timboflier215
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Twin 747 Possible?

Thu Jan 12, 2006 6:28 am

hey all!

i was watching a discovery programme the other day about the new GE engines. GE had its own 747 to test out the engines, and put one of them on in place of engine no 3. it looked HUGE compared to the other engines! they said that in flight, they were able to power down the other 3 engines and fly just using the GE. so my question is, with advances in engine technology, would it be possible to fly a 747-sized aircraft using just 2 engines? i know that take-off etc requires a whole lot more power than simply cruising, but does anyone think it could be possible in the future, as 2 engines would be cheaper to maintain than 4??

cheers!
 
kaitak744
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RE: Twin 747 Possible?

Thu Jan 12, 2006 6:39 am

Of coarse it would be possible. But on the 747 I doubt. There is not enough wing clearance to safely have 2 GE90s on the in-board pylons. Having them on the outboard positions would cause weight issues. So, yes it's possible but not on the 747.
 
dw747400
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RE: Twin 747 Possible?

Thu Jan 12, 2006 7:15 am

It is certainly possible--and in some ways, it has already happened. The Maximum takeoff weight of a 777-300ER is greater than that of the earliest 747 variants. Of course, the -300ER represents close to, if not the, limit in growth for the 777 series, while the 747-100 was the starting point of a series of aircraft that have gotten substantially heavier. Still, it is a twin that is heavier than some of the 747s out there.
CFI--Certfied Freakin Idiot
 
Tifoso
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RE: Twin 747 Possible?

Thu Jan 12, 2006 7:22 am

I have wondered about the same question.

Is it possible that Y3 is a twin 747?
 
timboflier215
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RE: Twin 747 Possible?

Thu Jan 12, 2006 7:31 am

thanks for the replies! i hadnt thought of the probs with putting the engines on the in-board pylons. im just surprised that boeing arent modifying the 747-8 wing so it could fit 2 engines.
 
ehho
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RE: Twin 747 Possible?

Thu Jan 12, 2006 7:37 am

Hey guys.. It has been done already!!


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Just joking of course, but the idea is still cool to think about.
"Get your facts first. Then you may distort them as much as you please" -- Mark Twain
 
whitehatter
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RE: Twin 747 Possible?

Thu Jan 12, 2006 7:39 am

There are calculations which show how much thrust would be needed for a twin of the 747's size, and they come out as requiring a lot more thrust than a Ge90 or Trent 8104 currently provides.

It's in relation to engine failure on takeoff. A twin needs sufficient power to continue its climb should an engine fail. With a quad the calculations are done for a single engine losing power and the other three being available.

I think it comes out as needing an engine in the 150,000lbs thrust region to effectively turn a 744 into a twin. And that creates a whole new set of engineering problems with the wing and pylons too.
Lead me not into temptation, I can find my own way there...
 
terryb99
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RE: Twin 747 Possible?

Thu Jan 12, 2006 7:41 am

Sounds like the 747 we had flying around Seattle years ago during the 777 engine testing. They installed one 777 engine in place of the standard 747 engine. It dwarfed the engine next to it. Was a strange site to see.
 
timboflier215
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RE: Twin 747 Possible?

Thu Jan 12, 2006 8:18 am

Quoting Terryb99 (Reply 7):
It dwarfed the engine next to it. Was a strange site to see.

hehe, yeah! the aircraft looked tres bizarre! youd imagine a 747 engine to be big, but they were nothing compared to the GE!
 
zvezda
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RE: Twin 747 Possible?

Thu Jan 12, 2006 8:43 am

Quoting Tifoso (Reply 3):

Is it possible that Y3 is a twin 747?

Y3 will almost certainly be a twin about the size of the B747, but it will definitely not be a B747.

Quoting Timboflier215 (Reply 4):
im just surprised that boeing arent modifying the 747-8 wing so it could fit 2 engines.

That would have been far too expensive to develop relative to the advantage. Four GEnx engines are perfect for the B747-8.
 
Gatorman96
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RE: Twin 747 Possible?

Thu Jan 12, 2006 8:46 am






It would be cool, but I can't imagine the 747 with anything less than 4 engines!
Cha brro
 
NYC777
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RE: Twin 747 Possible?

Fri Jan 13, 2006 2:27 am

Not only would you need as usbtanitally strengthened wing box but you have to have higher and stronger landing gear if you're going to hang two 150k lb of thrust engines on a plane the size of a 747. That said can you imagine the economics of such a plane...bye bye to 4 engines 4 long haul!!!!
That which does not kill me makes me stronger.
 
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OzarkD9S
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RE: Twin 747 Possible?

Fri Jan 13, 2006 2:35 am

Didn't Boeing do a tri-jet 747 study when they were designing the SP version? I seem to recall seeing a pic years and years ago. It looked like a cross between a 747 and an L-1011.
Next up: STL-OAK-RNO-LAS-ICT-STL
 
Ari
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RE: Twin 747 Possible?

Fri Jan 13, 2006 3:12 am

would it not be possible to have 4 engines,2 more powerful than the other 2,and only use the two more powerful engines during flight?

aRi
 
NYC777
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RE: Twin 747 Possible?

Fri Jan 13, 2006 3:21 am

Quoting Ari (Reply 13):
would it not be possible to have 4 engines,2 more powerful than the other 2,and only use the two more powerful engines during flight?

then you're dragging around the weight of two engines that are not doing anything. I think that would be highly inefficient.
That which does not kill me makes me stronger.
 
Geo772
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RE: Twin 747 Possible?

Fri Jan 13, 2006 3:25 am

The 747's wing would have to be completely redesigned were it to only have 2 engines.

The weight of the outboard engines reduces stress on the wing during flight, were the outboard engines not there then the wing would float up by an enormous amount, far more than it already does.

The 777-300ER already has a max takeoff weight greater than the 747-100, 351 tonnes as opposed to 340 tonnes.

There should be no reason why in twenty years time to see 450 tonne aircraft flying with only 2 engines, just not right now.
Flown on A300B4/600,A319/20/21,A332/3,A343,B727,B732/3/4/5/6/7/8,B741/2/4,B752/3,B762/3,B772/3,DC10,L1011-200,VC10,MD80,
 
ikramerica
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RE: Twin 747 Possible?

Fri Jan 13, 2006 3:32 am

Quoting Ari (Reply 13):
would it not be possible to have 4 engines,2 more powerful than the other 2,and only use the two more powerful engines during flight?

The new 748I will have 65k engines, roughly. 3 on takeoff is 195k, not 150k. So, using a 115k GE90, that leaves 80k, so the other two engines must be 40k each, which is probably less efficient weight wise than just have four 65k engines. Also, the plane would be overpowered.

2x115+2x40=310k
4x65=260k

That ability to make 50k more is a huge weight and efficiency penalty.

But as stated, the original 747-100 could fly with 2 GE90-115k engines, but engine out would pose a bit of a problem...
Of all the things to worry about... the Wookie has no pants.
 
tockeyhockey
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RE: Twin 747 Possible?

Fri Jan 13, 2006 5:23 am

if the 747x lost as much weight proportionally as the 767 in comparison to the 787, you could probably get the thrust figures to work out with a fully maxed out GE-90. however, there would be substantial redesign issues in the avionics, wing, cockpit, electrical systems, etc.

i wonder if boeing even looked at this as an option when it was dreaming up the 748.
 
timboflier215
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RE: Twin 747 Possible?

Fri Jan 13, 2006 5:28 am

thanks for the replies guys. i was just an interesting thought, but obv the economics of redesign etc are greater than any efficiency savings, or boeing would have gone with it no doubt. i cant imagine they dismissed it out hand; they would have looked at all possibilities, inc a twin im sure.
 
zvezda
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RE: Twin 747 Possible?

Fri Jan 13, 2006 9:50 pm

Quoting Tockeyhockey (Reply 17):

i wonder if boeing even looked at this as an option when it was dreaming up the 748.

Definitely not. Boeing considered three possible derivates from minimal to extensive. The B747-8 is a compromise between the minimal and medium original proposals. A twin would have been much more radical even than the most extensive proposal considered.
 
PanHAM
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RE: Twin 747 Possible?

Fri Jan 13, 2006 10:00 pm

Quoting EHHO (Reply 5):
Hey guys.. It has been done already!!



Quoting EHHO (Reply 5):
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Typically Dutch, always on the cheap side.......
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bmacleod
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RE: Twin 747 Possible?

Sat Jan 14, 2006 12:27 am

Hmmm. Maybe twinning the A380 is possible too?  rotfl   rotfl 

The sheer size and structure of the 747 is just to big for a twin-engine design. Even thinking of a twin-engine 747 is beyond logic.....
"What good are wings without the courage to fly?" - Atticus
 
Tifoso
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RE: Twin 747 Possible?

Sat Jan 14, 2006 12:30 am

Quoting Zvezda (Reply 9):
Y3 will almost certainly be a twin about the size of the B747, but it will definitely not be a B747.

Thanks Zvezda. Any reasoning behind this?
 
Molykote
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RE: Twin 747 Possible?

Sat Jan 14, 2006 12:38 am

Got to love the GE flying testbed with Pratts  Smile
Speedtape - The aspirin of aviation!
 
RichardPrice
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RE: Twin 747 Possible?

Sat Jan 14, 2006 12:46 am

Quoting Bmacleod (Reply 21):
Hmmm. Maybe twinning the A380 is possible too?

I have absolutely no links or proof for this, so dont even consider this gospel or anything, but I recall a TV interview in 2005 after the A380 first flew where an Airbus spokesman mentioned in an almost throwaway line that the A380 had been designed with only fitting two engines for a super capacity shorthaul shuttle aircraft in mind. This hasnt been mentioned anywhere else as far as I can see, but it was definately on a UK BBC news interview, I think it was either during a feature on the Broughton wing plant or a research centre in the southwest.

Now that would be cool.
 
zvezda
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RE: Twin 747 Possible?

Sat Jan 14, 2006 3:51 am

Quoting Bmacleod (Reply 21):
Maybe twinning the A380 is possible too?

If the design were started now, the WhaleJet would almost certainly be a twin.

Quoting Bmacleod (Reply 21):
The sheer size and structure of the 747 is just to big for a twin-engine design. Even thinking of a twin-engine 747 is beyond logic.....

That reminds me of the 1955 IBM research paper which proved that the most memory any computer would ever need for any application was 8K bytes.

Quoting Tifoso (Reply 22):

Thanks Zvezda. Any reasoning behind this?

The reason why Y3 will be a twin are the same as the reasons why the B777 is a twin: economics and dispatch reliability. In other words, all else being equal, airlines will pay more for a twin than for a quad because it will cost less to operate and generate a bit more revenue.
 
ikramerica
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RE: Twin 747 Possible?

Sat Jan 14, 2006 3:57 am

Quoting Molykote (Reply 23):
Got to love the GE flying testbed with Pratts

Just shows GE engines are too valuable in the marketplace to "waste" on a testbed...  Wink

Quoting Zvezda (Reply 25):
That reminds me of the 1955 IBM research paper which proved that the most memory any computer would ever need for any application was 8K bytes.

Bill Gates said the same thing about 640kB in the early 80s, and held to that for a LONG time.
Of all the things to worry about... the Wookie has no pants.
 
RichardPrice
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RE: Twin 747 Possible?

Sat Jan 14, 2006 4:15 am

Quoting Ikramerica (Reply 26):

Bill Gates said the same thing about 640kB in the early 80s, and held to that for a LONG time.

He never said anything of the sort, its a common urban myth thats constantly reiterated.
 
gigneil
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RE: Twin 747 Possible?

Sat Jan 14, 2006 4:20 am

Quoting Zvezda (Reply 25):
In other words, all else being equal, airlines will pay more for a twin than for a quad because it will cost less to operate and generate a bit more revenue.

Cost less to operate, sure. Generate more revenue?

N
 
zvezda
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RE: Twin 747 Possible?

Sat Jan 14, 2006 4:21 am

Quoting Ikramerica (Reply 26):

Bill Gates said the same thing about 640kB in the early 80s, and held to that for a LONG time.

Neither Airbus nor Boeing have ever exhibited Bill Gates' fondness for persisting with ancient technology. Airbus and Boeing innovate -- something Microsoft have never done.

GE, PW, and RR could develop 140,000 lbs thrust engines now and would for either Airbus or Boeing if an all-new 500 passenger airliner were to start development now. If Microsoft built airliner engines, they would have shrouded fans and would look like modern turbofans but internally would be driven by pistons.
 
WAH64D
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RE: Twin 747 Possible?

Sun Jan 15, 2006 10:53 pm

Quoting Ikramerica (Reply 26):
Just shows GE engines are too valuable in the marketplace to "waste" on a testbed...

Aren't they just. Think how many toasters and lightbulbs GE could make out of one GE90.
I AM the No-spotalotacus.
 
ehho
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RE: Twin 747 Possible?

Sun Jan 15, 2006 11:07 pm

Quoting PanHAM (Reply 20):
Typically Dutch, always on the cheap side.......

Oh yeah? We'll see at the Weltmannschaft!! I'll let you know when my compatriates will be singing "Schade Deutschland, alles ist vorbei.."

Just joking, in case you didn't notice! Big grin
"Get your facts first. Then you may distort them as much as you please" -- Mark Twain
 
Tifoso
Posts: 432
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RE: Twin 747 Possible?

Sun Jan 15, 2006 11:09 pm

Quoting Zvezda (Reply 25):
The reason why Y3 will be a twin are the same as the reasons why the B777 is a twin: economics and dispatch reliability. In other words, all else being equal, airlines will pay more for a twin than for a quad because it will cost less to operate and generate a bit more revenue.

I did not mean why it would be a twin, but would it not be a twin 747. Here's what you said:

Quoting Zvezda (Reply 9):

Y3 will almost certainly be a twin about the size of the B747, but it will definitely not be a B747.



Quoting Ikramerica (Reply 26):

Bill Gates said the same thing about 640kB in the early 80s, and held to that for a LONG time.

That is the biggest piece of mis-information that has floated around in the internet. Bill Gates has repeatedly denied saying this.

Quoting Zvezda (Reply 29):

Neither Airbus nor Boeing have ever exhibited Bill Gates' fondness for persisting with ancient technology. Airbus and Boeing innovate -- something Microsoft have never done.

I strongly disagree with this statement, but this should probably be discussed in Non-Av.
 
zvezda
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RE: Twin 747 Possible?

Sun Jan 15, 2006 11:12 pm

Quoting Tifoso (Reply 32):

I did not mean why it would be a twin, but would it not be a twin 747.

To make a twin B747 would require a completely new wing. When Boeing go to the expense of a completely new wing for a B747-size aircraft, they will start with a clean sheet of paper and develop a composite fuselage ala B787.
 
rampart
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RE: Twin 747 Possible?

Sun Jan 15, 2006 11:24 pm

Quoting Kaitak744 (Reply 1):
There is not enough wing clearance to safely have 2 GE90s on the in-board pylons. Having them on the outboard positions would cause weight issues. So, yes it's possible but not on the 747.

So you are saying the pic in reply 10 is nothing but a photo retouch?

-Rampart
 
Tifoso
Posts: 432
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RE: Twin 747 Possible?

Sun Jan 15, 2006 11:24 pm

Quoting Zvezda (Reply 33):
To make a twin B747 would require a completely new wing. When Boeing go to the expense of a completely new wing for a B747-size aircraft, they will start with a clean sheet of paper and develop a composite fuselage ala B787.

The addition of features like the partial FBW, bleed 787 engines makes me think that 748 maybe a stepping stone to an all composite, twin engined 747, i.e. Y3.
 
dw747400
Posts: 1091
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RE: Twin 747 Possible?

Mon Jan 16, 2006 12:08 am

Quoting Rampart (Reply 34):
So you are saying the pic in reply 10 is nothing but a photo retouch?

It is a real photo. Zvezda may be discussing clearence needs for an operational aircraft, which could differ from an experimental aircraft.

Quoting Tifoso (Reply 32):
That is the biggest piece of mis-information that has floated around in the internet.

I'd venture to guess there has been worse!

Quoting Tifoso (Reply 35):
The addition of features like the partial FBW, bleed 787 engines makes me think that 748 maybe a stepping stone to an all composite, twin engined 747, i.e. Y3.

I'm sure the experience gained would be useful, but I think the 787 would be the "stepping stone" to the Y3. The systems of the 748 have much more in common with the 744 than with the 787 or Y3 (I think that is safe to assume!). Even with the addition of extremely limited FBW (IIRC they are talking spoilers, which were FBW on the 757 and 767), it is, systems wise, a 747.
CFI--Certfied Freakin Idiot
 
rampart
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RE: Twin 747 Possible?

Mon Jan 16, 2006 2:12 am

Quoting Dw747400 (Reply 36):
It is a real photo. Zvezda may be discussing clearence needs for an operational aircraft, which could differ from an experimental aircraft.

I was actually quoting Kaitak744, who wasn't clear about differentiating an experimental aircraft from an operational one, only that "there wasn't enough wing clearance"; and I wasn't clear enough that I was being a little sarcastic and knew that the 747 pictured was a real aircraft. I can see now that there may be a difference between operational and experimental, but the test bed looks like it has clearance and sufficient wing strength (to hold two engines, or at least one and a half engines by GE90 standards).
 
dw747400
Posts: 1091
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RE: Twin 747 Possible?

Mon Jan 16, 2006 3:09 am

Quoting Rampart (Reply 37):

Your right... sorry about that. Must have been looking at the quotes in Reply 34 and 35 at the same time.

In terms of wing strength, the long term effects of adding that much power could me significant. Bigger engines produce more stress on the wing, and that creates more fatigue potential. This may not be a problem for testing, where I'm sure every bit of structure around that engine is reguarly inspected and the time in service is short, but over a 30 year life span it could be an issue. The 4 engines on the 747 wing are also placed to allow maximum wing bending relief. I'd imagine in order to be structually feasible, the two new engines would need to be placed between the mounts of the inboard and outboard engines on both sides. This probably would still be less efficient structually than the current setup, but more within reason.

Of course, the best solution would be an all new wing. With enough wing area, weight reduction, etc, you could probably reduce the need for installed thrust in an engine out scenario below that currently required by a 744, making the difference between the current GE90-115B and the "2747's" powerplant a bit more modest.

Of course, Boeing will be planning a clean-sheet design for the Y-3, but it is interesting to think about a 747 fuselage on all new composite wings, driven by a pair of GENX-style engines scaled up to the 125,000-140,000 pound thrust range.
CFI--Certfied Freakin Idiot