Boeing Nut
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Why No Twin Engine 747?

Sun May 13, 2001 10:55 am

Greetings!

I know it would not be economically feasable, and a lot of redesigning would be necessary but with the thrust available on 777 engines, why wouldn't it work?

GE90's are pushing 115,000 lbs of thrust. Some 747 engines are 55-60,000 lbs each so it would nearly be the same amount of total thrust. Any thoughts?

Regards
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LAX
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RE: Why No Twin Engine 747?

Sun May 13, 2001 10:57 am

Just imagine the size of those babies though!!
Even bigger than the already-enormous B777 engines, I would imagine!

I can't imagine Boeing ever considering this.
 
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RE: Why No Twin Engine 747?

Sun May 13, 2001 11:02 am

747 is bigger than 777. So 747 need 4 engines. The reason why 777 have 2 engines with powerful ones, because 777 can fly farther than 747 with these powerful engines.
 
N863DA
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RE: Why No Twin Engine 747?

Sun May 13, 2001 11:45 am

They do have a 747-sized airliner with two engines. It's called the 777-300.

Nowadays the extra effort of an upper deck is just not neccesary - the reason it was there in the first place was because it was generally accepted that the 747 would primarily be a freighter once most people traveled by Supersonic jet.

Why would airlines by a 747, with essentially a 1960s design, when they can have a 1990s technology 777-300 for about the same amount, just because the 747 would have two 777-style engines? There is no reason to reegine the 747 wen a similarly-sized aircraft already has two engines. And the 777-300 is far superior to the economics of a 747-classic, also! (Because of the thirty-year newer technology)

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DL727-200adv
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RE: Why No Twin Engine 747?

Sun May 13, 2001 12:46 pm

I think it would be quite possible for two GE90’s to provide adequate thrust to power a 744. I suspect that the real problem would come from the asymmetrical thrust resulting from an engine failure. When designing a twin, engine placement is largely determined as a result of consideration of thrust asymmetry in engine out situations. I’m not sure you could simply mount two GE90’s on a 744’s inboard engine mount points & have adequate single engine performance. Also, a twin must have adequate climb performance on only 50% power where as a quad only needs to demonstrate adequate climb performance on 75% power. This requires that a twin have a greater thrust to weight ratio than a quad. Contrary to what many people who argue 4 are better than 2 believe I doubt that a 744 or an A340 would be able to maintain level flight or climb with two engines out & a full load of fuel and pax.. I’m sure there are others on this form can comment better on this than I can. Many carriers operating the 744 as well as the A340 operate them on routes that would not be suitable for ETOPS operations.

From a technological standpoint I disagree with those who say that the 744 is basically 1960’s technology. Sure the basic airframe hasn’t changed significantly but the 744 has a fairly advanced flight deck & other significant improvements over the original 747 classics. The 777 flight deck is largely based on the 1989 design of the 744 flight deck. I don’t hear people saying that the new A340-600 is “based on 1970’s technology” even though the fuselage cross-section if I am not mistaken is the same as the original A300 fuselage cross section or that “the 737NG & 757 are based on 1950’s technology” even though they share the basic 707 fuselage cross-section. You don’t always need to re-invent the wheel to get an excellent product & the 744 is certainly no ancient low tech relic. Certainly Boeing could greatly improve the 744 if they decided to update it in the way they updated the 737 to create the 737NG however there is doubt that such a expensive re-design would end up being profitable due to the limited market for such a large aircraft especially when sharing that market with the all new A380. I think Boeing is doing the right thing putting their $$ into the new “Supercruser” which would have a much greater market & is already generating a lot of interest from the airlines. This way hopefully the Boeing Supercruser & the Airbus A380 will both be very successful & Boeing may still sell a good number of 744ER’s.

Just my $.02!  Smile

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Monocleman
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RE: Why No Twin Engine 747?

Sun May 13, 2001 1:14 pm

I saw once in a book about the development of the 777 a picture of a 747 with a GE90 777 engine in place of the #2 engine for flight testing. The cowl is significantly larger on those GE's than on the 747's, and I beleive the engine had only 13 inches of ground clearance. I guess that would fall under the category of "a lot of redesigning", Boeing nut...
 
L-188
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RE: Why No Twin Engine 747?

Sun May 13, 2001 7:59 pm

Then again there have been 3 and four engined 747's so why not a two engined one.


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EGGD
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RE: Why No Twin Engine 747?

Sun May 13, 2001 8:11 pm

Has anyone thought about wing bend and fuel flow. To have just 2 engines you would effectively have to redesign most of the 747.

It will never happen.

EGGD
 
Boeing Nut
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RE: Why No Twin Engine 747?

Sun May 13, 2001 10:30 pm

Monocleman,
Yea, I saw that 747 also in Boeing's/GE's flight test program. That would not be a good location for the engines because of the ground glearance (ground strikes) not to mention the astronomical FOD problems.

Wishihadalife,
Hey thanks! I have been under a rock for the last 30 years. I had no idea that a 747 had four engines! Whatever.

To everyone but wish, thanks for your input, like I said, I always been curious about that.

Regards
I'm not a real aeronautical engineer, I just play one on Airliners.net.
 
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RE: Why No Twin Engine 747?

Sun May 13, 2001 10:44 pm

Actually I meant three and five engined 747's ....Sorry about the typo folks
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