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soylentgreen
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Prospects For 4-engine Jetliners

Fri Dec 12, 2014 7:50 pm

I'm wondering people's thoughts on whether 380 or 747-8 production can continue long-term if either Airbus or Boeing end production of their respective jets.
 
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United787
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RE: Prospects For 4-engine Jetliners

Fri Dec 12, 2014 7:58 pm

Two current threads on the A388 and 748 should be enough to keep you busy for a while...

Airbus Considers Ending A380 Production - Part 2 (by American 767 Dec 11 2014 in Civil Aviation)

Boeing Announces New 747-8 Production Cut (by KarelXWB Dec 9 2014 in Civil Aviation)
 
soylentgreen
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RE: Prospects For 4-engine Jetliners

Fri Dec 12, 2014 8:01 pm

Better said - would one plane's production end help the other one survive for 5-10 more years?
 
Flyglobal
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RE: Prospects For 4-engine Jetliners

Fri Dec 12, 2014 8:36 pm

In my opinion there is a relatively simple answer:

basically we can agree that a 2 engine Jetliner with the same passenger capacity would walways be more economic compared to same size 4 engine Jetliners.

But there will always be a movable line: From which size and sales volume it is more efficient to use a dedicated engine development for a large plane concept.

In case of the A380 with rather low sales volumes those volumes are not enough to justify dedicated engines which would peobably need 30-50% more power then the ones of the 777-9. So at least for the next Gen. Engine the A380 would need 4 holers again - so that the A380 can share the engine technology with the smaller wide bodies and hence just increase a way larger volume.

When then probably 15 years later - the prospected sales volume of a plane in the size of teh A380 - lets say 2-3 times higher- then it probably would make sense to develop 2 two engine concept for the A380, or even an entirely new plane for this segment.

The market may not be large enough to have 2 competitors in this segment, even after the volume triples.
Currently the A380 is the winner and well be the only player from around 2020 - let’s say until 2030-2035...
But after that when volume triples + it may be time for a dedicated engine concept, or rather a new plane. (Probably from Boeing - when they see the market).

Regards

Flyglobal
 
LH707330
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RE: Prospects For 4-engine Jetliners

Fri Dec 12, 2014 9:01 pm

Quoting flyglobal (Reply 3):
basically we can agree that a 2 engine Jetliner with the same passenger capacity would walways be more economic compared to same size 4 engine Jetliners.

Only true if you assume the same engine tech and other things all equal. The reason you don't see engines bigger than a GE90-115B is that it's impossible to transport spares effectively. To your point, the production numbers would not cover the R&D for such a design, so if the engine guys decide it's not economical, it becomes cheaper for the airframer to take off-the-shelf engines to save on sale price and then have airlines take a small hit in fuel burn.
 
Burkhard
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RE: Prospects For 4-engine Jetliners

Fri Dec 12, 2014 9:13 pm

Quoting LH707330 (Reply 4):
The reason you don't see engines bigger than a GE90-115B is that

there is no material known to build the blades for it without having to replace them after every flight. Technology to build an A380 size and range twin is unknown, so at least 30 years away.
 
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LAX772LR
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RE: Prospects For 4-engine Jetliners

Fri Dec 12, 2014 10:22 pm

Quoting LH707330 (Reply 4):
The reason you don't see engines bigger than a GE90-115B is that it's impossible to transport spares effectively.

...the 77X's engine will be larger than the GE90-115.
 
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SEPilot
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RE: Prospects For 4-engine Jetliners

Fri Dec 12, 2014 11:03 pm

Quoting Burkhard (Reply 5):

there is no material known to build the blades for it without having to replace them after every flight. Technology to build an A380 size and range twin is unknown, so at least 30 years away.

My understanding is that the limit for current technology was about 150K lbs. thrust when the 77W was introduced (it may have grown since then.) With an appropriate wingspan I think that would be enough for an A380 sized twin. But that wingspan would be quite a bit greater than 80m, and there does not seem to be enough demand for an airliner that size. I also see your point about transporting it; I do not know how big it would be but there is a good chance that the fan would not fit in a 747 (the current 77W engines will not with the fan attached, but with the fan detached both parts will). I do not know how you can predict a breakthrough in 30 years for something we cannot do now; if we do not know how now there is no predicting when we will be able to figure out how to do it, unless there is a clear development path in place. When the original 777 engines were designed I am sure nobody would have predicted that within 15 years the output of one of them would be increased to 115K; that surely would have been seen as impossible. Breakthroughs occur almost always when there is a perceived need for them; and right now there is no perceived need for a bigger engine than the GE90-115. When there is someone will figure out how to build it.
 
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enilria
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RE: Prospects For 4-engine Jetliners

Fri Dec 12, 2014 11:07 pm

Quoting soylentgreen (Thread starter):
I'm wondering people's thoughts on whether 380 or 747-8 production can continue long-term if either Airbus or Boeing end production of their respective jets.
Quoting flyglobal (Reply 3):
basically we can agree that a 2 engine Jetliner with the same passenger capacity would walways be more economic compared to same size 4 engine Jetliners.

First, I must point out that Soylent Green is (spoiler) people, so please consider that.

Apart from that, I think what has happened is that the size of aircraft that must have four engines has become so large that the market has become smaller and smaller for four engined aircraft. Thus, with current technology I think they are on a long path to death. On the other hand, if we get supersonic going again or vertical takeoff or who knows what they could come right back.
 
strfyr51
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 1:23 am

The B747-8 will be going on with it's freighter config for Quite a while. With the Cockpit position and FWD Nose opening door. It's going to be a needed airplane, The A380 might yet become a Freighter to extend it's life but it's role as Not yet been defined to make it so. I'd see the A330, 800 and 900 to be very popular Freighters before the A380.
In the end I think this is the Last Hurrah for the big 4 engine Passenger liners. Too Much Too Late.
 
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sassiciai
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 2:07 am

I speak as a rank amateur in the matter of engines, but I somehow feel that there is too much blind sentiment in favour of ever-larger twin engined aircraft, and too much writing off of 4-engines as history.

Surely the important thing is the total fuel consumption to get from A to B with a given payload (I know it's oversimplified, with maintenance, price, etc also figuring). Perhaps today's largest engines do the job optimally, but what if tomorrow's technology cannot be scaled up initially to achieve B777-type power. Maybe it's too early to rule out new tech engines where 4 would be viable, but 2 inadequate

The P&W engines for the A320NEO, scaled up 100% or so, might that not offer a 4-engined widebody (new or a re-engined exisitng one like an A340) with great SFC?
 
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LAX772LR
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 2:39 am

Quoting sassiciai (Reply 10):
The P&W engines for the A320NEO, scaled up 100% or so, might that not offer a 4-engined widebody (new or a re-engined exisitng one like an A340) with great SFC?

Could it be great?
.......sure.

Would it be BETTER than a similar twin, in an almost every typical application?
.......99.9% chance that the answer is "no."

Which is the problem that you'll essentially always have for subsonic tube+wings designs smaller than about the 747-A380 size, so long as fossil fuels are the power source utilized.
 
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sassiciai
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 3:01 am

Quoting LAX772LR (Reply 11):
Would it be BETTER than a similar twin, in an almost every typical application?
.......99.9% chance that the answer is "no."

Is your answer fact-based, or heart-based? Please try to argue your point with some facts/calculations, that will enrich the debate.

Quoting LAX772LR (Reply 11):
so long as fossil fuels are the power source utilized.

Before I got to the P&W engine example, I spoke of "new technology" which, in my opinion, is not limited to fossil fuel engines!
 
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SEPilot
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 3:32 am

Quoting sassiciai (Reply 10):
Surely the important thing is the total fuel consumption to get from A to B with a given payload (I know it's oversimplified, with maintenance, price, etc also figuring). Perhaps today's largest engines do the job optimally, but what if tomorrow's technology cannot be scaled up initially to achieve B777-type power. Maybe it's too early to rule out new tech engines where 4 would be viable, but 2 inadequate

There are a number of reasons why a jet engine becomes more efficient as it gets larger. The only technology I foresee difficult (but not impossible) to scale up is the GTF; but if it proves successful with the A320 I believe that PW will be able to make it as large as necessary. But if not, I doubt that 4 GTF's will be more effficient than the best large conventional engine at the time.

I truly believe that the A380 will prove to be the last 4 engined jetliner ever built. Since we now are able to build engines large enough to power the largest aircraft that our airport infrastructure can accommodate, I believe all future airliners will be twins.
 
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sassiciai
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 3:52 am

Quoting SEPilot (Reply 13):
I believe all future airliners will be twins.



"Never say never" - I think your view cannot see beyond fossil fuel engines!

[Edited 2014-12-12 20:23:15]
 
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TWA772LR
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 4:13 am

Someone posted on an earlier thread that Boeing submitted a patent(?) for a triple aisle, 4-engined plane. It included 5, 4-wheel bogies as MLG. It was a monster!

Here it is:
If Boeing Never Built The 777?
(Reply 26 from Stitch)

Edited to add link.

[Edited 2014-12-12 20:18:55]
 
32andBelow
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 4:28 am

Quoting TWA772LR (Reply 15):

Someone posted on an earlier thread that Boeing submitted a patent(?) for a triple aisle, 4-engined plane. It included 5, 4-wheel bogies as MLG. It was a monster!

Here it is:
If Boeing Never Built The 777?
(Reply 26 from Stitch)

Edited to add link.

[Edited 2014-12-12 20:18:55]

I bet though could get 13 across in the same plane today!  
 
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SEPilot
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 4:42 am

Quoting sassiciai (Reply 14):

[quote=sassiciai,reply=14]Quoting SEPilot (Reply 13):
I believe all future airliners will be twins.



"Never say never" - I think your view cannot see beyond fossil fuel engines!

You may be right. But I can only go on what I know; who knows what may be discovered or developed in the future? But some technologies, once perfected, do not change significantly for centuries; others become obsolete because of new discoveries. I stated this as my opinion, which it is. It is based on my belief that oil is not an exhaustible resource, because I believe it is geologically generated deep in the earth and percolates to the surface, and unless we consume it faster than it is being produced (which I do not think we can) it will never run out. And the only other technology that I know of that has sufficient energy density to power airplanes is nuclear, and that has its own host of problems that we are nowhere near solving, and may never be able to. But I will concede your point. Something may come along to totally change everything.
 
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777Jet
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 5:42 am

"Prospects For 4-engine Jetliners"

Unless restrictions that prohibit twins from flying deep southern routes to / from Australia (Like SYD-SCL or SYD-JNB) are lifted there will always be a prospect for aircraft with more than two engines - but such markets are small and don't justify the existence of 4-holers alone. I'm not talking about ETOPS restrictions - I'm talking about restrictions by authorities such as CASA. If CASA continues to place such restrictions on twin operations by not allowing twins to fly deep southern ETOPS missions that they are certified for, I would hope that airlines wanting to use twins on those routes would just not fly the routes or drop them until CASA catches up with reality...

[Edited 2014-12-12 21:54:37]
 
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LAX772LR
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 5:53 am

Quoting sassiciai (Reply 12):
Is your answer fact-based, or heart-based?

My answer's reality based... or have you noticed the mad rush to create/purchase/operate quad-powered aircraft in any market type where twins are now capable of effectively competing?

No, you say?

Hmm, well ain't that somethin'-- must be one of those "heart-based" coincidences I guess.  

Quoting sassiciai (Reply 12):
I spoke of "new technology" which, in my opinion, is not limited to fossil fuel engines!

Well, keep dreaming. Because there's no "new technology" in the the most remoteeeeeeeeeeeeeeeeeeely foreseeable design future that's going to be free of fossil-fuel (or similar) power sources.

And by "or similar," I'm saying don't kid yourself with the "bio-fuel" hype, as it has the exact same specific issue of contention: the more engines you have, or the faster you want to go, the more you're gonna burn.
 
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sassiciai
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 7:24 am

Quoting LAX772LR (Reply 19):
My answer's reality based... or have you noticed the mad rush to create/purchase/operate quad-powered aircraft in any market type where twins are now capable of effectively competing?

I find it a bit of a stretch to call what you wrote "fact based". You are comparing today's situation with, er, today's situation, while blindly not considering what tomorrow's might be - you have given no support to your "fact" that a twin jet of today will be better than a GTF-inspired 4-engined plane of tomorrow. Perhaps you are right, perhaps not, but you certainly offer up no facts one way or another.

It's also a brave man who claims to see far out into the future with such certainty. Hope your stock portfolio is in a much better shape than mine!  
 
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LAX772LR
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 8:26 am

Quoting LAX772LR (Reply 19):
while blindly not considering what tomorrow's might be

so in other words, you missed that whole:


Quoting LAX772LR (Reply 19):
Well, keep dreaming. Because there's no "new technology" in the the most remoteeeeeeeeeeeeeeeeeeely foreseeable design future that's going to be free of fossil-fuel (or similar) power sources.


Quoting sassiciai (Reply 20):
you have given no support to your "fact" that a twin jet of today will be better than a GTF-inspired 4-engined plane of tomorrow.

I've neither said, nor implied, any such thing about a twinjet "of today" would be "better than" anything of "tomorrow"

I've simply said that so long as hydrocarbons are your mitigating factor, and the tube+wings design philosophy (that's been the hallmark of fixed-wing aviation since its inception) remains... you're overwhelmingly likely to see a twinjet utilize less fuel than a quad in similar application, for anything up to a 747/A380's size. Plain and simple. Your choice to accept it or not, is completely immaterial to the fact.
 
rwessel
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 8:37 am

Quoting LH707330 (Reply 4):
The reason you don't see engines bigger than a GE90-115B is that it's impossible to transport spares effectively.

This has come up before. I posted the following here a few years ago:

"Twice the thrust [relative to a GE90-115] would require a 41% bigger diameter fan. You'd need a bigger cargo door, but it would fit inside a 747, or even a 777. And the fan assembly should fit handily through the standard nose door of an An-124. It might even fit in a stock C-17."

So at worst you'd need some number of 747Fs or 777Fs modified with extra wide cargo doors. That would require some investment on the part of the engine manufacturer, but these could fly ordinary F missions most of the time, just so that enough are available on reasonable notice to move engines around the world. Or GE (or whoever) could just modify two or three high time 744s and have them dedicated to the job. Increasing engine reliability is going to make for fewer and fewer engine shipments as well. And I suspect that someone building a twin needing 200klb engines is going to demand rather higher reliability than what we already have with GE90s.

Or just hire an An124.
 
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SEPilot
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 8:51 am

Quoting rwessel (Reply 22):

"Twice the thrust [relative to a GE90-115] would require a 41% bigger diameter fan.

Isn't the fan for the 777X larger than the GE90-115? And it produces less thrust. So the fan for a 230K lb. thrust might be larger than 41% over the GE90-115. But until airports can handle aircraft larger than 80m x 80m I do not think the need will arise. I can see a larger twin than the 779, but not by much. The main difference would be that it would accommodate 11 abreast. It would also have larger folding wingtips (maybe 85m unfolded, 80 folded). And I would be surprised if it would need much more than about 130K lbs. thrust per engine.

[Edited 2014-12-13 00:52:22]
 
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LAX772LR
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 9:03 am

Quoting SEPilot (Reply 23):
I can see a larger twin than the 779, but not by much.

...rotation would sure be fun to watch!  
 
rwessel
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 9:42 am

Quoting SEPilot (Reply 23):
Isn't the fan for the 777X larger than the GE90-115? And it produces less thrust. So the fan for a 230K lb. thrust might be larger than 41% over the GE90-115.

The (current, I think) spec for the GE9x is a 133.5 inch fan and 105klbs of thrust. Compared to the GE90-115 at 128 inches and 115klbs.

And certainly fan diameters in relation to thrust have been on a slow but steady upwards march since the birth of the turbofan.

But my main point is that you could transport a substantially larger fan (and the example happened to be 181 inches) without too much trouble.
 
uta999
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 10:01 am

Would engines ever become so large / reliable, to allow single engine operation? I make that 50%-75% fuel reduction.

Presumably at the back and similar to a wide body VC10 in design, (minus the RR Conway engines sadly). The intake would be fenced to stop FOD or birdstrike and would be largely protected by the fuselage in front.

Work would need to be done to make it float, after a ditching and have live streaming of position / system data.

Not so long ago, twins were viewed by some, as potential suicide on oceanic routes.
 
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seahawk
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 10:10 am

By-Pass ratio will grow. The fan diameter will also grow. I think such an engine could be built, but it could only be fitred to a design without the engines hanging under the wings. Blended wing body or something.
 
md80fanatic
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 3:18 pm

This debate again?

There is an upper limit to fan size and that won't change. The larger the fan gets the closer the outer edge of the fan gets to supersonic. That changes the entire intake airflow dynamic, not to mention the higher chance of not being able to contain a blade separation.

Generally fuel burn is proportional to thrust. Generally, if you need 200,000 lbs of thrust, the fuel burn between 2 - 100,000 lb. engines, 4 - 50,000 lb. engines, or 8 - 25,000 lb. engines is very nearly equal. One of the major benefits of having numerous smaller engines is the potential for several different planes in a fleet to use the same powerplant. Military applications have seen such savings utilizing common engines for decades now.

In civil service though, there is the perception that multiple smaller engines is so last century. Now we need the absolute minimum number of giant hulky engines that when a mechanic stands in the intake he/she looks like a tiny flea. The perception is "This in the bleeding edge of technology".

Seriously, the latest greatest in turbofan technology only looks markedly more efficient on a new generation composite plane. Put a GenX on a 767 and the fuel savings would not be so impressive. It would be much quieter though, and have lower noxious emissions. Those are the areas where modern tech is most noticeable, engine weight, engine sound, and engine emissions.
 
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SEPilot
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 3:37 pm

Quoting uta999 (Reply 26):
Would engines ever become so large / reliable, to allow single engine operation? I make that 50%-75% fuel reduction.

In a word, no. The requirement for redundancy will never go away. Engines will never get that reliable.

Quoting md80fanatic (Reply 28):
Generally fuel burn is proportional to thrust. Generally, if you need 200,000 lbs of thrust, the fuel burn between 2 - 100,000 lb. engines, 4 - 50,000 lb. engines, or 8 - 25,000 lb. engines is very nearly equal.

I do not believe this is true at all. Jet engines get more efficient as they get larger for a number of reasons. First, the volume of air going through the engine relative to the surface area of the containment increases, which means there is less friction loss. Second, the amount of leakage by the blade tips is a smaller portion of the airflow. Third, the heat loss from air contacting the fixed parts is a smaller proportion, leading to more efficient combustion and more energy extracted. I am not a jet engine expert, but I know enough engineering and physics to understand this. With the same level of technology an engine twice the thrust of another will burn a lot less than twice as much fuel every time.
 
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seahawk
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 3:38 pm

GTF allows larger fans though.
 
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7BOEING7
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 5:14 pm

Quoting LH707330 (Reply 4):
The reason you don't see engines bigger than a GE90-115B is that it's impossible to transport spares effectively
Quoting rwessel (Reply 22):


Or just hire an An124.

  

That's what Boeing/GE do when there's an issue with an engine on a production airplane and they need a replacement rapidly.
 
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kanban
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 5:37 pm

Quoting rwessel (Reply 22):
"Twice the thrust [relative to a GE90-115] would require a 41% bigger diameter fan. You'd need a bigger cargo door, but it would fit inside a 747, or even a 777. And the fan assembly should fit handily through the standard nose door of an An-124. It might even fit in a stock C-17."

must be why Airbus is building more Belugas   
 
rwessel
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 9:01 pm

Quoting md80fanatic (Reply 28):
There is an upper limit to fan size and that won't change. The larger the fan gets the closer the outer edge of the fan gets to supersonic. That changes the entire intake airflow dynamic, not to mention the higher chance of not being able to contain a blade separation.

Fan blade tips are already supersonic. OTOH, fan tip speeds don't increase just because the engine is bigger.

Quoting md80fanatic (Reply 28):
Generally fuel burn is proportional to thrust. Generally, if you need 200,000 lbs of thrust, the fuel burn between 2 - 100,000 lb. engines, 4 - 50,000 lb. engines, or 8 - 25,000 lb. engines is very nearly equal. One of the major benefits of having numerous smaller engines is the potential for several different planes in a fleet to use the same power plant. Military applications have seen such savings utilizing common engines for decades now.

Various factors make larger engine inherently more efficient than smaller ones. Tip losses (around turbine and compressor blades), for example, are easier to contain on a larger device. The amount of surface drag a single 2X engine nacelle has is ~30% less than two 1X engines.

That's why you don't see many small turbines - they're inherently, due to their size, *really* inefficient.
 
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SEPilot
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 9:10 pm

Quoting rwessel (Reply 33):

Fan blade tips are already supersonic. OTOH, fan tip speeds don't increase just because the engine is bigger.

Only if the RPM's decrease. For the same RPM's the tip speeds will increase. Do larger engines run slower?
 
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zippyjet
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RE: Prospects For 4-engine Jetliners

Sat Dec 13, 2014 9:19 pm

Future multi-engined airliners? Maybe when a dedicated HSCT program gets going.
 
rwessel
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RE: Prospects For 4-engine Jetliners

Sun Dec 14, 2014 12:34 am

Quoting SEPilot (Reply 34):
Only if the RPM's decrease. For the same RPM's the tip speeds will increase. Do larger engines run slower?

Yes. Large modern turbofans mostly have maximum N1s that run the fan tip speed into the Mach 1.2-1.5 range.

Of course for something with a geared fan, the relationship between N1 and fan speed is a smidge more complicated.

That applies to the other stages as well. For example max N2 on a GE90 is about 10K RPM. Model airplane-sized turbojets run in the 100K RPM range.

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