]
Anon
 
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RE: Will There Ever Be A Twin Larger Than A 777?

Fri Mar 27, 2009 4:08 am



Quoting Jox (Reply 42):
Does all engines have to be of equal size? Would it make sense to combine two large wing-mounted engines with two mid-sized ones, mounted on the rear fuselage - MD-80 style ?



Quoting Tdscanuck (Reply 43):
Technically, no.

Wouldn't jetblast from the large, wing engines adversely affect the intakes of the two smaller rear engines in such an arrangement, or would it mostly be out of the way? What could be the effect on thrust?
"Everyone is entitled to my opinion." - Garfield
 
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RE: Will There Ever Be A Twin Larger Than A 777?

Fri Mar 27, 2009 6:49 am



Quoting Tdscanuck (Reply 43):

Having two types of engines instantly doubles your spares inventory. It also doubles your certification and integration work, although that may be surmountable.

Then why do APU's exist?
-Doc Lightning-

"The sky calls to us. If we do not destroy ourselves, we will one day venture to the stars."
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Zkpilot
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RE: Will There Ever Be A Twin Larger Than A 777?

Fri Mar 27, 2009 7:00 am

Any replacement for the A380 is likely to be a completely different design... ie a BWB That way the aircraft CAN have 3 engines (as they can be mounted in many locations without having the penalties associated with tube&wings 3 holers.
Such a BWB aircraft could seat anywhere from 500-1000+ passengers.
The other direction for aviation to go is the HST route using Hydrogen powered aircraft (Mach 5+). Quite simply so far as the 777/A350 goes there is little point in reinventing these aircraft (aside from some modifications). It is just too expensive to develop large new aircraft especially if its going to need even bigger new engines. They become subject to diminishing returns. The other factor with tube&wing designs is that there is a practical limit to their length..they start needed extra bracing, longer undercarriage..this is why Airbus came up with the A380 rather than updating the A340.
56 types. 38 countries. 24 airlines.
 
rwessel
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RE: Will There Ever Be A Twin Larger Than A 777?

Fri Mar 27, 2009 9:32 am



Quoting DocLightning (Reply 46):
Then why do APU's exist?

So you don't have to run the main engines for a bit of electrical power on the ground, and so that you can start the engines without a ground cart.

Besides, on many aircraft you can dispatch with the APU inop, which drastically reduces the maintenance burden. Not having the APU means you need ground electrical power and compressed air for starting - only an inconvenience at many airports.
 
keesje
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RE: Will There Ever Be A Twin Larger Than A 777?

Fri Mar 27, 2009 10:26 am



Quoting Nomadd22 (Reply 44):
APU that's been bantered about in a few threads.

Together with Henry Lam I did some threads. Henry even made a youtube.

http://www.youtube.com/watch?v=CVWQ5h5UOfk

Someone else made a flight simulator. Google for "Boeing Ecoliner"
"Never mistake motion for action." Ernest Hemingway

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