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Could There Ever Be A Twin-engined 747?  
User currently offlineDeltaXNA From United States of America, joined Mar 2013, 176 posts, RR: 0
Posted (1 year 3 months 4 days 1 hour ago) and read 6428 times:

Is it possibly? GE90's?

29 replies: All unread, showing first 25:
 
User currently offlineFlyingGoat From United States of America, joined Apr 2013, 148 posts, RR: 0
Reply 1, posted (1 year 3 months 4 days ago) and read 6407 times:

Nope. Max thrust on a 747 is roughly 60,000lbs per engine, give or take a bit depending on engine manufacture. Aircraft must be designed to take off with one engine out. Max engine thrust on a 747 with one engine out is around 180,000lbs. If you were to place two GE90s on a 747, your max engine thrust with an engine out would be 115,000lbs. This is no where near enough.

The 777-9X is pretty much a twin engine 747.


User currently offlineOldAeroGuy From United States of America, joined Dec 2004, 3476 posts, RR: 67
Reply 2, posted (1 year 3 months 3 days 17 hours ago) and read 6281 times:

The payload-range of the proposed 777-9X surpasses the 747-400. If built, it will be a twin-engine 747.


Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
User currently offlineCXB77L From Australia, joined Feb 2009, 2596 posts, RR: 5
Reply 3, posted (1 year 3 months 3 days 15 hours ago) and read 6248 times:
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Quoting DeltaXNA (Thread starter):
Is it possibly? GE90's?

If your question was whether the 747 can operate despite being equipped with only two engines, then the answer is no. The 747 is not designed as a twin.

The A330/A340 was unique in the sense that they were designed specifically as a twin and a quad. I could be wrong, but I do not believe that the same can be done with other aircraft families that are not designed specifically with this interchangeability. There cannot be a twin engine 747 any more than there can be a quad engined 767 (for example).

If your question was whether there can be a 747 sized twin, then the answer is yes. There already is one, the 777-300ER, and two more on the way: the A350-1000 and 777-9X.

Quoting OldAeroGuy (Reply 2):
The payload-range of the proposed 777-9X surpasses the 747-400.

The 777-300ER's payload-range already surpasses that of the 747-400.



Boeing 777 fanboy
User currently offline7BOEING7 From United States of America, joined Oct 2012, 1499 posts, RR: 8
Reply 4, posted (1 year 3 months 3 days 13 hours ago) and read 6198 times:

Quoting DeltaXNA (Thread starter):
Is it possibly? GE90's?

There could have been a twin engine 747 and almost was. In the mid to late 70's Boeing was looking at a twin 747SP with the expected increases in engine thrust coming. The original 747 only has about 46,000 pounds of thrust.


User currently offlineDevilfish From Philippines, joined Jan 2006, 4775 posts, RR: 1
Reply 5, posted (1 year 3 months 3 days 11 hours ago) and read 6149 times:

Truly a fascinating and engrossing topic...a quick glance at the bottom of the page shows four threads, no less.....


Twin Engined 747...is It Possible? (by Jcchristie Aug 3 2008 in Tech Ops)

Is It Possible To Make A Twin Engined B 747? (by United Airline Nov 17 2005 in Tech Ops)

Could The 747ADV Be A Twin? (by Tockeyhockey May 13 2005 in Tech Ops)

A Twin Engined 747? (by Trent_800 Jan 13 2002 in Tech Ops)


Doubtless we're in for many more.....

http://www.flightglobal.com/blogs/fl...hy-would-boeing-design-a-mid-.html

.....in various configurations.    ...not sure when it would cease being called a 747 though...    .



"Everyone is entitled to my opinion." - Garfield
User currently offlineflyingturtle From Switzerland, joined Oct 2011, 2285 posts, RR: 13
Reply 6, posted (1 year 3 months 3 days 10 hours ago) and read 6134 times:

Even if such engines could be built, the most striking argument...

Bigger engines need more ground clearance, which needs longer landing gear struts. Which needs a huge redesign.


And IMHO, the even more striking argument is that any real airliner should have four engines. Or at least three. 


David



Keeping calm is terrorism against those who want to live in fear.
User currently offlineBuyantukhaa From Mongolia, joined May 2004, 2864 posts, RR: 3
Reply 7, posted (1 year 3 months 3 days 9 hours ago) and read 6102 times:

Quoting FlyingGoat (Reply 1):
The 747 is not designed as a twin.

But seems to have been evolving in that direction  
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Click here for bigger photo!

Photo © Ben Kings




I scratch my head, therefore I am.
User currently offlinePapaChuck From United States of America, joined Aug 2010, 136 posts, RR: 0
Reply 8, posted (1 year 3 months 3 days 7 hours ago) and read 6052 times:

It could be done, but not in a way that would make any economical sense to any airline.

Start with a basic 747-8 so we can take advantage of the new wing. Let's assume that a GE-90 could be shoehorned under each wing and the ground clearance issues could be resolved without needing a complete wing or landing gear redesign. The rudder/vertical stabilizer would need modification as well to provide increased control authority in an engine-out scenario.

Now we have a basic airframe, but the weights are now going to work against us. Given the available thrust, let's assume that the MTOW would have to be restricted to the 777-300ER range, around 750,000 lbs. Boeing lists the OEW for the 777-300ER and the 747-8 as 370,000 lbs. and 434,600 lbs. respectively. Right away the 747 twin will have about 65,000 lbs. less useful load given a similar MTOW. Economically, that's enough to kill the project right there. The basic 747 airframe is just too beefy. I suppose you could do a fuselage shrink and find other ways to save weight, but it will always be heavier than the basic 777 airframe.

Back to the original question: could a 747 twin be built? Sure, but it would be a lame duck compared to the competition. The 747 was designed as a quad, and thus it shall always be.

PC



In-trail spacing is a team effort.
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16991 posts, RR: 67
Reply 9, posted (1 year 3 months 3 days 6 hours ago) and read 6017 times:

Technically, a 747 sized twin is tricky. You'd need to have engines that produce 40%+ more thrust than the current largest engines.

The economical conundrum is that, the larger the engine (or aircraft for that market) the smaller the market but the larger the investment. Developing a GE90 is much bigger gamble than developing a CFM56. Look, for example, at the difficulties experienced by P&W when the JT9D was developed. Unless engine technology changes rather drastically, it does not make sense to invest in developing a 160000lb thrust engine.

This leads us to "what's the point?" There's nothing inherently evil about four engines. Yes, very large twins have in the past twenty years shown themselves remarkably economical. However plenty of first line airlines are very happy operating very large quads. There is a weight point at which even the economy of a twin doesn't enable the construction of a twin.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineDarksnowynight From United States of America, joined Jan 2012, 1342 posts, RR: 3
Reply 10, posted (1 year 3 months 1 day 17 hours ago) and read 5659 times:

Quoting CXB77L (Reply 3):

The 777-300ER's payload-range already surpasses that of the 747-400.

Indeed, as the 779X will likely have the same relationship to the 748, especially once evolutional upgrades come online as well.

Quoting CXB77L (Reply 3):
There cannot be a twin engine 747 any more than there can be a quad engined 767 (for example).

I think there could be; it would just be a question of how useful it is. Enough Boeing customers would really have to love that hump to make it worthwhile.

It would almost certainly need a new wing; not just to accommodate the engines, but as well the effected center of gravity. With two fewer engines, that wing box will either have to be set a good deal further aft, or airlines will just have to be ok with tail-standing their planes until fueled.

There would also have to be a pretty comprehensive materials and processing upgrade as well, along with whatever further lightening they could get away with in order to have it so that a variant of today's GE-90 could actually loft that thing. On the plus side, that and larger tires would probably also allow for a simpler, dual carriage, six wheel bogie set up instead of what's there now, so we'd see further weight savings there.

I really think that a 160,000lb engine being required is total nonsense, as enough structure redesign would be required to effectively void that anyway. And I also think that designing a 747(I guess 9) in this fashion is not only feasible, but likely less costly than the 380 was for Airbus, and the 787 was for Boeing.

It would even be totally worth a look into... If there were not going to be a 779 or A350.

And so... This topic is a very good and interesting one, as a thought exercise, but it does fall firmly under the "Well, if your aunt had balls, she'd be your uncle" category.



Posting without Knowledge is simply Tolerated Vandalism... We are the Vandals.
User currently offlinemmo From Qatar, joined Apr 2013, 61 posts, RR: 0
Reply 11, posted (1 year 3 months 1 day 14 hours ago) and read 5588 times:

There is another factor that has not been mentioned. The entire rudder would have to be redesigned to allow for control with one engine out. Currently the 744 can handle two out on one side with the existing rudder. However, with the thrust available you would need the rudder would have to be redesigned to allow for a reasonable VMCA.

Too expensive and market is not big enough given existing or even potential products.



If we weren't all crazy we would all go insane
User currently offlineDeltal1011man From United States of America, joined Sep 2005, 9286 posts, RR: 14
Reply 12, posted (1 year 3 months 21 hours ago) and read 5377 times:

Quoting DeltaXNA (Thread starter):

Already have one. the 777-300ER is basically a 747. Sounds like a 777-9 will fully be able to do everything + what the 747-400 will do.

Quoting Starlionblue (Reply 9):
Technically, a 747 sized twin is tricky. You'd need to have engines that produce 40%+ more thrust than the current largest engines.

I guess I am a little confused at what you mean here.

2x GE90-115BL2=230,000lbs of thrust
4x PW4060=240,000lbs of thrust.

thats 10,000lbs of differences



yep.
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16991 posts, RR: 67
Reply 13, posted (1 year 3 months 21 hours ago) and read 5374 times:

Quoting Deltal1011man (Reply 12):
Quoting Starlionblue (Reply 9):
Technically, a 747 sized twin is tricky. You'd need to have engines that produce 40%+ more thrust than the current largest engines.

I guess I am a little confused at what you mean here.

2x GE90-115BL2=230,000lbs of thrust
4x PW4060=240,000lbs of thrust.

thats 10,000lbs of differences

You're calculating based on all engines running. You need to calculate based on one engine out while climbing out. In a worst case scenario, i.e. an engine out at V1, you will have three engines in a quad, but only one in a twin.

1x GE90-115BL2= 115,000lb of thrust.
3x PW4060= 180,000lb of thrust

With those numbers it is actually more like 56.5% than 40%, and that doesn't account for the extra drag of going sideways on one engine while climbing out. However I am willing to stipulate an airliner made of lighter materials than a 747-400, so I think the 40% number is reasonable.

[Edited 2013-04-23 03:03:46]

Quoting mmo (Reply 11):
There is another factor that has not been mentioned. The entire rudder would have to be redesigned to allow for control with one engine out. Currently the 744 can handle two out on one side with the existing rudder. However, with the thrust available you would need the rudder would have to be redesigned to allow for a reasonable VMCA.

I don't think a rudder redesign need be so dramatic. Besides, they have the 747SP fin and rudder as a starting point. The 747SP fin was taller and the rudder had a double hinge for more authority given the shorter moment arm.


[Edited 2013-04-23 03:10:28]

[Edited 2013-04-23 03:11:03]


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineDeltal1011man From United States of America, joined Sep 2005, 9286 posts, RR: 14
Reply 14, posted (1 year 3 months 20 hours ago) and read 5358 times:

Quoting Starlionblue (Reply 13):

You're calculating based on all engines running. You need to calculate based on one engine out while climbing out. In a worst case scenario, i.e. an engine out at V1, you will have three engines in a quad, but only one in a twin.

ahh didn't even think about n engine out.



yep.
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16991 posts, RR: 67
Reply 15, posted (1 year 3 months 20 hours ago) and read 5356 times:

Quoting Deltal1011man (Reply 14):
Quoting Starlionblue (Reply 13):

You're calculating based on all engines running. You need to calculate based on one engine out while climbing out. In a worst case scenario, i.e. an engine out at V1, you will have three engines in a quad, but only one in a twin.

ahh didn't even think about n engine out.

No worries. Most people don't. A twin has way more power than "needed" when all engines are running. That's why a 757, 330 or 777 can blast off from the runway compared to a 747 or 340. With an engine out it is another story. This is one of the reasons the 340 has been favored by airlines with lots of hot and high ops, for example SA out of JNB.

[Edited 2013-04-23 04:02:56]


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinemmo From Qatar, joined Apr 2013, 61 posts, RR: 0
Reply 16, posted (1 year 3 months 20 hours ago) and read 5346 times:

Quoting Starlionblue (Reply 13):
I don't think a rudder redesign need be so dramatic. Besides, they have the 747SP fin and rudder as a starting point. The 747SP fin was taller and the rudder had a double hinge for more authority given the shorter moment arm.


Actually, I think it would be quite a redesign. The SP rudder was for a much shorter body. The SP was shorter than the 100/200 while the 400 is longer and the -8 even longer. Most likely the redesign/production and certification would make it just too expensive when you have the 773ER and the 779X waiting in the wings. With over 10,000 hours in all models it is truly a great aircraft. However, it really can not compete with the 773ER.



If we weren't all crazy we would all go insane
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16991 posts, RR: 67
Reply 17, posted (1 year 3 months 20 hours ago) and read 5340 times:

Quoting mmo (Reply 16):
Quoting Starlionblue (Reply 13):
I don't think a rudder redesign need be so dramatic. Besides, they have the 747SP fin and rudder as a starting point. The 747SP fin was taller and the rudder had a double hinge for more authority given the shorter moment arm.

Actually, I think it would be quite a redesign. The SP rudder was for a much shorter body. The SP was shorter than the 100/200 while the 400 is longer and the -8 even longer

The SP rudder and fin were indeed for a much shorter body. For this reason the fin was longer and the rudder had more authority than the ordinary 747 fin and rudder. A longer body means you can get away with a shorter fin and less powerful rudder. However given more powerful engines you need a longer fin and more powerful rudder.

I think the 747SP fin would do just fine, but I don't think Boeing would go for a 40 year old design. The 777-900X would be longer but have more powerful engines, design features that work in different directions with regards to fin and rudder. The current 777 fin/rudder design probably works, perhaps with a fin extension and worst case with a double hinged rudder.

[Edited 2013-04-23 04:25:09]


"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlinemmo From Qatar, joined Apr 2013, 61 posts, RR: 0
Reply 18, posted (1 year 3 months 19 hours ago) and read 5325 times:

Quoting Starlionblue (Reply 17):
The 777-900X would be longer but have more powerful engines, design features that work in different directions with regards to fin and rudder. The current 777 fin/rudder design probably works, perhaps with a fin extension and worst case with a double hinged rudder.

Not quite. The 779X will actually have a lower MTOW than the current 773ER, with less powerful engines than the current GE115s. However, on paper, it will have a better range/payload combination than the current 773ER.

Believe me, after flying the SP for about 450 hours, I know how it works. My point was the SP rudder is for that length body. More importantly, the adverse thrust and asymmetrical yaw would require a very robust rudder. The rudder for all of the various models was not designed for that type of situation.



If we weren't all crazy we would all go insane
User currently offlineStarlionblue From Greenland, joined Feb 2004, 16991 posts, RR: 67
Reply 19, posted (1 year 3 months 18 hours ago) and read 5319 times:

Quoting mmo (Reply 18):
Not quite. The 779X will actually have a lower MTOW than the current 773ER, with less powerful engines than the current GE115s. However, on paper, it will have a better range/payload combination than the current 773ER.

Believe me, after flying the SP for about 450 hours, I know how it works. My point was the SP rudder is for that length body. More importantly, the adverse thrust and asymmetrical yaw would require a very robust rudder. The rudder for all of the various models was not designed for that type of situation.

Fair enough. However my point was that Boeing have a lot of rudder design experience. If you say that the 779X will have less powerful engines than the 773ER then presumably the current 773ER rudder will be more than enough.

My 747SP comment was half in jest. Sorry that was not clear. Besides, this thread is about a twin 747, not the 777-900X. Two quite different beasts.



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineDarksnowynight From United States of America, joined Jan 2012, 1342 posts, RR: 3
Reply 20, posted (1 year 3 months 17 hours ago) and read 5290 times:

Quoting mmo (Reply 16):
The SP was shorter than the 100/200 while the 400 is longer and the -8 even longer.

The 400 is not longer than the 100/200. It has the extended hump like the 300 & some 100s & 200s, but the aircraft is identical in length. For that, you will need the LCF or the 8.



Posting without Knowledge is simply Tolerated Vandalism... We are the Vandals.
User currently offlinemmo From Qatar, joined Apr 2013, 61 posts, RR: 0
Reply 21, posted (1 year 3 months 17 hours ago) and read 5290 times:

Quoting Starlionblue (Reply 19):
My 747SP comment was half in jest. Sorry that was not clear. Besides, this thread is about a twin 747, not the 777-900X. Two quite different beasts.

I do realize that. However, the issue is the 779X will most likely cannibalize what little 747-8I sales are left. The economics on that aircraft will be just too hard to beat. In reality, almost anything can be done from an engineering perspective, but the economics just aren't there anymore. The 779X will, I am afraid, be the last nail in the coffin for the 747 family.



If we weren't all crazy we would all go insane
User currently offlineOldAeroGuy From United States of America, joined Dec 2004, 3476 posts, RR: 67
Reply 22, posted (1 year 3 months 14 hours ago) and read 5225 times:

Quoting CXB77L (Reply 3):
Quoting OldAeroGuy (Reply 2):
The payload-range of the proposed 777-9X surpasses the 747-400.

The 777-300ER's payload-range already surpasses that of the 747-400.

Yes but with some 50 less seats, the 773ER could be argued as not quite a 744 replacement. Since the 779X and 744 seat counts are virtually identical, the 779X is more effectively a 744 replacement.



Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
User currently offlineCitationJet From United States of America, joined Mar 2003, 2420 posts, RR: 3
Reply 23, posted (1 year 2 months 4 weeks 1 day 20 hours ago) and read 5029 times:

Here is a great photo of one:

http://www.cardatabase.net/modifieda...earch/photo_search.php?id=00005184




Boeing Flown: 701,702,703;717;720;721,722;731,732,733,734,735,737,738,739;741,742,743,744,747SP;752,753;762,763;772,773.
User currently onlinerwessel From United States of America, joined Jan 2007, 2310 posts, RR: 2
Reply 24, posted (1 year 2 months 4 weeks 1 day ago) and read 4884 times:
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Quoting CXB77L (Reply 3):
The A330/A340 was unique in the sense that they were designed specifically as a twin and a quad. I could be wrong, but I do not believe that the same can be done with other aircraft families that are not designed specifically with this interchangeability. There cannot be a twin engine 747 any more than there can be a quad engined 767 (for example).

Certainly aircraft families have evolved different numbers of engines at times. The B-36, BN Islander, Hawker Trident and Sikorsky CH-53 are examples, and you might consider the An-124/An-225 another. And while never built, there was a proposal to re-engine B-52's with four modern turbofans (replacing the eight old TF-33s).

So while the A330/340 were certainly designed with both options from day one, it's not out of the realm of possibility that such a change could occur on a different aircraft.


ed: "An-123/An-224"?? Sheesh!

[Edited 2013-04-24 23:52:23]

25 Post contains images Starlionblue : Absolutely agreed. However I think it might be simpler to start from the 777 than from the 747 if you need a 747-400 capacity twin. Perhaps a hybrid
26 Viscount724 : Depends on the configuration. KLM's 77Ws (10-abreast in Y) have 425 seats, 10 more than their all-passenger 744s. 7 fewer J seats but 17 more Y. 77W
27 OldAeroGuy : Ah, the 10 ab 777, so dreaded by Anet readers combined with reduced seat pitch. Not a convincing argument for equivalent pax capacity between a 773ER
28 Darksnowynight : How is it not convincing? More is more. There are quite a few 400+ 77Ws out there, and they all carry more cargo (and further) than any 744 can. I'd
29 Starlionblue : Yes, it can carry more pax, but you can make a 744 just as dense and then it would carry more pax. For an airline, numbers alone aren't enough. Airli
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